validation of characters length is finished

Cargo.lock

@@ -479,6 +479,7 @@ dependencies = [
  "common",
  "crossterm",
  "ratatui",
+ "regex",
  "serde",
  "thiserror",
  "tokio",

canvas/.gitignore

@@ -0,0 +1 @@
+docs_prompts/

canvas/Cargo.toml

@@ -23,6 +23,7 @@ thiserror = { workspace = true }
 tracing = "0.1.41"
 tracing-subscriber = "0.3.19"
 async-trait.workspace = true
+regex = { workspace = true, optional = true }
 
 [dev-dependencies]
 tokio-test = "0.4.4"
@@ -32,6 +33,7 @@ default = []
 gui = ["ratatui"]
 autocomplete = ["tokio"]
 cursor-style = ["crossterm"]
+validation = ["regex"]
 
 [[example]]
 name = "autocomplete"
@@ -42,3 +44,7 @@ path = "examples/autocomplete.rs"
 name = "canvas_gui_demo"
 required-features = ["gui"]
 path = "examples/canvas_gui_demo.rs"
+
+[[example]]
+name = "validation_1"
+required-features = ["gui", "validation"]

canvas/docs/new_function_to_config.txt

@@ -1,77 +0,0 @@
-❯ git status
-On branch main
-Your branch is ahead of 'origin/main' by 1 commit.
-  (use "git push" to publish your local commits)
-
-Changes not staged for commit:
-  (use "git add <file>..." to update what will be committed)
-  (use "git restore <file>..." to discard changes in working directory)
-	modified:   src/canvas/actions/handlers/edit.rs
-	modified:   src/canvas/actions/types.rs
-
-no changes added to commit (use "git add" and/or "git commit -a")
-❯ git --no-pager diff
-diff --git a/canvas/src/canvas/actions/handlers/edit.rs b/canvas/src/canvas/actions/handlers/edit.rs
-index a26fe6f..fa1becb 100644
---- a/canvas/src/canvas/actions/handlers/edit.rs
-+++ b/canvas/src/canvas/actions/handlers/edit.rs
-@@ -29,6 +29,21 @@ pub async fn handle_edit_action<S: CanvasState>(
-             Ok(ActionResult::success())
-         }
-
-+        CanvasAction::SelectAll => {
-+            // Select all text in current field
-+            let current_input = state.get_current_input();
-+            let text_length = current_input.len();
-+
-+            // Set cursor to start and select all
-+            state.set_current_cursor_pos(0);
-+            // TODO: You'd need to add selection state to CanvasState trait
-+            // For now, just move cursor to end to "select" all
-+            state.set_current_cursor_pos(text_length);
-+            *ideal_cursor_column = text_length;
-+
-+            Ok(ActionResult::success_with_message(&format!("Selected all {} characters", text_length)))
-+        }
-+
-         CanvasAction::DeleteBackward => {
-             let cursor_pos = state.current_cursor_pos();
-             if cursor_pos > 0 {
-@@ -323,6 +338,13 @@ impl ActionHandlerIntrospection for EditHandler {
-             is_required: false,
-         });
-
-+        actions.push(ActionSpec {
-+            name: "select_all".to_string(),
-+            description: "Select all text in current field".to_string(),
-+            examples: vec!["Ctrl+a".to_string()],
-+            is_required: false, // Optional action
-+        });
-+
-         HandlerCapabilities {
-             mode_name: "edit".to_string(),
-             actions,
-diff --git a/canvas/src/canvas/actions/types.rs b/canvas/src/canvas/actions/types.rs
-index 433a4d5..3794596 100644
---- a/canvas/src/canvas/actions/types.rs
-+++ b/canvas/src/canvas/actions/types.rs
-@@ -31,6 +31,8 @@ pub enum CanvasAction {
-     NextField,
-     PrevField,
-
-+    SelectAll,
-+
-     // Autocomplete actions
-     TriggerAutocomplete,
-     SuggestionUp,
-@@ -62,6 +64,7 @@ impl CanvasAction {
-             "move_word_end_prev" => Self::MoveWordEndPrev,
-             "next_field" => Self::NextField,
-             "prev_field" => Self::PrevField,
-+            "select_all" => Self::SelectAll,
-             "trigger_autocomplete" => Self::TriggerAutocomplete,
-             "suggestion_up" => Self::SuggestionUp,
-             "suggestion_down" => Self::SuggestionDown,
-╭─      ~/Doc/p/komp_ac/canvas  on    main ⇡1 !2 
-╰─
-

canvas/examples/validation_1.rs

@@ -0,0 +1,831 @@
+// examples/validation_1.rs
+//! Demonstrates field validation with the canvas library
+//!
+//! This example REQUIRES the `validation` feature to compile.
+//!
+//! Run with:
+//! cargo run --example validation_1 --features "gui,validation"
+//!
+//! This will fail without validation:
+//! cargo run --example validation_1 --features "gui"
+
+// REQUIRE validation feature - example won't compile without it
+#[cfg(not(feature = "validation"))]
+compile_error!(
+    "This example requires the 'validation' feature. \
+     Run with: cargo run --example validation_1 --features \"gui,validation\""
+);
+
+use std::io;
+use crossterm::{
+    event::{
+        self, DisableMouseCapture, EnableMouseCapture, Event, KeyCode, KeyModifiers,
+    },
+    execute,
+    terminal::{
+        disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen,
+    },
+};
+use ratatui::{
+    backend::{Backend, CrosstermBackend},
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Block, Borders, Paragraph, Wrap},
+    Frame, Terminal,
+};
+
+use canvas::{
+    canvas::{
+        gui::render_canvas_default,
+        modes::AppMode,
+    },
+    DataProvider, FormEditor,
+    ValidationConfig, ValidationConfigBuilder, CharacterLimits, ValidationResult,
+};
+
+// Import CountMode from the validation module directly
+use canvas::validation::limits::CountMode;
+
+// Enhanced FormEditor that demonstrates validation functionality
+struct ValidationFormEditor<D: DataProvider> {
+    editor: FormEditor<D>,
+    has_unsaved_changes: bool,
+    debug_message: String,
+    command_buffer: String,
+    validation_enabled: bool,
+    field_switch_blocked: bool,
+    block_reason: Option<String>,
+}
+
+impl<D: DataProvider> ValidationFormEditor<D> {
+    fn new(data_provider: D) -> Self {
+        let mut editor = FormEditor::new(data_provider);
+        
+        // Enable validation by default
+        editor.set_validation_enabled(true);
+        
+        Self {
+            editor,
+            has_unsaved_changes: false,
+            debug_message: "🔍 Validation Demo - Try typing in different fields!".to_string(),
+            command_buffer: String::new(),
+            validation_enabled: true,
+            field_switch_blocked: false,
+            block_reason: None,
+        }
+    }
+
+    // === COMMAND BUFFER HANDLING ===
+    fn clear_command_buffer(&mut self) {
+        self.command_buffer.clear();
+    }
+
+    fn add_to_command_buffer(&mut self, ch: char) {
+        self.command_buffer.push(ch);
+    }
+
+    fn get_command_buffer(&self) -> &str {
+        &self.command_buffer
+    }
+
+    fn has_pending_command(&self) -> bool {
+        !self.command_buffer.is_empty()
+    }
+
+    // === VALIDATION CONTROL ===
+    fn toggle_validation(&mut self) {
+        self.validation_enabled = !self.validation_enabled;
+        self.editor.set_validation_enabled(self.validation_enabled);
+        
+        if self.validation_enabled {
+            self.debug_message = "✅ Validation ENABLED - Try exceeding limits!".to_string();
+        } else {
+            self.debug_message = "❌ Validation DISABLED - No limits enforced".to_string();
+        }
+    }
+
+    fn check_field_switch_allowed(&self) -> (bool, Option<String>) {
+        if !self.validation_enabled {
+            return (true, None);
+        }
+        
+        let can_switch = self.editor.can_switch_fields();
+        let reason = if !can_switch {
+            self.editor.field_switch_block_reason()
+        } else {
+            None
+        };
+        
+        (can_switch, reason)
+    }
+
+    fn get_validation_status(&self) -> String {
+        if !self.validation_enabled {
+            return "❌ DISABLED".to_string();
+        }
+
+        if self.field_switch_blocked {
+            return "🚫 SWITCH BLOCKED".to_string();
+        }
+
+        let summary = self.editor.validation_summary();
+        if summary.has_errors() {
+            format!("❌ {} ERRORS", summary.error_fields)
+        } else if summary.has_warnings() {
+            format!("⚠️  {} WARNINGS", summary.warning_fields)
+        } else if summary.validated_fields > 0 {
+            format!("✅ {} VALID", summary.valid_fields)
+        } else {
+            "🔍 READY".to_string()
+        }
+    }
+
+    fn validate_current_field(&mut self) {
+        let result = self.editor.validate_current_field();
+        match result {
+            ValidationResult::Valid => {
+                self.debug_message = "✅ Current field is valid!".to_string();
+            }
+            ValidationResult::Warning { message } => {
+                self.debug_message = format!("⚠️  Warning: {}", message);
+            }
+            ValidationResult::Error { message } => {
+                self.debug_message = format!("❌ Error: {}", message);
+            }
+        }
+    }
+
+    fn validate_all_fields(&mut self) {
+        let field_count = self.editor.data_provider().field_count();
+        for i in 0..field_count {
+            self.editor.validate_field(i);
+        }
+        
+        let summary = self.editor.validation_summary();
+        self.debug_message = format!(
+            "🔍 Validated all fields: {} valid, {} warnings, {} errors",
+            summary.valid_fields, summary.warning_fields, summary.error_fields
+        );
+    }
+
+    fn clear_validation_results(&mut self) {
+        self.editor.clear_validation_results();
+        self.debug_message = "🧹 Cleared all validation results".to_string();
+    }
+
+    // === ENHANCED MOVEMENT WITH VALIDATION ===
+    fn move_left(&mut self) {
+        self.editor.move_left();
+        self.field_switch_blocked = false;
+        self.block_reason = None;
+    }
+
+    fn move_right(&mut self) {
+        self.editor.move_right();
+        self.field_switch_blocked = false;
+        self.block_reason = None;
+    }
+
+    fn move_up(&mut self) {
+        match self.editor.move_up() {
+            Ok(()) => {
+                self.update_field_validation_status();
+                self.field_switch_blocked = false;
+                self.block_reason = None;
+            }
+            Err(e) => {
+                self.field_switch_blocked = true;
+                self.block_reason = Some(e.to_string());
+                self.debug_message = format!("🚫 Field switch blocked: {}", e);
+            }
+        }
+    }
+
+    fn move_down(&mut self) {
+        match self.editor.move_down() {
+            Ok(()) => {
+                self.update_field_validation_status();
+                self.field_switch_blocked = false;
+                self.block_reason = None;
+            }
+            Err(e) => {
+                self.field_switch_blocked = true;
+                self.block_reason = Some(e.to_string());
+                self.debug_message = format!("🚫 Field switch blocked: {}", e);
+            }
+        }
+    }
+
+    fn move_line_start(&mut self) {
+        self.editor.move_line_start();
+    }
+
+    fn move_line_end(&mut self) {
+        self.editor.move_line_end();
+    }
+
+    fn move_word_next(&mut self) {
+        self.editor.move_word_next();
+    }
+
+    fn move_word_prev(&mut self) {
+        self.editor.move_word_prev();
+    }
+
+    fn move_word_end(&mut self) {
+        self.editor.move_word_end();
+    }
+
+    fn move_first_line(&mut self) {
+        self.editor.move_first_line();
+    }
+
+    fn move_last_line(&mut self) {
+        self.editor.move_last_line();
+    }
+
+    fn update_field_validation_status(&mut self) {
+        if !self.validation_enabled {
+            return;
+        }
+
+        if let Some(result) = self.editor.current_field_validation() {
+            match result {
+                ValidationResult::Valid => {
+                    self.debug_message = format!("Field {}: ✅ Valid", self.editor.current_field() + 1);
+                }
+                ValidationResult::Warning { message } => {
+                    self.debug_message = format!("Field {}: ⚠️  {}", self.editor.current_field() + 1, message);
+                }
+                ValidationResult::Error { message } => {
+                    self.debug_message = format!("Field {}: ❌ {}", self.editor.current_field() + 1, message);
+                }
+            }
+        } else {
+            self.debug_message = format!("Field {}: 🔍 Not validated yet", self.editor.current_field() + 1);
+        }
+    }
+
+    // === MODE TRANSITIONS ===
+    fn enter_edit_mode(&mut self) {
+        self.editor.enter_edit_mode();
+        self.debug_message = "✏️  INSERT MODE - Type to test validation".to_string();
+    }
+
+    fn enter_append_mode(&mut self) {
+        self.editor.enter_append_mode();
+        self.debug_message = "✏️  INSERT (append) - Validation active".to_string();
+    }
+
+    fn exit_edit_mode(&mut self) {
+        self.editor.exit_edit_mode();
+        self.debug_message = "🔒 NORMAL MODE - Press 'v' to validate current field".to_string();
+        self.update_field_validation_status();
+    }
+
+    fn insert_char(&mut self, ch: char) -> anyhow::Result<()> {
+        let result = self.editor.insert_char(ch);
+        if result.is_ok() {
+            self.has_unsaved_changes = true;
+            // Show real-time validation feedback
+            if let Some(validation_result) = self.editor.current_field_validation() {
+                match validation_result {
+                    ValidationResult::Valid => {
+                        // Don't spam with valid messages, just show character count if applicable
+                        if let Some(limits) = self.get_current_field_limits() {
+                            if let Some(status) = limits.status_text(self.editor.current_text()) {
+                                self.debug_message = format!("✏️  {}", status);
+                            }
+                        }
+                    }
+                    ValidationResult::Warning { message } => {
+                        self.debug_message = format!("⚠️  {}", message);
+                    }
+                    ValidationResult::Error { message } => {
+                        self.debug_message = format!("❌ {}", message);
+                    }
+                }
+            }
+        }
+        Ok(result?)
+    }
+
+    fn get_current_field_limits(&self) -> Option<&CharacterLimits> {
+        let validation_state = self.editor.validation_state();
+        let config = validation_state.get_field_config(self.editor.current_field())?;
+        config.character_limits.as_ref()
+    }
+
+    // === DELETE OPERATIONS ===
+    fn delete_backward(&mut self) -> anyhow::Result<()> {
+        let result = self.editor.delete_backward();
+        if result.is_ok() {
+            self.has_unsaved_changes = true;
+            self.debug_message = "⌫ Deleted character".to_string();
+        }
+        Ok(result?)
+    }
+
+    fn delete_forward(&mut self) -> anyhow::Result<()> {
+        let result = self.editor.delete_forward();
+        if result.is_ok() {
+            self.has_unsaved_changes = true;
+            self.debug_message = "⌦ Deleted character".to_string();
+        }
+        Ok(result?)
+    }
+
+    // === DELEGATE TO ORIGINAL EDITOR ===
+    fn current_field(&self) -> usize {
+        self.editor.current_field()
+    }
+
+    fn cursor_position(&self) -> usize {
+        self.editor.cursor_position()
+    }
+
+    fn mode(&self) -> AppMode {
+        self.editor.mode()
+    }
+
+    fn current_text(&self) -> &str {
+        self.editor.current_text()
+    }
+
+    fn data_provider(&self) -> &D {
+        self.editor.data_provider()
+    }
+
+    fn ui_state(&self) -> &canvas::EditorState {
+        self.editor.ui_state()
+    }
+
+    fn set_mode(&mut self, mode: AppMode) {
+        self.editor.set_mode(mode);
+    }
+
+    fn next_field(&mut self) {
+        match self.editor.next_field() {
+            Ok(()) => {
+                self.update_field_validation_status();
+                self.field_switch_blocked = false;
+                self.block_reason = None;
+            }
+            Err(e) => {
+                self.field_switch_blocked = true;
+                self.block_reason = Some(e.to_string());
+                self.debug_message = format!("🚫 Cannot move to next field: {}", e);
+            }
+        }
+    }
+
+    fn prev_field(&mut self) {
+        match self.editor.prev_field() {
+            Ok(()) => {
+                self.update_field_validation_status();
+                self.field_switch_blocked = false;
+                self.block_reason = None;
+            }
+            Err(e) => {
+                self.field_switch_blocked = true;
+                self.block_reason = Some(e.to_string());
+                self.debug_message = format!("🚫 Cannot move to previous field: {}", e);
+            }
+        }
+    }
+
+    // === STATUS AND DEBUG ===
+    fn set_debug_message(&mut self, msg: String) {
+        self.debug_message = msg;
+    }
+
+    fn debug_message(&self) -> &str {
+        &self.debug_message
+    }
+
+    fn has_unsaved_changes(&self) -> bool {
+        self.has_unsaved_changes
+    }
+}
+
+// Demo form data with different validation rules
+struct ValidationDemoData {
+    fields: Vec<(String, String)>,
+}
+
+impl ValidationDemoData {
+    fn new() -> Self {
+        Self {
+            fields: vec![
+                ("👤 Name (max 20)".to_string(), "".to_string()),
+                ("📧 Email (max 50, warn@40)".to_string(), "".to_string()),
+                ("🔑 Password (5-20 chars)".to_string(), "".to_string()),
+                ("🔢 ID (min 3, max 10)".to_string(), "".to_string()),
+                ("📝 Comment (min 10, max 100)".to_string(), "".to_string()),
+                ("🏷️  Tag (max 30, bytes)".to_string(), "".to_string()),
+                ("🌍 Unicode (width, min 2)".to_string(), "".to_string()),
+            ],
+        }
+    }
+}
+
+impl DataProvider for ValidationDemoData {
+    fn field_count(&self) -> usize {
+        self.fields.len()
+    }
+
+    fn field_name(&self, index: usize) -> &str {
+        &self.fields[index].0
+    }
+
+    fn field_value(&self, index: usize) -> &str {
+        &self.fields[index].1
+    }
+
+    fn set_field_value(&mut self, index: usize, value: String) {
+        self.fields[index].1 = value;
+    }
+
+    fn supports_autocomplete(&self, _field_index: usize) -> bool {
+        false
+    }
+
+    fn display_value(&self, _index: usize) -> Option<&str> {
+        None
+    }
+
+    // 🎯 NEW: Validation configuration per field
+    fn validation_config(&self, field_index: usize) -> Option<ValidationConfig> {
+        match field_index {
+            0 => Some(ValidationConfig::with_max_length(20)), // Name: simple 20 char limit
+            1 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(
+                        CharacterLimits::new(50).with_warning_threshold(40)
+                    )
+                    .build()
+            ), // Email: 50 chars with warning at 40
+            2 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(CharacterLimits::new_range(5, 20))
+                    .build()
+            ), // Password: must be 5-20 characters (blocks field switching if 1-4 chars)
+            3 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(CharacterLimits::new_range(3, 10))
+                    .build()
+            ), // ID: must be 3-10 characters (blocks field switching if 1-2 chars)
+            4 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(CharacterLimits::new_range(10, 100))
+                    .build()
+            ), // Comment: must be 10-100 characters (blocks field switching if 1-9 chars)
+            5 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(
+                        CharacterLimits::new(30).with_count_mode(CountMode::Bytes)
+                    )
+                    .build()
+            ), // Tag: 30 bytes (useful for UTF-8)
+            6 => Some(
+                ValidationConfigBuilder::new()
+                    .with_character_limits(
+                        CharacterLimits::new_range(2, 20).with_count_mode(CountMode::DisplayWidth)
+                    )
+                    .build()
+            ), // Unicode: 2-20 display width (useful for CJK characters, blocks if 1 char)
+            _ => None,
+        }
+    }
+}
+
+/// Handle key presses with validation-focused commands
+fn handle_key_press(
+    key: KeyCode,
+    modifiers: KeyModifiers,
+    editor: &mut ValidationFormEditor<ValidationDemoData>,
+) -> anyhow::Result<bool> {
+    let mode = editor.mode();
+
+    // Quit handling
+    if (key == KeyCode::Char('q') && modifiers.contains(KeyModifiers::CONTROL))
+        || (key == KeyCode::Char('c') && modifiers.contains(KeyModifiers::CONTROL))
+        || key == KeyCode::F(10)
+    {
+        return Ok(false);
+    }
+
+    match (mode, key, modifiers) {
+        // === MODE TRANSITIONS ===
+        (AppMode::ReadOnly, KeyCode::Char('i'), _) => {
+            editor.enter_edit_mode();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('a'), _) => {
+            editor.enter_append_mode();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('A'), _) => {
+            editor.move_line_end();
+            editor.enter_edit_mode();
+            editor.clear_command_buffer();
+        }
+
+        // Escape: Exit edit mode
+        (_, KeyCode::Esc, _) => {
+            if mode == AppMode::Edit {
+                editor.exit_edit_mode();
+            } else {
+                editor.clear_command_buffer();
+            }
+        }
+
+        // === VALIDATION COMMANDS ===
+        (AppMode::ReadOnly, KeyCode::Char('v'), _) => {
+            editor.validate_current_field();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('V'), _) => {
+            editor.validate_all_fields();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('c'), _) => {
+            editor.clear_validation_results();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::F(1), _) => {
+            editor.toggle_validation();
+        }
+
+        // === MOVEMENT ===
+        (AppMode::ReadOnly, KeyCode::Char('h'), _) | (AppMode::ReadOnly, KeyCode::Left, _) => {
+            editor.move_left();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('l'), _) | (AppMode::ReadOnly, KeyCode::Right, _) => {
+            editor.move_right();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('j'), _) | (AppMode::ReadOnly, KeyCode::Down, _) => {
+            editor.move_down();
+            editor.clear_command_buffer();
+        }
+        (AppMode::ReadOnly, KeyCode::Char('k'), _) | (AppMode::ReadOnly, KeyCode::Up, _) => {
+            editor.move_up();
+            editor.clear_command_buffer();
+        }
+
+        // === EDIT MODE MOVEMENT ===
+        (AppMode::Edit, KeyCode::Left, _) => {
+            editor.move_left();
+        }
+        (AppMode::Edit, KeyCode::Right, _) => {
+            editor.move_right();
+        }
+        (AppMode::Edit, KeyCode::Up, _) => {
+            editor.move_up();
+        }
+        (AppMode::Edit, KeyCode::Down, _) => {
+            editor.move_down();
+        }
+
+        // === DELETE OPERATIONS ===
+        (AppMode::Edit, KeyCode::Backspace, _) => {
+            editor.delete_backward()?;
+        }
+        (AppMode::Edit, KeyCode::Delete, _) => {
+            editor.delete_forward()?;
+        }
+
+        // === TAB NAVIGATION ===
+        (_, KeyCode::Tab, _) => {
+            editor.next_field();
+        }
+        (_, KeyCode::BackTab, _) => {
+            editor.prev_field();
+        }
+
+        // === CHARACTER INPUT ===
+        (AppMode::Edit, KeyCode::Char(c), m) if !m.contains(KeyModifiers::CONTROL) => {
+            editor.insert_char(c)?;
+        }
+
+        // === DEBUG/INFO COMMANDS ===
+        (AppMode::ReadOnly, KeyCode::Char('?'), _) => {
+            let summary = editor.editor.validation_summary();
+            editor.set_debug_message(format!(
+                "Field {}/{}, Pos {}, Mode: {:?}, Validation: {} fields configured, {} validated",
+                editor.current_field() + 1,
+                editor.data_provider().field_count(),
+                editor.cursor_position(),
+                editor.mode(),
+                summary.total_fields,
+                summary.validated_fields
+            ));
+        }
+
+        _ => {
+            if editor.has_pending_command() {
+                editor.clear_command_buffer();
+                editor.set_debug_message("Invalid command sequence".to_string());
+            }
+        }
+    }
+
+    Ok(true)
+}
+
+fn run_app<B: Backend>(
+    terminal: &mut Terminal<B>,
+    mut editor: ValidationFormEditor<ValidationDemoData>,
+) -> io::Result<()> {
+    loop {
+        terminal.draw(|f| ui(f, &editor))?;
+
+        if let Event::Key(key) = event::read()? {
+            match handle_key_press(key.code, key.modifiers, &mut editor) {
+                Ok(should_continue) => {
+                    if !should_continue {
+                        break;
+                    }
+                }
+                Err(e) => {
+                    editor.set_debug_message(format!("Error: {}", e));
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+fn ui(f: &mut Frame, editor: &ValidationFormEditor<ValidationDemoData>) {
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([Constraint::Min(8), Constraint::Length(12)])
+        .split(f.area());
+
+    render_enhanced_canvas(f, chunks[0], editor);
+    render_validation_status(f, chunks[1], editor);
+}
+
+fn render_enhanced_canvas(
+    f: &mut Frame,
+    area: Rect,
+    editor: &ValidationFormEditor<ValidationDemoData>,
+) {
+    render_canvas_default(f, area, &editor.editor);
+}
+
+fn render_validation_status(
+    f: &mut Frame,
+    area: Rect,
+    editor: &ValidationFormEditor<ValidationDemoData>,
+) {
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([
+            Constraint::Length(3), // Status bar
+            Constraint::Length(4), // Validation summary
+            Constraint::Length(5), // Help
+        ])
+        .split(area);
+
+    // Status bar with validation information
+    let mode_text = match editor.mode() {
+        AppMode::Edit => "INSERT",
+        AppMode::ReadOnly => "NORMAL",
+        _ => "OTHER",
+    };
+
+    let validation_status = editor.get_validation_status();
+    let status_text = if editor.has_pending_command() {
+        format!("-- {} -- {} [{}] | Validation: {}", 
+                mode_text, editor.debug_message(), editor.get_command_buffer(), validation_status)
+    } else if editor.has_unsaved_changes() {
+        format!("-- {} -- [Modified] {} | Validation: {}", 
+                mode_text, editor.debug_message(), validation_status)
+    } else {
+        format!("-- {} -- {} | Validation: {}", 
+                mode_text, editor.debug_message(), validation_status)
+    };
+
+    let status = Paragraph::new(Line::from(Span::raw(status_text)))
+        .block(Block::default().borders(Borders::ALL).title("🔍 Validation Status"));
+
+    f.render_widget(status, chunks[0]);
+
+    // Validation summary with field switching info
+    let summary = editor.editor.validation_summary();
+    let summary_text = if editor.validation_enabled {
+        let switch_info = if editor.field_switch_blocked {
+            format!("\n🚫 Field switching blocked: {}", 
+                   editor.block_reason.as_deref().unwrap_or("Unknown reason"))
+        } else {
+            let (can_switch, reason) = editor.check_field_switch_allowed();
+            if !can_switch {
+                format!("\n⚠️  Field switching will be blocked: {}",
+                       reason.as_deref().unwrap_or("Unknown reason"))
+            } else {
+                "\n✅ Field switching allowed".to_string()
+            }
+        };
+        
+        format!(
+            "📊 Validation Summary: {} fields configured, {} validated{}\n\
+             ✅ Valid: {}  ⚠️  Warnings: {}  ❌ Errors: {}  📈 Progress: {:.0}%",
+            summary.total_fields,
+            summary.validated_fields,
+            switch_info,
+            summary.valid_fields,
+            summary.warning_fields,
+            summary.error_fields,
+            summary.completion_percentage() * 100.0
+        )
+    } else {
+        "❌ Validation is currently DISABLED\nPress F1 to enable validation".to_string()
+    };
+
+    let summary_style = if summary.has_errors() {
+        Style::default().fg(Color::Red)
+    } else if summary.has_warnings() {
+        Style::default().fg(Color::Yellow)
+    } else {
+        Style::default().fg(Color::Green)
+    };
+
+    let validation_summary = Paragraph::new(summary_text)
+        .block(Block::default().borders(Borders::ALL).title("📈 Validation Overview"))
+        .style(summary_style)
+        .wrap(Wrap { trim: true });
+
+    f.render_widget(validation_summary, chunks[1]);
+
+    // Enhanced help text
+    let help_text = match editor.mode() {
+        AppMode::ReadOnly => {
+            "🔍 VALIDATION DEMO: Different fields have different limits!\n\
+             Fields with MINIMUM requirements will block field switching if too short!\n\
+             Movement: hjkl/arrows=move, Tab/Shift+Tab=fields\n\
+             Edit: i/a/A=insert modes, Esc=normal\n\
+             Validation: v=validate current, V=validate all, c=clear results, F1=toggle\n\
+             ?=info, Ctrl+C/Ctrl+Q=quit"
+        }
+        AppMode::Edit => {
+            "✏️  INSERT MODE - Type to test validation limits!\n\
+             Some fields have MINIMUM character requirements!\n\
+             Try typing 1-2 chars in Password/ID/Comment fields, then try to switch!\n\
+             arrows=move, Backspace/Del=delete, Esc=normal, Tab=next field\n\
+             Field switching may be BLOCKED if minimum requirements not met!"
+        }
+        _ => "🔍 Validation Demo Active!"
+    };
+
+    let help = Paragraph::new(help_text)
+        .block(Block::default().borders(Borders::ALL).title("🚀 Validation Commands"))
+        .style(Style::default().fg(Color::Gray))
+        .wrap(Wrap { trim: true });
+
+    f.render_widget(help, chunks[2]);
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Print feature status
+    println!("🔍 Canvas Validation Demo");
+    println!("✅ validation feature: ENABLED");
+    println!("🚀 Field validation: ACTIVE");
+    println!("🚫 Field switching validation: ACTIVE");
+    println!("📊 Try typing in fields with minimum requirements!");
+    println!("   - Password (min 5): Type 1-4 chars, then try to switch fields");
+    println!("   - ID (min 3): Type 1-2 chars, then try to switch fields");
+    println!("   - Comment (min 10): Type 1-9 chars, then try to switch fields");
+    println!("   - Unicode (min 2): Type 1 char, then try to switch fields");
+    println!();
+
+    enable_raw_mode()?;
+    let mut stdout = io::stdout();
+    execute!(stdout, EnterAlternateScreen, EnableMouseCapture)?;
+    let backend = CrosstermBackend::new(stdout);
+    let mut terminal = Terminal::new(backend)?;
+
+    let data = ValidationDemoData::new();
+    let editor = ValidationFormEditor::new(data);
+
+    let res = run_app(&mut terminal, editor);
+
+    disable_raw_mode()?;
+    execute!(
+        terminal.backend_mut(),
+        LeaveAlternateScreen,
+        DisableMouseCapture
+    )?;
+    terminal.show_cursor()?;
+
+    if let Err(err) = res {
+        println!("{:?}", err);
+    }
+
+    println!("🔍 Validation demo completed!");
+    Ok(())
+}

canvas/src/canvas/state.rs

@@ -10,15 +10,19 @@ pub struct EditorState {
     pub(crate) current_field: usize,
     pub(crate) cursor_pos: usize,
     pub(crate) ideal_cursor_column: usize,
-    
-    // Mode state  
+
+    // Mode state
     pub(crate) current_mode: AppMode,
-    
+
     // Autocomplete state
     pub(crate) autocomplete: AutocompleteUIState,
-    
+
     // Selection state (for vim visual mode)
     pub(crate) selection: SelectionState,
+    
+    // Validation state (only available with validation feature)
+    #[cfg(feature = "validation")]
+    pub(crate) validation: crate::validation::ValidationState,
 }
 
 #[derive(Debug, Clone)]
@@ -50,52 +54,61 @@ impl EditorState {
                 active_field: None,
             },
             selection: SelectionState::None,
+            #[cfg(feature = "validation")]
+            validation: crate::validation::ValidationState::new(),
         }
     }
-    
+
     // ===================================================================
     // READ-ONLY ACCESS: User can fetch UI state for compatibility
     // ===================================================================
-    
+
     /// Get current field index (for user's business logic)
     pub fn current_field(&self) -> usize {
         self.current_field
     }
-    
-    /// Get current cursor position (for user's business logic)  
+
+    /// Get current cursor position (for user's business logic)
     pub fn cursor_position(&self) -> usize {
         self.cursor_pos
     }
 
     /// Get ideal cursor column (for vim-like behavior)
-    pub fn ideal_cursor_column(&self) -> usize {  // ADD THIS
+    pub fn ideal_cursor_column(&self) -> usize {
         self.ideal_cursor_column
     }
-    
+
     /// Get current mode (for user's business logic)
     pub fn mode(&self) -> AppMode {
         self.current_mode
     }
-    
+
     /// Check if autocomplete is active (for user's business logic)
     pub fn is_autocomplete_active(&self) -> bool {
         self.autocomplete.is_active
     }
-    
+
     /// Check if autocomplete is loading (for user's business logic)
     pub fn is_autocomplete_loading(&self) -> bool {
         self.autocomplete.is_loading
     }
-    
+
     /// Get selection state (for user's business logic)
     pub fn selection_state(&self) -> &SelectionState {
         &self.selection
     }
     
+    /// Get validation state (for user's business logic)
+    /// Only available when the 'validation' feature is enabled
+    #[cfg(feature = "validation")]
+    pub fn validation_state(&self) -> &crate::validation::ValidationState {
+        &self.validation
+    }
+
     // ===================================================================
     // INTERNAL MUTATIONS: Only library modifies these
     // ===================================================================
-    
+
     pub(crate) fn move_to_field(&mut self, field_index: usize, field_count: usize) {
         if field_index < field_count {
             self.current_field = field_index;
@@ -103,7 +116,7 @@ impl EditorState {
             self.cursor_pos = 0;
         }
     }
-    
+
     pub(crate) fn set_cursor(&mut self, position: usize, max_position: usize, for_edit_mode: bool) {
         if for_edit_mode {
             // Edit mode: can go past end for insertion
@@ -114,14 +127,14 @@ impl EditorState {
         }
         self.ideal_cursor_column = self.cursor_pos;
     }
-    
+
     pub(crate) fn activate_autocomplete(&mut self, field_index: usize) {
         self.autocomplete.is_active = true;
         self.autocomplete.is_loading = true;
         self.autocomplete.active_field = Some(field_index);
         self.autocomplete.selected_index = None;
     }
-    
+
     pub(crate) fn deactivate_autocomplete(&mut self) {
         self.autocomplete.is_active = false;
         self.autocomplete.is_loading = false;

canvas/src/data_provider.rs

@@ -27,6 +27,13 @@ pub trait DataProvider {
     fn display_value(&self, _index: usize) -> Option<&str> {
         None // Default: use actual value
     }
+    
+    /// Get validation configuration for a field (optional)
+    /// Only available when the 'validation' feature is enabled
+    #[cfg(feature = "validation")]
+    fn validation_config(&self, _field_index: usize) -> Option<crate::validation::ValidationConfig> {
+        None
+    }
 }
 
 /// Optional: User implements this for autocomplete data

canvas/src/editor.rs

@@ -26,10 +26,29 @@ pub struct FormEditor<D: DataProvider> {
 
 impl<D: DataProvider> FormEditor<D> {
     pub fn new(data_provider: D) -> Self {
-        Self {
+        let mut editor = Self {
             ui_state: EditorState::new(),
             data_provider,
             suggestions: Vec::new(),
+        };
+        
+        // Initialize validation configurations if validation feature is enabled
+        #[cfg(feature = "validation")]
+        {
+            editor.initialize_validation();
+        }
+        
+        editor
+    }
+    
+    /// Initialize validation configurations from data provider
+    #[cfg(feature = "validation")]
+    fn initialize_validation(&mut self) {
+        let field_count = self.data_provider.field_count();
+        for field_index in 0..field_count {
+            if let Some(config) = self.data_provider.validation_config(field_index) {
+                self.ui_state.validation.set_field_config(field_index, config);
+            }
         }
     }
 
@@ -81,6 +100,25 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn suggestions(&self) -> &[SuggestionItem] {
         &self.suggestions
     }
+    
+    /// Get validation state (for user's business logic)
+    /// Only available when the 'validation' feature is enabled
+    #[cfg(feature = "validation")]
+    pub fn validation_state(&self) -> &crate::validation::ValidationState {
+        self.ui_state.validation_state()
+    }
+    
+    /// Get validation result for current field
+    #[cfg(feature = "validation")]
+    pub fn current_field_validation(&self) -> Option<&crate::validation::ValidationResult> {
+        self.ui_state.validation.get_field_result(self.ui_state.current_field)
+    }
+    
+    /// Get validation result for specific field
+    #[cfg(feature = "validation")]
+    pub fn field_validation(&self, field_index: usize) -> Option<&crate::validation::ValidationResult> {
+        self.ui_state.validation.get_field_result(field_index)
+    }
 
     // ===================================================================
     // SYNC OPERATIONS: No async needed for basic editing
@@ -96,13 +134,36 @@ impl<D: DataProvider> FormEditor<D> {
         let cursor_pos = self.ui_state.cursor_pos;
 
         // Get current text from user
-        let mut current_text = self.data_provider.field_value(field_index).to_string();
+        let current_text = self.data_provider.field_value(field_index);
+
+        // Validate character insertion if validation is enabled
+        #[cfg(feature = "validation")]
+        {
+            let validation_result = self.ui_state.validation.validate_char_insertion(
+                field_index,
+                current_text,
+                cursor_pos,
+                ch,
+            );
+            
+            // Reject input if validation failed with error
+            if !validation_result.is_acceptable() {
+                // Log validation failure for debugging
+                tracing::debug!(
+                    "Character insertion rejected for field {}: {:?}",
+                    field_index,
+                    validation_result
+                );
+                return Ok(()); // Silently reject invalid input
+            }
+        }
 
         // Insert character
-        current_text.insert(cursor_pos, ch);
+        let mut new_text = current_text.to_string();
+        new_text.insert(cursor_pos, ch);
 
         // Update user's data
-        self.data_provider.set_field_value(field_index, current_text);
+        self.data_provider.set_field_value(field_index, new_text);
 
         // Update library's UI state
         self.ui_state.cursor_pos += 1;
@@ -137,6 +198,19 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn move_to_next_field(&mut self) {
         let field_count = self.data_provider.field_count();
         let next_field = (self.ui_state.current_field + 1) % field_count;
+        
+        // Validate current field content before moving if validation is enabled
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text().to_string(); // Convert to String to avoid borrow conflicts
+            let _validation_result = self.ui_state.validation.validate_field_content(
+                self.ui_state.current_field,
+                &current_text,
+            );
+            // Note: We don't prevent field switching on validation failure,
+            // just record the validation state
+        }
+        
         self.ui_state.move_to_field(next_field, field_count);
 
         // Clamp cursor to new field
@@ -166,7 +240,7 @@ impl<D: DataProvider> FormEditor<D> {
                 if new_mode != AppMode::Highlight {
                     self.ui_state.selection = SelectionState::None;
                 }
-                
+
                 #[cfg(feature = "cursor-style")]
                 {
                     let _ = CursorManager::update_for_mode(new_mode);
@@ -178,22 +252,95 @@ impl<D: DataProvider> FormEditor<D> {
     /// Enter edit mode with cursor positioned for append (vim 'a' command)
     pub fn enter_append_mode(&mut self) {
         let current_text = self.current_text();
-        
+
         // Calculate append position: always move right, even at line end
         let append_pos = if current_text.is_empty() {
             0
         } else {
             (self.ui_state.cursor_pos + 1).min(current_text.len())
         };
-        
+
         // Set cursor position for append
         self.ui_state.cursor_pos = append_pos;
         self.ui_state.ideal_cursor_column = append_pos;
-        
+
         // Enter edit mode (which will update cursor style)
         self.set_mode(AppMode::Edit);
     }
 
+    // ===================================================================
+    // VALIDATION METHODS (only available with validation feature)
+    // ===================================================================
+    
+    /// Enable or disable validation
+    #[cfg(feature = "validation")]
+    pub fn set_validation_enabled(&mut self, enabled: bool) {
+        self.ui_state.validation.set_enabled(enabled);
+    }
+    
+    /// Check if validation is enabled
+    #[cfg(feature = "validation")]
+    pub fn is_validation_enabled(&self) -> bool {
+        self.ui_state.validation.is_enabled()
+    }
+    
+    /// Set validation configuration for a specific field
+    #[cfg(feature = "validation")]
+    pub fn set_field_validation(&mut self, field_index: usize, config: crate::validation::ValidationConfig) {
+        self.ui_state.validation.set_field_config(field_index, config);
+    }
+    
+    /// Remove validation configuration for a specific field
+    #[cfg(feature = "validation")]
+    pub fn remove_field_validation(&mut self, field_index: usize) {
+        self.ui_state.validation.remove_field_config(field_index);
+    }
+    
+    /// Manually validate current field content
+    #[cfg(feature = "validation")]
+    pub fn validate_current_field(&mut self) -> crate::validation::ValidationResult {
+        let field_index = self.ui_state.current_field;
+        let current_text = self.current_text().to_string();
+        self.ui_state.validation.validate_field_content(field_index, &current_text)
+    }
+    
+    /// Manually validate specific field content
+    #[cfg(feature = "validation")]
+    pub fn validate_field(&mut self, field_index: usize) -> Option<crate::validation::ValidationResult> {
+        if field_index < self.data_provider.field_count() {
+            let text = self.data_provider.field_value(field_index).to_string();
+            Some(self.ui_state.validation.validate_field_content(field_index, &text))
+        } else {
+            None
+        }
+    }
+    
+    /// Clear validation results for all fields
+    #[cfg(feature = "validation")]
+    pub fn clear_validation_results(&mut self) {
+        self.ui_state.validation.clear_all_results();
+    }
+    
+    /// Get validation summary for all fields
+    #[cfg(feature = "validation")]
+    pub fn validation_summary(&self) -> crate::validation::ValidationSummary {
+        self.ui_state.validation.summary()
+    }
+    
+    /// Check if field switching is allowed from current field
+    #[cfg(feature = "validation")]
+    pub fn can_switch_fields(&self) -> bool {
+        let current_text = self.current_text();
+        self.ui_state.validation.allows_field_switch(self.ui_state.current_field, current_text)
+    }
+    
+    /// Get reason why field switching is blocked (if any)
+    #[cfg(feature = "validation")]
+    pub fn field_switch_block_reason(&self) -> Option<String> {
+        let current_text = self.current_text();
+        self.ui_state.validation.field_switch_block_reason(self.ui_state.current_field, current_text)
+    }
+
     // ===================================================================
     // ASYNC OPERATIONS: Only autocomplete needs async
     // ===================================================================
@@ -255,6 +402,15 @@ impl<D: DataProvider> FormEditor<D> {
                 // Close autocomplete
                 self.ui_state.deactivate_autocomplete();
                 self.suggestions.clear();
+                
+                // Validate the new content if validation is enabled
+                #[cfg(feature = "validation")]
+                {
+                    let _validation_result = self.ui_state.validation.validate_field_content(
+                        field_index,
+                        &suggestion.value_to_store,
+                    );
+                }
 
                 return Some(suggestion.display_text);
             }
@@ -263,35 +419,81 @@ impl<D: DataProvider> FormEditor<D> {
     }
 
     // ===================================================================
-    // ADD THESE MISSING MOVEMENT METHODS
+    // MOVEMENT METHODS (keeping existing implementations)
     // ===================================================================
 
     /// Move to previous field (vim k / up arrow)
-    pub fn move_up(&mut self) {
+    pub fn move_up(&mut self) -> Result<()> {
         let field_count = self.data_provider.field_count();
         if field_count == 0 {
-            return;
+            return Ok(());
         }
-        
+
+        // Check if field switching is allowed (minimum character enforcement)
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text();
+            if !self.ui_state.validation.allows_field_switch(self.ui_state.current_field, current_text) {
+                if let Some(reason) = self.ui_state.validation.field_switch_block_reason(self.ui_state.current_field, current_text) {
+                    tracing::debug!("Field switch blocked: {}", reason);
+                    return Err(anyhow::anyhow!("Cannot switch fields: {}", reason));
+                }
+            }
+        }
+
+        // Validate current field before moving
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text().to_string(); // Convert to String to avoid borrow conflicts
+            let _validation_result = self.ui_state.validation.validate_field_content(
+                self.ui_state.current_field,
+                &current_text,
+            );
+        }
+
         let current_field = self.ui_state.current_field;
         let new_field = current_field.saturating_sub(1);
-        
+
         self.ui_state.move_to_field(new_field, field_count);
         self.clamp_cursor_to_current_field();
+        Ok(())
     }
 
-    /// Move to next field (vim j / down arrow) 
-    pub fn move_down(&mut self) {
+    /// Move to next field (vim j / down arrow)
+    pub fn move_down(&mut self) -> Result<()> {
         let field_count = self.data_provider.field_count();
         if field_count == 0 {
-            return;
+            return Ok(());
         }
-        
+
+        // Check if field switching is allowed (minimum character enforcement)
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text();
+            if !self.ui_state.validation.allows_field_switch(self.ui_state.current_field, current_text) {
+                if let Some(reason) = self.ui_state.validation.field_switch_block_reason(self.ui_state.current_field, current_text) {
+                    tracing::debug!("Field switch blocked: {}", reason);
+                    return Err(anyhow::anyhow!("Cannot switch fields: {}", reason));
+                }
+            }
+        }
+
+        // Validate current field before moving
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text().to_string(); // Convert to String to avoid borrow conflicts
+            let _validation_result = self.ui_state.validation.validate_field_content(
+                self.ui_state.current_field,
+                &current_text,
+            );
+        }
+
         let current_field = self.ui_state.current_field;
         let new_field = (current_field + 1).min(field_count - 1);
-        
+
         self.ui_state.move_to_field(new_field, field_count);
         self.clamp_cursor_to_current_field();
+        Ok(())
     }
 
     /// Move to first field (vim gg)
@@ -300,7 +502,7 @@ impl<D: DataProvider> FormEditor<D> {
         if field_count == 0 {
             return;
         }
-        
+
         self.ui_state.move_to_field(0, field_count);
         self.clamp_cursor_to_current_field();
     }
@@ -311,20 +513,20 @@ impl<D: DataProvider> FormEditor<D> {
         if field_count == 0 {
             return;
         }
-        
+
         let last_field = field_count - 1;
         self.ui_state.move_to_field(last_field, field_count);
         self.clamp_cursor_to_current_field();
     }
 
     /// Move to previous field (alternative to move_up)
-    pub fn prev_field(&mut self) {
-        self.move_up();
+    pub fn prev_field(&mut self) -> Result<()> {
+        self.move_up()
     }
 
-    /// Move to next field (alternative to move_down) 
-    pub fn next_field(&mut self) {
-        self.move_down();
+    /// Move to next field (alternative to move_down)
+    pub fn next_field(&mut self) -> Result<()> {
+        self.move_down()
     }
 
     /// Move to start of current field (vim 0)
@@ -340,7 +542,7 @@ impl<D: DataProvider> FormEditor<D> {
         use crate::canvas::actions::movement::line::line_end_position;
         let current_text = self.current_text();
         let is_edit_mode = self.ui_state.current_mode == AppMode::Edit;
-        
+
         let new_pos = line_end_position(current_text, is_edit_mode);
         self.ui_state.cursor_pos = new_pos;
         self.ui_state.ideal_cursor_column = new_pos;
@@ -350,21 +552,21 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn move_word_next(&mut self) {
         use crate::canvas::actions::movement::word::find_next_word_start;
         let current_text = self.current_text();
-        
+
         if current_text.is_empty() {
             return;
         }
-        
+
         let new_pos = find_next_word_start(current_text, self.ui_state.cursor_pos);
         let is_edit_mode = self.ui_state.current_mode == AppMode::Edit;
-        
+
         // Clamp to valid bounds for current mode
         let final_pos = if is_edit_mode {
             new_pos.min(current_text.len())
         } else {
             new_pos.min(current_text.len().saturating_sub(1))
         };
-        
+
         self.ui_state.cursor_pos = final_pos;
         self.ui_state.ideal_cursor_column = final_pos;
     }
@@ -373,11 +575,11 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn move_word_prev(&mut self) {
         use crate::canvas::actions::movement::word::find_prev_word_start;
         let current_text = self.current_text();
-        
+
         if current_text.is_empty() {
             return;
         }
-        
+
         let new_pos = find_prev_word_start(current_text, self.ui_state.cursor_pos);
         self.ui_state.cursor_pos = new_pos;
         self.ui_state.ideal_cursor_column = new_pos;
@@ -387,21 +589,21 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn move_word_end(&mut self) {
         use crate::canvas::actions::movement::word::find_word_end;
         let current_text = self.current_text();
-        
+
         if current_text.is_empty() {
             return;
         }
-        
+
         let current_pos = self.ui_state.cursor_pos;
         let new_pos = find_word_end(current_text, current_pos);
-        
+
         // If we didn't move, try next word
         let final_pos = if new_pos == current_pos && current_pos + 1 < current_text.len() {
             find_word_end(current_text, current_pos + 1)
         } else {
             new_pos
         };
-        
+
         // Clamp for read-only mode
         let is_edit_mode = self.ui_state.current_mode == AppMode::Edit;
         let clamped_pos = if is_edit_mode {
@@ -409,7 +611,7 @@ impl<D: DataProvider> FormEditor<D> {
         } else {
             final_pos.min(current_text.len().saturating_sub(1))
         };
-        
+
         self.ui_state.cursor_pos = clamped_pos;
         self.ui_state.ideal_cursor_column = clamped_pos;
     }
@@ -418,11 +620,11 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn move_word_end_prev(&mut self) {
         use crate::canvas::actions::movement::word::find_prev_word_end;
         let current_text = self.current_text();
-        
+
         if current_text.is_empty() {
             return;
         }
-        
+
         let new_pos = find_prev_word_end(current_text, self.ui_state.cursor_pos);
         self.ui_state.cursor_pos = new_pos;
         self.ui_state.ideal_cursor_column = new_pos;
@@ -433,21 +635,30 @@ impl<D: DataProvider> FormEditor<D> {
         if self.ui_state.current_mode != AppMode::Edit {
             return Ok(()); // Silently ignore in non-edit modes
         }
-        
+
         if self.ui_state.cursor_pos == 0 {
             return Ok(()); // Nothing to delete
         }
-        
+
         let field_index = self.ui_state.current_field;
         let mut current_text = self.data_provider.field_value(field_index).to_string();
-        
+
         if self.ui_state.cursor_pos <= current_text.len() {
             current_text.remove(self.ui_state.cursor_pos - 1);
-            self.data_provider.set_field_value(field_index, current_text);
+            self.data_provider.set_field_value(field_index, current_text.clone());
             self.ui_state.cursor_pos -= 1;
             self.ui_state.ideal_cursor_column = self.ui_state.cursor_pos;
+            
+            // Validate the new content if validation is enabled
+            #[cfg(feature = "validation")]
+            {
+                let _validation_result = self.ui_state.validation.validate_field_content(
+                    field_index,
+                    &current_text,
+                );
+            }
         }
-        
+
         Ok(())
     }
 
@@ -456,21 +667,40 @@ impl<D: DataProvider> FormEditor<D> {
         if self.ui_state.current_mode != AppMode::Edit {
             return Ok(()); // Silently ignore in non-edit modes
         }
-        
+
         let field_index = self.ui_state.current_field;
         let mut current_text = self.data_provider.field_value(field_index).to_string();
-        
+
         if self.ui_state.cursor_pos < current_text.len() {
             current_text.remove(self.ui_state.cursor_pos);
-            self.data_provider.set_field_value(field_index, current_text);
+            self.data_provider.set_field_value(field_index, current_text.clone());
+            
+            // Validate the new content if validation is enabled
+            #[cfg(feature = "validation")]
+            {
+                let _validation_result = self.ui_state.validation.validate_field_content(
+                    field_index,
+                    &current_text,
+                );
+            }
         }
-        
+
         Ok(())
     }
 
     /// Exit edit mode to read-only mode (vim Escape)
-    // TODO this is still flickering, I have no clue how to fix it
-    pub fn exit_edit_mode(&mut self) {
+    pub fn exit_edit_mode(&mut self) -> Result<()> {
+        // Validate current field content when exiting edit mode
+        #[cfg(feature = "validation")]
+        {
+            let current_text = self.current_text();
+            if !self.ui_state.validation.allows_field_switch(self.ui_state.current_field, current_text) {
+                if let Some(reason) = self.ui_state.validation.field_switch_block_reason(self.ui_state.current_field, current_text) {
+                    return Err(anyhow::anyhow!("Cannot exit edit mode: {}", reason));
+                }
+            }
+        }
+        
         // Adjust cursor position when transitioning from edit to normal mode
         let current_text = self.current_text();
         if !current_text.is_empty() {
@@ -485,6 +715,8 @@ impl<D: DataProvider> FormEditor<D> {
         self.set_mode(AppMode::ReadOnly);
         // Deactivate autocomplete when exiting edit mode
         self.ui_state.deactivate_autocomplete();
+
+        Ok(())
     }
 
     /// Enter edit mode from read-only mode (vim i/a/o)
@@ -500,44 +732,62 @@ impl<D: DataProvider> FormEditor<D> {
     fn clamp_cursor_to_current_field(&mut self) {
         let current_text = self.current_text();
         let is_edit_mode = self.ui_state.current_mode == AppMode::Edit;
-        
+
         use crate::canvas::actions::movement::line::safe_cursor_position;
         let safe_pos = safe_cursor_position(
-            current_text, 
-            self.ui_state.ideal_cursor_column, 
+            current_text,
+            self.ui_state.ideal_cursor_column,
             is_edit_mode
         );
-        
+
         self.ui_state.cursor_pos = safe_pos;
     }
 
-  
+
     /// Set the value of the current field
     pub fn set_current_field_value(&mut self, value: String) {
         let field_index = self.ui_state.current_field;
-        self.data_provider.set_field_value(field_index, value);
+        self.data_provider.set_field_value(field_index, value.clone());
         // Reset cursor to start of field
         self.ui_state.cursor_pos = 0;
         self.ui_state.ideal_cursor_column = 0;
+        
+        // Validate the new content if validation is enabled
+        #[cfg(feature = "validation")]
+        {
+            let _validation_result = self.ui_state.validation.validate_field_content(
+                field_index,
+                &value,
+            );
+        }
     }
-    
+
     /// Set the value of a specific field by index
     pub fn set_field_value(&mut self, field_index: usize, value: String) {
         if field_index < self.data_provider.field_count() {
-            self.data_provider.set_field_value(field_index, value);
+            self.data_provider.set_field_value(field_index, value.clone());
             // If we're modifying the current field, reset cursor
             if field_index == self.ui_state.current_field {
                 self.ui_state.cursor_pos = 0;
                 self.ui_state.ideal_cursor_column = 0;
             }
+            
+            // Validate the new content if validation is enabled
+            #[cfg(feature = "validation")]
+            {
+                let _validation_result = self.ui_state.validation.validate_field_content(
+                    field_index,
+                    &value,
+                );
+            }
         }
     }
-    
+
     /// Clear the current field (set to empty string)
     pub fn clear_current_field(&mut self) {
         self.set_current_field_value(String::new());
     }
-    
+
     /// Get mutable access to data provider (for advanced operations)
     pub fn data_provider_mut(&mut self) -> &mut D {
         &mut self.data_provider
@@ -547,16 +797,16 @@ impl<D: DataProvider> FormEditor<D> {
     pub fn set_cursor_position(&mut self, position: usize) {
         let current_text = self.current_text();
         let is_edit_mode = self.ui_state.current_mode == AppMode::Edit;
-        
+
         // Clamp to valid bounds for current mode
         let max_pos = if is_edit_mode {
             current_text.len() // Edit mode: can go past end
         } else {
             current_text.len().saturating_sub(1).max(0) // Read-only: stay within text
         };
-        
+
         let clamped_pos = position.min(max_pos);
-        
+
         // Update cursor position directly
         self.ui_state.cursor_pos = clamped_pos;
         self.ui_state.ideal_cursor_column = clamped_pos;
@@ -565,7 +815,7 @@ impl<D: DataProvider> FormEditor<D> {
     /// Get cursor position for display (respects mode-specific positioning rules)
     pub fn display_cursor_position(&self) -> usize {
         let current_text = self.current_text();
-        
+
         match self.ui_state.current_mode {
             AppMode::Edit => {
                 // Edit mode: cursor can be past end of text
@@ -606,7 +856,7 @@ impl<D: DataProvider> FormEditor<D> {
             self.ui_state.selection = SelectionState::Characterwise {
                 anchor: (self.ui_state.current_field, self.ui_state.cursor_pos),
             };
-            
+
             #[cfg(feature = "cursor-style")]
             {
                 let _ = CursorManager::update_for_mode(AppMode::Highlight);
@@ -621,7 +871,7 @@ impl<D: DataProvider> FormEditor<D> {
             self.ui_state.selection = SelectionState::Linewise {
                 anchor_field: self.ui_state.current_field,
             };
-            
+
             #[cfg(feature = "cursor-style")]
             {
                 let _ = CursorManager::update_for_mode(AppMode::Highlight);
@@ -634,7 +884,7 @@ impl<D: DataProvider> FormEditor<D> {
         if self.ui_state.current_mode == AppMode::Highlight {
             self.ui_state.current_mode = AppMode::ReadOnly;
             self.ui_state.selection = SelectionState::None;
-            
+
             #[cfg(feature = "cursor-style")]
             {
                 let _ = CursorManager::update_for_mode(AppMode::ReadOnly);

canvas/src/lib.rs

@@ -8,6 +8,10 @@ pub mod data_provider;
 #[cfg(feature = "autocomplete")]
 pub mod autocomplete;
 
+// Only include validation module if feature is enabled
+#[cfg(feature = "validation")]
+pub mod validation;
+
 #[cfg(feature = "cursor-style")]
 pub use canvas::CursorManager;
 
@@ -26,6 +30,14 @@ pub use canvas::modes::AppMode;
 // Actions and results (for users who want to handle actions manually)
 pub use canvas::actions::{CanvasAction, ActionResult};
 
+// Validation exports (only when validation feature is enabled)
+#[cfg(feature = "validation")]
+pub use validation::{
+    ValidationConfig, ValidationResult, ValidationError,
+    CharacterLimits, ValidationConfigBuilder, ValidationState,
+    ValidationSummary,
+};
+
 // Theming and GUI
 #[cfg(feature = "gui")]
 pub use canvas::theme::{CanvasTheme, DefaultCanvasTheme};

canvas/src/validation/config.rs

@@ -0,0 +1,235 @@
+// src/validation/config.rs
+//! Validation configuration types and builders
+
+use crate::validation::CharacterLimits;
+use serde::{Deserialize, Serialize};
+
+/// Main validation configuration for a field
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct ValidationConfig {
+    /// Character limit configuration
+    pub character_limits: Option<CharacterLimits>,
+    
+    /// Future: Predefined patterns
+    #[serde(skip)]
+    pub patterns: Option<()>, // Placeholder for future implementation
+    
+    /// Future: Reserved characters
+    #[serde(skip)]
+    pub reserved_chars: Option<()>, // Placeholder for future implementation
+    
+    /// Future: Custom formatting
+    #[serde(skip)]
+    pub custom_formatting: Option<()>, // Placeholder for future implementation
+    
+    /// Future: External validation
+    #[serde(skip)]
+    pub external_validation: Option<()>, // Placeholder for future implementation
+}
+
+/// Builder for creating validation configurations
+#[derive(Debug, Default)]
+pub struct ValidationConfigBuilder {
+    config: ValidationConfig,
+}
+
+impl ValidationConfigBuilder {
+    /// Create a new validation config builder
+    pub fn new() -> Self {
+        Self::default()
+    }
+    
+    /// Set character limits for the field
+    pub fn with_character_limits(mut self, limits: CharacterLimits) -> Self {
+        self.config.character_limits = Some(limits);
+        self
+    }
+    
+    /// Set maximum number of characters (convenience method)
+    pub fn with_max_length(mut self, max_length: usize) -> Self {
+        self.config.character_limits = Some(CharacterLimits::new(max_length));
+        self
+    }
+    
+    /// Build the final validation configuration
+    pub fn build(self) -> ValidationConfig {
+        self.config
+    }
+}
+
+/// Result of a validation operation
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ValidationResult {
+    /// Validation passed
+    Valid,
+    
+    /// Validation failed with warning (input still accepted)
+    Warning { message: String },
+    
+    /// Validation failed with error (input rejected)
+    Error { message: String },
+}
+
+impl ValidationResult {
+    /// Check if the validation result allows the input
+    pub fn is_acceptable(&self) -> bool {
+        matches!(self, ValidationResult::Valid | ValidationResult::Warning { .. })
+    }
+    
+    /// Check if the validation result is an error
+    pub fn is_error(&self) -> bool {
+        matches!(self, ValidationResult::Error { .. })
+    }
+    
+    /// Get the message if there is one
+    pub fn message(&self) -> Option<&str> {
+        match self {
+            ValidationResult::Valid => None,
+            ValidationResult::Warning { message } => Some(message),
+            ValidationResult::Error { message } => Some(message),
+        }
+    }
+    
+    /// Create a warning result
+    pub fn warning(message: impl Into<String>) -> Self {
+        ValidationResult::Warning { message: message.into() }
+    }
+    
+    /// Create an error result
+    pub fn error(message: impl Into<String>) -> Self {
+        ValidationResult::Error { message: message.into() }
+    }
+}
+
+impl ValidationConfig {
+    /// Create a new empty validation configuration
+    pub fn new() -> Self {
+        Self::default()
+    }
+    
+    /// Create a configuration with just character limits
+    pub fn with_max_length(max_length: usize) -> Self {
+        ValidationConfigBuilder::new()
+            .with_max_length(max_length)
+            .build()
+    }
+    
+    /// Validate a character insertion at a specific position
+    pub fn validate_char_insertion(
+        &self,
+        current_text: &str,
+        position: usize,
+        character: char,
+    ) -> ValidationResult {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            if let Some(result) = limits.validate_insertion(current_text, position, character) {
+                if !result.is_acceptable() {
+                    return result;
+                }
+            }
+        }
+        
+        // Future: Add other validation types here
+        
+        ValidationResult::Valid
+    }
+    
+    /// Validate the current text content
+    pub fn validate_content(&self, text: &str) -> ValidationResult {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            if let Some(result) = limits.validate_content(text) {
+                if !result.is_acceptable() {
+                    return result;
+                }
+            }
+        }
+        
+        // Future: Add other validation types here
+        
+        ValidationResult::Valid
+    }
+    
+    /// Check if any validation rules are configured
+    pub fn has_validation(&self) -> bool {
+        self.character_limits.is_some()
+        // || self.patterns.is_some()
+        // || self.reserved_chars.is_some()
+        // || self.custom_formatting.is_some()
+        // || self.external_validation.is_some()
+    }
+    pub fn allows_field_switch(&self, text: &str) -> bool {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            if !limits.allows_field_switch(text) {
+                return false;
+            }
+        }
+        
+        // Future: Add other validation types here
+        
+        true
+    }
+    
+    /// Get reason why field switching is blocked (if any)
+    pub fn field_switch_block_reason(&self, text: &str) -> Option<String> {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            if let Some(reason) = limits.field_switch_block_reason(text) {
+                return Some(reason);
+            }
+        }
+        
+        // Future: Add other validation types here
+        
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_validation_config_builder() {
+        let config = ValidationConfigBuilder::new()
+            .with_max_length(10)
+            .build();
+        
+        assert!(config.character_limits.is_some());
+        assert_eq!(config.character_limits.unwrap().max_length(), Some(10));
+    }
+    
+    #[test]
+    fn test_validation_result() {
+        let valid = ValidationResult::Valid;
+        assert!(valid.is_acceptable());
+        assert!(!valid.is_error());
+        assert_eq!(valid.message(), None);
+        
+        let warning = ValidationResult::warning("Too long");
+        assert!(warning.is_acceptable());
+        assert!(!warning.is_error());
+        assert_eq!(warning.message(), Some("Too long"));
+        
+        let error = ValidationResult::error("Invalid");
+        assert!(!error.is_acceptable());
+        assert!(error.is_error());
+        assert_eq!(error.message(), Some("Invalid"));
+    }
+    
+    #[test]
+    fn test_config_with_max_length() {
+        let config = ValidationConfig::with_max_length(5);
+        assert!(config.has_validation());
+        
+        // Test valid insertion
+        let result = config.validate_char_insertion("test", 4, 'x');
+        assert!(result.is_acceptable());
+        
+        // Test invalid insertion (would exceed limit)
+        let result = config.validate_char_insertion("tests", 5, 'x');
+        assert!(!result.is_acceptable());
+    }
+}

canvas/src/validation/limits.rs

@@ -0,0 +1,424 @@
+// src/validation/limits.rs
+//! Character limits validation implementation
+
+use crate::validation::ValidationResult;
+use serde::{Deserialize, Serialize};
+use unicode_width::UnicodeWidthStr;
+
+/// Character limits configuration for a field
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct CharacterLimits {
+    /// Maximum number of characters allowed (None = unlimited)
+    max_length: Option<usize>,
+    
+    /// Minimum number of characters required (None = no minimum)
+    min_length: Option<usize>,
+    
+    /// Warning threshold (warn when approaching max limit)
+    warning_threshold: Option<usize>,
+    
+    /// Count mode: characters vs display width
+    count_mode: CountMode,
+}
+
+/// How to count characters for limit checking
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub enum CountMode {
+    /// Count actual characters (default)
+    Characters,
+    
+    /// Count display width (useful for CJK characters)
+    DisplayWidth,
+    
+    /// Count bytes (rarely used, but available)
+    Bytes,
+}
+
+impl Default for CountMode {
+    fn default() -> Self {
+        CountMode::Characters
+    }
+}
+
+/// Result of a character limit check
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum LimitCheckResult {
+    /// Within limits
+    Ok,
+    
+    /// Approaching limit (warning)
+    Warning { current: usize, max: usize },
+    
+    /// At or exceeding limit (error)
+    Exceeded { current: usize, max: usize },
+    
+    /// Below minimum length
+    TooShort { current: usize, min: usize },
+}
+
+impl CharacterLimits {
+    /// Create new character limits with just max length
+    pub fn new(max_length: usize) -> Self {
+        Self {
+            max_length: Some(max_length),
+            min_length: None,
+            warning_threshold: None,
+            count_mode: CountMode::default(),
+        }
+    }
+    
+    /// Create new character limits with min and max
+    pub fn new_range(min_length: usize, max_length: usize) -> Self {
+        Self {
+            max_length: Some(max_length),
+            min_length: Some(min_length),
+            warning_threshold: None,
+            count_mode: CountMode::default(),
+        }
+    }
+    
+    /// Set warning threshold (when to show warning before hitting limit)
+    pub fn with_warning_threshold(mut self, threshold: usize) -> Self {
+        self.warning_threshold = Some(threshold);
+        self
+    }
+    
+    /// Set count mode (characters vs display width vs bytes)
+    pub fn with_count_mode(mut self, mode: CountMode) -> Self {
+        self.count_mode = mode;
+        self
+    }
+    
+    /// Get maximum length
+    pub fn max_length(&self) -> Option<usize> {
+        self.max_length
+    }
+    
+    /// Get minimum length
+    pub fn min_length(&self) -> Option<usize> {
+        self.min_length
+    }
+    
+    /// Get warning threshold
+    pub fn warning_threshold(&self) -> Option<usize> {
+        self.warning_threshold
+    }
+    
+    /// Get count mode
+    pub fn count_mode(&self) -> CountMode {
+        self.count_mode
+    }
+    
+    /// Count characters/width/bytes according to the configured mode
+    fn count(&self, text: &str) -> usize {
+        match self.count_mode {
+            CountMode::Characters => text.chars().count(),
+            CountMode::DisplayWidth => text.width(),
+            CountMode::Bytes => text.len(),
+        }
+    }
+    
+    /// Check if inserting a character would exceed limits
+    pub fn validate_insertion(
+        &self,
+        current_text: &str,
+        _position: usize,
+        character: char,
+    ) -> Option<ValidationResult> {
+        let current_count = self.count(current_text);
+        let char_count = match self.count_mode {
+            CountMode::Characters => 1,
+            CountMode::DisplayWidth => {
+                let char_str = character.to_string();
+                char_str.width()
+            },
+            CountMode::Bytes => character.len_utf8(),
+        };
+        let new_count = current_count + char_count;
+        
+        // Check max length
+        if let Some(max) = self.max_length {
+            if new_count > max {
+                return Some(ValidationResult::error(format!(
+                    "Character limit exceeded: {}/{}", 
+                    new_count, 
+                    max
+                )));
+            }
+            
+            // Check warning threshold
+            if let Some(warning_threshold) = self.warning_threshold {
+                if new_count >= warning_threshold && current_count < warning_threshold {
+                    return Some(ValidationResult::warning(format!(
+                        "Approaching character limit: {}/{}", 
+                        new_count, 
+                        max
+                    )));
+                }
+            }
+        }
+        
+        None // No validation issues
+    }
+    
+    /// Validate the current content
+    pub fn validate_content(&self, text: &str) -> Option<ValidationResult> {
+        let count = self.count(text);
+        
+        // Check minimum length
+        if let Some(min) = self.min_length {
+            if count < min {
+                return Some(ValidationResult::warning(format!(
+                    "Minimum length not met: {}/{}", 
+                    count, 
+                    min
+                )));
+            }
+        }
+        
+        // Check maximum length
+        if let Some(max) = self.max_length {
+            if count > max {
+                return Some(ValidationResult::error(format!(
+                    "Character limit exceeded: {}/{}", 
+                    count, 
+                    max
+                )));
+            }
+            
+            // Check warning threshold
+            if let Some(warning_threshold) = self.warning_threshold {
+                if count >= warning_threshold {
+                    return Some(ValidationResult::warning(format!(
+                        "Approaching character limit: {}/{}", 
+                        count, 
+                        max
+                    )));
+                }
+            }
+        }
+        
+        None // No validation issues
+    }
+    
+    /// Get the current status of the text against limits
+    pub fn check_limits(&self, text: &str) -> LimitCheckResult {
+        let count = self.count(text);
+        
+        // Check max length first
+        if let Some(max) = self.max_length {
+            if count > max {
+                return LimitCheckResult::Exceeded { current: count, max };
+            }
+            
+            // Check warning threshold
+            if let Some(warning_threshold) = self.warning_threshold {
+                if count >= warning_threshold {
+                    return LimitCheckResult::Warning { current: count, max };
+                }
+            }
+        }
+        
+        // Check min length
+        if let Some(min) = self.min_length {
+            if count < min {
+                return LimitCheckResult::TooShort { current: count, min };
+            }
+        }
+        
+        LimitCheckResult::Ok
+    }
+    
+    /// Get a human-readable status string
+    pub fn status_text(&self, text: &str) -> Option<String> {
+        match self.check_limits(text) {
+            LimitCheckResult::Ok => {
+                // Show current/max if we have a max limit
+                if let Some(max) = self.max_length {
+                    Some(format!("{}/{}", self.count(text), max))
+                } else {
+                    None
+                }
+            },
+            LimitCheckResult::Warning { current, max } => {
+                Some(format!("{}/{} (approaching limit)", current, max))
+            },
+            LimitCheckResult::Exceeded { current, max } => {
+                Some(format!("{}/{} (exceeded)", current, max))
+            },
+            LimitCheckResult::TooShort { current, min } => {
+                Some(format!("{}/{} minimum", current, min))
+            },
+        }
+    }
+    pub fn allows_field_switch(&self, text: &str) -> bool {
+        if let Some(min) = self.min_length {
+            let count = self.count(text);
+            // Allow switching if field is empty OR meets minimum requirement
+            count == 0 || count >= min
+        } else {
+            true // No minimum requirement, always allow switching
+        }
+    }
+    
+    /// Get reason why field switching is not allowed (if any)
+    pub fn field_switch_block_reason(&self, text: &str) -> Option<String> {
+        if let Some(min) = self.min_length {
+            let count = self.count(text);
+            if count > 0 && count < min {
+                return Some(format!(
+                    "Field must be empty or have at least {} characters (currently: {})",
+                    min, count
+                ));
+            }
+        }
+        None
+    }
+}
+
+impl Default for CharacterLimits {
+    fn default() -> Self {
+        Self {
+            max_length: Some(30), // Default 30 character limit as specified
+            min_length: None,
+            warning_threshold: None,
+            count_mode: CountMode::default(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_character_limits_creation() {
+        let limits = CharacterLimits::new(10);
+        assert_eq!(limits.max_length(), Some(10));
+        assert_eq!(limits.min_length(), None);
+        
+        let range_limits = CharacterLimits::new_range(5, 15);
+        assert_eq!(range_limits.min_length(), Some(5));
+        assert_eq!(range_limits.max_length(), Some(15));
+    }
+    
+    #[test]
+    fn test_default_limits() {
+        let limits = CharacterLimits::default();
+        assert_eq!(limits.max_length(), Some(30));
+    }
+    
+    #[test]
+    fn test_character_counting() {
+        let limits = CharacterLimits::new(5);
+        
+        // Test character mode (default)
+        assert_eq!(limits.count("hello"), 5);
+        assert_eq!(limits.count("héllo"), 5); // Accented character counts as 1
+        
+        // Test display width mode
+        let limits = limits.with_count_mode(CountMode::DisplayWidth);
+        assert_eq!(limits.count("hello"), 5);
+        
+        // Test bytes mode
+        let limits = limits.with_count_mode(CountMode::Bytes);
+        assert_eq!(limits.count("hello"), 5);
+        assert_eq!(limits.count("héllo"), 6); // é takes 2 bytes in UTF-8
+    }
+    
+    #[test]
+    fn test_insertion_validation() {
+        let limits = CharacterLimits::new(5);
+        
+        // Valid insertion
+        let result = limits.validate_insertion("test", 4, 'x');
+        assert!(result.is_none()); // No validation issues
+        
+        // Invalid insertion (would exceed limit)
+        let result = limits.validate_insertion("tests", 5, 'x');
+        assert!(result.is_some());
+        assert!(!result.unwrap().is_acceptable());
+    }
+    
+    #[test]
+    fn test_content_validation() {
+        let limits = CharacterLimits::new_range(3, 10);
+        
+        // Too short
+        let result = limits.validate_content("hi");
+        assert!(result.is_some());
+        assert!(result.unwrap().is_acceptable()); // Warning, not error
+        
+        // Just right
+        let result = limits.validate_content("hello");
+        assert!(result.is_none());
+        
+        // Too long
+        let result = limits.validate_content("hello world!");
+        assert!(result.is_some());
+        assert!(!result.unwrap().is_acceptable()); // Error
+    }
+    
+    #[test]
+    fn test_warning_threshold() {
+        let limits = CharacterLimits::new(10).with_warning_threshold(8);
+        
+        // Below warning threshold
+        let result = limits.validate_insertion("1234567", 7, 'x');
+        assert!(result.is_none());
+        
+        // At warning threshold
+        let result = limits.validate_insertion("1234567", 7, 'x');
+        assert!(result.is_none()); // This brings us to 8 chars
+        
+        let result = limits.validate_insertion("12345678", 8, 'x');
+        assert!(result.is_some());
+        assert!(result.unwrap().is_acceptable()); // Warning, not error
+    }
+    
+    #[test]
+    fn test_status_text() {
+        let limits = CharacterLimits::new(10);
+        
+        assert_eq!(limits.status_text("hello"), Some("5/10".to_string()));
+        
+        let limits = limits.with_warning_threshold(8);
+        assert_eq!(limits.status_text("12345678"), Some("8/10 (approaching limit)".to_string()));
+        assert_eq!(limits.status_text("1234567890x"), Some("11/10 (exceeded)".to_string()));
+    }
+    
+    #[test]
+    fn test_field_switch_blocking() {
+        let limits = CharacterLimits::new_range(3, 10);
+        
+        // Empty field: should allow switching
+        assert!(limits.allows_field_switch(""));
+        assert!(limits.field_switch_block_reason("").is_none());
+        
+        // Field with content below minimum: should block switching
+        assert!(!limits.allows_field_switch("hi"));
+        assert!(limits.field_switch_block_reason("hi").is_some());
+        assert!(limits.field_switch_block_reason("hi").unwrap().contains("at least 3 characters"));
+        
+        // Field meeting minimum: should allow switching
+        assert!(limits.allows_field_switch("hello"));
+        assert!(limits.field_switch_block_reason("hello").is_none());
+        
+        // Field exceeding maximum: should still allow switching (validation shows error but doesn't block)
+        assert!(limits.allows_field_switch("this is way too long"));
+        assert!(limits.field_switch_block_reason("this is way too long").is_none());
+    }
+    
+    #[test]
+    fn test_field_switch_no_minimum() {
+        let limits = CharacterLimits::new(10); // Only max, no minimum
+        
+        // Should always allow switching when there's no minimum
+        assert!(limits.allows_field_switch(""));
+        assert!(limits.allows_field_switch("a"));
+        assert!(limits.allows_field_switch("hello"));
+        
+        assert!(limits.field_switch_block_reason("").is_none());
+        assert!(limits.field_switch_block_reason("a").is_none());
+    }
+}

canvas/src/validation/mod.rs

@@ -0,0 +1,26 @@
+//! Validation module for canvas form fields
+
+pub mod config;
+pub mod limits;
+pub mod state;
+
+// Re-export main types
+pub use config::{ValidationConfig, ValidationResult, ValidationConfigBuilder};
+pub use limits::{CharacterLimits, LimitCheckResult};
+pub use state::{ValidationState, ValidationSummary};
+
+/// Validation error types
+#[derive(Debug, Clone, thiserror::Error)]
+pub enum ValidationError {
+    #[error("Character limit exceeded: {current}/{max}")]
+    CharacterLimitExceeded { current: usize, max: usize },
+    
+    #[error("Invalid character '{char}' at position {position}")]
+    InvalidCharacter { char: char, position: usize },
+    
+    #[error("Validation configuration error: {message}")]
+    ConfigurationError { message: String },
+}
+
+/// Result type for validation operations
+pub type Result<T> = std::result::Result<T, ValidationError>;

canvas/src/validation/state.rs

@@ -0,0 +1,399 @@
+// src/validation/state.rs
+//! Validation state management
+
+use crate::validation::{ValidationConfig, ValidationResult};
+use std::collections::HashMap;
+
+/// Validation state for all fields in a form
+#[derive(Debug, Clone, Default)]
+pub struct ValidationState {
+    /// Validation configurations per field index
+    field_configs: HashMap<usize, ValidationConfig>,
+    
+    /// Current validation results per field index
+    field_results: HashMap<usize, ValidationResult>,
+    
+    /// Track which fields have been validated
+    validated_fields: std::collections::HashSet<usize>,
+    
+    /// Global validation enabled/disabled
+    enabled: bool,
+}
+
+impl ValidationState {
+    /// Create a new validation state
+    pub fn new() -> Self {
+        Self {
+            field_configs: HashMap::new(),
+            field_results: HashMap::new(),
+            validated_fields: std::collections::HashSet::new(),
+            enabled: true,
+        }
+    }
+    
+    /// Enable or disable validation globally
+    pub fn set_enabled(&mut self, enabled: bool) {
+        self.enabled = enabled;
+        if !enabled {
+            // Clear all validation results when disabled
+            self.field_results.clear();
+            self.validated_fields.clear();
+        }
+    }
+    
+    /// Check if validation is enabled
+    pub fn is_enabled(&self) -> bool {
+        self.enabled
+    }
+    
+    /// Set validation configuration for a field
+    pub fn set_field_config(&mut self, field_index: usize, config: ValidationConfig) {
+        if config.has_validation() {
+            self.field_configs.insert(field_index, config);
+        } else {
+            self.field_configs.remove(&field_index);
+            self.field_results.remove(&field_index);
+            self.validated_fields.remove(&field_index);
+        }
+    }
+    
+    /// Get validation configuration for a field
+    pub fn get_field_config(&self, field_index: usize) -> Option<&ValidationConfig> {
+        self.field_configs.get(&field_index)
+    }
+    
+    /// Remove validation configuration for a field
+    pub fn remove_field_config(&mut self, field_index: usize) {
+        self.field_configs.remove(&field_index);
+        self.field_results.remove(&field_index);
+        self.validated_fields.remove(&field_index);
+    }
+    
+    /// Validate character insertion for a field
+    pub fn validate_char_insertion(
+        &mut self,
+        field_index: usize,
+        current_text: &str,
+        position: usize,
+        character: char,
+    ) -> ValidationResult {
+        if !self.enabled {
+            return ValidationResult::Valid;
+        }
+        
+        if let Some(config) = self.field_configs.get(&field_index) {
+            let result = config.validate_char_insertion(current_text, position, character);
+            
+            // Store the validation result
+            self.field_results.insert(field_index, result.clone());
+            self.validated_fields.insert(field_index);
+            
+            result
+        } else {
+            ValidationResult::Valid
+        }
+    }
+    
+    /// Validate field content
+    pub fn validate_field_content(
+        &mut self,
+        field_index: usize,
+        text: &str,
+    ) -> ValidationResult {
+        if !self.enabled {
+            return ValidationResult::Valid;
+        }
+        
+        if let Some(config) = self.field_configs.get(&field_index) {
+            let result = config.validate_content(text);
+            
+            // Store the validation result
+            self.field_results.insert(field_index, result.clone());
+            self.validated_fields.insert(field_index);
+            
+            result
+        } else {
+            ValidationResult::Valid
+        }
+    }
+    
+    /// Get current validation result for a field
+    pub fn get_field_result(&self, field_index: usize) -> Option<&ValidationResult> {
+        self.field_results.get(&field_index)
+    }
+    
+    /// Check if a field has been validated
+    pub fn is_field_validated(&self, field_index: usize) -> bool {
+        self.validated_fields.contains(&field_index)
+    }
+    
+    /// Clear validation result for a field
+    pub fn clear_field_result(&mut self, field_index: usize) {
+        self.field_results.remove(&field_index);
+        self.validated_fields.remove(&field_index);
+    }
+    
+    /// Clear all validation results
+    pub fn clear_all_results(&mut self) {
+        self.field_results.clear();
+        self.validated_fields.clear();
+    }
+    
+    /// Get all field indices that have validation configured
+    pub fn validated_field_indices(&self) -> impl Iterator<Item = usize> + '_ {
+        self.field_configs.keys().copied()
+    }
+    
+    /// Get all field indices with validation errors
+    pub fn fields_with_errors(&self) -> impl Iterator<Item = usize> + '_ {
+        self.field_results
+            .iter()
+            .filter(|(_, result)| result.is_error())
+            .map(|(index, _)| *index)
+    }
+    
+    /// Get all field indices with validation warnings
+    pub fn fields_with_warnings(&self) -> impl Iterator<Item = usize> + '_ {
+        self.field_results
+            .iter()
+            .filter(|(_, result)| matches!(result, ValidationResult::Warning { .. }))
+            .map(|(index, _)| *index)
+    }
+    
+    /// Check if any field has validation errors
+    pub fn has_errors(&self) -> bool {
+        self.field_results.values().any(|result| result.is_error())
+    }
+    
+    /// Check if any field has validation warnings
+    pub fn has_warnings(&self) -> bool {
+        self.field_results.values().any(|result| matches!(result, ValidationResult::Warning { .. }))
+    }
+    
+    /// Get total count of fields with validation configured
+    pub fn validated_field_count(&self) -> usize {
+        self.field_configs.len()
+    }
+    
+    /// Check if field switching is allowed for a specific field
+    pub fn allows_field_switch(&self, field_index: usize, text: &str) -> bool {
+        if !self.enabled {
+            return true;
+        }
+        
+        if let Some(config) = self.field_configs.get(&field_index) {
+            config.allows_field_switch(text)
+        } else {
+            true // No validation configured, allow switching
+        }
+    }
+    
+    /// Get reason why field switching is blocked (if any)
+    pub fn field_switch_block_reason(&self, field_index: usize, text: &str) -> Option<String> {
+        if !self.enabled {
+            return None;
+        }
+        
+        if let Some(config) = self.field_configs.get(&field_index) {
+            config.field_switch_block_reason(text)
+        } else {
+            None // No validation configured
+        }
+    }
+    pub fn summary(&self) -> ValidationSummary {
+        let total_validated = self.validated_fields.len();
+        let errors = self.fields_with_errors().count();
+        let warnings = self.fields_with_warnings().count();
+        let valid = total_validated - errors - warnings;
+        
+        ValidationSummary {
+            total_fields: self.field_configs.len(),
+            validated_fields: total_validated,
+            valid_fields: valid,
+            warning_fields: warnings,
+            error_fields: errors,
+        }
+    }
+}
+
+/// Summary of validation state across all fields
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ValidationSummary {
+    /// Total number of fields with validation configured
+    pub total_fields: usize,
+    
+    /// Number of fields that have been validated
+    pub validated_fields: usize,
+    
+    /// Number of fields with valid validation results
+    pub valid_fields: usize,
+    
+    /// Number of fields with warnings
+    pub warning_fields: usize,
+    
+    /// Number of fields with errors
+    pub error_fields: usize,
+}
+
+impl ValidationSummary {
+    /// Check if all configured fields are valid
+    pub fn is_all_valid(&self) -> bool {
+        self.error_fields == 0 && self.validated_fields == self.total_fields
+    }
+    
+    /// Check if there are any errors
+    pub fn has_errors(&self) -> bool {
+        self.error_fields > 0
+    }
+    
+    /// Check if there are any warnings
+    pub fn has_warnings(&self) -> bool {
+        self.warning_fields > 0
+    }
+    
+    /// Get completion percentage (validated fields / total fields)
+    pub fn completion_percentage(&self) -> f32 {
+        if self.total_fields == 0 {
+            1.0
+        } else {
+            self.validated_fields as f32 / self.total_fields as f32
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::validation::{CharacterLimits, ValidationConfigBuilder};
+
+    #[test]
+    fn test_validation_state_creation() {
+        let state = ValidationState::new();
+        assert!(state.is_enabled());
+        assert_eq!(state.validated_field_count(), 0);
+    }
+    
+    #[test]
+    fn test_enable_disable() {
+        let mut state = ValidationState::new();
+        
+        // Add some validation config
+        let config = ValidationConfigBuilder::new()
+            .with_max_length(10)
+            .build();
+        state.set_field_config(0, config);
+        
+        // Validate something
+        let result = state.validate_field_content(0, "test");
+        assert!(result.is_acceptable());
+        assert!(state.is_field_validated(0));
+        
+        // Disable validation
+        state.set_enabled(false);
+        assert!(!state.is_enabled());
+        assert!(!state.is_field_validated(0)); // Should be cleared
+        
+        // Validation should now return valid regardless
+        let result = state.validate_field_content(0, "this is way too long for the limit");
+        assert!(result.is_acceptable());
+    }
+    
+    #[test]
+    fn test_field_config_management() {
+        let mut state = ValidationState::new();
+        
+        let config = ValidationConfigBuilder::new()
+            .with_max_length(5)
+            .build();
+        
+        // Set config
+        state.set_field_config(0, config);
+        assert_eq!(state.validated_field_count(), 1);
+        assert!(state.get_field_config(0).is_some());
+        
+        // Remove config
+        state.remove_field_config(0);
+        assert_eq!(state.validated_field_count(), 0);
+        assert!(state.get_field_config(0).is_none());
+    }
+    
+    #[test]
+    fn test_character_insertion_validation() {
+        let mut state = ValidationState::new();
+        
+        let config = ValidationConfigBuilder::new()
+            .with_max_length(5)
+            .build();
+        state.set_field_config(0, config);
+        
+        // Valid insertion
+        let result = state.validate_char_insertion(0, "test", 4, 'x');
+        assert!(result.is_acceptable());
+        
+        // Invalid insertion
+        let result = state.validate_char_insertion(0, "tests", 5, 'x');
+        assert!(!result.is_acceptable());
+        
+        // Check that result was stored
+        assert!(state.is_field_validated(0));
+        let stored_result = state.get_field_result(0);
+        assert!(stored_result.is_some());
+        assert!(!stored_result.unwrap().is_acceptable());
+    }
+    
+    #[test]
+    fn test_validation_summary() {
+        let mut state = ValidationState::new();
+        
+        // Configure two fields
+        let config1 = ValidationConfigBuilder::new().with_max_length(5).build();
+        let config2 = ValidationConfigBuilder::new().with_max_length(10).build();
+        state.set_field_config(0, config1);
+        state.set_field_config(1, config2);
+        
+        // Validate field 0 (valid)
+        state.validate_field_content(0, "test");
+        
+        // Validate field 1 (error)
+        state.validate_field_content(1, "this is too long");
+        
+        let summary = state.summary();
+        assert_eq!(summary.total_fields, 2);
+        assert_eq!(summary.validated_fields, 2);
+        assert_eq!(summary.valid_fields, 1);
+        assert_eq!(summary.error_fields, 1);
+        assert_eq!(summary.warning_fields, 0);
+        
+        assert!(!summary.is_all_valid());
+        assert!(summary.has_errors());
+        assert!(!summary.has_warnings());
+        assert_eq!(summary.completion_percentage(), 1.0);
+    }
+    
+    #[test]
+    fn test_error_and_warning_tracking() {
+        let mut state = ValidationState::new();
+        
+        let config = ValidationConfigBuilder::new()
+            .with_character_limits(
+                CharacterLimits::new_range(3, 10).with_warning_threshold(8)
+            )
+            .build();
+        state.set_field_config(0, config);
+        
+        // Too short (warning)
+        state.validate_field_content(0, "hi");
+        assert!(state.has_warnings());
+        assert!(!state.has_errors());
+        
+        // Just right
+        state.validate_field_content(0, "hello");
+        assert!(!state.has_warnings());
+        assert!(!state.has_errors());
+        
+        // Too long (error)
+        state.validate_field_content(0, "hello world!");
+        assert!(!state.has_warnings());
+        assert!(state.has_errors());
+    }
+}