validation passed to the canvas library now compiled

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 +33,8 @@ default = []
 gui = ["ratatui"]
 autocomplete = ["tokio"]
 cursor-style = ["crossterm"]
+regex = ["dep:regex"]
+validation = ["regex"]
 
 [[example]]
 name = "autocomplete"

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/src/canvas/state.rs

@@ -19,6 +19,10 @@ pub struct EditorState {
 
     // 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)]
@@ -50,6 +54,8 @@ impl EditorState {
                 active_field: None,
             },
             selection: SelectionState::None,
+            #[cfg(feature = "validation")]
+            validation: crate::validation::ValidationState::new(),
         }
     }
 
@@ -68,7 +74,7 @@ impl EditorState {
     }
 
     /// 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
     }
 
@@ -92,6 +98,13 @@ impl EditorState {
         &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
     // ===================================================================

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);
+            }
         }
     }
 
@@ -82,6 +101,25 @@ impl<D: DataProvider> FormEditor<D> {
         &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
@@ -194,6 +268,65 @@ impl<D: DataProvider> FormEditor<D> {
         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()
+    }
+
     // ===================================================================
     // ASYNC OPERATIONS: Only autocomplete needs async
     // ===================================================================
@@ -256,6 +389,15 @@ impl<D: DataProvider> FormEditor<D> {
                 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);
             }
         }
@@ -263,7 +405,7 @@ impl<D: DataProvider> FormEditor<D> {
     }
 
     // ===================================================================
-    // ADD THESE MISSING MOVEMENT METHODS
+    // MOVEMENT METHODS (keeping existing implementations)
     // ===================================================================
 
     /// Move to previous field (vim k / up arrow)
@@ -273,6 +415,16 @@ impl<D: DataProvider> FormEditor<D> {
             return;
         }
 
+        // 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);
 
@@ -287,6 +439,16 @@ impl<D: DataProvider> FormEditor<D> {
             return;
         }
 
+        // 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);
 
@@ -443,9 +605,18 @@ impl<D: DataProvider> FormEditor<D> {
 
         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(())
@@ -462,15 +633,33 @@ impl<D: DataProvider> FormEditor<D> {
 
         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) {
+        // Validate current field content when exiting edit mode
+        #[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,
+            );
+        }
+        
         // Adjust cursor position when transitioning from edit to normal mode
         let current_text = self.current_text();
         if !current_text.is_empty() {
@@ -515,21 +704,39 @@ impl<D: DataProvider> FormEditor<D> {
     /// 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,
+                );
+            }
         }
     }
 

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 +1,208 @@
+//! 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()
+    }
+}
+
+#[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 +1,365 @@
+//! 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))
+            },
+        }
+    }
+}
+
+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()));
+    }
+}

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 +1,374 @@
+//! 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()
+    }
+    
+    /// Get validation summary
+    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());
+    }
+}