computed fields are working perfectly well now

canvas/src/canvas/state.rs

@@ -23,6 +23,10 @@ pub struct EditorState {
     // Validation state (only available with validation feature)
     #[cfg(feature = "validation")]
     pub(crate) validation: crate::validation::ValidationState,
+
+    /// Computed fields state (only when computed feature is enabled)
+    #[cfg(feature = "computed")]
+    pub(crate) computed: Option<crate::computed::ComputedState>,
 }
 
 #[derive(Debug, Clone)]
@@ -56,6 +60,8 @@ impl EditorState {
             selection: SelectionState::None,
             #[cfg(feature = "validation")]
             validation: crate::validation::ValidationState::new(),
+            #[cfg(feature = "computed")]
+            computed: None,
         }
     }
 
@@ -68,6 +74,15 @@ impl EditorState {
         self.current_field
     }
 
+    /// Check if field is computed
+    #[cfg(feature = "computed")]
+    pub fn is_computed_field(&self, field_index: usize) -> bool {
+        self.computed
+            .as_ref()
+            .map(|state| state.is_computed_field(field_index))
+            .unwrap_or(false)
+    }
+
     /// Get current cursor position (for user's business logic)
     pub fn cursor_position(&self) -> usize {
         self.cursor_pos

canvas/src/computed/mod.rs

@@ -0,0 +1,5 @@
+pub mod provider;
+pub mod state;
+
+pub use provider::{ComputedContext, ComputedProvider};
+pub use state::ComputedState;

canvas/src/computed/provider.rs

@@ -0,0 +1,31 @@
+// ================================================================================================
+// COMPUTED FIELDS - Provider and Context
+// ================================================================================================
+
+/// Context information provided to computed field calculations
+#[derive(Debug, Clone)]
+pub struct ComputedContext<'a> {
+    /// All field values in the form (index -> value)
+    pub field_values: &'a [&'a str],
+    /// The field index being computed
+    pub target_field: usize,
+    /// Current field that user is editing (if any)
+    pub current_field: Option<usize>,
+}
+
+/// User implements this to provide computed field logic
+pub trait ComputedProvider {
+    /// Compute value for a field based on other field values.
+    /// Called automatically when any field changes.
+    fn compute_field(&mut self, context: ComputedContext) -> String;
+
+    /// Check if this provider handles the given field.
+    fn handles_field(&self, field_index: usize) -> bool;
+
+    /// Get list of field dependencies for optimization.
+    /// If field A depends on fields [1, 3], only recompute A when fields 1 or 3 change.
+    /// Default: depend on all fields (always recompute) with a reasonable upper bound.
+    fn field_dependencies(&self, _field_index: usize) -> Vec<usize> {
+        (0..100).collect()
+    }
+}

canvas/src/computed/state.rs

@@ -0,0 +1,88 @@
+/* file: canvas/src/computed/state.rs */
+/*
+Add computed state module file implementing caching and dependencies
+*/
+
+// ================================================================================================
+// COMPUTED FIELDS - State: caching and dependencies
+// ================================================================================================
+
+use std::collections::{HashMap, HashSet};
+
+/// Internal state for computed field management
+#[derive(Debug, Clone)]
+pub struct ComputedState {
+    /// Cached computed values (field_index -> computed_value)
+    computed_values: HashMap<usize, String>,
+    /// Field dependency graph (field_index -> depends_on_fields)
+    dependencies: HashMap<usize, Vec<usize>>,
+    /// Track which fields are computed (display-only)
+    computed_fields: HashSet<usize>,
+}
+
+impl ComputedState {
+    /// Create a new, empty computed state
+    pub fn new() -> Self {
+        Self {
+            computed_values: HashMap::new(),
+            dependencies: HashMap::new(),
+            computed_fields: HashSet::new(),
+        }
+    }
+
+    /// Register a field as computed with its dependencies
+    ///
+    /// - `field_index`: the field that is computed (display-only)
+    /// - `dependencies`: indices of fields this computed field depends on
+    pub fn register_computed_field(&mut self, field_index: usize, mut dependencies: Vec<usize>) {
+        // Deduplicate dependencies to keep graph lean
+        dependencies.sort_unstable();
+        dependencies.dedup();
+
+        self.computed_fields.insert(field_index);
+        self.dependencies.insert(field_index, dependencies);
+    }
+
+    /// Check if a field is computed (read-only, skip editing/navigation)
+    pub fn is_computed_field(&self, field_index: usize) -> bool {
+        self.computed_fields.contains(&field_index)
+    }
+
+    /// Get cached computed value for a field, if available
+    pub fn get_computed_value(&self, field_index: usize) -> Option<&String> {
+        self.computed_values.get(&field_index)
+    }
+
+    /// Update cached computed value for a field
+    pub fn set_computed_value(&mut self, field_index: usize, value: String) {
+        self.computed_values.insert(field_index, value);
+    }
+
+    /// Get fields that should be recomputed when `changed_field` changed
+    ///
+    /// This scans the dependency graph and returns all computed fields
+    /// that list `changed_field` as a dependency.
+    pub fn fields_to_recompute(&self, changed_field: usize) -> Vec<usize> {
+        self.dependencies
+            .iter()
+            .filter_map(|(field, deps)| {
+                if deps.contains(&changed_field) {
+                    Some(*field)
+                } else {
+                    None
+                }
+            })
+            .collect()
+    }
+
+    /// Iterator over all computed field indices
+    pub fn computed_fields(&self) -> impl Iterator<Item = usize> + '_ {
+        self.computed_fields.iter().copied()
+    }
+}
+
+impl Default for ComputedState {
+    fn default() -> Self {
+        Self::new()
+    }
+}

canvas/src/data_provider.rs

@@ -34,6 +34,20 @@ pub trait DataProvider {
     fn validation_config(&self, _field_index: usize) -> Option<crate::validation::ValidationConfig> {
         None
     }
+
+    /// Check if field is computed (display-only, skip in navigation)
+    /// Default: not computed
+    #[cfg(feature = "computed")]
+    fn is_computed_field(&self, _field_index: usize) -> bool {
+        false
+    }
+
+    /// Get computed field value if this is a computed field.
+    /// Returns None for regular fields. Default: not computed.
+    #[cfg(feature = "computed")]
+    fn computed_field_value(&self, _field_index: usize) -> Option<String> {
+        None
+    }
 }
 
 /// Optional: User implements this for suggestions data

canvas/src/editor.rs

@@ -668,6 +668,45 @@ impl<D: DataProvider> FormEditor<D> {
             return Ok(());
         }
 
+        // Skip computed fields during navigation when feature enabled
+        #[cfg(feature = "computed")]
+        {
+            if let Some(computed_state) = &self.ui_state.computed {
+                // Find previous non-computed field
+                let mut candidate = self.ui_state.current_field;
+                for _ in 0..field_count {
+                    candidate = candidate.saturating_sub(1);
+                    if !computed_state.is_computed_field(candidate) {
+                        // Validate and move as usual
+                        #[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));
+                                }
+                            }
+                        }
+                        #[cfg(feature = "validation")]
+                        {
+                            let current_text = self.current_text().to_string();
+                            let _validation_result = self.ui_state.validation.validate_field_content(
+                                self.ui_state.current_field,
+                                &current_text,
+                            );
+                        }
+                        self.ui_state.move_to_field(candidate, field_count);
+                        self.clamp_cursor_to_current_field();
+                        return Ok(());
+                    }
+                    if candidate == 0 {
+                        break;
+                    }
+                }
+            }
+        }
+
         // Check if field switching is allowed (minimum character enforcement)
         #[cfg(feature = "validation")]
         {
@@ -705,6 +744,45 @@ impl<D: DataProvider> FormEditor<D> {
             return Ok(());
         }
 
+        // Skip computed fields during navigation when feature enabled
+        #[cfg(feature = "computed")]
+        {
+            if let Some(computed_state) = &self.ui_state.computed {
+                // Find next non-computed field
+                let mut candidate = self.ui_state.current_field;
+                for _ in 0..field_count {
+                    candidate = (candidate + 1).min(field_count - 1);
+                    if !computed_state.is_computed_field(candidate) {
+                        // Validate and move as usual
+                        #[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));
+                                }
+                            }
+                        }
+                        #[cfg(feature = "validation")]
+                        {
+                            let current_text = self.current_text().to_string();
+                            let _validation_result = self.ui_state.validation.validate_field_content(
+                                self.ui_state.current_field,
+                                &current_text,
+                            );
+                        }
+                        self.ui_state.move_to_field(candidate, field_count);
+                        self.clamp_cursor_to_current_field();
+                        return Ok(());
+                    }
+                    if candidate == field_count - 1 {
+                        break;
+                    }
+                }
+            }
+        }
+
         // Check if field switching is allowed (minimum character enforcement)
         #[cfg(feature = "validation")]
         {
@@ -763,6 +841,112 @@ impl<D: DataProvider> FormEditor<D> {
         self.move_up()
     }
 
+    // ================================================================================================
+    // COMPUTED FIELDS (behind 'computed' feature)
+    // ================================================================================================
+
+    /// Initialize computed fields from provider and computed provider
+    #[cfg(feature = "computed")]
+    pub fn set_computed_provider<C>(&mut self, mut provider: C)
+    where
+        C: crate::computed::ComputedProvider,
+    {
+        // Initialize computed state
+        self.ui_state.computed = Some(crate::computed::ComputedState::new());
+
+        // Register computed fields and their dependencies
+        let field_count = self.data_provider.field_count();
+        for field_index in 0..field_count {
+            if provider.handles_field(field_index) {
+                let deps = provider.field_dependencies(field_index);
+                if let Some(computed_state) = &mut self.ui_state.computed {
+                    computed_state.register_computed_field(field_index, deps);
+                }
+            }
+        }
+
+        // Initial computation of all computed fields
+        self.recompute_all_fields(&mut provider);
+    }
+
+    /// Recompute specific computed fields
+    #[cfg(feature = "computed")]
+    pub fn recompute_fields<C>(&mut self, provider: &mut C, field_indices: &[usize])
+    where
+        C: crate::computed::ComputedProvider,
+    {
+        if let Some(computed_state) = &mut self.ui_state.computed {
+            // Collect all field values for context
+            let field_values: Vec<String> = (0..self.data_provider.field_count())
+                .map(|i| {
+                    if computed_state.is_computed_field(i) {
+                        // Use cached computed value
+                        computed_state
+                            .get_computed_value(i)
+                            .cloned()
+                            .unwrap_or_default()
+                    } else {
+                        // Use regular field value
+                        self.data_provider.field_value(i).to_string()
+                    }
+                })
+                .collect();
+
+            let field_refs: Vec<&str> = field_values.iter().map(|s| s.as_str()).collect();
+
+            // Recompute specified fields
+            for &field_index in field_indices {
+                if provider.handles_field(field_index) {
+                    let context = crate::computed::ComputedContext {
+                        field_values: &field_refs,
+                        target_field: field_index,
+                        current_field: Some(self.ui_state.current_field),
+                    };
+
+                    let computed_value = provider.compute_field(context);
+                    computed_state.set_computed_value(field_index, computed_value);
+                }
+            }
+        }
+    }
+
+    /// Recompute all computed fields
+    #[cfg(feature = "computed")]
+    pub fn recompute_all_fields<C>(&mut self, provider: &mut C)
+    where
+        C: crate::computed::ComputedProvider,
+    {
+        if let Some(computed_state) = &self.ui_state.computed {
+            let computed_fields: Vec<usize> = computed_state.computed_fields().collect();
+            self.recompute_fields(provider, &computed_fields);
+        }
+    }
+
+    /// Trigger recomputation when field changes (call this after set_field_value)
+    #[cfg(feature = "computed")]
+    pub fn on_field_changed<C>(&mut self, provider: &mut C, changed_field: usize)
+    where
+        C: crate::computed::ComputedProvider,
+    {
+        if let Some(computed_state) = &self.ui_state.computed {
+            let fields_to_update = computed_state.fields_to_recompute(changed_field);
+            if !fields_to_update.is_empty() {
+                self.recompute_fields(provider, &fields_to_update);
+            }
+        }
+    }
+
+    /// Enhanced getter that returns computed values for computed fields when available
+    #[cfg(feature = "computed")]
+    pub fn effective_field_value(&self, field_index: usize) -> String {
+        if let Some(computed_state) = &self.ui_state.computed {
+            if let Some(computed_value) = computed_state.get_computed_value(field_index) {
+                return computed_value.clone();
+            }
+        }
+        self.data_provider.field_value(field_index).to_string()
+    }
+
     /// Move to next field (alternative to move_down)
     pub fn next_field(&mut self) -> Result<()> {
         self.move_down()
@@ -960,6 +1144,15 @@ impl<D: DataProvider> FormEditor<D> {
 
     /// Enter edit mode from read-only mode (vim i/a/o)
     pub fn enter_edit_mode(&mut self) {
+        #[cfg(feature = "computed")]
+        {
+            if let Some(computed_state) = &self.ui_state.computed {
+                if computed_state.is_computed_field(self.ui_state.current_field) {
+                    // Can't edit computed fields - silently ignore
+                    return;
+                }
+            }
+        }
         self.set_mode(AppMode::Edit);
     }
 

canvas/src/lib.rs

@@ -12,6 +12,10 @@ pub mod suggestions;
 #[cfg(feature = "validation")]
 pub mod validation;
 
+// Only include computed module if feature is enabled
+#[cfg(feature = "computed")]
+pub mod computed;
+
 #[cfg(feature = "cursor-style")]
 pub use canvas::CursorManager;
 
@@ -41,6 +45,10 @@ pub use validation::{
     CustomFormatter, FormattingResult, PositionMapper, DefaultPositionMapper,
 };
 
+// Computed exports (only when computed feature is enabled)
+#[cfg(feature = "computed")]
+pub use computed::{ComputedProvider, ComputedContext, ComputedState};
+
 // Theming and GUI
 #[cfg(feature = "gui")]
 pub use canvas::theme::{CanvasTheme, DefaultCanvasTheme};