# Editor Implementation Plan

## 1. Design Principles

- **Single-Owner Pattern**: The logic goroutine is the exclusive authority for modifying the editor buffer, cursor, and selection state.
- **Asynchronous I/O**: File saving and loading operations are delegated to the worker pool. The UI never blocks on disk operations.
- **Buffer-Based Editing**: For performance, the editor will eventually utilize a gap buffer or rope data structure. For MVP, string manipulation is acceptable if performance targets are met.
- **Event-Driven**: Keyboard input, mouse interactions, and menu actions are passed through the existing `inputChan` to the logic goroutine.

## 2. Core State Structure

The `State` struct in `internal/editor/state.go` will be extended to track active editing session data:

```go
type EditorState struct {
    Buffer          string        // Document content (or gap buffer)
    CursorPosition  int           // Byte offset
    SelectionStart  int           // -1 if no selection
    SelectionEnd    int           // -1 if no selection
    UndoStack       []EditCommand // For undo/redo
    Dirty           bool          // Needs save
}
```

## 3. Implementation Phases

### Phase 1: Basic Buffer Management & Cursor
- [ ] Define `EditorState` (Cursor, Selection, Dirty flag).
- [ ] Implement cursor navigation (Arrow keys: Left, Right, Up, Down).
- [ ] Implement basic buffer updates (Insert character, Delete/Backspace).
- [ ] Implement cursor display and blink animation.
- [ ] Update `EditorLayout` to display cursor and selection highlight.

### Phase 2: File IO Integration
- [ ] Implement `SaveFile` handler: Dispatch `WriteFileTask` to worker pool.
- [ ] Implement `LoadFile` handler: Dispatch `ReadFileTask` to worker pool (existing in `logic.go`).
- [ ] Status bar integration: Show "Saving..." indicator, "Modified" status.

### Phase 3: Text Editing Operations
- [ ] Implement Cut/Copy/Paste interactions.
- [ ] Implement multi-line text navigation (Home/End, PageUp/PageDown).
- [ ] Implement text selection display and mouse interaction.
- [ ] Implement soft-wrap toggle (already exists, need to verify logic).

### Phase 4: Polish & Advanced Features
- [ ] Undo/Redo stack implementation.
- [ ] Performance testing with large files (>1MB).

---

## 4. Interaction Flow (Example: Keyboard/Mouse Input)

1. **User** performs an action (types a character, taps an icon).
2. **UI (Renderer)** registers the element's interaction (`event.Op` for keys, `gesture.Add` for mouse) within its clip context.
3. **Main Loop** captures the event (using `key.Filter` for keys, `gesture.Update` for mouse).
4. **Main Loop** generates an `InputEvent` and sends it to `inputChan`.
5. **Logic Goroutine** receives the event, triggers the corresponding `Handler` in `TheState`.
6. **Logic Goroutine** modifies state, and sends updated elements back through `frameChan`.
7. **Renderer** paints the new frame.

---

## 5. Performance Targets

| Operation | Target | Mechanism |
|---|---|---|
| Typing latency | < 16ms | Single-owner logic update, immediate frame redraw |
| File Load (1MB) | < 100ms | Async worker pool read, background loading |
| File Save | < 100ms | Async worker pool write |
| Undo/Redo | < 10ms | O(1) or O(N) memory-based buffer update |

---

## 7. Input Handling Mechanism

### 7.1 Mouse/Touch Input
- Uses `gesture.Click` and `gesture.Scroll`.
- Registered via `event.Op` and gesture `Add()` within the clip context of the element.
- Processed by `Renderer.CheckGestures` and dispatched via `InputEvent` to the logic goroutine.

### 7.2 Keyboard Input
- **Registration**: Elements register as input handlers using `event.Op(gtx.Ops, elementID)`. This tags the current clip context for input routing.
- **Focus**: Focus is managed by the logic goroutine. When an element is focused, `key.FocusCmd{Tag: elementID}` is submitted to the operation stack.
- **Filtering**: Keyboard events are processed in the main loop using `key.Filter{Focus: focusedElementID}` to ensure events are only routed to the active element.
- **Routing**: `key.Event` (for key presses) and `key.EditEvent` (for text input) are converted into `InputEvent` structs and sent to the logic goroutine via `inputChan` for state updates.