# Phase 4 Implementation Summary - Heading Blocks Migration

## Overview
Successfully migrated all heading blocks (h1, h2, h3) to the new block handler architecture using a unified HeadingBlockHandler class.

## Changes Made

### 1. Created Unified Heading Handler
- **File**: `blocks/text/heading.block.ts`
- Implemented `HeadingBlockHandler` class extending `BaseBlockHandler`
- Single handler class that accepts heading level (1, 2, or 3) in constructor
- Extracted all heading rendering logic from `dees-wysiwyg-block.ts`
- Extracted heading setup logic with full text editing support:
  - Input handling with cursor tracking
  - Selection handling with Shadow DOM support
  - Focus/blur management
  - Composition events for IME support
  - Split content functionality
- Extracted all heading-specific styles for all three levels

### 2. Registration Updates
- **File**: `wysiwyg.blockregistration.ts`
- Registered three heading handlers using the same class:
  - `heading-1` → `new HeadingBlockHandler('heading-1')`
  - `heading-2` → `new HeadingBlockHandler('heading-2')`
  - `heading-3` → `new HeadingBlockHandler('heading-3')`
- Updated imports to include HeadingBlockHandler

### 3. Updated Exports
- **File**: `blocks/index.ts`
- Exported `HeadingBlockHandler` class
- Removed TODO comment for heading handler

### 4. Handler Implementation Details
- **Dynamic Level Handling**: The handler determines the heading level from the block type
- **Shared Styles**: All heading levels share the same style method but render different CSS
- **Placeholder Support**: Each level has its own placeholder text
- **Full Text Editing**: Inherits all paragraph-like functionality:
  - Cursor position tracking
  - Text selection with Shadow DOM awareness
  - Content splitting for Enter key handling
  - Focus management with cursor positioning

## Key Features Preserved
✅ All three heading levels render with correct styles
✅ Font sizes: h1 (32px), h2 (24px), h3 (20px)
✅ Proper font weights and line heights
✅ Theme-aware colors using cssManager.bdTheme
✅ Contenteditable functionality
✅ Selection and cursor tracking
✅ Keyboard navigation
✅ Focus/blur handling
✅ Placeholder text for empty headings

## Architecture Benefits
1. **Code Reuse**: Single handler class for all heading levels
2. **Consistency**: All headings share the same behavior
3. **Maintainability**: Changes to heading behavior only need to be made once
4. **Type Safety**: Heading level is type-checked at construction
5. **Scalability**: Easy to add more heading levels if needed

## Testing Results
- ✅ TypeScript compilation successful
- ✅ All three heading handlers registered correctly
- ✅ Render method produces correct HTML with proper classes
- ✅ Placeholders set correctly for each level
- ✅ All handlers are instances of HeadingBlockHandler

## Next Steps
Continue with Phase 5 to migrate remaining text blocks:
- Quote block
- Code block
- List block

Each will follow the same pattern but with their specific requirements.