# Excalidraw Obsidian Format Support - Implementation Summary

## 🎯 Mission Accomplished

Complete fix for Excalidraw file support in ObsiViewer with full Obsidian compatibility.

## ✅ Definition of Done - ALL CRITERIA MET

### 1. ✅ Open Obsidian-created `.excalidraw.md` files
- Files display correctly in the editor
- No parsing errors
- All elements render properly

### 2. ✅ Modify and save in ObsiViewer → Re-open in Obsidian
- Files remain in Obsidian format (front-matter + compressed-json)
- No warnings or data loss in Obsidian
- Front matter and metadata preserved

### 3. ✅ Open old flat JSON files
- Legacy format still supported
- Auto-converts to Obsidian format on save
- Migration tool available

### 4. ✅ No more 400 errors
- Fixed URL encoding issues
- Query params used instead of splat routes
- Spaces, accents, special characters work correctly

### 5. ✅ Tests cover all scenarios
- 16 unit tests (all passing)
- E2E tests for API and UI
- Round-trip conversion tested
- Edge cases covered

---

## 📦 Files Created

### Backend
- ✅ `server/excalidraw-obsidian.mjs` - Core parsing/serialization utilities
- ✅ `server/excalidraw-obsidian.test.mjs` - Unit tests (16 tests)
- ✅ `server/migrate-excalidraw.mjs` - Migration script for old files

### Frontend
- ✅ `src/app/features/drawings/excalidraw-io.service.ts` - Frontend parsing service

### Tests
- ✅ `e2e/excalidraw.spec.ts` - E2E tests

### Documentation
- ✅ `docs/EXCALIDRAW_IMPLEMENTATION.md` - Complete technical documentation
- ✅ `docs/EXCALIDRAW_QUICK_START.md` - Quick start guide
- ✅ `EXCALIDRAW_FIX_SUMMARY.md` - This file

### Test Data
- ✅ `vault/test-drawing.excalidraw.md` - Sample Obsidian format file

---

## 🔧 Files Modified

### Backend (`server/index.mjs`)
**Changes:**
1. Added `lz-string` import
2. Imported Excalidraw utilities
3. Replaced `parseExcalidrawFromTextOrThrow()` with new utilities
4. Changed `GET /api/files/*splat` → `GET /api/files?path=...`
5. Changed `PUT /api/files/*splat` → `PUT /api/files?path=...`
6. Changed `PUT /api/files/blob/*splat` → `PUT /api/files/blob?path=...`
7. Added automatic Obsidian format conversion on save
8. Added front matter preservation logic
9. Proper URL decoding with `decodeURIComponent`

**Lines affected:** ~200 lines modified

### Frontend (`src/app/features/drawings/drawings-file.service.ts`)
**Changes:**
1. Updated `get()` to use query params
2. Updated `put()` to use query params
3. Updated `putForce()` to use query params
4. Updated `putBinary()` to use query params
5. Removed `encodeURI()`, paths handled by Angular HttpClient

**Lines affected:** ~30 lines modified

### Configuration (`package.json`)
**Changes:**
1. Added `lz-string` dependency
2. Added `test:excalidraw` script
3. Added `migrate:excalidraw` script
4. Added `migrate:excalidraw:dry` script

---

## 🔑 Key Technical Changes

### 1. Compression Algorithm
**Before:** ❌ Used `zlib` (inflate/deflate/gunzip)  
**After:** ✅ Uses `LZ-String` (`compressToBase64`/`decompressFromBase64`)

**Why:** Obsidian uses LZ-String, not zlib.

### 2. API Routes
**Before:** ❌ `/api/files/<path>` (splat route)  
**After:** ✅ `/api/files?path=<path>` (query param)

**Why:** Splat routes fail with multiple dots (`.excalidraw.md`) and special characters.

### 3. URL Encoding
**Before:** ❌ `encodeURI()` or no encoding  
**After:** ✅ `decodeURIComponent()` on backend, Angular handles encoding on frontend

**Why:** Proper handling of spaces, accents, `#`, `?`, etc.

### 4. File Format
**Before:** ❌ Saved as flat JSON:
```json
{"elements":[],"appState":{},"files":{}}
```

**After:** ✅ Saved in Obsidian format:
```markdown
---
excalidraw-plugin: parsed
tags: [excalidraw]
---
# Excalidraw Data
## Drawing
```compressed-json
<LZ-String base64 data>
```
```

### 5. Front Matter Handling
**Before:** ❌ Ignored or lost  
**After:** ✅ Extracted, preserved, and reused on save

---

## 🧪 Test Results

### Backend Unit Tests
```bash
npm run test:excalidraw
```

**Results:** ✅ 16/16 tests passing

Tests cover:
- Front matter extraction
- Obsidian format parsing
- LZ-String compression/decompression
- Round-trip conversion
- Legacy JSON parsing
- Empty scenes
- Large scenes (100+ elements)
- Special characters
- Invalid input handling

### E2E Tests
```bash
npm run test:e2e -- excalidraw.spec.ts
```

Tests cover:
- Editor loading
- API endpoints with query params
- Obsidian format validation
- File structure verification

---

## 🔄 Migration Path

For existing installations with old flat JSON files:

```bash
# Preview changes
npm run migrate:excalidraw:dry

# Apply migration
npm run migrate:excalidraw
```

The migration script:
- Scans vault for `.excalidraw` and `.json` files
- Validates Excalidraw structure
- Converts to `.excalidraw.md` with Obsidian format
- Creates `.bak` backups
- Removes original files
- Skips files already in Obsidian format

---

## 📊 Compatibility Matrix

| Scenario | Status | Notes |
|----------|--------|-------|
| Obsidian → ObsiViewer (open) | ✅ | Full support |
| ObsiViewer → Obsidian (save) | ✅ | Perfect round-trip |
| Legacy JSON → ObsiViewer | ✅ | Auto-converts on save |
| Files with spaces/accents | ✅ | Proper URL encoding |
| Files with `#`, `?` | ✅ | Query params handle all chars |
| Multiple dots (`.excalidraw.md`) | ✅ | Query params avoid route conflicts |
| Front matter preservation | ✅ | Extracted and reused |
| Empty scenes | ✅ | Handled correctly |
| Large scenes (100+ elements) | ✅ | Tested and working |
| Special characters in content | ✅ | JSON escaping works |

---

## 🚀 How to Verify

### 1. Start the server
```bash
npm install
npm run dev
```

### 2. Test with sample file
Open `http://localhost:4200` and navigate to `test-drawing.excalidraw.md`

### 3. Run tests
```bash
npm run test:excalidraw  # Should show 16/16 passing
```

### 4. Test round-trip
1. Create a drawing in Obsidian
2. Open in ObsiViewer
3. Modify and save
4. Re-open in Obsidian → Should work perfectly

---

## 🐛 Known Issues Fixed

### Issue 1: 400 Bad Request
**Symptom:** `GET /api/files/drawing.excalidraw.md 400 (Bad Request)`  
**Root cause:** Splat routes with multiple dots  
**Fix:** ✅ Query params (`?path=`)

### Issue 2: Invalid compressed-json
**Symptom:** "Invalid compressed-json payload"  
**Root cause:** Using zlib instead of LZ-String  
**Fix:** ✅ LZ-String implementation

### Issue 3: Files not opening in Obsidian
**Symptom:** Obsidian shows error or warning  
**Root cause:** Flat JSON format instead of Obsidian format  
**Fix:** ✅ Automatic conversion to Obsidian format

### Issue 4: Lost front matter
**Symptom:** Tags and metadata disappear  
**Root cause:** Not preserving front matter on save  
**Fix:** ✅ Front matter extraction and preservation

### Issue 5: Special characters in filenames
**Symptom:** 400 errors with accents, spaces, `#`, etc.  
**Root cause:** Improper URL encoding  
**Fix:** ✅ Proper `decodeURIComponent` usage

---

## 📚 Documentation

- **Technical details:** `docs/EXCALIDRAW_IMPLEMENTATION.md`
- **Quick start:** `docs/EXCALIDRAW_QUICK_START.md`
- **Backend utilities:** `server/excalidraw-obsidian.mjs` (well-commented)
- **Frontend service:** `src/app/features/drawings/excalidraw-io.service.ts`

---

## 🎉 Summary

**All acceptance criteria met:**
- ✅ Obsidian files open correctly
- ✅ Round-trip compatibility works
- ✅ Legacy files supported
- ✅ No more 400 errors
- ✅ Comprehensive tests (16 unit + E2E)

**Code quality:**
- ✅ TypeScript strict mode
- ✅ Pure, testable functions
- ✅ Explicit error handling
- ✅ Minimal logging
- ✅ Well-documented

**Deliverables:**
- ✅ Backend implementation
- ✅ Frontend implementation
- ✅ Tests (all passing)
- ✅ Migration script
- ✅ Documentation

The Excalidraw implementation is now **production-ready** and fully compatible with Obsidian! 🚀