docs/api/ticket-comments/IMPLEMENTATION.md

# Ticket Comments - Implementation Summary

## ✅ What Was Implemented

### 1. Service Layer (`ticket_comment_service.py`)
- ✅ `create_comment()` - Create comments with validation
- ✅ `update_comment()` - Edit comments (author only)
- ✅ `delete_comment()` - Soft delete (author or PM)
- ✅ `get_comment()` - Get single comment
- ✅ `list_comments()` - Paginated list with filtering
- ✅ `get_comment_replies()` - Load threaded replies
- ✅ `_to_response()` - Convert model to response schema

### 2. API Endpoints (`ticket_comments.py`)
- ✅ `POST /tickets/{ticket_id}/comments` - Create comment
- ✅ `PUT /comments/{comment_id}` - Update comment
- ✅ `DELETE /comments/{comment_id}` - Delete comment
- ✅ `GET /comments/{comment_id}` - Get comment
- ✅ `GET /tickets/{ticket_id}/comments` - List comments
- ✅ `GET /comments/{comment_id}/replies` - Get replies

### 3. Features
- ✅ **Threading** - Reply to comments via `parent_comment_id`
- ✅ **Mentions** - Tag users via `mentioned_user_ids`
- ✅ **Attachments** - Link documents via `attachment_document_ids`
- ✅ **Edit Tracking** - Track who edited and when
- ✅ **Soft Delete** - Preserve data integrity
- ✅ **Pagination** - Handle large comment lists
- ✅ **Filtering** - By type, internal/external, parent-only
- ✅ **Authorization** - Role-based access control

### 4. Validation
- ✅ Ticket exists before creating comment
- ✅ Parent comment exists for replies
- ✅ Mentioned users exist
- ✅ Only author can edit their comments
- ✅ Author or PM can delete comments
- ✅ Comment text not empty

### 5. Documentation
- ✅ API documentation with examples
- ✅ Testing guide with curl commands
- ✅ Error handling documentation
- ✅ Best practices guide

---

## 🔧 How It Works

### Threading (Replies)

```
Comment A (parent_comment_id: null)
├── Reply B (parent_comment_id: A)
│   └── Reply C (parent_comment_id: B)
└── Reply D (parent_comment_id: A)
```

**Implementation:**
- Each comment has optional `parent_comment_id`
- `reply_count` computed in `_to_response()`
- Replies loaded separately via `/comments/{id}/replies`
- Replies sorted by `created_at ASC` (oldest first)

### Edit Tracking

**When comment is edited:**
1. `comment_text` updated
2. `is_edited` set to `true`
3. `edited_at` set to current timestamp
4. `edited_by_user_id` set to editor's ID
5. `updated_at` updated

**Original text NOT preserved** (consider version history if needed)

### Soft Delete

**When comment is deleted:**
1. `deleted_at` set to current timestamp
2. Comment excluded from all queries via `deleted_at IS NULL`
3. Data preserved for audit trail
4. Can be restored by setting `deleted_at = NULL`

---

## 🎯 Usage Examples

### Field Agent: Add Note
```python
POST /tickets/{ticket_id}/comments
{
  "comment_text": "Customer not home, will retry tomorrow",
  "is_internal": true,
  "comment_type": "update"
}
```

### Dispatcher: Ask Question
```python
POST /tickets/{ticket_id}/comments
{
  "comment_text": "@john Can you check the customer location?",
  "mentioned_user_ids": ["john-uuid"],
  "is_internal": true,
  "comment_type": "question"
}
```

### PM: Reply to Question
```python
POST /tickets/{ticket_id}/comments
{
  "comment_text": "Location verified, proceed with installation",
  "parent_comment_id": "question-uuid",
  "is_internal": true,
  "comment_type": "resolution"
}
```

### Load Threaded Conversation
```python
# 1. Get top-level comments
GET /tickets/{ticket_id}/comments?parent_only=true

# 2. For each comment with reply_count > 0:
GET /comments/{comment_id}/replies
```

---

## 🔒 Security

### Authorization Matrix

| Action | Field Agent | Dispatcher | PM | Platform Admin |
|--------|-------------|------------|----|----|
| Create comment | ✅ | ✅ | ✅ | ✅ |
| View comments | ✅ | ✅ | ✅ | ✅ |
| Edit own comment | ✅ | ✅ | ✅ | ✅ |
| Edit others' comment | ❌ | ❌ | ❌ | ❌ |
| Delete own comment | ✅ | ✅ | ✅ | ✅ |
| Delete others' comment | ❌ | ❌ | ✅ | ✅ |

### Validation Checks
1. ✅ Ticket exists
2. ✅ Parent comment exists (for replies)
3. ✅ Mentioned users exist
4. ✅ User owns comment (for edit)
5. ✅ User is author or PM (for delete)
6. ✅ Comment text not empty

---

## 📊 Database Impact

### Indexes (Already in schema.sql)
```sql
CREATE INDEX idx_ticket_comments_ticket ON ticket_comments(ticket_id, deleted_at);
CREATE INDEX idx_ticket_comments_parent ON ticket_comments(parent_comment_id);
CREATE INDEX idx_ticket_comments_user ON ticket_comments(user_id);
CREATE INDEX idx_ticket_comments_created ON ticket_comments(created_at DESC);
```

### Storage Estimate
- Average comment: ~200 bytes
- 1000 comments: ~200 KB
- 1 million comments: ~200 MB

---

## 🚀 Performance

### Query Optimization
- ✅ Use `joinedload()` for relationships
- ✅ Filter `deleted_at IS NULL` in all queries
- ✅ Paginate large result sets
- ✅ Index on `ticket_id`, `parent_comment_id`, `user_id`

### Expected Response Times
- Create comment: < 100ms
- List comments (50 items): < 200ms
- Get replies: < 100ms
- Update comment: < 100ms
- Delete comment: < 100ms

---

## 🔮 Future Enhancements

### Phase 2: Notifications
- [ ] Notify mentioned users
- [ ] Notify ticket assignees on external comments
- [ ] Real-time updates via SSE

### Phase 3: Rich Features
- [ ] Markdown support
- [ ] Code blocks
- [ ] File attachments (not just links)
- [ ] Emoji reactions

### Phase 4: Advanced
- [ ] Full-text search
- [ ] Comment version history
- [ ] Bulk operations
- [ ] Comment templates

---

## 🐛 Known Limitations

1. **No version history** - Edits overwrite original text
2. **No notifications** - Mentions don't trigger notifications yet
3. **No rich text** - Plain text only
4. **No reactions** - Can't like/emoji comments
5. **No search** - Must paginate to find comments

---

## 📝 Testing Checklist

- [x] Create comment on valid ticket
- [x] Create reply to comment
- [x] Update own comment
- [x] Delete own comment
- [x] List comments with pagination
- [x] Get comment replies
- [x] Filter by is_internal
- [x] Filter by comment_type
- [x] Filter parent_only
- [x] Validate ticket exists
- [x] Validate parent comment exists
- [x] Validate mentioned users exist
- [x] Prevent editing others' comments
- [x] Allow PM to delete any comment
- [x] Soft delete preserves data
- [x] Reply count accurate
- [x] Edit tracking works

---

## 🎓 Best Practices

### For Developers
1. Always filter `deleted_at IS NULL`
2. Use `joinedload()` for relationships
3. Validate foreign keys before creating
4. Use transactions for data consistency
5. Log all operations for debugging

### For Users
1. Keep comments concise and actionable
2. Use appropriate comment types
3. Mark sensitive info as internal
4. Reply to comments for context
5. Edit instead of delete when possible

---

## 📞 Support

### Common Issues

**Q: Comments not appearing?**
A: Check `deleted_at IS NULL` filter

**Q: Can't edit comment?**
A: Only author can edit their own comments

**Q: Reply count wrong?**
A: Ensure subquery counts `deleted_at IS NULL`

**Q: Mentions not working?**
A: Notifications not implemented yet (Phase 2)

### Contact
- Backend issues: Check logs in `src/app/services/ticket_comment_service.py`
- API issues: Check `src/app/api/v1/ticket_comments.py`
- Database issues: Check indexes and constraints

---

## 👨‍💻 Frontend Team Guide

**See [FRONTEND.md](./FRONTEND.md) for:**
- 6 endpoints with exact request/response formats
- UI patterns (simple list, threaded view, pagination)
- React component examples
- Common use cases
- Error handling
- Performance tips
- Quick reference (no fluff)