# Backend Implementation Summary

## Overview
This document summarizes the critical backend features implemented for the Adopt-a-Street application.

## Implemented Features

### 1. Point System with Transactions ✅

**Models Created:**
- `/models/PointTransaction.js` - Tracks all point transactions with audit trail

**Key Features:**
- Atomic point awarding using MongoDB transactions
- Point transaction history with user reference
- Balance tracking after each transaction
- Transaction types: street_adoption, task_completion, post_creation, event_participation, reward_redemption

**Point Values:**
- Street Adoption: +100 points
- Task Completion: +50 points
- Post Creation: +10 points
- Event Participation: +75 points

**Service Implementation:**
- `/services/gamificationService.js` - Centralized gamification logic
- `awardPoints()` - Generic point awarding function
- `awardStreetAdoptionPoints()` - Award points for street adoption
- `awardTaskCompletionPoints()` - Award points for task completion
- `awardPostCreationPoints()` - Award points for post creation
- `awardEventParticipationPoints()` - Award points for event participation
- `deductRewardPoints()` - Deduct points for reward redemption

**Integrated Routes:**
- `POST /api/streets/:id/adopt` - Awards points on street adoption
- `PUT /api/tasks/:id` - Awards points on task completion
- `POST /api/posts` - Awards points on post creation
- `PUT /api/events/rsvp/:id` - Awards points on event RSVP
- `POST /api/rewards/redeem/:id` - Deducts points on reward redemption

---

### 2. Badge System with Auto-Awarding ✅

**Models Created:**
- `/models/Badge.js` - Badge definitions with criteria
- `/models/UserBadge.js` - User badge awards with timestamps

**Badge Categories:**
1. **Street Adoption Badges** (4 badges)
   - First Adoption (1 street) - Common
   - Street Adopter (5 streets) - Rare
   - Neighborhood Champion (10 streets) - Epic
   - City Guardian (25 streets) - Legendary

2. **Task Completion Badges** (4 badges)
   - First Task (1 task) - Common
   - Task Master (10 tasks) - Rare
   - Dedicated Worker (50 tasks) - Epic
   - Maintenance Legend (100 tasks) - Legendary

3. **Post Creation Badges** (4 badges)
   - First Post (1 post) - Common
   - Social Butterfly (25 posts) - Rare
   - Community Voice (100 posts) - Epic
   - Social Media Star (250 posts) - Legendary

4. **Event Participation Badges** (4 badges)
   - Event Participant (1 event) - Common
   - Community Leader (5 events) - Rare
   - Event Enthusiast (15 events) - Epic
   - Community Pillar (30 events) - Legendary

5. **Point Collection Badges** (3 badges)
   - Point Collector (1,000 points) - Rare
   - Point Hoarder (5,000 points) - Epic
   - Point Master (10,000 points) - Legendary

**Service Functions:**
- `checkAndAwardBadges(userId, session)` - Checks and awards eligible badges
- `getUserBadgeProgress(userId)` - Gets user's progress towards all badges
- `getUserStats(userId)` - Retrieves user's achievement statistics

**Routes Created:**
- `GET /api/badges` - List all available badges
- `GET /api/badges/progress` - Get authenticated user's badge progress
- `GET /api/badges/users/:userId` - Get badges earned by a user
- `GET /api/badges/:badgeId` - Get specific badge details

**Seeder Script:**
- `/scripts/seedBadges.js` - Seeds initial 19 badges
- Run with: `bun run seed:badges`

---

### 3. Comments System for Posts ✅

**Model Created:**
- `/models/Comment.js` - Comment model with user and post references

**Routes Created:**
- `GET /api/posts/:postId/comments` - List comments (paginated)
- `POST /api/posts/:postId/comments` - Create comment
- `DELETE /api/posts/:postId/comments/:commentId` - Delete own comment

**Features:**
- Comment validation (max 500 characters)
- Comment count tracking on posts
- Socket.IO real-time notifications:
  - `newComment` event - Emitted when comment is created
  - `commentDeleted` event - Emitted when comment is deleted
- User population (name, profilePicture)
- Pagination support

**Post Model Updates:**
- Added `commentsCount` field
- Auto-increments/decrements on comment creation/deletion

---

### 4. Pagination for All List Endpoints ✅

**Middleware Created:**
- `/middleware/pagination.js` - Reusable pagination middleware

**Pagination Parameters:**
- `page` (default: 1) - Current page number
- `limit` (default: 10, max: 100) - Items per page

**Response Format:**
```json
{
  "data": [...],
  "pagination": {
    "currentPage": 1,
    "totalPages": 10,
    "totalCount": 95,
    "itemsPerPage": 10,
    "hasNextPage": true,
    "hasPrevPage": false
  }
}
```

**Updated Routes:**
- `GET /api/streets` - Paginated street listing
- `GET /api/tasks` - Paginated task listing
- `GET /api/posts` - Paginated post listing
- `GET /api/events` - Paginated event listing
- `GET /api/rewards` - Paginated reward listing
- `GET /api/reports` - Paginated report listing
- `GET /api/posts/:postId/comments` - Paginated comment listing

**Performance Optimizations:**
- Added indexes for pagination queries
- Proper sorting by creation date or relevance
- Population of referenced data (users, streets, etc.)

---

### 5. Image Upload with Multer & Cloudinary ✅

**Configuration:**
- `/config/cloudinary.js` - Cloudinary configuration and helpers
- `/middleware/upload.js` - Multer configuration with validation

**Upload Specifications:**
- File size limit: 5MB
- Allowed formats: JPG, JPEG, PNG, GIF, WebP
- Storage: Memory storage (buffer-based)
- Cloudinary optimization:
  - Max dimensions: 1000x1000px
  - Auto quality optimization
  - Auto format selection (WebP where supported)

**Image Upload Endpoints:**
- `POST /api/posts` - Create post with optional image
- `POST /api/posts/:id/image` - Add/update image on existing post
- `POST /api/reports` - Create report with optional image
- `POST /api/reports/:id/image` - Add/update image on existing report

**Features:**
- Image deletion when replacing images
- Public ID tracking for Cloudinary cleanup
- Error handling for invalid file types/sizes
- Authorization checks (users can only modify their own content)

**Model Updates:**
- **Post Model:**
  - `imageUrl` - Cloudinary URL
  - `cloudinaryPublicId` - For deletion tracking

- **Report Model:**
  - `imageUrl` - Cloudinary URL
  - `cloudinaryPublicId` - For deletion tracking

**Environment Variables:**
```env
CLOUDINARY_CLOUD_NAME=your_cloudinary_cloud_name
CLOUDINARY_API_KEY=your_cloudinary_api_key
CLOUDINARY_API_SECRET=your_cloudinary_api_secret
```

---

## File Structure

```
backend/
├── config/
│   └── cloudinary.js                 # Cloudinary configuration
├── middleware/
│   ├── pagination.js                 # Pagination middleware
│   └── upload.js                     # Multer upload middleware
├── models/
│   ├── Badge.js                      # Badge definitions
│   ├── Comment.js                    # Post comments
│   ├── PointTransaction.js           # Point transaction history
│   └── UserBadge.js                  # User badge awards
├── routes/
│   ├── badges.js                     # Badge routes (NEW)
│   ├── comments.js                   # Comment routes (NEW)
│   ├── events.js                     # Updated with points & pagination
│   ├── posts.js                      # Updated with points, images & pagination
│   ├── reports.js                    # Updated with images & pagination
│   ├── rewards.js                    # Updated with point deduction & pagination
│   ├── streets.js                    # Updated with pagination
│   └── tasks.js                      # Updated with pagination
├── scripts/
│   └── seedBadges.js                 # Badge seeding script
├── services/
│   └── gamificationService.js        # Gamification logic
├── .env.example                      # Updated with Cloudinary vars
├── package.json                      # Added seed:badges script
└── server.js                         # Updated with new routes & Socket.IO
```

---

## Database Schema Changes

### User Model Updates
- `points` field already existed
- Virtual `earnedBadges` population
- Indexes on `email` and `points`

### New Collections
1. **PointTransactions**
   - Indexes: `user`, `type`, `user + createdAt`, `type + createdAt`

2. **Badges**
   - Indexes: `criteria.type + criteria.threshold`, `rarity`, `order`

3. **UserBadges**
   - Unique compound index: `user + badge`
   - Index: `user + earnedAt`

4. **Comments**
   - Compound index: `post + createdAt`
   - Indexes: `user`, `post`

---

## API Endpoints Summary

### New Endpoints

**Badges:**
- `GET /api/badges` - List all badges
- `GET /api/badges/progress` - User's badge progress (authenticated)
- `GET /api/badges/users/:userId` - User's earned badges
- `GET /api/badges/:badgeId` - Badge details

**Comments:**
- `GET /api/posts/:postId/comments` - List comments (paginated)
- `POST /api/posts/:postId/comments` - Create comment
- `DELETE /api/posts/:postId/comments/:commentId` - Delete comment

**Image Uploads:**
- `POST /api/posts/:id/image` - Add/update post image
- `POST /api/reports/:id/image` - Add/update report image

### Updated Endpoints (Breaking Changes)

All list endpoints now return paginated responses:
- `GET /api/streets?page=1&limit=10`
- `GET /api/tasks?page=1&limit=10`
- `GET /api/posts?page=1&limit=10`
- `GET /api/events?page=1&limit=10`
- `GET /api/rewards?page=1&limit=10`
- `GET /api/reports?page=1&limit=10`

Point-awarding endpoints now return additional data:
```json
{
  "street": {...},
  "pointsAwarded": 100,
  "newBalance": 150,
  "badgesEarned": [...]
}
```

---

## Socket.IO Events

### New Events
- `joinPost` - Join a post room for comment updates
- `newComment` - Emitted when comment is created on a post
- `commentDeleted` - Emitted when comment is deleted

### Updated Events
- `joinEvent` - Now uses `event_${eventId}` room naming
- `eventUpdate` - Now emits to `event_${eventId}` rooms

---

## Testing & Setup

### Initial Setup
1. Install dependencies (already done):
   ```bash
   bun install
   ```

2. Configure environment variables:
   ```bash
   cp .env.example .env
   # Edit .env with your Cloudinary credentials
   ```

3. Seed badges:
   ```bash
   bun run seed:badges
   ```

4. Start server:
   ```bash
   bun run dev
   ```

### Verify Installation
```bash
# Check for linting errors
bunx eslint .

# Run tests
bun test
```

---

## Security Features

1. **MongoDB Transactions:**
   - Point awards are atomic
   - Prevents double-awarding
   - Rollback on errors

2. **Image Upload Security:**
   - File type validation
   - File size limits (5MB)
   - Authorization checks
   - Cloudinary public ID tracking

3. **Comment Security:**
   - Max length validation (500 chars)
   - Authorization for deletion
   - Input sanitization (trim)

4. **Pagination Security:**
   - Max limit enforcement (100 items)
   - Parameter validation

---

## Performance Considerations

1. **Database Indexes:**
   - All pagination queries have proper indexes
   - User points indexed for leaderboards
   - Comment queries optimized with compound indexes

2. **Cloudinary Optimization:**
   - Auto image compression
   - Format optimization (WebP)
   - Dimension limiting (1000x1000)

3. **Transaction Efficiency:**
   - Badge checking uses single stats query
   - Batch badge evaluation
   - Minimal database round-trips

---

## Breaking Changes

⚠️ **Frontend Updates Required:**

1. **Pagination:** All list endpoints now return paginated responses. Frontend must handle the new response format with `data` and `pagination` fields.

2. **Point Awards:** POST/PUT endpoints that award points now return additional fields (`pointsAwarded`, `newBalance`, `badgesEarned`).

3. **Socket.IO Rooms:** Event rooms now use `event_${eventId}` naming convention.

---

## Next Steps

### Recommended Frontend Updates
1. Update API clients to handle paginated responses
2. Add pagination UI components
3. Display badge progress and earned badges
4. Add comment components to posts
5. Implement image upload for posts and reports
6. Add real-time comment notifications via Socket.IO
7. Display point awards and badge unlocks as toast notifications

### Optional Backend Enhancements
1. Add badge progress tracking (partial completion)
2. Implement consecutive day badges
3. Add leaderboard endpoints (top points, most badges)
4. Add badge showcasing/favorites
5. Implement comment likes/replies (threading)
6. Add image moderation
7. Implement point transaction history endpoint
8. Add user point adjustment endpoint (admin only)

---

## Dependencies

All required dependencies are already installed:
- `multer` - File upload handling
- `cloudinary` - Image storage and optimization
- `mongoose` - MongoDB ODM with transaction support

---

## Documentation

### For Developers
- All functions include JSDoc comments
- Complex logic includes inline comments
- Error handling with proper status codes
- Consistent response formats

### For API Users
- All endpoints follow RESTful conventions
- Consistent error response format
- Proper HTTP status codes
- Validation messages included

---

## Summary

✅ **Fully Implemented:**
1. Point system with transaction tracking
2. Badge system with 19 auto-awarded badges
3. Comments system with real-time updates
4. Pagination for all list endpoints
5. Image uploads with Cloudinary integration

✅ **All routes updated and tested**
✅ **Database models created with proper indexes**
✅ **Socket.IO events configured**
✅ **Environment configuration documented**
✅ **Seeding script created**

The backend is now feature-complete and ready for frontend integration!
