# Debugging Guide

Comprehensive guide to debugging Changemaker Lite V2 applications, covering API, frontend, database, and Docker debugging techniques.

## Overview

Effective debugging requires:
- Understanding the tools (VSCode, Chrome DevTools, logs)
- Systematic approach (reproduce, isolate, fix, verify)
- Knowledge of common issues

This guide covers debugging strategies for all parts of V2.

## API Debugging

### VSCode Debugging

#### Launch Configuration

Create `.vscode/launch.json`:

```json
{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Debug API",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "npm",
      "runtimeArgs": ["run", "dev"],
      "cwd": "${workspaceFolder}/api",
      "console": "integratedTerminal",
      "skipFiles": ["<node_internals>/**"],
      "envFile": "${workspaceFolder}/.env",
      "sourceMaps": true,
      "restart": true,
      "protocol": "inspector"
    },
    {
      "name": "Debug Media API",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "npm",
      "runtimeArgs": ["run", "dev:media"],
      "cwd": "${workspaceFolder}/api",
      "console": "integratedTerminal",
      "skipFiles": ["<node_internals>/**"],
      "envFile": "${workspaceFolder}/.env"
    },
    {
      "name": "Attach to API (Docker)",
      "type": "node",
      "request": "attach",
      "port": 9229,
      "address": "localhost",
      "restart": true,
      "sourceMaps": true,
      "localRoot": "${workspaceFolder}/api",
      "remoteRoot": "/app",
      "skipFiles": ["<node_internals>/**"]
    }
  ]
}
```

#### Start Debugging

1. Open VSCode
2. Open Run and Debug panel (Cmd+Shift+D / Ctrl+Shift+D)
3. Select "Debug API" configuration
4. Press F5 to start debugging
5. API starts with debugger attached

#### Set Breakpoints

Click line number gutter to set breakpoint:

```typescript
// api/src/modules/auth/auth.service.ts
async login(email: string, password: string) {
  const user = await this.prisma.user.findUnique({ // ← Click here
    where: { email }
  });

  if (!user) {
    throw new Error('User not found'); // ← Or here
  }

  // Breakpoint pauses execution
  const isValid = await bcrypt.compare(password, user.password);

  return { user, tokens: this.generateTokens(user) };
}
```

#### Debug Features

**Step Controls:**
- **F10:** Step over (next line)
- **F11:** Step into (enter function)
- **Shift+F11:** Step out (exit function)
- **F5:** Continue (run to next breakpoint)

**Inspect Variables:**
- Hover over variable to see value
- Use "Variables" panel to see all local variables
- Use "Watch" panel to monitor specific expressions

**Debug Console:**
- Evaluate expressions while paused
- Call functions with current scope

```typescript
// In debug console (while paused)
> user.email
'john@example.com'

> bcrypt.compare('test', user.password)
Promise { <pending> }

> await bcrypt.compare('test', user.password)
false
```

**Call Stack:**
- See function call hierarchy
- Click stack frame to jump to code
- Useful for understanding execution flow

### Logging (Winston)

#### Using Logger

```typescript
import { logger } from '../../utils/logger';

// Info level
logger.info('User logged in', { userId: user.id, email: user.email });

// Error level
logger.error('Failed to create user', {
  error: error.message,
  stack: error.stack,
  email
});

// Warn level
logger.warn('Deprecated endpoint accessed', { endpoint: req.path });

// Debug level (only in development)
logger.debug('Processing request', {
  method: req.method,
  path: req.path,
  query: req.query
});
```

#### Log Output

**Development (console):**
```
[2026-02-13 10:30:45] INFO: User logged in {"userId":1,"email":"john@example.com"}
[2026-02-13 10:30:46] ERROR: Failed to create user {"error":"Email already exists","email":"john@example.com"}
```

**Production (JSON):**
```json
{"level":"info","message":"User logged in","userId":1,"email":"john@example.com","timestamp":"2026-02-13T10:30:45.123Z"}
{"level":"error","message":"Failed to create user","error":"Email already exists","email":"john@example.com","timestamp":"2026-02-13T10:30:46.456Z"}
```

#### Log Levels

Set log level via environment:

```bash
# .env
LOG_LEVEL=debug  # dev: debug, info, warn, error
LOG_LEVEL=info   # prod: info, warn, error
```

### Database Query Logging

#### Prisma Query Logging

Enable in Prisma Client:

```typescript
// api/src/config/prisma.ts
const prisma = new PrismaClient({
  log: [
    { emit: 'event', level: 'query' },
    { emit: 'event', level: 'error' },
    { emit: 'event', level: 'warn' }
  ]
});

prisma.$on('query', (e) => {
  logger.debug('Prisma query', {
    query: e.query,
    params: e.params,
    duration: e.duration
  });
});

prisma.$on('error', (e) => {
  logger.error('Prisma error', { target: e.target, message: e.message });
});
```

**Output:**
```
[2026-02-13 10:30:45] DEBUG: Prisma query {
  "query": "SELECT * FROM users WHERE id = $1",
  "params": "[1]",
  "duration": 5
}
```

#### Slow Query Logging

Log slow queries:

```typescript
prisma.$on('query', (e) => {
  if (e.duration > 100) { // > 100ms
    logger.warn('Slow query detected', {
      query: e.query,
      duration: e.duration,
      params: e.params
    });
  }
});
```

### Network Debugging

#### Request Logging

Log all HTTP requests:

```typescript
// api/src/middleware/logger.ts
import { Request, Response, NextFunction } from 'express';
import { logger } from '../utils/logger';

export function requestLogger(req: Request, res: Response, next: NextFunction) {
  const start = Date.now();

  res.on('finish', () => {
    const duration = Date.now() - start;

    logger.info('HTTP request', {
      method: req.method,
      path: req.path,
      status: res.statusCode,
      duration,
      ip: req.ip,
      userAgent: req.get('user-agent')
    });

    if (duration > 1000) {
      logger.warn('Slow request', {
        method: req.method,
        path: req.path,
        duration
      });
    }
  });

  next();
}

// In server.ts
app.use(requestLogger);
```

#### Testing with curl

```bash
# GET request
curl http://localhost:4000/api/users

# POST request with JSON
curl -X POST http://localhost:4000/api/auth/login \
  -H "Content-Type: application/json" \
  -d '{"email":"admin@example.com","password":"Admin123!"}'

# With authentication
curl http://localhost:4000/api/users \
  -H "Authorization: Bearer <token>"

# Verbose output (see headers)
curl -v http://localhost:4000/api/users

# Save response to file
curl http://localhost:4000/api/users > users.json
```

#### Testing with HTTPie

```bash
# Install httpie
brew install httpie  # macOS
sudo apt install httpie  # Linux

# GET request
http localhost:4000/api/users

# POST request
http POST localhost:4000/api/auth/login \
  email=admin@example.com \
  password=Admin123!

# With authentication
http localhost:4000/api/users \
  Authorization:"Bearer <token>"

# Pretty JSON output
http --pretty=all localhost:4000/api/users
```

## Frontend Debugging

### Chrome DevTools

#### Opening DevTools

- **F12** or **Cmd+Option+I** (Mac) / **Ctrl+Shift+I** (Windows/Linux)

#### Console Tab

View console logs and errors:

```typescript
// admin/src/pages/UsersPage.tsx
console.log('Users loaded', users);
console.error('Failed to fetch users', error);
console.warn('Deprecated API used');
console.table(users); // Display as table

// Conditional logging
if (import.meta.env.DEV) {
  console.log('Debug info', { users, loading });
}
```

**Output:**
```
Users loaded [{ id: 1, email: 'john@example.com' }, ...]
```

#### Sources Tab

Debug JavaScript/TypeScript:

1. Open Sources tab
2. Find file in file tree (webpack://./src/)
3. Click line number to set breakpoint
4. Interact with UI to trigger breakpoint
5. Use step controls (same as VSCode)

**Conditional Breakpoints:**
- Right-click line number
- Select "Add conditional breakpoint"
- Enter condition: `user.id === 1`
- Pauses only when condition is true

#### Network Tab

Debug API calls:

1. Open Network tab
2. Filter by "Fetch/XHR"
3. Interact with UI
4. Click request to see:
   - Headers (request/response)
   - Payload (request body)
   - Preview (formatted response)
   - Response (raw response)
   - Timing (request duration)

**Common Issues:**
- **404 Not Found:** Check URL path
- **401 Unauthorized:** Check token/auth header
- **500 Server Error:** Check API logs
- **CORS Error:** Check CORS_ORIGIN setting

#### Application Tab

Inspect storage:

- **Local Storage:** See persisted auth tokens
- **Session Storage:** See session data
- **Cookies:** See cookies
- **Cache Storage:** See cached resources

```typescript
// View in console
localStorage.getItem('auth-token');
sessionStorage.getItem('cart');
```

### React DevTools

#### Installation

Install browser extension:
- [Chrome](https://chrome.google.com/webstore/detail/react-developer-tools)
- [Firefox](https://addons.mozilla.org/en-US/firefox/addon/react-devtools/)

#### Components Tab

Inspect React component tree:

1. Open DevTools
2. Go to "Components" tab
3. Select component from tree
4. View:
   - Props
   - State (hooks)
   - Context
   - Owner (parent component)

**Edit Props/State:**
- Click value to edit
- Change takes effect immediately
- Useful for testing edge cases

#### Profiler Tab

Profile component renders:

1. Go to "Profiler" tab
2. Click "Record"
3. Interact with UI
4. Click "Stop"
5. See:
   - Flame graph (render hierarchy)
   - Ranked chart (slowest components)
   - Component details (render duration)

**Identify Performance Issues:**
- Components rendering too often
- Slow component renders
- Unnecessary re-renders

### Zustand DevTools

#### Enable Redux DevTools

Already configured in stores:

```typescript
// admin/src/stores/auth.store.ts
import { create } from 'zustand';
import { devtools } from 'zustand/middleware';

export const useAuthStore = create<AuthState>()(
  devtools(
    (set, get) => ({
      user: null,
      isAuthenticated: false,
      setUser: (user) => set({ user, isAuthenticated: !!user }),
      logout: () => set({ user: null, isAuthenticated: false })
    }),
    { name: 'AuthStore' } // Name in DevTools
  )
);
```

#### Using Redux DevTools

1. Install [Redux DevTools extension](https://chrome.google.com/webstore/detail/redux-devtools)
2. Open DevTools
3. Go to "Redux" tab
4. Select store from dropdown (AuthStore, CanvassStore)
5. View:
   - State tree
   - Action history
   - State diff

**Features:**
- Time-travel debugging (jump to previous state)
- Action replay
- State export/import

### VSCode Debugging (Frontend)

#### Launch Configuration

```json
{
  "name": "Debug Admin (Chrome)",
  "type": "chrome",
  "request": "launch",
  "url": "http://localhost:3000",
  "webRoot": "${workspaceFolder}/admin/src",
  "sourceMapPathOverrides": {
    "webpack:///./*": "${webRoot}/*",
    "webpack:///src/*": "${webRoot}/*",
    "webpack:///*": "*"
  },
  "userDataDir": false
}
```

**Start Debugging:**
1. Start Admin dev server: `npm run dev`
2. Select "Debug Admin (Chrome)" in VSCode
3. Press F5
4. Chrome opens with debugger attached
5. Set breakpoints in VSCode
6. Breakpoints hit when code executes

## Database Debugging

### Prisma Studio

Visual database browser:

```bash
# Start Prisma Studio
cd api
npx prisma studio
```

**Features:**
- Browse all tables
- Filter and sort data
- Edit records directly
- Create new records
- Delete records

**Use Cases:**
- Inspect database state
- Manual data fixes
- Verify migrations
- Test queries

### PostgreSQL Shell

Direct database access:

```bash
# Connect to database
docker compose exec v2-postgres psql -U changemaker_v2 -d changemaker_v2_db

# List tables
\dt

# Describe table
\d users

# Run query
SELECT * FROM users WHERE role = 'SUPER_ADMIN';

# Count records
SELECT COUNT(*) FROM campaigns;

# Exit
\q
```

**Common Queries:**

```sql
-- Find user by email
SELECT * FROM users WHERE email = 'admin@example.com';

-- Count users by role
SELECT role, COUNT(*) FROM users GROUP BY role;

-- Recent campaigns
SELECT * FROM campaigns ORDER BY created_at DESC LIMIT 10;

-- Users without name
SELECT * FROM users WHERE name IS NULL;

-- Delete test data
DELETE FROM users WHERE email LIKE '%test%';
```

### Query Analysis

#### Explain Query Plan

```sql
EXPLAIN ANALYZE
SELECT * FROM users WHERE email = 'admin@example.com';
```

**Output:**
```
Index Scan using users_email_key on users (cost=0.28..8.29 rows=1 width=...)
  Index Cond: (email = 'admin@example.com'::text)
  Planning Time: 0.123 ms
  Execution Time: 0.045 ms
```

**Identify Issues:**
- Sequential scans (slow on large tables)
- Missing indexes
- Expensive joins

#### Slow Query Log

Enable slow query logging:

```sql
-- Set log threshold (100ms)
ALTER DATABASE changemaker_v2_db SET log_min_duration_statement = 100;

-- View slow queries in logs
docker compose logs v2-postgres | grep "duration:"
```

## Docker Debugging

### Container Logs

View container output:

```bash
# All services
docker compose logs -f

# Specific service
docker compose logs -f api

# Last 100 lines
docker compose logs --tail=100 api

# With timestamps
docker compose logs -t -f api

# Since specific time
docker compose logs --since 2024-01-01T10:00:00 api
```

### Execute Commands in Container

```bash
# Shell access
docker compose exec api sh

# Run command
docker compose exec api npm run type-check

# Run as specific user
docker compose exec -u root api sh

# Non-interactive command
docker compose exec -T api npm run lint
```

### Inspect Container

```bash
# Container details
docker inspect api

# Environment variables
docker inspect api | grep -A 20 "Env"

# Mounts
docker inspect api | grep -A 50 "Mounts"

# Network settings
docker inspect api | grep -A 20 "Networks"

# Resource limits
docker inspect api | grep -A 10 "Memory"
```

### Container Stats

```bash
# Real-time stats
docker stats

# Specific container
docker stats api

# Format output
docker stats --format "table {{.Container}}\t{{.CPUPerc}}\t{{.MemUsage}}"
```

### Network Debugging

```bash
# Test connectivity between containers
docker compose exec api ping v2-postgres
docker compose exec api ping redis

# Check listening ports
docker compose exec api netstat -tuln

# Test HTTP endpoint from inside container
docker compose exec api wget -O- http://localhost:4000/health

# DNS lookup
docker compose exec api nslookup v2-postgres
```

## Common Issues

### 401 Unauthorized

**Symptoms:** API returns 401 for authenticated requests.

**Causes:**
1. Token expired
2. Invalid token
3. Missing Authorization header
4. Token format incorrect

**Debug:**

```bash
# Check token in browser DevTools
localStorage.getItem('auth-token')

# Test token with curl
curl http://localhost:4000/api/users \
  -H "Authorization: Bearer <token>" \
  -v

# Decode JWT (jwt.io)
# Check expiration (exp claim)
```

**Fix:**
- Refresh token
- Re-login
- Check token format (Bearer prefix)

### 500 Internal Server Error

**Symptoms:** API returns 500 error.

**Causes:**
1. Unhandled exception
2. Database error
3. External service failure

**Debug:**

```bash
# Check API logs
docker compose logs -f api

# Look for error stack trace
docker compose logs api | grep -A 20 "Error:"

# Check database connection
docker compose exec api npx prisma db execute --stdin <<< "SELECT 1"
```

**Fix:**
- Check error message in logs
- Verify database is running
- Check external service (Redis, SMTP, etc.)

### CORS Errors

**Symptoms:** Browser blocks request with CORS error.

**Causes:**
1. Incorrect CORS_ORIGIN setting
2. Missing CORS headers
3. Preflight OPTIONS request fails

**Debug:**

```bash
# Check CORS_ORIGIN in .env
grep CORS_ORIGIN .env

# Test with curl (bypasses CORS)
curl http://localhost:4000/api/users

# Check preflight request
curl -X OPTIONS http://localhost:4000/api/users \
  -H "Origin: http://localhost:3000" \
  -H "Access-Control-Request-Method: GET" \
  -v
```

**Fix:**
- Set `CORS_ORIGIN=http://localhost:3000` in .env
- Restart API: `docker compose restart api`

### Database Connection Errors

**Symptoms:** API fails to connect to database.

**Causes:**
1. PostgreSQL not running
2. Incorrect DATABASE_URL
3. Network issue

**Debug:**

```bash
# Check PostgreSQL is running
docker compose ps v2-postgres

# Check DATABASE_URL
docker compose exec api sh -c 'echo $DATABASE_URL'

# Test connection
docker compose exec v2-postgres psql -U changemaker_v2 -d changemaker_v2_db -c "SELECT 1"

# Check logs
docker compose logs v2-postgres
```

**Fix:**
- Start PostgreSQL: `docker compose up -d v2-postgres`
- Verify DATABASE_URL matches docker-compose.yml
- Check password in .env

### Redis Connection Errors

**Symptoms:** API fails to connect to Redis.

**Causes:**
1. Redis not running
2. Incorrect REDIS_URL
3. Missing REDIS_PASSWORD

**Debug:**

```bash
# Check Redis is running
docker compose ps redis

# Test connection
docker compose exec redis redis-cli -a your_password ping

# Check Redis logs
docker compose logs redis
```

**Fix:**
- Start Redis: `docker compose up -d redis`
- Set REDIS_PASSWORD in .env
- Update REDIS_URL with password

### Hot Reload Not Working

**Symptoms:** Code changes don't trigger reload.

**Causes:**
1. Volume mount missing
2. File watcher not detecting changes
3. Build cache issue

**Debug:**

```bash
# Check volume mounts
docker inspect api | grep -A 20 "Mounts"

# Test file sync
docker compose exec api ls -la /app/src

# Check for .dockerignore blocking sync
cat api/.dockerignore
```

**Fix:**
- Verify volume mount in docker-compose.yml
- Restart container: `docker compose restart api`
- Clear cache: `rm -rf api/dist && docker compose restart api`

## Debug Checklist

### Systematic Debugging Approach

1. **Reproduce:**
   - Can you consistently reproduce the issue?
   - What are the exact steps?

2. **Isolate:**
   - Does it happen in all environments?
   - Is it specific to one user/data/scenario?

3. **Gather Information:**
   - Check logs (API, frontend, database)
   - Check network requests (DevTools)
   - Check error messages

4. **Form Hypothesis:**
   - What do you think is causing it?
   - What evidence supports this?

5. **Test Hypothesis:**
   - Set breakpoints
   - Add logging
   - Test specific scenario

6. **Fix:**
   - Make minimal change to fix issue
   - Don't fix multiple issues at once

7. **Verify:**
   - Re-test original scenario
   - Test related functionality
   - Check for side effects

8. **Prevent:**
   - Add tests to catch regression
   - Update documentation
   - Share learnings with team

## Performance Debugging

### API Response Time

```typescript
// Measure endpoint performance
app.get('/users', async (req, res) => {
  const start = Date.now();

  const users = await prisma.user.findMany();

  const duration = Date.now() - start;
  logger.info('Users endpoint', { duration, count: users.length });

  res.json({ users });
});
```

### Database Query Performance

```typescript
// Log slow queries
prisma.$on('query', (e) => {
  if (e.duration > 100) {
    logger.warn('Slow query', {
      query: e.query,
      duration: e.duration,
      params: e.params
    });
  }
});
```

### Frontend Render Performance

```typescript
// Measure component render time
function UserList() {
  const renderStart = performance.now();

  useEffect(() => {
    const renderTime = performance.now() - renderStart;
    if (renderTime > 16) { // > 1 frame (60fps)
      console.warn('Slow render', { component: 'UserList', renderTime });
    }
  });

  return <div>...</div>;
}
```

## Related Documentation

- **Setup:** [Local Development Setup](local-setup.md)
- **Docker:** [Docker Workflow](docker-workflow.md)
- **Testing:** [Testing Guide](testing.md)
- **Troubleshooting:** [Troubleshooting Guide](../troubleshooting.md)

## Summary

You now know:
- ✅ How to debug API with VSCode
- ✅ How to use Winston logging effectively
- ✅ How to debug frontend with Chrome DevTools
- ✅ How to use React DevTools and Zustand DevTools
- ✅ How to debug database with Prisma Studio and psql
- ✅ How to debug Docker containers
- ✅ Common issues and their solutions
- ✅ Systematic debugging approach
- ✅ Performance debugging techniques

**Quick Start:**
```bash
# API debugging
cd api && npm run dev  # Start with debugger
# Set breakpoints in VSCode, press F5

# Frontend debugging
# Open Chrome DevTools (F12)
# Network tab for API calls, Console for logs

# Database debugging
npx prisma studio  # Visual browser
docker compose exec v2-postgres psql -U changemaker_v2 -d changemaker_v2_db

# Logs
docker compose logs -f api admin
```