server.js

const express = require('express');
const cors = require('cors');
const Database = require('better-sqlite3');

const app = express();
app.use(cors());
app.use(express.json());

// Initialize database
const db = new Database('tasks.db');

// Create table if not exists
db.exec(`
  CREATE TABLE IF NOT EXISTS tasks (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    title TEXT NOT NULL,
    description TEXT,
    status TEXT DEFAULT 'pending',
    due_date TEXT,
    created_at TEXT DEFAULT CURRENT_TIMESTAMP,
    updated_at TEXT DEFAULT CURRENT_TIMESTAMP
  )
`);

// Middleware to update timestamp
app.use((req, res, next) => {
  if (['POST', 'PUT', 'PATCH'].includes(req.method)) {
    req.body.updated_at = new Date().toISOString();
  }
  next();
});

// Helper function
const getTask = (id) => {
  const task = db.prepare('SELECT * FROM tasks WHERE id = ?').get(id);
  return task;
};

// GET /api/tasks - List all tasks
app.get('/api/tasks', (req, res) => {
  try {
    const { status, limit = 50, offset = 0 } = req.query;
    
    let query = 'SELECT * FROM tasks WHERE 1=1';
    const params = [];
    
    if (status) {
      query += ' AND status = ?';
      params.push(status);
    }
    
    query += ' ORDER BY created_at DESC LIMIT ? OFFSET ?';
    params.push(parseInt(limit), parseInt(offset));
    
    const tasks = db.prepare(query).all(...params);
    res.json(tasks);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// GET /api/tasks/:id - Get a single task
app.get('/api/tasks/:id', (req, res) => {
  try {
    const task = getTask(req.params.id);
    
    if (!task) {
      return res.status(404).json({ error: 'Task not found' });
    }
    
    res.json(task);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// POST /api/tasks - Create a new task
app.post('/api/tasks', (req, res) => {
  try {
    const { title, description, status = 'pending', due_date } = req.body;
    
    if (!title) {
      return res.status(400).json({ error: 'Title is required' });
    }
    
    const validStatuses = ['pending', 'in_progress', 'completed'];
    if (!validStatuses.includes(status)) {
      return res.status(400).json({ error: 'Invalid status' });
    }
    
    const result = db.prepare(`
      INSERT INTO tasks (title, description, status, due_date)
      VALUES (?, ?, ?, ?)
    `).run(title, description, status, due_date || null);
    
    const task = getTask(result.lastInsertRowid);
    res.status(201).json(task);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// PUT /api/tasks/:id - Update a task
app.put('/api/tasks/:id', (req, res) => {
  try {
    const { title, description, status, due_date } = req.body;
    
    const existingTask = getTask(req.params.id);
    if (!existingTask) {
      return res.status(404).json({ error: 'Task not found' });
    }
    
    const updates = [];
    const values = [];
    
    if (title !== undefined) {
      updates.push('title = ?');
      values.push(title);
    }
    if (description !== undefined) {
      updates.push('description = ?');
      values.push(description);
    }
    if (status !== undefined) {
      const validStatuses = ['pending', 'in_progress', 'completed'];
      if (!validStatuses.includes(status)) {
        return res.status(400).json({ error: 'Invalid status' });
      }
      updates.push('status = ?');
      values.push(status);
    }
    if (due_date !== undefined) {
      updates.push('due_date = ?');
      values.push(due_date || null);
    }
    
    if (updates.length === 0) {
      return res.status(400).json({ error: 'No fields to update' });
    }
    
    updates.push('updated_at = CURRENT_TIMESTAMP');
    values.push(req.params.id);
    
    db.prepare(`
      UPDATE tasks SET ${updates.join(', ')}
      WHERE id = ?
    `).run(...values);
    
    const task = getTask(req.params.id);
    res.json(task);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// PATCH /api/tasks/:id/status - Update task status
app.patch('/api/tasks/:id/status', (req, res) => {
  try {
    const { status } = req.body;
    
    const validStatuses = ['pending', 'in_progress', 'completed'];
    if (!validStatuses.includes(status)) {
      return res.status(400).json({ error: 'Invalid status' });
    }
    
    const existingTask = getTask(req.params.id);
    if (!existingTask) {
      return res.status(404).json({ error: 'Task not found' });
    }
    
    db.prepare(`
      UPDATE tasks 
      SET status = ?, updated_at = CURRENT_TIMESTAMP
      WHERE id = ?
    `).run(status, req.params.id);
    
    const task = getTask(req.params.id);
    res.json(task);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// DELETE /api/tasks/:id - Delete a task
app.delete('/api/tasks/:id', (req, res) => {
  try {
    const existingTask = getTask(req.params.id);
    if (!existingTask) {
      return res.status(404).json({ error: 'Task not found' });
    }
    
    db.prepare('DELETE FROM tasks WHERE id = ?').run(req.params.id);
    
    res.json({ message: 'Task deleted successfully' });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

// GET /api/tasks/stats - Get task statistics
app.get('/api/tasks/stats', (req, res) => {
  try {
    const stats = db.prepare(`
      SELECT 
        status,
        COUNT(*) as count
      FROM tasks
      GROUP BY status
    `).all();
    
    const result = {
      pending: 0,
      in_progress: 0,
      completed: 0
    };
    
    stats.forEach(stat => {
      result[stat.status] = stat.count;
    });
    
    result.total = Object.values(result).reduce((a, b) => a + b, 0);
    
    res.json(result);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

const PORT = process.env.PORT || 3000;

app.listen(PORT, () => {
  console.log(`Task API server running on port ${PORT}`);
});

// Graceful shutdown
process.on('SIGINT', () => {
  db.close();
  process.exit(0);
});