const express = require('express');
const cors = require('cors');
const pool = require('./db');
const { createClient } = require('redis');

const app = express();
const PORT = process.env.PORT || 3000;

// Middleware
app.use(cors());
app.use(express.json());

// Redis client
let redisClient;
const CACHE_TTL = 30; // seconds

async function initRedis() {
  try {
    redisClient = createClient({
      url: `redis://${process.env.REDIS_HOST || 'redis'}:${process.env.REDIS_PORT || 6379}`
    });
    redisClient.on('error', (err) => console.error('Redis error:', err));
    await redisClient.connect();
    console.log('Connected to Redis');
  } catch (err) {
    console.error('Failed to connect to Redis:', err.message);
    redisClient = null;
  }
}

// Helper: invalidate cache
async function invalidateCache() {
  if (redisClient && redisClient.isOpen) {
    try {
      await redisClient.del('tasks:all');
    } catch (err) {
      console.error('Cache invalidation error:', err.message);
    }
  }
}

// Health check
app.get('/api/health', async (req, res) => {
  try {
    await pool.query('SELECT 1');
    const redisOk = redisClient && redisClient.isOpen;
    res.json({
      status: 'healthy',
      database: 'connected',
      cache: redisOk ? 'connected' : 'disconnected',
      timestamp: new Date().toISOString()
    });
  } catch (err) {
    res.status(503).json({ status: 'unhealthy', error: err.message });
  }
});

// GET /api/tasks — List all tasks (with Redis caching)
app.get('/api/tasks', async (req, res) => {
  try {
    // Try cache first
    if (redisClient && redisClient.isOpen) {
      const cached = await redisClient.get('tasks:all');
      if (cached) {
        return res.json({ tasks: JSON.parse(cached), source: 'cache' });
      }
    }

    const result = await pool.query(
      'SELECT * FROM tasks ORDER BY created_at DESC'
    );

    // Store in cache
    if (redisClient && redisClient.isOpen) {
      await redisClient.setEx('tasks:all', CACHE_TTL, JSON.stringify(result.rows));
    }

    res.json({ tasks: result.rows, source: 'database' });
  } catch (err) {
    console.error('Error fetching tasks:', err);
    res.status(500).json({ error: 'Failed to fetch tasks' });
  }
});

// POST /api/tasks — Create a new task
app.post('/api/tasks', async (req, res) => {
  try {
    const { title, description } = req.body;
    if (!title || title.trim() === '') {
      return res.status(400).json({ error: 'Title is required' });
    }

    const result = await pool.query(
      'INSERT INTO tasks (title, description) VALUES ($1, $2) RETURNING *',
      [title.trim(), (description || '').trim()]
    );

    await invalidateCache();
    res.status(201).json({ task: result.rows[0] });
  } catch (err) {
    console.error('Error creating task:', err);
    res.status(500).json({ error: 'Failed to create task' });
  }
});

// PUT /api/tasks/:id — Update a task
app.put('/api/tasks/:id', async (req, res) => {
  try {
    const { id } = req.params;
    const { title, description, completed } = req.body;

    const result = await pool.query(
      `UPDATE tasks 
       SET title = COALESCE($1, title), 
           description = COALESCE($2, description), 
           completed = COALESCE($3, completed),
           updated_at = CURRENT_TIMESTAMP
       WHERE id = $4 RETURNING *`,
      [title, description, completed, id]
    );

    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Task not found' });
    }

    await invalidateCache();
    res.json({ task: result.rows[0] });
  } catch (err) {
    console.error('Error updating task:', err);
    res.status(500).json({ error: 'Failed to update task' });
  }
});

// DELETE /api/tasks/:id — Delete a task
app.delete('/api/tasks/:id', async (req, res) => {
  try {
    const { id } = req.params;
    const result = await pool.query(
      'DELETE FROM tasks WHERE id = $1 RETURNING *',
      [id]
    );

    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Task not found' });
    }

    await invalidateCache();
    res.json({ message: 'Task deleted', task: result.rows[0] });
  } catch (err) {
    console.error('Error deleting task:', err);
    res.status(500).json({ error: 'Failed to delete task' });
  }
});

// Start server
async function start() {
  await initRedis();
  app.listen(PORT, '0.0.0.0', () => {
    console.log(`Task Manager API running on port ${PORT}`);
  });
}

start();