const express = require('express');
const sqlite3 = require('sqlite3').verbose();
const path = require('path');
const bodyParser = require('body-parser');
const fs = require('fs');

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

// Middleware
app.use(bodyParser.json());
app.use(express.static(path.join(__dirname, '../public')));

// Ensure data directory exists
const dataDir = path.join(__dirname, '../data');
if (!fs.existsSync(dataDir)) {
    fs.mkdirSync(dataDir, { recursive: true });
}

// Initialize SQLite database
const dbPath = process.env.DATABASE_PATH || path.join(dataDir, 'tasks.db');
const db = new sqlite3.Database(dbPath, (err) => {
    if (err) {
        console.error('Error opening database:', err);
    } else {
        console.log('Connected to SQLite database at:', dbPath);
        initDatabase();
    }
});

function initDatabase() {
    db.run(`
        CREATE TABLE IF NOT EXISTS tasks (
            id TEXT PRIMARY KEY,
            title TEXT NOT NULL,
            description TEXT,
            size TEXT NOT NULL,
            reward TEXT,
            completed INTEGER DEFAULT 0,
            position INTEGER,
            subtasks TEXT,
            created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
            updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
        )
    `);
}

// API Routes

// Get all tasks
app.get('/api/tasks', (req, res) => {
    db.all('SELECT * FROM tasks ORDER BY position ASC, created_at ASC', [], (err, rows) => {
        if (err) {
            console.error('Error fetching tasks:', err);
            return res.status(500).json({ error: 'Failed to fetch tasks' });
        }

        const tasks = rows.map(row => ({
            id: row.id,
            title: row.title,
            description: row.description,
            size: row.size,
            reward: row.reward,
            completed: row.completed === 1,
            subtasks: row.subtasks ? JSON.parse(row.subtasks) : []
        }));

        res.json(tasks);
    });
});

// Create a new task
app.post('/api/tasks', (req, res) => {
    const { title, description, size, reward } = req.body;
    const id = Date.now().toString();

    db.run(
        `INSERT INTO tasks (id, title, description, size, reward, position) 
         VALUES (?, ?, ?, ?, ?, (SELECT COALESCE(MAX(position), 0) + 1 FROM tasks))`,
        [id, title, description || '', size, reward || ''],
        function(err) {
            if (err) {
                console.error('Error creating task:', err);
                return res.status(500).json({ error: 'Failed to create task' });
            }

            res.json({
                id,
                title,
                description: description || '',
                size,
                reward: reward || '',
                completed: false,
                subtasks: []
            });
        }
    );
});

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

    db.run(
        `UPDATE tasks 
         SET title = ?, description = ?, size = ?, reward = ?, completed = ?, subtasks = ?, updated_at = CURRENT_TIMESTAMP
         WHERE id = ?`,
        [
            title,
            description || '',
            size,
            reward || '',
            completed ? 1 : 0,
            JSON.stringify(subtasks || []),
            id
        ],
        function(err) {
            if (err) {
                console.error('Error updating task:', err);
                return res.status(500).json({ error: 'Failed to update task' });
            }

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

            res.json({ success: true });
        }
    );
});

// Delete a task
app.delete('/api/tasks/:id', (req, res) => {
    const { id } = req.params;

    db.run('DELETE FROM tasks WHERE id = ?', [id], function(err) {
        if (err) {
            console.error('Error deleting task:', err);
            return res.status(500).json({ error: 'Failed to delete task' });
        }

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

        res.json({ success: true });
    });
});

// Reorder tasks
app.post('/api/tasks/reorder', (req, res) => {
    const taskIds = req.body;

    if (!Array.isArray(taskIds)) {
        return res.status(400).json({ error: 'Invalid task order data' });
    }

    const promises = taskIds.map((id, index) => {
        return new Promise((resolve, reject) => {
            db.run('UPDATE tasks SET position = ? WHERE id = ?', [index, id], (err) => {
                if (err) reject(err);
                else resolve();
            });
        });
    });

    Promise.all(promises)
        .then(() => res.json({ success: true }))
        .catch(err => {
            console.error('Error reordering tasks:', err);
            res.status(500).json({ error: 'Failed to reorder tasks' });
        });
});

// Serve the main HTML file
app.get('/', (req, res) => {
    res.sendFile(path.join(__dirname, '../public/index.html'));
});

// Start server
app.listen(PORT, () => {
    console.log(`🚀 Learning Progress Tracker running on http://localhost:${PORT}`);
});

// Graceful shutdown
process.on('SIGINT', () => {
    db.close((err) => {
        if (err) {
            console.error('Error closing database:', err);
        } else {
            console.log('Database connection closed');
        }
        process.exit(0);
    });
});