import express from 'express';
import { createServer } from 'http';
import { Server } from 'socket.io';
import path from 'path';
import { fileURLToPath } from 'url';
import fs from 'fs/promises';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

export function startServer(categorySyncer, categoryProductsSyncer) {
    const app = express();
    const httpServer = createServer(app);
    const io = new Server(httpServer);

    const PORT = process.env.SERVER_PORT || 3000;
    const HOST = process.env.SERVER_HOST || '0.0.0.0';
    const CACHE_DIR = process.env.CACHE_LOCATION || './cache';

    // Cache for ETags and data
    const cache = {
        categories: { etag: null, data: null },
        html: { etag: null, data: null },
        products: new Map() // id -> { etag, data }
    };

    // Function to calculate ETag for categories
    async function updateCategoriesCache() {
        try {
            const treePath = path.join(CACHE_DIR, 'category_tree.json');
            const data = await fs.readFile(treePath, 'utf-8');
            const crypto = await import('crypto');
            cache.categories.etag = crypto.createHash('md5').update(data).digest('hex');
            cache.categories.data = data;
        } catch (err) {
            // Silently skip if file doesn't exist yet (will be created on first sync)
            if (err.code !== 'ENOENT') {
                console.error('Error updating categories cache:', err);
            }
        }
    }

    // Function to calculate ETag for a specific category's products
    async function updateProductCache(id) {
        try {
            const productPath = path.join(CACHE_DIR, 'products', `category_${id}.json`);
            const data = await fs.readFile(productPath, 'utf-8');
            const crypto = await import('crypto');
            const etag = crypto.createHash('md5').update(data).digest('hex');
            cache.products.set(id, { etag, data });
        } catch (err) {
            // If file missing, remove from cache
            if (err.code === 'ENOENT') {
                cache.products.delete(id);
            } else {
                console.error(`Error updating product cache for category ${id}:`, err);
            }
        }
    }

    // Function to calculate ETag for HTML
    async function updateHtmlCache() {
        try {
            const htmlPath = path.join(__dirname, 'index.html');
            const data = await fs.readFile(htmlPath, 'utf-8');
            const crypto = await import('crypto');
            cache.html.etag = crypto.createHash('md5').update(data).digest('hex');
            cache.html.data = data;
        } catch (err) {
            console.error('Error updating HTML cache:', err);
        }
    }

    // Initialize caches on startup
    updateHtmlCache();
    updateCategoriesCache();

    // Update categories cache when sync completes
    if (categorySyncer) {
        categorySyncer.on('synced', ({ changed }) => {
            if (changed) {
                updateCategoriesCache();
                io.emit('categoriesUpdated');
            }
        });
    }

    // Update product cache when category products update
    if (categoryProductsSyncer) {
        categoryProductsSyncer.on('categoryUpdated', ({ id }) => {
            updateProductCache(id);
            io.emit('categoryProductsUpdated', { id });
        });
    }

    // Socket.io connection
    io.on('connection', (socket) => {
        console.log('🔌 Client connected');
        socket.on('disconnect', () => {
            console.log('🔌 Client disconnected');
        });
    });

    // Serve category tree JSON (with ETag for conditional caching)
    app.get('/api/categories', async (req, res) => {
        try {
            // Check if client has cached version
            if (req.headers['if-none-match'] === cache.categories.etag) {
                return res.status(304).end(); // Not Modified
            }

            // Set cache headers with ETag
            res.set('Cache-Control', 'public, max-age=60, must-revalidate');
            res.set('ETag', cache.categories.etag);

            res.json(JSON.parse(cache.categories.data));
        } catch (err) {
            res.status(500).json({ error: 'Failed to load category tree' });
        }
    });

    // Serve category products JSON (with ETag)
    app.get('/api/categories/:id/products', async (req, res) => {
        try {
            const id = parseInt(req.params.id);
            
            // Lazy load if not in cache
            if (!cache.products.has(id)) {
                await updateProductCache(id);
            }

            const cached = cache.products.get(id);

            if (!cached) {
                return res.status(404).json({ error: 'Category products not found' });
            }

            // Check if client has cached version
            if (req.headers['if-none-match'] === cached.etag) {
                return res.status(304).end(); // Not Modified
            }

            // Set cache headers with ETag
            res.set('Cache-Control', 'public, max-age=60, must-revalidate');
            res.set('ETag', cached.etag);
            
            res.json(JSON.parse(cached.data));
        } catch (err) {
            console.error(`Error serving products for category ${req.params.id}:`, err);
            res.status(500).json({ error: 'Failed to load products' });
        }
    });

    // Serve category images (long cache - images rarely change)
    app.get('/img/cat/:id.avif', (req, res) => {
        const { id } = req.params;
        const imagePath = path.join(CACHE_DIR, 'img', 'categories', `${id}.avif`);

        // Cache images for 1 year (immutable content)
        res.set('Cache-Control', 'public, max-age=31536000, immutable');

        res.sendFile(path.resolve(imagePath), (err) => {
            if (err) {
                res.status(404).send('Image not found');
            }
        });
    });

    // Serve index.html (with ETag for conditional caching)
    app.get('/', async (req, res) => {
        try {
            // Check if client has cached version
            if (req.headers['if-none-match'] === cache.html.etag) {
                return res.status(304).end(); // Not Modified
            }

            // Set cache headers with ETag
            res.set('Cache-Control', 'public, max-age=300, must-revalidate');
            res.set('ETag', cache.html.etag);
            res.set('Content-Type', 'text/html');

            res.send(cache.html.data);
        } catch (err) {
            console.error('Error serving index.html:', err);
            res.status(500).send('Error loading page');
        }
    });

    httpServer.listen(PORT, HOST, () => {
        console.log(`🌐 Server running on http://${HOST}:${PORT}`);
    });
}