/**
 * AI Camera Hub - Lumi | Backend Server
 * 
 * Serves images from save_images_v3/ and save_images_v4/ folders,
 * provides API for image listing, annotation CRUD, and auto-save.
 */

const express = require('express');
const cors = require('cors');
const fs = require('fs');
const path = require('path');

const app = express();
const PORT = process.env.PORT || 3001;

// ========== PATHS ==========
// Image directories (relative to project root)
const PROJECT_ROOT = path.join(__dirname, '..');
const V3_DIR = path.join(PROJECT_ROOT, 'save_images_v3');
const V4_DIR = path.join(PROJECT_ROOT, 'save_images_v4');
const ANNOTATIONS_FILE = path.join(PROJECT_ROOT, 'annotations.json');

// Supported image extensions
const IMAGE_EXTENSIONS = /\.(jpg|jpeg|png|gif|bmp|webp|tiff|svg)$/i;

// ========== MIDDLEWARE ==========
app.use(cors());
app.use(express.json({ limit: '10mb' }));

// Serve frontend (index.html at project root)
app.use(express.static(PROJECT_ROOT));

// Serve image files statically
app.use('/images/v3', express.static(V3_DIR));
app.use('/images/v4', express.static(V4_DIR));

// Log requests in development
app.use((req, res, next) => {
  const timestamp = new Date().toISOString();
  console.log(`[${timestamp}] ${req.method} ${req.url}`);
  next();
});

// ========== API ROUTES ==========

/**
 * GET /api/images
 * Returns list of matched images from both v3 and v4 folders.
 * Images are matched by filename.
 */
app.get('/api/images', (req, res) => {
  try {
    let v3Files = [];
    let v4Files = [];

    // Read v3 directory
    if (fs.existsSync(V3_DIR)) {
      v3Files = fs.readdirSync(V3_DIR)
        .filter(f => IMAGE_EXTENSIONS.test(f));
    } else {
      console.warn('⚠️  save_images_v3 directory not found at:', V3_DIR);
    }

    // Read v4 directory
    if (fs.existsSync(V4_DIR)) {
      v4Files = fs.readdirSync(V4_DIR)
        .filter(f => IMAGE_EXTENSIONS.test(f));
    } else {
      console.warn('⚠️  save_images_v4 directory not found at:', V4_DIR);
    }

    // Match images by filename
    const v3Set = new Set(v3Files);
    const v4Set = new Set(v4Files);
    const allNames = new Set([...v3Files, ...v4Files]);

    const matched = [];
    allNames.forEach(name => {
      matched.push({
        name,
        hasV3: v3Set.has(name),
        hasV4: v4Set.has(name),
      });
    });

    // Sort alphabetically
    matched.sort((a, b) => a.name.localeCompare(b.name, undefined, { numeric: true }));

    console.log(`✅ Found ${matched.length} images (v3: ${v3Files.length}, v4: ${v4Files.length})`);
    res.json({ images: matched, total: matched.length });
  } catch (err) {
    console.error('❌ Error listing images:', err);
    res.status(500).json({ error: err.message });
  }
});

/**
 * GET /api/annotations
 * Returns saved annotations from annotations.json.
 */
app.get('/api/annotations', (req, res) => {
  try {
    if (fs.existsSync(ANNOTATIONS_FILE)) {
      const data = fs.readFileSync(ANNOTATIONS_FILE, 'utf8');
      const parsed = JSON.parse(data);
      console.log(`📋 Loaded annotations for ${Object.keys(parsed).length} images`);
      res.json(parsed);
    } else {
      console.log('📋 No existing annotations file, returning empty object');
      res.json({});
    }
  } catch (err) {
    console.error('❌ Error reading annotations:', err);
    res.status(500).json({ error: err.message });
  }
});

/**
 * POST /api/annotations
 * Saves annotations to annotations.json.
 * Auto-creates backup before overwriting.
 */
app.post('/api/annotations', (req, res) => {
  try {
    const annotations = req.body;

    // Create backup if file exists
    if (fs.existsSync(ANNOTATIONS_FILE)) {
      const backupPath = ANNOTATIONS_FILE.replace('.json', `_backup_${Date.now()}.json`);
      fs.copyFileSync(ANNOTATIONS_FILE, backupPath);
      
      // Keep only last 5 backups
      const backupDir = path.dirname(ANNOTATIONS_FILE);
      const backups = fs.readdirSync(backupDir)
        .filter(f => f.startsWith('annotations_backup_'))
        .sort()
        .map(f => path.join(backupDir, f));
      
      while (backups.length > 5) {
        fs.unlinkSync(backups.shift());
      }
    }

    // Write new annotations
    fs.writeFileSync(
      ANNOTATIONS_FILE,
      JSON.stringify(annotations, null, 2),
      'utf8'
    );

    const count = Object.keys(annotations).length;
    console.log(`💾 Saved annotations for ${count} images`);
    res.json({ success: true, count });
  } catch (err) {
    console.error('❌ Error saving annotations:', err);
    res.status(500).json({ error: err.message });
  }
});

/**
 * GET /api/export
 * Export annotations as downloadable JSON file.
 */
app.get('/api/export', (req, res) => {
  try {
    if (!fs.existsSync(ANNOTATIONS_FILE)) {
      return res.status(404).json({ error: 'No annotations found' });
    }
    const data = fs.readFileSync(ANNOTATIONS_FILE, 'utf8');
    const filename = `annotations_export_${new Date().toISOString().slice(0, 10)}.json`;
    res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
    res.setHeader('Content-Type', 'application/json');
    res.send(data);
  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

// SPA fallback - serve index.html for any unmatched routes
app.get('*', (req, res) => {
  const indexPath = path.join(PROJECT_ROOT, 'index.html');
  if (fs.existsSync(indexPath)) {
    res.sendFile(indexPath);
  } else {
    res.status(404).send('Frontend not found. Place index.html in project root.');
  }
});

// ========== START SERVER ==========
app.listen(PORT, () => {
  console.log('');
  console.log('═══════════════════════════════════════════════════════════');
  console.log('  🎯 AI Camera Hub - Lumi | Error Analysis Dashboard');
  console.log('═══════════════════════════════════════════════════════════');
  console.log(`  Server:  http://localhost:${PORT}`);
  console.log(`  API:     http://localhost:${PORT}/api/images`);
  console.log('');
  console.log(`  v3 path: ${V3_DIR}`);
  console.log(`  v4 path: ${V4_DIR}`);
  console.log(`  Save to: ${ANNOTATIONS_FILE}`);
  console.log('');
  console.log('  Press Ctrl+C to stop');
  console.log('═══════════════════════════════════════════════════════════');
  console.log('');

  // Create image directories if they don't exist
  [V3_DIR, V4_DIR].forEach(dir => {
    if (!fs.existsSync(dir)) {
      fs.mkdirSync(dir, { recursive: true });
      console.log(`📁 Created directory: ${dir}`);
    }
  });
});