/**
 * DashCaddy Self-Updater
 * Polls for new versions, downloads and stages updates,
 * triggers host-side updater for API container rebuilds.
 *
 * Frontend files are updated directly (zero-downtime).
 * API files require a container rebuild via the host-side systemd service.
 */

const EventEmitter = require('events');
const https = require('https');
const http = require('http');
const fs = require('fs');
const fsp = require('fs').promises;
const path = require('path');
const crypto = require('crypto');
const { execSync } = require('child_process');
const zlib = require('zlib');

const isWindows = process.platform === 'win32';

const DEFAULTS = {
  CHECK_INTERVAL: 30 * 60 * 1000,  // 30 minutes
  UPDATE_URL: 'https://get.dashcaddy.net/release',
  MIRROR_URL: 'https://get2.dashcaddy.net/release',
  UPDATES_DIR: isWindows ? 'C:/caddy/updates' : '/app/updates',
  // API_SOURCE_DIR is the HOST path — written to trigger.json for the host-side updater
  API_SOURCE_DIR: isWindows ? 'C:/caddy/sites/dashcaddy-api' : '/etc/dashcaddy/sites/dashcaddy-api',
  // FRONTEND_DIR is the container path — dashboard is volume-mounted at /app/dashboard
  FRONTEND_DIR: isWindows ? 'C:/caddy/sites/status' : '/app/dashboard',
  MAX_BACKUPS: 3,
  HEALTH_TIMEOUT: 60000,
  DOWNLOAD_TIMEOUT: 120000,
};

class SelfUpdater extends EventEmitter {
  constructor(options = {}) {
    super();
    this.config = {
      enabled: options.enabled !== false,
      checkInterval: parseInt(options.checkInterval || DEFAULTS.CHECK_INTERVAL, 10),
      updateUrl: options.updateUrl || DEFAULTS.UPDATE_URL,
      mirrorUrl: options.mirrorUrl || DEFAULTS.MIRROR_URL,
      updatesDir: options.updatesDir || DEFAULTS.UPDATES_DIR,
      apiSourceDir: options.apiSourceDir || DEFAULTS.API_SOURCE_DIR,
      frontendDir: options.frontendDir || DEFAULTS.FRONTEND_DIR,
      maxBackups: parseInt(options.maxBackups || DEFAULTS.MAX_BACKUPS, 10),
    };

    this.status = 'idle'; // idle | checking | downloading | applying | waiting
    this.checkTimer = null;
    this.lastCheckTime = null;
    this.lastCheckResult = null;

    // Ensure directories exist
    this._ensureDirs();
  }

  // ── Lifecycle ──

  start() {
    if (!this.config.enabled || this.checkTimer) return;

    console.log('[SelfUpdater] Starting auto-update checks every %ds', this.config.checkInterval / 1000);

    // First check after a short delay (let server finish startup)
    setTimeout(() => {
      this._autoCheckAndApply();
      this.checkTimer = setInterval(() => this._autoCheckAndApply(), this.config.checkInterval);
    }, 15000);
  }

  stop() {
    if (this.checkTimer) {
      clearInterval(this.checkTimer);
      this.checkTimer = null;
    }
  }

  // ── Version Info ──

  getLocalVersion() {
    try {
      const pkg = JSON.parse(fs.readFileSync(path.join(__dirname, 'package.json'), 'utf8'));
      let commit = null;
      try {
        commit = fs.readFileSync(path.join(__dirname, 'VERSION'), 'utf8').trim();
      } catch (_) {}
      return { version: pkg.version, commit };
    } catch (e) {
      return { version: '0.0.0', commit: null };
    }
  }

  getStatus() {
    return this.status;
  }

  // ── Check for Updates ──

  async checkForUpdate() {
    this.status = 'checking';
    try {
      let remote;
      try {
        remote = await this._fetchJson(`${this.config.updateUrl}/version.json`);
      } catch (primaryErr) {
        console.warn('[SelfUpdater] Primary server failed:', primaryErr.message, '— trying mirror');
        try {
          remote = await this._fetchJson(`${this.config.mirrorUrl}/version.json`);
        } catch (mirrorErr) {
          this.status = 'idle';
          this.lastCheckTime = Date.now();
          this.lastCheckResult = { available: false, error: 'Update servers unreachable' };
          return this.lastCheckResult;
        }
      }

      const local = this.getLocalVersion();
      const available = this._isNewer(local, remote);

      this.lastCheckTime = Date.now();
      this.lastCheckResult = { available, local, remote };
      this.status = 'idle';

      if (available) {
        this.emit('update-available', remote);
      }

      return this.lastCheckResult;
    } catch (e) {
      this.status = 'idle';
      this.lastCheckTime = Date.now();
      this.lastCheckResult = { available: false, error: e.message };
      return this.lastCheckResult;
    }
  }

  // ── Apply Update ──

  async applyUpdate(remoteInfo) {
    if (this.status !== 'idle' && this.status !== 'checking') {
      throw new Error(`Update already in progress (status: ${this.status})`);
    }

    const local = this.getLocalVersion();
    const stagingDir = path.join(this.config.updatesDir, 'staging');

    try {
      // 1. Download
      this.status = 'downloading';
      this.emit('update-progress', { step: 'downloading', version: remoteInfo.version });

      const tarballUrl = `${this.config.updateUrl}/${remoteInfo.tarball}`;
      const tarballPath = path.join(this.config.updatesDir, remoteInfo.tarball);
      await this._downloadFile(tarballUrl, tarballPath);

      // 2. Verify SHA-256
      const hash = await this._computeSha256(tarballPath);
      if (hash !== remoteInfo.sha256) {
        await fsp.unlink(tarballPath).catch(() => {});
        throw new Error(`SHA-256 mismatch: expected ${remoteInfo.sha256}, got ${hash}`);
      }

      // 3. Extract
      this.status = 'applying';
      this.emit('update-progress', { step: 'extracting', version: remoteInfo.version });

      await this._cleanDir(stagingDir);
      await this._extractTarball(tarballPath, stagingDir);

      // 4. Apply frontend files directly (zero-downtime)
      const frontendSrc = this._findDir(stagingDir, 'status');
      if (frontendSrc) {
        await this._copyDir(frontendSrc, this.config.frontendDir, [
          'dist', 'css', 'assets', 'vendor', 'index.html', 'sw.js'
        ]);
        this.emit('update-progress', { step: 'frontend-updated', version: remoteInfo.version });
      }

      // 5. Trigger API rebuild (Linux only — host-side systemd service)
      const apiSrc = this._findDir(stagingDir, 'dashcaddy-api');
      if (apiSrc && !isWindows) {
        this.status = 'waiting';
        this.emit('update-progress', { step: 'triggering-rebuild', version: remoteInfo.version });

        const trigger = {
          action: 'update',
          version: remoteInfo.version,
          commit: remoteInfo.commit,
          fromVersion: local.version,
          stagingDir: apiSrc,
          apiSourceDir: this.config.apiSourceDir,
          timestamp: new Date().toISOString(),
        };
        await fsp.writeFile(
          path.join(this.config.updatesDir, 'trigger.json'),
          JSON.stringify(trigger, null, 2)
        );

        // The host-side systemd service will handle the rest.
        // After container restart, checkPostUpdateResult() reads the result.
        this._addToHistory({
          version: remoteInfo.version,
          fromVersion: local.version,
          timestamp: new Date().toISOString(),
          status: 'pending',
          frontendUpdated: !!frontendSrc,
          apiUpdated: true,
        });
      } else if (isWindows) {
        // Windows: frontend updated, API needs manual restart
        this._addToHistory({
          version: remoteInfo.version,
          fromVersion: local.version,
          timestamp: new Date().toISOString(),
          status: 'partial',
          frontendUpdated: !!frontendSrc,
          apiUpdated: false,
          note: 'API update requires manual container restart on Windows',
        });
        this.status = 'idle';
      }

      // Clean up tarball
      await fsp.unlink(tarballPath).catch(() => {});

      return {
        success: true,
        fromVersion: local.version,
        toVersion: remoteInfo.version,
        frontendUpdated: !!frontendSrc,
        apiUpdated: !isWindows && !!apiSrc,
      };
    } catch (e) {
      this.status = 'idle';
      this._addToHistory({
        version: remoteInfo.version,
        fromVersion: local.version,
        timestamp: new Date().toISOString(),
        status: 'failed',
        error: e.message,
      });
      throw e;
    }
  }

  // ── Post-Update Result ──

  async checkPostUpdateResult() {
    const resultPath = path.join(this.config.updatesDir, 'result.json');
    try {
      const data = await fsp.readFile(resultPath, 'utf8');
      const result = JSON.parse(data);
      // Delete the result file so we don't process it again
      await fsp.unlink(resultPath).catch(() => {});

      // Update history
      const history = this.getUpdateHistory();
      const pending = history.find(h => h.status === 'pending');
      if (pending) {
        pending.status = result.success ? 'success' : 'rolled-back';
        pending.duration = result.duration;
        if (result.error) pending.error = result.error;
        this._saveHistory(history);
      }

      this.status = 'idle';
      return result;
    } catch (_) {
      return null;
    }
  }

  // ── Rollback ──

  async rollbackToVersion(version) {
    if (isWindows) throw new Error('Auto-rollback not supported on Windows');

    const backupDir = path.join(this.config.updatesDir, 'backups', version);
    try {
      await fsp.access(backupDir);
    } catch (_) {
      throw new Error(`No backup found for version ${version}`);
    }

    const local = this.getLocalVersion();
    const trigger = {
      action: 'rollback',
      version: version,
      fromVersion: local.version,
      stagingDir: backupDir,
      apiSourceDir: this.config.apiSourceDir,
      timestamp: new Date().toISOString(),
    };

    this.status = 'waiting';
    await fsp.writeFile(
      path.join(this.config.updatesDir, 'trigger.json'),
      JSON.stringify(trigger, null, 2)
    );

    this._addToHistory({
      version: version,
      fromVersion: local.version,
      timestamp: new Date().toISOString(),
      status: 'pending',
      rollback: true,
    });
  }

  getAvailableRollbacks() {
    const backupsDir = path.join(this.config.updatesDir, 'backups');
    try {
      return fs.readdirSync(backupsDir)
        .filter(d => fs.statSync(path.join(backupsDir, d)).isDirectory())
        .sort()
        .reverse();
    } catch (_) {
      return [];
    }
  }

  // ── History ──

  getUpdateHistory() {
    const historyPath = path.join(this.config.updatesDir, 'self-update-history.json');
    try {
      return JSON.parse(fs.readFileSync(historyPath, 'utf8'));
    } catch (_) {
      return [];
    }
  }

  // ── Private Methods ──

  async _autoCheckAndApply() {
    try {
      const result = await this.checkForUpdate();
      if (result.available && result.remote) {
        console.log('[SelfUpdater] Update available: %s → %s', result.local.version, result.remote.version);
        await this.applyUpdate(result.remote);
      }
    } catch (e) {
      console.error('[SelfUpdater] Auto-update error:', e.message);
    }
  }

  _isNewer(local, remote) {
    if (!remote || !remote.version) return false;
    // Compare semver: split into [major, minor, patch]
    const lv = (local.version || '0.0.0').split('.').map(Number);
    const rv = remote.version.split('.').map(Number);
    for (let i = 0; i < 3; i++) {
      if ((rv[i] || 0) > (lv[i] || 0)) return true;
      if ((rv[i] || 0) < (lv[i] || 0)) return false;
    }
    // Same version — check commit hash
    if (remote.commit && local.commit && remote.commit !== local.commit) return true;
    return false;
  }

  _addToHistory(entry) {
    const history = this.getUpdateHistory();
    history.unshift(entry);
    // Keep last 50 entries
    if (history.length > 50) history.length = 50;
    this._saveHistory(history);
  }

  _saveHistory(history) {
    const historyPath = path.join(this.config.updatesDir, 'self-update-history.json');
    try {
      fs.writeFileSync(historyPath, JSON.stringify(history, null, 2));
    } catch (e) {
      console.error('[SelfUpdater] Failed to save history:', e.message);
    }
  }

  async _ensureDirs() {
    for (const dir of [this.config.updatesDir, path.join(this.config.updatesDir, 'staging'), path.join(this.config.updatesDir, 'backups')]) {
      await fsp.mkdir(dir, { recursive: true }).catch(() => {});
    }
  }

  async _fetchJson(url) {
    return new Promise((resolve, reject) => {
      const mod = url.startsWith('https') ? https : http;
      const req = mod.get(url, { timeout: 15000 }, (res) => {
        if (res.statusCode !== 200) {
          res.resume();
          return reject(new Error(`HTTP ${res.statusCode} from ${url}`));
        }
        let data = '';
        res.on('data', chunk => data += chunk);
        res.on('end', () => {
          try {
            resolve(JSON.parse(data));
          } catch (e) {
            reject(new Error('Invalid JSON from ' + url));
          }
        });
      });
      req.on('error', reject);
      req.on('timeout', () => { req.destroy(); reject(new Error('Timeout fetching ' + url)); });
    });
  }

  async _downloadFile(url, dest) {
    return new Promise((resolve, reject) => {
      const mod = url.startsWith('https') ? https : http;
      const file = fs.createWriteStream(dest);
      const req = mod.get(url, { timeout: DEFAULTS.DOWNLOAD_TIMEOUT }, (res) => {
        if (res.statusCode !== 200) {
          file.close();
          fs.unlinkSync(dest);
          return reject(new Error(`HTTP ${res.statusCode} downloading ${url}`));
        }
        res.pipe(file);
        file.on('finish', () => { file.close(resolve); });
      });
      req.on('error', (e) => {
        file.close();
        fs.unlink(dest, () => {});
        reject(e);
      });
      req.on('timeout', () => { req.destroy(); reject(new Error('Download timeout')); });
    });
  }

  async _computeSha256(filePath) {
    return new Promise((resolve, reject) => {
      const hash = crypto.createHash('sha256');
      const stream = fs.createReadStream(filePath);
      stream.on('data', chunk => hash.update(chunk));
      stream.on('end', () => resolve(hash.digest('hex')));
      stream.on('error', reject);
    });
  }

  async _extractTarball(tarballPath, destDir) {
    await fsp.mkdir(destDir, { recursive: true });
    // Use tar command (available on Linux, and Git Bash on Windows)
    try {
      execSync(`tar xzf "${tarballPath}" -C "${destDir}" --strip-components=1`, { stdio: 'pipe' });
    } catch (e) {
      throw new Error('Failed to extract tarball: ' + e.message);
    }
  }

  _findDir(baseDir, name) {
    const direct = path.join(baseDir, name);
    if (fs.existsSync(direct)) return direct;
    // Also check one level deeper (e.g., dashcaddy/dashcaddy-api)
    try {
      for (const entry of fs.readdirSync(baseDir)) {
        const sub = path.join(baseDir, entry, name);
        if (fs.existsSync(sub)) return sub;
      }
    } catch (_) {}
    return null;
  }

  async _copyDir(src, dest, items) {
    await fsp.mkdir(dest, { recursive: true });
    for (const item of items) {
      const srcPath = path.join(src, item);
      const destPath = path.join(dest, item);
      try {
        const stat = await fsp.stat(srcPath);
        if (stat.isDirectory()) {
          await this._copyDirRecursive(srcPath, destPath);
        } else {
          await fsp.copyFile(srcPath, destPath);
        }
      } catch (_) {
        // Item may not exist in the update — skip
      }
    }
  }

  async _copyDirRecursive(src, dest) {
    await fsp.mkdir(dest, { recursive: true });
    const entries = await fsp.readdir(src, { withFileTypes: true });
    for (const entry of entries) {
      const srcPath = path.join(src, entry.name);
      const destPath = path.join(dest, entry.name);
      if (entry.isDirectory()) {
        await this._copyDirRecursive(srcPath, destPath);
      } else {
        await fsp.copyFile(srcPath, destPath);
      }
    }
  }

  async _cleanDir(dir) {
    try {
      await fsp.rm(dir, { recursive: true, force: true });
    } catch (_) {}
    await fsp.mkdir(dir, { recursive: true });
  }
}

// Singleton
const selfUpdater = new SelfUpdater({
  enabled: process.env.DASHCADDY_UPDATE_ENABLED !== 'false',
  checkInterval: process.env.DASHCADDY_UPDATE_INTERVAL,
  updateUrl: process.env.DASHCADDY_UPDATE_URL,
  mirrorUrl: process.env.DASHCADDY_MIRROR_URL,
  updatesDir: process.env.DASHCADDY_UPDATES_DIR,
  apiSourceDir: process.env.DASHCADDY_API_SOURCE_DIR,
  frontendDir: process.env.DASHCADDY_FRONTEND_DIR,
});

module.exports = selfUpdater;