// src/integrations/webex/WebexServiceAppAuth.js
import axios from 'axios';
import { promises as fs } from 'node:fs';
import path from 'node:path';
import { Mutex } from 'async-mutex';
import { logger } from '../../utils/logger.js';   // ← Your new custom logger

class WebexServiceAppAuth {
  static #instance = null;

  constructor({
    clientId = process.env.WEBEX_CLIENT_ID,
    clientSecret = process.env.WEBEX_CLIENT_SECRET,
    tokensFilePath = process.env.WEBEX_TOKENS_PATH 
      || path.join(process.cwd(), 'tokens', 'webex-service-tokens.json'),
  } = {}) {
    // Singleton pattern
    if (WebexServiceAppAuth.#instance) {
      return WebexServiceAppAuth.#instance;
    }

    // Required validation
    if (!clientId) {
      throw new Error('WEBEX_CLIENT_ID is required (set it in environment variables)');
    }
    if (!clientSecret) {
      throw new Error('WEBEX_CLIENT_SECRET is required (set it in environment variables)');
    }

    this.clientId = clientId;
    this.clientSecret = clientSecret;
    // Always resolve to an absolute path (based on cwd at startup).
    // This makes error logs and fs operations unambiguous whether running locally or in Docker.
    // .env should prefer a *relative* path like ./config/webex-service-tokens.json
    // so the same .env works both on host (cwd=project root) and inside container (cwd=/app + volume mount).
    this.tokensFilePath = path.resolve(tokensFilePath);

    // Token state
    this.accessToken = null;
    this.refreshToken = null;
    this.expiresAt = 0; // Unix timestamp in ms

    // Serializes loadTokens() + refresh() so concurrent callers (cron, webhook,
    // HTTP request, framework event firing at the same time) don't issue
    // parallel refresh requests. Cisco rotates the refresh_token on every use,
    // so a race here would invalidate one of the in-flight refreshes and we'd
    // lose our credentials until manual re-bootstrap.
    this._authMutex = new Mutex();

    WebexServiceAppAuth.#instance = this;

    logger('webex:auth', 'WebexServiceAppAuth initialized with environment variables');
  }

  /**
   * Load persisted tokens from file
   */
  async loadTokens() {
    try {
      const data = await fs.readFile(this.tokensFilePath, 'utf8');
      const tokens = JSON.parse(data);

      this.accessToken = tokens.accessToken;
      this.refreshToken = tokens.refreshToken;
      this.expiresAt = tokens.expiresAt || 0;

      logger('webex:auth', 'Webex tokens successfully loaded from file');
    } catch (err) {
      if (err.code === 'ENOENT') {
        logger('webex:auth', `No tokens file found at ${this.tokensFilePath}`, 'warn');
        logger('webex:auth', 'You need to bootstrap initial tokens once (see documentation)', 'warn');
      } else {
        logger('webex:auth', `Failed to load tokens file: ${err.message}`, 'error');
      }
      throw err;
    }
  }

  /**
   * Save current token state to file
   */
  async saveTokens() {
    const payload = {
      accessToken: this.accessToken,
      refreshToken: this.refreshToken,
      expiresAt: this.expiresAt,
      updatedAt: new Date().toISOString(),
    };

    try {
      await fs.mkdir(path.dirname(this.tokensFilePath), { recursive: true });
      await fs.writeFile(this.tokensFilePath, JSON.stringify(payload, null, 2), 'utf8');
      logger('webex:auth', `Webex tokens saved to ${this.tokensFilePath}`);
    } catch (err) {
      logger('webex:auth', `Failed to save tokens: ${err.message}`, 'error');
      throw err;
    }
  }

  /**
   * Refresh access token using the current refresh token
   */
  async refresh() {
    if (!this.refreshToken) {
      throw new Error(
        'No refresh token available. ' +
        'Bootstrap initial access_token + refresh_token first ' +
        '(via Developer Portal or Applications Token API).'
      );
    }

    try {
      const params = new URLSearchParams({
        grant_type: 'refresh_token',
        client_id: this.clientId,
        client_secret: this.clientSecret,
        refresh_token: this.refreshToken,
      });

      const response = await axios.post('https://webexapis.com/v1/access_token', params, {
        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
        timeout: 10000,
      });

      const data = response.data;

      this.accessToken = data.access_token;
      this.refreshToken = data.refresh_token; // Cisco rotates refresh tokens
      this.expiresAt = Date.now() + (data.expires_in * 1000) - (5 * 60 * 1000); // 5 min safety buffer

      await this.saveTokens();

      logger('webex:auth', `Tokens refreshed successfully — new access token expires in ${data.expires_in} seconds`);
      return this.accessToken;

    } catch (err) {
      const errorDetail = err.response?.data || err.message;
      logger('webex:auth', `Token refresh failed: ${errorDetail}`, 'error');

      if (err.response?.status === 400 || err.response?.status === 401) {
        throw new Error(
          'Refresh token may be invalid or revoked. ' +
          'You will need to bootstrap new tokens manually.'
        );
      }

      throw err;
    }
  }

  /**
   * Get a currently valid access token.
   * Will refresh automatically if expired or near expiry.
   *
   * The whole "check + refresh" path runs inside a mutex so concurrent callers
   * never trigger overlapping token rotations.
   */
  async getAccessToken() {
    // Fast path: already-valid in-memory token, no lock needed.
    if (this.accessToken && Date.now() < this.expiresAt) {
      return this.accessToken;
    }

    return this._authMutex.runExclusive(async () => {
      // Re-check inside the critical section — another caller may have
      // already loaded/refreshed while we were waiting for the lock.
      if (this.accessToken && Date.now() < this.expiresAt) {
        return this.accessToken;
      }

      // Lazy-load on first use
      if (!this.accessToken && !this.refreshToken) {
        try {
          await this.loadTokens();
        } catch (err) {
          throw new Error('Tokens not loaded and no file present – bootstrap required');
        }
      }

      if (this.accessToken && Date.now() < this.expiresAt) {
        return this.accessToken;
      }

      logger('webex:auth', 'Access token expired or missing → refreshing...');
      return this.refresh();
    });
  }

  /**
   * Force a refresh (useful for testing or recovery).
   * Also serialized through the auth mutex so it can't race a normal getAccessToken().
   */
  async forceRefresh() {
    logger('webex:auth', 'Forcing token refresh...', 'warn');
    return this._authMutex.runExclusive(() => this.refresh());
  }

  /**
   * Clear all token state (for logout/testing)
   */
  clearTokens() {
    this.accessToken = null;
    this.refreshToken = null;
    this.expiresAt = 0;
    logger('webex:auth', 'Webex token state cleared', 'warn');
  }
}

export default WebexServiceAppAuth;