const logger = require('../utils/logger');
const RequestValidator = require('./validation');
const UserAgentFilter = require('./userAgentFilter');

/**
 * Request Processing Pipeline - Equivalent to Kamailio's main request_route
 * This is the primary entry point for all SIP requests received by Drachtio
 */
class RequestProcessor {
  constructor(srf) {
    this.srf = srf;
    this.validator = new RequestValidator();
    this.uaFilter = new UserAgentFilter();
  }

  /**
   * Handle OPTIONS requests (equivalent to kamailio.cfg:297-301)
   */
  handleOptions(req, res) {
    logger.info('[OPTIONS] Options request from %s:%s | Call-ID: %s',
      req.source_address, req.source_port, req.get('Call-ID'));
    res.send(200, 'OK');
  }

  /**
   * Handle CANCEL requests (equivalent to kamailio.cfg:196-201)
   */
  handleCancel(req, res) {
    const callId = req.get('Call-ID');
    logger.info('[CANCEL] CANCEL: Call-ID: %s', callId);

    // Check if transaction exists
    if (this.srf.hasUacTransaction(callId)) {
      // Relay the CANCEL to the appropriate destination
      this.srf.createUacRequest('CANCEL', req.uri, {
        headers: {
          'Call-ID': callId,
          'CSeq': req.get('CSeq'),
          'From': req.get('From'),
          'To': req.get('To'),
          'Via': req.get('Via'),
          'Route': req.get('Route'),
          'Max-Forwards': req.get('Max-Forwards')
        }
      })
      .then(() => {
        res.send(200, 'OK');
      })
      .catch((err) => {
        logger.error('[CANCEL] Failed to relay CANCEL: %s', err.message);
        res.send(500, 'Server Error');
      });
    } else {
      res.send(481, 'Transaction Does Not Exist');
    }
  }

  /**
   * Handle in-dialog requests (equivalent to kamailio.cfg:239-241)
   */
  handleInDialog(req, res, next) {
    if (req.has('To') && req.getParsedHeader('to').params.tag && req.method !== 'INVITE') {
      logger.info('[WITHINDLG] %s request | Call-ID: %s', req.method, req.get('Call-ID'));
      // Pass to in-dialog handler
      next();
    } else {
      next();
    }
  }

  /**
   * Handle presence-related requests (equivalent to kamailio.cfg:304)
   */
  handlePresence(req, res) {
    if (req.method === 'PUBLISH' || req.method === 'SUBSCRIBE') {
      logger.info('[PRESENCE] %s request from %s:%s | Call-ID: %s',
        req.method, req.source_address, req.source_port, req.get('Call-ID'));
      res.send(404, 'Not here');
      return true;
    }
    return false;
  }

  /**
   * Handle requests that don't match specific routes (equivalent to kamailio.cfg:312-315)
   */
  handleUnmatchedRequest(req, res) {
    logger.warn('[MAIN_ROUTE] No specific route found for method: %s to %s | Call-ID: %s',
      req.method, req.uri.user, req.get('Call-ID'));
    res.send(501, 'Not Implemented - No action found for destination or method');
  }

  /**
   * Main request processing pipeline
   */
  processRequest() {
    return (req, res, next) => {
      logger.debug('[REQUEST_PROCESSOR] Processing %s request from %s:%s',
        req.method, req.source_address, req.source_port);

      // Apply validation middleware
      this.validator.middleware()(req, res, () => {
        // Apply User-Agent filtering
        this.uaFilter.middleware()(req, res, () => {
          // Handle specific method types
          switch (req.method) {
            case 'OPTIONS':
              this.handleOptions(req, res);
              break;

            case 'CANCEL':
              this.handleCancel(req, res);
              break;

            case 'REGISTER':
              // Pass to registration handler
              next();
              break;

            case 'INVITE':
              // Pass to INVITE handler
              next();
              break;

            default:
              // Handle in-dialog requests
              this.handleInDialog(req, res, () => {
                // Check for presence requests
                if (!this.handlePresence(req, res)) {
                  // If no specific handler, return error
                  this.handleUnmatchedRequest(req, res);
                }
              });
              break;
          }
        });
      });
    };
  }
}

module.exports = RequestProcessor;