'use strict';

const debug = require('debug')('queue');
const endMw = require('express-end');

const MiniQueue = require('mini-queue');


const expressQueueMw = function(config) {

  debug('Initializing: config:', config);

  const self = {};
  const rejectHandler = config.rejectHandler || defaultRejectHandler;

  self.jobQueue = new MiniQueue(config);

  // When any task has gone to `process` state,
  // wait for `end` event of `res` object (`job.data.res`)
  // then leave the `process` state
  self.jobQueue.on('process', function(job, done) {
    //job.data.res.removeAllListeners('end'); // Remove listener which was set in on(queued) event
    job.data.res.once('end', function() {     // `end` event is sent on res.end() by `express-end` middleware package
      done();
    });
    job.data.next();
  });

  self.jobQueue.on('reject', function(job) {
    debug('Rejected ' + job.data.req.path);
    rejectHandler(job.data.req, job.data.res);
  });

  self.queueMw = function(req,res,next) {

    const data = { req: req, res: res, next: next };
    const job = self.jobQueue.createJob(data);

    // Set listeners for logging
    res.once('close',  function() { job.log('resOnClose');  }); // Closed from remote end
    res.once('end',    function() { job.log('resOnEnd');    }); // Sent on res.end() by express-end
    res.once('finish', function() { job.log('resOnFinish'); });

    // Handle disconnect from client while in queue
    res.once('close',  function() {
      if (job.status === 'queue') {
        // Return HTTP 204 No Content
        // - it must not be sent as the connection is already close by Client
        job.data.res.status(204).end();
        self.jobQueue._cancelJob(job);
      }
    });


  };

  // merge `end` and `queue` middlewares
  const resultMw = function(req, res, next) {
    endMw(req, res, function () {     // Inject res.end() handler to emit 'end' event
      self.queueMw(req, res, next); // Use this middleware
    });
  };

  // expose queue
  resultMw.queue = self.jobQueue;

  return resultMw;
};

function defaultRejectHandler(req, res) {
  res.status(503).send('Service Unavailable');
}

module.exports = expressQueueMw;