'use strict';

var debug = require('./util/debug')('queue');

function JobQueue(metadataBackend, jobPublisher) {
    this.metadataBackend = metadataBackend;
    this.jobPublisher = jobPublisher;
}

module.exports = JobQueue;

var QUEUE = {
    DB: 5,
    PREFIX: 'batch:queue:',
    INDEX: 'batch:indexes:queue'
};

module.exports.QUEUE = QUEUE;

JobQueue.prototype.enqueue = function (user, jobId, callback) {
    debug('JobQueue.enqueue user=%s, jobId=%s', user, jobId);

    this.metadataBackend.redisMultiCmd(QUEUE.DB, [
        [ 'LPUSH', QUEUE.PREFIX + user, jobId ],
        [ 'SADD', QUEUE.INDEX, user ]
    ], function (err) {
        if (err) {
            return callback(err);
        }

        this.jobPublisher.publish(user);
        callback();
    }.bind(this));
};

JobQueue.prototype.size = function (user, callback) {
    this.metadataBackend.redisCmd(QUEUE.DB, 'LLEN', [ QUEUE.PREFIX + user ], callback);
};

JobQueue.prototype.dequeue = function (user, callback) {
    var dequeueScript = [
        'local job_id = redis.call("RPOP", KEYS[1])',
        'if redis.call("LLEN", KEYS[1]) == 0 then',
        '   redis.call("SREM", KEYS[2], ARGV[1])',
        'end',
        'return job_id'
    ].join('\n');

    var redisParams = [
        dequeueScript, //lua source code
        2, // Two "keys" to pass
        QUEUE.PREFIX + user, //KEYS[1], the key of the queue
        QUEUE.INDEX, //KEYS[2], the key of the index
        user // ARGV[1] - value of the element to remove from the index
    ];

    this.metadataBackend.redisCmd(QUEUE.DB, 'EVAL', redisParams, function (err, jobId) {
        debug('JobQueue.dequeued user=%s, jobId=%s', user, jobId);
        return callback(err, jobId);
    });
};

JobQueue.prototype.enqueueFirst = function (user, jobId, callback) {
    debug('JobQueue.enqueueFirst user=%s, jobId=%s', user, jobId);
    this.metadataBackend.redisCmd(QUEUE.DB, 'RPUSH', [ QUEUE.PREFIX + user, jobId ], callback);
};