var Parse = require('parse/node').Parse;
var gcm = require('node-gcm');
var randomstring = require('randomstring');

var GCMTimeToLiveMax = 4 * 7 * 24 * 60 * 60; // GCM allows a max of 4 weeks
var GCMRegistrationTokensMax = 1000;

function GCM(apiKey) {
  this.sender = new gcm.Sender(apiKey);
}

/**
 * Send gcm request.
 * @param {Object} data The data we need to send, the format is the same with api request body
 * @param {Array} registrationTokens A array of registration tokens
 * @returns {Object} A promise which is resolved after we get results from gcm
 */
GCM.prototype.send = function (data, registrationTokens) {
  if (registrationTokens.length >= GCMRegistrationTokensMax) {
    throw new Parse.Error(Parse.Error.PUSH_MISCONFIGURED,
                          'Too many registration tokens for a GCM request.');
  }
  var pushId = randomstring.generate({
    length: 10,
    charset: 'alphanumeric'
  });
  var timeStamp = Date.now();
  var expirationTime;
  // We handle the expiration_time convertion in push.js, so expiration_time is a valid date
  // in Unix epoch time in milliseconds here
  if (data['expiration_time']) {
    expirationTime = data['expiration_time'];
  }
  // Generate gcm payload
  var gcmPayload = generateGCMPayload(data.data, pushId, timeStamp, expirationTime);
  // Make and send gcm request
  var message = new gcm.Message(gcmPayload);
  var promise = new Parse.Promise();
  this.sender.send(message, { registrationTokens: registrationTokens }, 5, function (error, response) {
    // TODO: Use the response from gcm to generate and save push report
    // TODO: If gcm returns some deviceTokens are invalid, set tombstone for the installation
    promise.resolve();
  });
  return promise;
}

/**
 * Generate the gcm payload from the data we get from api request.
 * @param {Object} coreData The data field under api request body
 * @param {String} pushId A random string
 * @param {Number} timeStamp A number whose format is the Unix Epoch
 * @param {Number|undefined} expirationTime A number whose format is the Unix Epoch or undefined
 * @returns {Object} A promise which is resolved after we get results from gcm
 */
var generateGCMPayload = function(coreData, pushId, timeStamp, expirationTime) {
  var payloadData =  {
    'time': new Date(timeStamp).toISOString(),
    'push_id': pushId,
    'data': JSON.stringify(coreData)
  }
  var payload = {
    priority: 'normal',
    data: payloadData
  };
  if (expirationTime) {
   // The timeStamp and expiration is in milliseconds but gcm requires second
    var timeToLive = Math.floor((expirationTime - timeStamp) / 1000);
    if (timeToLive < 0) {
      timeToLive = 0;
    }
    if (timeToLive >= GCMTimeToLiveMax) {
      timeToLive = GCMTimeToLiveMax;
    }
    payload.timeToLive = timeToLive;
  }
  return payload;
}

if (typeof process !== 'undefined' && process.env.NODE_ENV === 'test') {
  GCM.generateGCMPayload = generateGCMPayload;
}
module.exports = GCM;