var defaultOptions = {
  date: "June 7, 2087 15:03:25",
  refresh: 1000,
  offset: 0,
  onEnd: function() {
    return;
  },
  render: function (date) {
    this.el.innerHTML = date.years + " years, " +
                        date.days  + " days, " +
                        this.leadingZeros(date.hours) + " hours, " +
                        this.leadingZeros(date.min) + " min and " +
                        this.leadingZeros(date.sec) + " sec";
  }
};

/**
 * Countdown constructor
 * @param {HTMLElement} el      DOM node of the countdown
 * @param {Object}      options (optional) Options for the plugin
 */
var Countdown = function(el, options) {

  /**
   * Reference to the DOM element
   * @type {HTMLElement}
   */
  this.el = el;

  /**
   * Options of the countdown plugin
   * @type {Object}
   */
  this.options = {};

  /**
   * Interval reference or false if counter is stopped
   * @type {Mixed}
   */
  this.interval = false;

  // merge default options and options into this.options
  for (var i in defaultOptions) {
    if (defaultOptions.hasOwnProperty(i)) {
      this.options[i] = typeof options[i] !== 'undefined' ? options[i] : defaultOptions[i];

      if (i === 'date' && typeof this.options.date !== 'object') {
        this.options.date = new Date(this.options.date);
      }

      // bind context for functions
      if (typeof this.options[i] === 'function') {
        this.options[i] = this.options[i].bind(this);
      }
    }
  }

  /**
   * Get the difference between now and the end date
   * @return {Object} Object with the diff information (years, days, hours, min, sec, millisec)
   */
  this.getDiffDate = function() {
    var diff = (this.options.date.getTime() - Date.now() + this.options.offset) / 1000;

    var dateData = {
      years:    0,
      days:     0,
      hours:    0,
      min:      0,
      sec:      0,
      millisec: 0
    };

    if (diff <= 0) {
      if (this.interval) {
        this.stop();
        this.options.onEnd();
      }
      return dateData;
    }

    if (diff >= (365.25 * 86400)) {
      dateData.years = Math.floor(diff / (365.25 * 86400));
      diff -= dateData.years * 365.25 * 86400;
    }

    if (diff >= 86400) {
      dateData.days = Math.floor(diff / 86400);
      diff -= dateData.days * 86400;
    }

    if (diff >= 3600) {
      dateData.hours = Math.floor(diff / 3600);
      diff -= dateData.hours * 3600;
    }

    if (diff >= 60) {
      dateData.min = Math.floor(diff / 60);
      diff -= dateData.min * 60;
    }

    dateData.sec = Math.round(diff);

    dateData.millisec = diff % 1 * 1000;

    return dateData;
  }.bind(this);

  /**
   * Add leading zeros to a number
   * @param  {Number} num    Input number
   * @param  {Number} length Length of the desired output
   * @return {String}        String of the desired length with leading zeros
   */
  this.leadingZeros = function(num, length) {
    length = length || 2;
    num = String(num);
    if (num.length > length) {
      return num;
    }
    return (Array(length + 1).join('0') + num).substr(-length);
  };

  /**
   * Update the end date of the countdown
   * @param  {Mixed}     newDate Date object or a String/Number that can be passed to the Date constructor
   * @return {Countdown}         Countdown instance
   */
  this.update = function(newDate) {
    if (typeof newDate !== 'object') {
      newDate = new Date(newDate);
    }
    this.options.date = newDate;
    this.render();
    return this;
  }.bind(this);

  /**
   * Stop the countdown refresh / rerender
   * @return {Countdown} Countdown instance
   */
  this.stop = function() {
    if (this.interval) {
      clearInterval(this.interval);
      this.interval = false;
    }
    return this;
  }.bind(this);

  /**
   * Render the countdown
   * @return {Countdown} Countdown instance
   */
  this.render = function() {
    this.options.render(this.getDiffDate());
    return this;
  }.bind(this);

  /**
   * Start the countdown
   * @return {Countdown} Countdown instance
   */
  this.start = function() {
    // don't start if the countdown is already started
    if (this.interval) { return; }

    this.render();

    if (this.options.refresh) {
      this.interval = setInterval(this.render, this.options.refresh);
    }

    return this;
  }.bind(this);

  /**
   * Update the offset
   * @param  {Number}    offset New offset in ms
   * @return {Countdown}        Countdown instance
   */
  this.updateOffset = function(offset) {
    this.options.offset = offset;
    return this;
  }.bind(this);


  // initial start of the countdown or initial render
  this.start();
};

module.exports = Countdown;