/*!
 * transition-to-from-auto 0.5.2
 * https://github.com/75lb/transition-to-from-auto
 * Copyright 2015 Lloyd Brookes <75pound@gmail.com>
 */

/**
@module
@alias transition
*/
(function(window, document) {
  'use strict';

  var getComputedStyle = window.getComputedStyle;
  var isTransition = 'data-ttfaInTransition';

  var elements = [];
  var data = [];

  // Transition detecting
  var transitionProp = false;
  var transitionEnd = false;
  var testStyle = document.createElement('a').style;
  var testProp;

  if (testStyle[(testProp = 'webkitTransition')] !== undefined) {
    transitionProp = testProp;
    transitionEnd = testProp + 'End';
  }

  if (testStyle[(testProp = 'transition')] !== undefined) {
    transitionProp = testProp;
    transitionEnd = testProp + 'end';
  }

  function process(options, data) {
    var el = options.element;
    var val = options.val;
    var prop = options.prop;
    var style = el.style;
    var startVal;
    var autoVal;

    if (!transitionProp) {
      return (style[prop] = val);
    }

    if (el.hasAttribute(isTransition)) {
      el.removeEventListener(transitionEnd, data.l);
    } else {
      style[transitionProp] = 'none';

      startVal = getComputedStyle(el)[prop];
      style[prop] = 'auto';
      autoVal = getComputedStyle(el)[prop];

      // Interrupt
      if (startVal === val || (val === 'auto' && startVal === autoVal)) {
        return;
      }

      data.auto = autoVal;
      el.setAttribute(isTransition, 1);

      // Transition
      style[prop] = startVal;
      el.offsetWidth;
      style[transitionProp] = options.style;
    }

    style[prop] = val === 'auto' ? data.auto : val;

    data.l = function(e) {
      if (e.propertyName === prop) {
        el.removeAttribute(isTransition);
        el.removeEventListener(transitionEnd, data.l);
        if (val === 'auto') {
          /* avoid transition flashes in Safari */
          style[transitionProp] = 'none';
          style[prop] = val;
        }
      }
    };

    el.addEventListener(transitionEnd, data.l);
  }

  /**
    @param options {Object}
    @param options.element {string | element} - The DOM element or selector to transition
    @param options.val {string} - The value you want to transition to
    @param [options.prop] {string} - The CSS property to transition, defaults to `"height"`
    @param [options.style] {string} - The desired value for the `transition` CSS property (e.g. `"height 1s"`). If specified, this value is added inline and will override your CSS. Leave this value blank if you already have it defined in your stylesheet.
    @alias module:transition-to-from-auto
    */
  function transition(options) {
    var element = options.element;
    var datum;
    var index;

    if (typeof element === 'string') {
      element = document.querySelector(element);
    }

    element = options.element = element instanceof Node ? element : false;
    options.prop = options.prop || 'height';
    options.style = options.style || '';

    if (element) {
      index = elements.indexOf(element);
      if (~index) {
        datum = data[index];
      } else {
        datum = {};
        elements.push(element);
        data.push(datum);
      }

      process(options, datum);
    }
  }

  /**
    The name of the vendor-specific transition CSS property
    @type {string}
    @example
    el.style[transition.prop + 'Duration'] = '1s';
    */
  transition.prop = transitionProp;

  /**
   * The name of the [transition end event](https://developer.mozilla.org/en-US/docs/Web/Events/transitionend) in the current browser (typically `"transitionend"` or `"webkitTransitionEnd"`)
   * @type {string}
   * @example
   * el.addEventListener(transition.end, function(){
   *     // the transition ended..
   * });
   */
  transition.end = transitionEnd;

  if (typeof module === 'object' && module.exports) {
    module.exports = transition;
  } else if (typeof define === 'function' && define.amd) {
    define(function() {
      return transition;
    });
  } else {
    window.transition = transition;
  }
})(window, document);