// This code is MIT licensed: http://creativecommons.org/licenses/MIT/
// Zenbe Inc (2009).
 
// Ensure our Zenbe namespaces exist.
window.zen = window.zen || {};
window.zen.util = window.zen.util || {};
 
/**
* The DropManager class provides a pleasant API for observing HTML5 drag-n-drop 
* events, cleaning up the data that they return, and triggering the appropriate 
* callbacks. With the drag and drop API so far, there are generally three types
* of data we're interested in: HTML, URLs, and plain text. On drop, your 
* callback will receive a pre-processed drop object with corresponding 'url', 
* 'html' and 'text' properties.
*
* To use it, instantiate a new DropManager, passing in an element to use as a 
* drop target, as well as an (optional) callbacks object, with (optional) 
* callbacks for drop, dragenter, dragover and dragleave:
*
*   new zen.util.DropManager($('drop_target'), {
*     drop : function(event, dropData) { ... process data here ... }
*   });
*
*/
window.zen.util.DropManager = Class.create({
  
  SUPPORTED_TYPES : ['text/uri-list', 'text/x-moz-url', 'text/html', 
                     'text/plain', 'Url', 'Text'],
  
  IMAGE_LINK_DETECTOR : (/^\s*<a.+?<img.+?src=['"](\S+?)['"].*?>\s*<\/a>\s*$/i),
  URL_DETECTOR        : (/(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%@!\-\/]))?/),
  
  /**
  * Registers all of the drop handlers that we'll need for dealing with
  * drop-related actions on the target element.
  */
  initialize : function(element, callbacks) {
    this.enabled = true;
    this.callbacks = callbacks || {};
    this.el = element;
    
    this.el.observe('dragenter',  this._boundDragEnter  = this._onDragEnter.bind(this));
    this.el.observe('dragover',   this._boundDragOver   = this._onDragOver.bind(this));
    this.el.observe('dragleave',  this._boundDragLeave  = this._onDragLeave.bind(this));
    this.el.observe('drop',       this._boundDrop       = this._onDrop.bind(this));
  },
  
  /**
  * Removes all of the drop handlers from the target element.
  */
  destroy : function() {
    this.el.stopObserving('dragenter',  this._boundDragEnter);
    this.el.stopObserving('dragover',   this._boundDragOver);
    this.el.stopObserving('dragleave',  this._boundDragLeave);
    this.el.stopObserving('drop',       this._boundDrop);
  },
  
  /**
  * Turn the DropManager's callbacks on and off. If disabled, none of your
  * passed-in callbacks will be fired until the DropManager is re-enabled.
  */
  setEnabled : function(enabled) {
    this.enabled = enabled;
  },
  
  /**
  * Does the DropManager support the drop event? Returns true if we're enabled,
  * and we support at least one of the drop's mime types.
  * @function ?
  */
  supports : function(ev) {
    if (!this.enabled) return false;
    var types = $A(ev.dataTransfer.types);
    if (!types.any()) return true; // IE doesn't give us any types whatsoever.
    return this.SUPPORTED_TYPES.any(function(t){ return types.include(t); });
  },
  
  /**
  * Internal function to post-process the drop data to pull out HTML image links
  * (<a><img></a>). The desired url is probably for the image, not the link.
  * In addition, some versions of webkit pass perfectly good urls as just 
  * text/plain -- pull 'em out.
  */
  _postProcess : function(data) {
    var textPart = data.html || data.text;
    var match = textPart && textPart.match(this.IMAGE_LINK_DETECTOR);
    if (match) data.url = match[1];
    match = data.text && !data.url && data.text.match(this.URL_DETECTOR);
    if (match) data.url = data.text;
    return data;
  },
  
  /**
  * On drop, we pull out our preferred and supported mime-types, process them
  * for links, and return the resulting drop object to the provided callback.
  * @function ?
  */
  _onDrop : function(ev) {
    ev.preventDefault();
    if (!this.supports(ev)) return false;
    var dt = ev.dataTransfer;
    try {
      var data = {
        url  : dt.getData('text/uri-list') || dt.getData('text/x-moz-url'),
        html : dt.getData('text/html').stripScripts(),
        text : dt.getData('text/plain')
      };
    } catch(e) { // IE doesn't support mime types yet.
      var data = {
        url  : dt.getData('Url'),
        text : dt.getData('Text')
      };
    }
    data = this._postProcess(data);
    if (this.callbacks.drop) this.callbacks.drop(ev, data);
  },
  
  /**
  * On drag enter, enable dropping on the drop target.
  * @function ?
  */
  _onDragEnter : function(ev) {
    ev.preventDefault();
    if (!this.supports(ev)) return false;
    try { // IE Doesn't allow this property to be set ... but Webkit requires it.
      ev.dataTransfer.effectAllowed = 'all';
      ev.dataTransfer.dropEffect = 'copy';
    } catch(e){}
    if (this.callbacks.dragenter) this.callbacks.dragenter(ev);
  },
  
  /**
  * On drag over, enable dropping on the drop target.
  * @function ?
  */
  _onDragOver : function(ev) {
    ev.preventDefault();
    if (!this.supports(ev)) return false;
    try { // IE Doesn't allow this property to be set ... but Webkit requires it.
      ev.dataTransfer.effectAllowed = 'all';
      ev.dataTransfer.dropEffect = 'copy';
    } catch(e){}
    if (this.callbacks.dragover) this.callbacks.dragover(ev);
  },
  
  /**
  * Not much to do for drag leave.
  * @function ?
  */
  _onDragLeave : function(ev) {
    ev.preventDefault();
    if (!this.supports(ev)) return false;
    if (this.callbacks.dragleave) this.callbacks.dragleave(ev);
  }
  
});