(function(globals) {
  
  var

  get = function get(url, callback) {
    var e  = document.createElement("script");
    e.src  = url;
    e.type = "text/javascript";
    document.getElementsByTagName("head")[0].appendChild(e); 
  },
  
  extractAlbumId = function extractAlbumId( url ) {
    if( matches = url.match( /\/albumid\/([0-9]+)/ ) ) {
      return matches[1];
    }
    return null;
  },
  
  extractPhotoId = function extractPhotoId( url ) {
    if( matches = url.match( /\/photoid\/([0-9]+)/ ) ) {
      return matches[1];
    }
    return null;
  },
  
  constructEntryUrl = function constructEntryUrl( user, albumId, photoId ) {
    return "https://picasaweb.google.com/data/entry/base/"
          + "user/"  + user
          + ( albumId ? "/albumid/" + albumId : "" )
          + ( photoId ? "/photoid/" + photoId : "" );
  },
  
  // executed in scope of viewer
  processAlbums = function processAlbums( data ) {
    var albums = data.feed.entry;
    for( var a=0; a<albums.length; a++ ) {

      var album = albums[a];

      var id = album.link[0].href.replace( /\?.*$/, "" );

      this.addAlbum( {
        id     : extractAlbumId(id),
        title  : album.title.$t,
        thumb  : album['media$group']['media$thumbnail'][0].url
      } );

      var cb = registerCallback( (function(viewer) { 
        return function(data) { processPhotos.call(viewer, data); } })(this));
      var base = album.link[0].href;
      var url = base + "&kind=photo&max-results=1000&thumbsize=75,100" 
                     + "&hl=en_US&access=public" +
                     "&callback=__google_photo_cb__[" + cb + "]";
      get( url );
    }
  },
    
  // executed in scope of viewer
  processPhotos = function processPhotos( data ) {
    var albumId  = extractAlbumId(data.feed.id.$t);
    var photos = data.feed.entry;
    for( var p=0; p<photos.length; p++ ) {
      var photo = photos[p];
      var id = extractPhotoId(photo.id.$t.replace( /\?.*$/, "" ));
      this.addPhoto( albumId, {
        id      : id,
        title   : photo.title.$t,
        thumb   : photo['media$group']['media$thumbnail'][0].url,
        preview : photo['media$group']['media$thumbnail'][1].url,
        src     : photo.content.src
      } );
    }
  },
  
  registerCallback = function registerCallback( callback ) {
    window.__google_photo_cb__.push(callback);
    return __google_photo_cb__.length - 1;
  },

  provider = globals.providers.google = [];
  
  // add a global entry to store globally accessible callback functions
  window.__google_photo_cb__ = [];
  
  provider.connect = function connect( userId ) {
    return new provider.connection( userId );
  };
  
  provider.connection = function connection( userId ) {
    this.userId = userId;
    this.handleOnLoad = null;
  };

  provider.connection.prototype.populate = function populate( viewer ) {
    var cb = registerCallback( function(data) { 
      processAlbums.call(viewer, data);
    } );
    
    var base = "https://picasaweb.google.com/data/feed/base/user/" 
               + this.userId + "?alt=json-in-script&hl=en_US&access=public";
    var url = base + "&kind=album&max-results=1000&callback=__google_photo_cb__["+cb+"]";
    get( url );
  };
  
} )( Photo || window);