/**
 * Loads a file from disk and returns a binary string
 *
 *  Copyright (C) 2012  Mike Gerwitz
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * The file uses a number of features introduced in the HTML5 and ECMAScript
 * specs, as it depends on FileReader.
 */


/**
 * Load file into memory as binary string from a given file element
 *
 * This class handles the loading of only a single file (as that is all this
 * project requires).
 */
ltjs.FileLoader = Class( 'FileLoader',
{
    /**
     * DOM file element to watch
     * @type {HTMLInputElement}
     */
    'private _element': null,

    /**
     * Callback to call on file load
     * @type {function(Error,string)}
     */
    'private _callback': null,


    /**
     * Initialize file loader, monitoring the given file element
     *
     * @param  {HtmlInputElement}  element  file element to monitor
     */
    __construct: function( element )
    {
        if ( element.type !== 'file' )
        {
            throw TypeError( 'Expected file element, given ' + element.type );
        }

        this._element = element;
    },


    /**
     * Bind callback to file load event
     *
     * The given callback will be called when the file is loaded. It must accept
     * two arguments: the first will be used to indicate an error (otherwise
     * null) and the second argument will contain the binary string of data
     * (unless an error occurred, in which case it will be undefined).
     *
     * @param  {function(Error,string)}  callback  file load callback
     *
     * @return  {FileLoader}  self
     */
    'public onLoad': function( callback )
    {
        this._callback = callback;

        // we do not want to monitor the change event until *after* a callback
        // is registered (it is otherwise pointless)
        this._element.addEventListener( 'change', this._loadFile.bind( this ) );

        // attempt to load file immediately (in case a file has already been
        // selected)
        this._loadFile( { target: this._element } );

        return this;
    },


    /**
     * Process file and invokes callback with result
     *
     * Called on filename change.
     *
     * @param  {Object}  event  change event
     *
     * @return  {undefined}
     */
    'private _loadFile': function( event )
    {
        var _self = this,
            files = event.target.files;

        if ( files.length === 0 ) return;

        var reader = new FileReader();
        reader.onload = function( revent )
        {
            _self._callback.call( this.__inst, null, revent.target.result );
        };
        reader.onerror = function( e )
        {
            _self._callback.call( this.__inst, e );
        };

        // load file
        reader.readAsBinaryString( files[ 0 ] );
    }
} );