lasertank-js/lib/MapSet.js

/**
 * Handles the loading of LVL files
 *
 *  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/>.
 *
 *
 * Maps (the term "level" is used in the game) are stored in a fixed-width LVL
 * file.
 */


/**
 * Handles delegation of LVL data
 *
 * This acts as a Map factory, leaving all processing responsibilities to the
 * Map instance. Consequently, any custom map format would be supported,
 * provided that the appropriate Map is handling it.
 */
ltjs.MapSet = Class( 'MapSet',
{
    /**
     * Raw level set data (binary)
     * @type {string}
     */
    'private _data': '',

    /**
     * Constructor used to create new map instances
     * @type {Function}
     */
    'private _mapCtor': null,

    /**
     * Number of maps in the given LVL data
     * @type {number}
     */
    'private _mapCount': 0,


    /**
     * Initialize map set with LVL data and a Map constructor
     *
     * The Map constructor is used in place of a separate Map factory.
     *
     * @param  {string}    data      binary LVL data
     * @param  {ltjs.Map}  map_ctor  Map constructor
     */
    __construct: function( data, map_ctor )
    {
        this._data    = ''+( data );
        this._mapCtor = map_ctor;

        // perform a simple integrity check on the provided data
        this._mapDataCheck();
    },


    /**
     * Perform a simple map data integrity check
     *
     * This is intended to throw an error if we believe the LVL data to be
     * invalid, or if the LVL data is invalid for the given Map constructor.
     * The check will simply ensure that the map size (in bytes) divides into
     * the total LVL size (in bytes) without any remainder.
     *
     * This is by no means fool-proof, but it should catch most.
     *
     * @return  {undefined}
     */
    'private _mapDataCheck': function()
    {
        var n = ( this._data.length / this._mapCtor.getMapSize() );

        // if the result is not an integer, then it is either not an LVL, the
        // file is corrupt, or we were given the wrong Map constructor
        if ( n % 1 )
        {
            throw Error( 'Invalid or corrupt LVL data' );
        }

        // we already calculated it, so we may as well store it
        this._mapCount = n;
    },


    /**
     * Load a level by the given number (e.g. level 1)
     *
     * @param  {number}  id  number of level to load, 1-indexed
     */
    'public getMapByNumber': function( id )
    {
        return this._mapCtor( this._data, id );
    },


    /**
     * Retrieve the number of maps in the LVL file
     *
     * @return  {number}  number of maps
     */
    'public getMapCount': function()
    {
        return this._mapCount;
    },
} );