/**
 * Represents the result of performing a standard ("dumb") diff on bucket data
 *
 *  Copyright (C) 2017 R-T Specialty, LLC.
 *
 *  This file is part of the Liza Data Collection Framework
 *
 *  liza is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

var Class             = require( 'easejs' ).Class,
    BucketDiffContext = require( './BucketDiffContext' );
    BucketDiffResult  = require( './BucketDiffResult' );


/**
 * Result of performing a standard ("dumb") diff on bucket data
 *
 * This class handles the heavy lifting with regards to requesting
 * information about a diff---the actual diff algorithm need only provide a
 * list of the changes, which an instance of this class may either return
 * directly or retrieve the field data from the provided context.
 */
module.exports = Class( 'StdBucketDiffResult' )
    .implement( BucketDiffResult )
    .extend(
{
    /**
     * Context used to produce the diff
     * @type {BucketDiffContext}
     */
    'private _context': null,

    /**
     * List of flags describing field changes
     * @type {Object}
     */
    'private _changes': null,


    __construct: function( context, changes )
    {
        if ( !( Class.isA( BucketDiffContext, context ) ) )
        {
            throw TypeError(
                "Expected BucketDiffContext; received " + context
            );
        }

        this._context = context;
        this._changes = changes;
    },


    /**
     * Describes what fields have changed using boolean flags; does not include
     * unchanged fields
     *
     * As an example:
     *   { field: [ false, true, false ] }
     *
     * @return {Object} hash of arrays of boolean flags representing changes
     */
    'public describeChanged': function()
    {
        return this._changes;
    },


    /**
     * Describes changes in values by listing either undefined if no change or
     * an array containing, respectively, the current and previous values for
     * each index
     *
     * As an example:
     *   { field: [ undefined, [ 'current', 'prev' ], undefined ] }
     *
     * @return {Object} value changes
     */
    'public describeChangedValues': function()
    {
        var ret = {};

        for ( var field in this._changes )
        {
            var change = this._changes[ field ],
                i      = change.length,
                values = this._context.getFieldValues( field );

            ret[ field ] = [];
            while ( i-- )
            {
                if ( change[ i ] !== true )
                {
                    ret[ field ][ i ] = undefined;
                    continue;
                }

                // return both the current and previous values respectively
                ret[ field ][ i ] = [
                    values[ 0 ][ i ],
                    values[ 1 ][ i ],
                ];
            }
        }

        return ret;
    }
} );