/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2019 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

var Length = require('./Length');

/**
 * Extends the start and end points of a Line by the given amounts.
 *
 * The amounts can be positive or negative. Positive points will increase the length of the line,
 * while negative ones will decrease it.
 *
 * If no `right` value is provided it will extend the length of the line equally in both directions.
 *
 * Pass a value of zero to leave the start or end point unchanged.
 *
 * @function Phaser.Geom.Line.Extend
 * @since 3.16.0
 *
 * @param {Phaser.Geom.Line} line - The line instance to extend.
 * @param {number} left - The amount to extend the start of the line by.
 * @param {number} [right] - The amount to extend the end of the line by. If not given it will be set to the `left` value.
 *
 * @return {Phaser.Geom.Line} The modified Line instance.
 */
var Extend = function (line, left, right)
{
    if (right === undefined) { right = left; }

    var length = Length(line);

    var slopX = line.x2 - line.x1;
    var slopY = line.y2 - line.y1;

    if (left)
    {
        line.x1 = line.x1 - slopX / length * left;
        line.y1 = line.y1 - slopY / length * left;
    }

    if (right)
    {
        line.x2 = line.x2 + slopX / length * right;
        line.y2 = line.y2 + slopY / length * right;
    }

    return line;
};

module.exports = Extend;