/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2018 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

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

/**
 * Separates two overlapping bodies on the Y-axis (vertically).
 *
 * Separation involves moving two overlapping bodies so they don't overlap anymore and adjusting their velocities based on their mass. This is a core part of collision detection.
 *
 * The bodies won't be separated if there is no vertical overlap between them, if they are static, or if either one uses custom logic for its separation.
 *
 * @function Phaser.Physics.Arcade.SeparateY
 * @since 3.0.0
 *
 * @param {Phaser.Physics.Arcade.Body} body1 - The first Body to separate.
 * @param {Phaser.Physics.Arcade.Body} body2 - The second Body to separate.
 * @param {boolean} overlapOnly - If `true`, the bodies will only have their overlap data set and no separation will take place.
 * @param {number} bias - A value to add to the delta value during overlap checking. Used to prevent sprite tunneling.
 *
 * @return {boolean} `true` if the two bodies overlap vertically, otherwise `false`.
 */
var SeparateY = function (body1, body2, overlapOnly, bias)
{
    var overlap = GetOverlapY(body1, body2, overlapOnly, bias);

    //  Can't separate two immovable bodies, or a body with its own custom separation logic
    if (overlapOnly || overlap === 0 || (body1.immovable && body2.immovable) || body1.customSeparateY || body2.customSeparateY)
    {
        //  return true if there was some overlap, otherwise false
        return (overlap !== 0) || (body1.embedded && body2.embedded);
    }

    //  Adjust their positions and velocities accordingly (if there was any overlap)
    var v1 = body1.velocity.y;
    var v2 = body2.velocity.y;

    if (!body1.immovable && !body2.immovable)
    {
        overlap *= 0.5;

        body1.y -= overlap;
        body2.y += overlap;

        var nv1 = Math.sqrt((v2 * v2 * body2.mass) / body1.mass) * ((v2 > 0) ? 1 : -1);
        var nv2 = Math.sqrt((v1 * v1 * body1.mass) / body2.mass) * ((v1 > 0) ? 1 : -1);
        var avg = (nv1 + nv2) * 0.5;

        nv1 -= avg;
        nv2 -= avg;

        body1.velocity.y = avg + nv1 * body1.bounce.y;
        body2.velocity.y = avg + nv2 * body2.bounce.y;
    }
    else if (!body1.immovable)
    {
        body1.y -= overlap;
        body1.velocity.y = v2 - v1 * body1.bounce.y;

        //  This is special case code that handles things like horizontal moving platforms you can ride
        if (body2.moves)
        {
            body1.x += (body2.x - body2.prev.x) * body2.friction.x;
        }
    }
    else
    {
        body2.y += overlap;
        body2.velocity.y = v1 - v2 * body2.bounce.y;

        //  This is special case code that handles things like horizontal moving platforms you can ride
        if (body1.moves)
        {
            body2.x += (body1.x - body1.prev.x) * body1.friction.x;
        }
    }

    //  If we got this far then there WAS overlap, and separation is complete, so return true
    return true;
};

module.exports = SeparateY;