/**
 * @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 CONST = require('./const');
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. This is our priority body.
 * @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)
{
    // console.log('SeparateY start', body1.gameObject.name, body2.gameObject.name);

    var overlap = GetOverlapY(body1, body2, overlapOnly, bias);

    var velocity1 = body1.velocity;
    var velocity2 = body2.velocity;

    var body1Immovable = (body1.physicsType === CONST.STATIC_BODY || body1.immovable);
    var body2Immovable = (body2.physicsType === CONST.STATIC_BODY || body2.immovable);

    //  Can't separate two immovable bodies, or a body with its own custom separation logic
    if (overlapOnly || (body1Immovable && body2Immovable) || 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 based on the amount of overlap
    var v1 = velocity1.y;
    var v2 = velocity2.y;

    //  At this point, the velocity from gravity, world rebounds, etc has been factored in.
    //  The body is moving the direction it wants to, but may be blocked.

    if (!body1Immovable && !body2Immovable)
    {
        //  Neither body is immovable, so they get an equal amount of separation and a new velocity based on mass
        //  Share the overlap equally if both bodies are unblocked

        overlap *= 0.5;

        body1.y -= body1.getMoveY(overlap, true);
        body2.y += body2.getMoveY(overlap, true);

        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;

        velocity1.y = avg + nv1 * body1.bounce.y;
        velocity2.y = avg + nv2 * body2.bounce.y;
    }
    else if (!body1Immovable)
    {
        //  Body2 is immovable, but Body1 can move, so it gets all the separation unless blocked

        body1.y -= body1.getMoveY(overlap, true);

        velocity1.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 += body1.getMoveX((body2.deltaX()) * body2.friction.x, true);
        }
    }
    else if (!body2Immovable)
    {
        //  Body1 is immovable, but Body2 can move, so it gets all the separation unless blocked
        body2.y += body2.getMoveY(overlap, true);

        velocity2.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 += body2.getMoveX((body1.deltaX()) * body1.friction.x, true);
        }
    }

    //  It's possible both bodies were equally immovable, in which case neither of them have moved

    /*
    var blocked1 = body1.blocked;
    var blocked2 = body2.blocked;

    //  Set flags
    if (overlap < 0)
    {
        //  body1 was moving down
        body1.setTouchingDown();
        body2.setTouchingUp();

        if (blocked2.down)
        {
            body1.setBlockedDown();

            //  If we're still moving, but blocked, and the velocity hasn't inversed (i.e. rebounded) we should zero it.
            if (velocity1.y > 0)
            {
                velocity1.y = 0;
            }
        }
    }
    else
    {
        //  body1 was moving up
    }
    */

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

module.exports = SeparateY;