/**
 * System takes care of updating all the entities (based on their component data)
 * @param apiSystem GameLib.API.System
 * @constructor
 */
GameLib.System.Animation = function(
    apiSystem
) {
    GameLib.System.call(
        this,
        apiSystem
    );
};

GameLib.System.Animation.prototype = Object.create(GameLib.System.prototype);
GameLib.System.Animation.prototype.constructor = GameLib.System.Animation;

GameLib.System.Animation.prototype.start = function() {

    GameLib.System.prototype.start.call(this);

    this.animationEntities = GameLib.EntityManager.Instance.findEntities([GameLib.D3.Animation]);

    this.animationEntities.map(
        function(animationEntity) {

            /**
             * Get all meshes and all animation components
             */
            var meshComponents      = animationEntity.getComponents(GameLib.D3.Mesh);
            var animationComponents = animationEntity.getComponents(GameLib.D3.Animation);

            animationComponents.map(function(animation){

                meshComponents.map(function(mesh){

                    if (animation.rotationSpeed) {

                        /**
                         * Back up the current property descriptor
                         */
                        mesh.animationObject = {
                            backupAngleDescriptor   : Object.getOwnPropertyDescriptor(mesh.quaternion, 'angle'),
                            targetAngle             : mesh.quaternion.angle,
                            angleIncrement          : true,
                            intermediateAngle       : mesh.quaternion.angle,
                            subscription            : null
                        };

                        var getIntermediateAngle = function() {
                            return mesh.animationObject.intermediateAngle;
                        };

                        var animateRotation = function(value) {

                            mesh.animationObject.intermediateAngle = value;

                            var done = false;

                            if (mesh.animationObject.angleIncrement) {
                                /**
                                 * We are rotating upwards
                                 */
                                if (value >= mesh.animationObject.targetAngle) {
                                    /**
                                     * We need to stop
                                     */
                                    done = true;
                                }
                            } else {
                                /**
                                 * We are rotating downwards
                                 */
                                if (value <= mesh.animationObject.targetAngle) {
                                    /**
                                     * We need to stop
                                     */
                                    done = true;
                                }
                            }

                            if (done) {

                                /**
                                 * Stop subscribing to before render events
                                 */
                                mesh.animationObject.subscription.remove();

                                /**
                                 *
                                 * @type {null}
                                 */
                                mesh.animationObject.subscription = null;

                                /**
                                 * Start checking again for animation requests
                                 */
                                Object.defineProperty(
                                    mesh.quaternion,
                                    'angle',
                                    {
                                        'get' : getIntermediateAngle,
                                        'set' : animationCheck,
                                        'configurable' : true
                                    }
                                );

                                /**
                                 * Set our target angle value
                                 */
                                mesh.animationObject.intermediateAngle = mesh.animationObject.targetAngle;

                                /**
                                 * Update our actual angle
                                 */
                                mesh.quaternion.angle = mesh.animationObject.targetAngle;

                                /**
                                 * Update our instance
                                 */
                                mesh.updateInstance();

                                /**
                                 * Now we say that our intermediate angle is zero, because we will apply our rotation
                                 * and this will prevent us from re-registering a new 'animationRender' event
                                 */
                                mesh.animationObject.intermediateAngle = 0;

                                /**
                                 * Apply our position, rotation and scale to the mesh
                                 */
                                mesh.applyPositionRotationScale();
                            }
                        };
                        
                        var animationCheck = function(value) {

                            /**
                             * Check if we have work to do
                             */
                            if (mesh.animationObject.intermediateAngle === value) {
                                /**
                                 * Nothing to do
                                 */
                                return;
                            } else if (mesh.animationObject.intermediateAngle > value) {
                                /**
                                 * We will rotate towards by decrementing
                                 */
                                mesh.animationObject.angleIncrement = false;
                            } else {
                                /**
                                 * We will rotate towards by incrementing
                                 */
                                mesh.animationObject.angleIncrement = true;
                            }

                            /**
                             * We say what our target angle is - when we reach our target angle, we want
                             * to stop our animation
                             */
                            mesh.animationObject.targetAngle = value;

                            /**
                             * Now override the setter again
                             */
                            Object.defineProperty(
                                mesh.quaternion,
                                'angle',
                                {
                                    'get' : getIntermediateAngle,
                                    'set' : animateRotation,
                                    'configurable' : true
                                }
                            );

                            /**
                             * Now we subscribe to 'before render' events, and slowly increment the value
                             * @type {{fn, remove}}
                             */
                            mesh.animationObject.subscription = GameLib.Event.Subscribe(
                                GameLib.Event.BEFORE_RENDER,
                                function(data) {

                                    var increment = Math.abs(animation.rotationSpeed);

                                    if (mesh.angleIncrement) {
                                        increment *= -1;
                                    }

                                    mesh.quaternion.angle = (data.delta * increment) + mesh.animationObject.intermediateAngle;

                                    var backup = mesh.updateRotationFromAxisAngle;

                                    mesh.updateRotationFromAxisAngle = true;
                                    mesh.updateInstance();
                                    mesh.updateRotationFromAxisAngle = backup;
                                }
                            );
                        };


                        /**
                         * Override the property descriptor - to slowly increment the angle, but report back its
                         * target angle as its actual angle.
                         */
                        Object.defineProperty(
                            mesh.quaternion,
                            'angle',
                            {
                                'get' : getIntermediateAngle,
                                'set' : animationCheck,
                                'configurable' : true
                            }
                        );
                    }
                });
            });
        }
    );
};

/**
 * Stop Animation System
 */
GameLib.System.Animation.prototype.stop = function() {

    GameLib.System.prototype.stop.call(this);

    this.animationEntities = GameLib.EntityManager.Instance.findEntities([GameLib.D3.Animation]);

    this.animationEntities.map(
        function(animationEntity) {

            /**
             * Get all meshes and all animation components
             */
            var meshComponents = animationEntity.getComponents(GameLib.D3.Mesh);
            var animationComponents = animationEntity.getComponents(GameLib.D3.Animation);

            animationComponents.map(
                function (animation) {

                    meshComponents.map(
                        function (mesh) {

                            if (animation.rotationSpeed) {

                                if (mesh.animationObject) {

                                    if (mesh.animationObject.backupAngleDescriptor) {
                                        Object.defineProperty(
                                            mesh.quaternion,
                                            'angle',
                                            mesh.animationObject.backupAngleDescriptor
                                        )
                                    }

                                    if (mesh.animationObject.targetAngle) {
                                        mesh.quaternion.angle = mesh.animationObject.targetAngle;
                                    }

                                    if (mesh.animationObject.subscription) {
                                        mesh.animationObject.subscription.remove();
                                    }

                                    delete mesh.animationObject;
                                }
                            }
                        }
                    )
                }
            )
        }
    );
};