module BABYLON {
    /**
     * A behavior that when attached to a mesh will allow the mesh to be dragged around the screen based on pointer events
     */
    export class PointerDragBehavior implements Behavior<Mesh> {
        private _attachedNode: Node; 
        private _dragPlane: Mesh;
        private _scene:Scene;
        private _pointerObserver:Nullable<Observer<PointerInfo>>;
        private static planeScene:Scene;
        private _draggingID = -1;
        
        /**
         *  Fires each time the attached mesh is dragged with the pointer
         */
        public onDragObservable = new Observable<{delta:Vector3, dragPlanePoint:Vector3}>()
        /**
         *  Fires each time a drag begins (eg. mouse down on mesh)
         */
        public onDragStartObservable = new Observable<{dragPlanePoint:Vector3}>()
        /**
         *  Fires each time a drag ends (eg. mouse release after drag)
         */
        public onDragEndObservable = new Observable<{dragPlanePoint:Vector3}>()
        /**
         *  If the attached mesh should be moved when dragged
         */
        public moveAttached = true;
        /**
         *  Mesh with the position where the drag plane should be placed
         */
        public _dragPlaneParent:Nullable<Mesh>=null;
        
        /**
         * Creates a pointer drag behavior that can be attached to a mesh
         * @param options The drag axis or normal of the plane that will be dragged accross
         */
        constructor(private options:{dragAxis?:Vector3, dragPlaneNormal?:Vector3}){
            var optionCount = 0;
            if(options.dragAxis){
                optionCount++;
            }
            if(options.dragPlaneNormal){
                optionCount++;
            }
            if(optionCount > 1){
                throw "Multiple drag modes specified in dragBehavior options. Only one expected";
            }
            if(optionCount < 1){
                throw "At least one drag mode option must be specified";
            }
        }

        /**
         *  The name of the behavior
         */
        public get name(): string {
            return "PointerDrag";
        }

        /**
         *  Initializes the behavior
         */
        public init() {}

        /**
         * Attaches the drag behavior the passed in mesh
         * @param ownerNode The mesh that will be dragged around once attached
         */
        public attach(ownerNode: Mesh): void {
            this._scene = ownerNode.getScene();
            this._attachedNode = ownerNode;

            // Initialize drag plane to not interfere with existing scene
            if(!PointerDragBehavior.planeScene){
                PointerDragBehavior.planeScene = new BABYLON.Scene(this._scene.getEngine())
                this._scene.getEngine().scenes.pop();
            }
            this._dragPlane = BABYLON.Mesh.CreatePlane("pointerDragPlane", 1000, PointerDragBehavior.planeScene, false, BABYLON.Mesh.DOUBLESIDE);

            // State of the drag
            var dragging = false
            var lastPosition = new BABYLON.Vector3(0,0,0);
            var delta = new BABYLON.Vector3(0,0,0);

            this._pointerObserver = this._scene.onPointerObservable.add((pointerInfo)=>{
                if (pointerInfo.type == BABYLON.PointerEventTypes.POINTERDOWN) {
                    if(!dragging && pointerInfo.pickInfo && pointerInfo.pickInfo.hit && pointerInfo.pickInfo.pickedMesh && pointerInfo.pickInfo.ray){
                        if(this._attachedNode == pointerInfo.pickInfo.pickedMesh){
                            this._updateDragPlanePosition(pointerInfo.pickInfo.ray);
                            var pickedPoint = this._pickWithRayOnDragPlane(pointerInfo.pickInfo.ray)
                            if(pickedPoint){
                                dragging = true;
                                this._draggingID = (<PointerEvent>pointerInfo.event).pointerId;
                                lastPosition.copyFrom(pickedPoint);
                                this.onDragStartObservable.notifyObservers({dragPlanePoint: pickedPoint});
                            }
                        }
                    }
                }else if(pointerInfo.type == BABYLON.PointerEventTypes.POINTERUP){
                    if(this._draggingID == (<PointerEvent>pointerInfo.event).pointerId){
                        dragging = false;
                        this._draggingID = -1;
                        this.onDragEndObservable.notifyObservers({dragPlanePoint: lastPosition});
                    }
                }else if(pointerInfo.type == BABYLON.PointerEventTypes.POINTERMOVE){
                    if(this._draggingID == (<PointerEvent>pointerInfo.event).pointerId && dragging && pointerInfo.pickInfo && pointerInfo.pickInfo.ray){
                        var pickedPoint = this._pickWithRayOnDragPlane(pointerInfo.pickInfo.ray)
                        this._updateDragPlanePosition(pointerInfo.pickInfo.ray);
                        if (pickedPoint) {
                            // depending on the drag mode option drag accordingly
                            if(this.options.dragAxis){
                                //get the closest point on the dragaxis from the selected mesh to the picked point location
                                // https://www.opengl.org/discussion_boards/showthread.php/159717-Closest-point-on-a-Vector-to-a-point
                                this.options.dragAxis.scaleToRef(BABYLON.Vector3.Dot(pickedPoint.subtract(lastPosition), this.options.dragAxis), delta);
                            }else{
                                pickedPoint.subtractToRef(lastPosition, delta);
                            }
                            if(this.moveAttached){
                                (<Mesh>this._attachedNode).position.addInPlace(delta);
                                
                            }
                            this.onDragObservable.notifyObservers({delta: delta, dragPlanePoint: pickedPoint});
                            lastPosition.copyFrom(pickedPoint);
                        }
                    }
                }
            });
        }

        private _pickWithRayOnDragPlane(ray:Nullable<Ray>){
            if(!ray){
                return null;
            }
            var pickResult = PointerDragBehavior.planeScene.pickWithRay(ray, (m)=>{return m == this._dragPlane})
            if (pickResult && pickResult.hit && pickResult.pickedMesh && pickResult.pickedPoint) {
                return pickResult.pickedPoint;
            }else{
                return null;
            }
        }

        // Position the drag plane based on the attached mesh position, for single axis rotate the plane along the axis to face the camera
        private _updateDragPlanePosition(ray:Ray){
            var pointA = this._dragPlaneParent ? this._dragPlaneParent.position : (<Mesh>this._attachedNode).position // center
            if(this.options.dragAxis){
                var camPos = ray.origin;

                // Calculate plane normal in direction of camera but perpendicular to drag axis
                var pointB = pointA.add(this.options.dragAxis); // towards drag axis
                var pointC = pointA.add(camPos.subtract(pointA).normalize()); // towards camera
                // Get perpendicular line from direction to camera and drag axis
                var lineA = pointB.subtract(pointA);
                var lineB = pointC.subtract(pointA);
                var perpLine = BABYLON.Vector3.Cross(lineA, lineB);
                // Get perpendicular line from previous result and drag axis to adjust lineB to be perpendiculat to camera
                var norm = BABYLON.Vector3.Cross(lineA, perpLine).normalize();

                this._dragPlane.position.copyFrom(pointA);
                this._dragPlane.lookAt(pointA.add(norm));
            }else if(this.options.dragPlaneNormal){
                this._dragPlane.position.copyFrom(pointA);
                this._dragPlane.lookAt(pointA.add(this.options.dragPlaneNormal));
            }
            this._dragPlane.computeWorldMatrix(true);
        }

        /**
         *  Detaches the behavior from the mesh
         */
        public detach(): void {
            if(this._pointerObserver){
                this._scene.onPointerObservable.remove(this._pointerObserver);
            }
        }
    }
}