module BABYLON {

    /**
     * A particle represents one of the element emitted by a particle system.
     * This is mainly define by its coordinates, direction, velocity and age.
     */
    export class Particle {
        private static _Count = 0;
        /**
         * Unique ID of the particle
         */
        public id:number;
        /**
         * The world position of the particle in the scene.
         */
        public position = Vector3.Zero();

        /**
         * The world direction of the particle in the scene.
         */
        public direction = Vector3.Zero();

        /**
         * The color of the particle.
         */
        public color = new Color4(0, 0, 0, 0);

        /**
         * The color change of the particle per step.
         */
        public colorStep = new Color4(0, 0, 0, 0);

        /**
         * Defines how long will the life of the particle be.
         */
        public lifeTime = 1.0;

        /**
         * The current age of the particle.
         */
        public age = 0;

        /**
         * The current size of the particle.
         */
        public size = 0;

        /**
         * The current scale of the particle.
         */
        public scale = new Vector2(1, 1);        

        /**
         * The current angle of the particle.
         */
        public angle = 0;

        /**
         * Defines how fast is the angle changing.
         */
        public angularSpeed = 0;

        /**
         * Defines the cell index used by the particle to be rendered from a sprite.
         */
        public cellIndex: number = 0;  

        /**
         * The information required to support color remapping
         */
        public remapData: Vector4;

        /** @hidden */
        public _randomCellOffset?: number;

        /** @hidden */
        public _initialDirection: Nullable<Vector3>;

        /** @hidden */
        public _attachedSubEmitters: Nullable<Array<SubEmitter>> = null;

        /** @hidden */
        public _initialStartSpriteCellID: number;
        /** @hidden */
        public _initialEndSpriteCellID: number;

        /** @hidden */
        public _currentColorGradient: Nullable<ColorGradient>;
        /** @hidden */
        public _currentColor1 = new Color4(0, 0, 0, 0);
        /** @hidden */
        public _currentColor2 = new Color4(0, 0, 0, 0);

        /** @hidden */
        public _currentSizeGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentSize1 = 0;
        /** @hidden */
        public _currentSize2 = 0;      
        
        /** @hidden */
        public _currentAngularSpeedGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentAngularSpeed1 = 0;
        /** @hidden */
        public _currentAngularSpeed2 = 0;          

        /** @hidden */
        public _currentVelocityGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentVelocity1 = 0;
        /** @hidden */
        public _currentVelocity2 = 0;           
        
        /** @hidden */
        public _currentLimitVelocityGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentLimitVelocity1 = 0;
        /** @hidden */
        public _currentLimitVelocity2 = 0;       
        
        /** @hidden */
        public _currentDragGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentDrag1 = 0;
        /** @hidden */
        public _currentDrag2 = 0;  

        /** @hidden */
        public _randomNoiseCoordinates1: Vector3;
        /** @hidden */
        public _randomNoiseCoordinates2: Vector3;
     

        /**
         * Creates a new instance Particle
         * @param particleSystem the particle system the particle belongs to
         */
        constructor(
            /**
             * The particle system the particle belongs to.
             */
            public particleSystem: ParticleSystem) {
            this.id = Particle._Count++;
            if (!this.particleSystem.isAnimationSheetEnabled) {
                return;
            }

            this.updateCellInfoFromSystem();
        }

        private updateCellInfoFromSystem(): void {
            this.cellIndex = this.particleSystem.startSpriteCellID;
        }

        /**
         * Defines how the sprite cell index is updated for the particle
         */
        public updateCellIndex(): void {
            let offsetAge = this.age;
            let changeSpeed = this.particleSystem.spriteCellChangeSpeed;

            if (this.particleSystem.spriteRandomStartCell) {
                if (this._randomCellOffset === undefined) {         
                    this._randomCellOffset = Math.random() * this.lifeTime;
                }

                if (changeSpeed === 0) { // Special case when speed = 0 meaning we want to stay on initial cell
                    changeSpeed = 1;
                    offsetAge = this._randomCellOffset;
                } else {
                    offsetAge += this._randomCellOffset;
                }
            }

            let dist = (this._initialEndSpriteCellID - this._initialStartSpriteCellID);
            let ratio = Scalar.Clamp(((offsetAge * changeSpeed) % this.lifeTime) / this.lifeTime);

            this.cellIndex = this._initialStartSpriteCellID + (ratio * dist) | 0;
        }

        /** @hidden */
        public _inheritParticleInfoToSubEmitter(subEmitter: SubEmitter) {
            if ((<AbstractMesh>subEmitter.particleSystem.emitter).position) {
                var emitterMesh = (<AbstractMesh>subEmitter.particleSystem.emitter);
                emitterMesh.position.copyFrom(this.position);
                if (subEmitter.inheritDirection) { 
                    emitterMesh.position.subtractToRef(this.direction, BABYLON.Tmp.Vector3[0]);
                    // Look at using Y as forward
                    emitterMesh.lookAt(BABYLON.Tmp.Vector3[0], 0, Math.PI / 2);
                }
            } else {
                var emitterPosition = (<Vector3>subEmitter.particleSystem.emitter);
                emitterPosition.copyFrom(this.position);
            }
            // Set inheritedVelocityOffset to be used when new particles are created
            this.direction.scaleToRef(subEmitter.inheritedVelocityAmount / 2, Tmp.Vector3[0]);
            subEmitter.particleSystem._inheritedVelocityOffset.copyFrom(Tmp.Vector3[0]);
        }

        /** @hidden */
        public _inheritParticleInfoToSubEmitters() {
            if (this._attachedSubEmitters && this._attachedSubEmitters.length > 0) {
                this._attachedSubEmitters.forEach((subEmitter) => {
                    this._inheritParticleInfoToSubEmitter(subEmitter);
                });
            }
        }

        /** @hidden */
        public _reset() {
            this.age = 0;
            this._currentColorGradient = null;
            this._currentSizeGradient = null;
            this._currentAngularSpeedGradient = null;
            this._currentVelocityGradient = null;
            this._currentLimitVelocityGradient = null;
            this._currentDragGradient = null;
            this.cellIndex = this.particleSystem.startSpriteCellID;
            this._randomCellOffset = undefined;
        }

        /**
         * Copy the properties of particle to another one.
         * @param other the particle to copy the information to.
         */
        public copyTo(other: Particle) {
            other.position.copyFrom(this.position);
            if (this._initialDirection) {
                if (other._initialDirection) {
                    other._initialDirection.copyFrom(this._initialDirection);
                } else {
                    other._initialDirection = this._initialDirection.clone();
                }
            } else {
                other._initialDirection = null;
            }
            other.direction.copyFrom(this.direction);
            other.color.copyFrom(this.color);
            other.colorStep.copyFrom(this.colorStep);
            other.lifeTime = this.lifeTime;
            other.age = this.age;
            other._randomCellOffset = this._randomCellOffset;
            other.size = this.size;
            other.scale.copyFrom(this.scale);
            other.angle = this.angle;
            other.angularSpeed = this.angularSpeed;
            other.particleSystem = this.particleSystem;
            other.cellIndex = this.cellIndex;
            other.id = this.id;
            other._attachedSubEmitters = this._attachedSubEmitters;
            if (this._currentColorGradient) {
                other._currentColorGradient = this._currentColorGradient;
                other._currentColor1.copyFrom(this._currentColor1);
                other._currentColor2.copyFrom(this._currentColor2);
            }
            if (this._currentSizeGradient) {
                other._currentSizeGradient = this._currentSizeGradient;
                other._currentSize1 = this._currentSize1;
                other._currentSize2 = this._currentSize2;
            }
            if (this._currentAngularSpeedGradient) {
                other._currentAngularSpeedGradient = this._currentAngularSpeedGradient;
                other._currentAngularSpeed1 = this._currentAngularSpeed1;
                other._currentAngularSpeed2 = this._currentAngularSpeed2;
            }        
            if (this._currentVelocityGradient) {
                other._currentVelocityGradient = this._currentVelocityGradient;
                other._currentVelocity1 = this._currentVelocity1;
                other._currentVelocity2 = this._currentVelocity2;
            }     
            if (this._currentLimitVelocityGradient) {
                other._currentLimitVelocityGradient = this._currentLimitVelocityGradient;
                other._currentLimitVelocity1 = this._currentLimitVelocity1;
                other._currentLimitVelocity2 = this._currentLimitVelocity2;
            }     
            if (this._currentDragGradient) {
                other._currentDragGradient = this._currentDragGradient;
                other._currentDrag1 = this._currentDrag1;
                other._currentDrag2 = this._currentDrag2;
            }                                   
            if (this.particleSystem.isAnimationSheetEnabled) {
                other._initialStartSpriteCellID = this._initialStartSpriteCellID;
                other._initialEndSpriteCellID = this._initialEndSpriteCellID;
            }
            if (this.particleSystem.useRampGradients) {
                other.remapData.copyFrom(this.remapData);
            }
            if (this._randomNoiseCoordinates1) {
                if (other._randomNoiseCoordinates1) {
                    other._randomNoiseCoordinates1.copyFrom(this._randomNoiseCoordinates1);
                    other._randomNoiseCoordinates2.copyFrom(this._randomNoiseCoordinates2);
                } else {
                    other._randomNoiseCoordinates1 = this._randomNoiseCoordinates1.clone();
                    other._randomNoiseCoordinates2 = this._randomNoiseCoordinates2.clone();
                }
            }
        }
    }
}