GameLib.D3.Vector3 = function(x, y, z) {

    this.x = 0;
    this.y = 0;
    this.z = 0;

    if (x) {
        this.x = x;
    }

    if (y) {
        this.y = y;
    }

    if (z) {
        this.z = z;
    }
};

GameLib.D3.Vector3.prototype.subtract = function (v) {

    if (v instanceof GameLib.D3.Vector3) {
        this.x -= v.x;
        this.y -= v.y;
        this.z -= v.z;
    }

    if (v instanceof GameLib.D3.Vector4) {
        console.warn("trying to subtract vector of bigger length (4 vs 3))");
    }

    return this;
};

GameLib.D3.Vector3.prototype.cross = function (v) {
    return new GameLib.D3.Vector3(
        this.y * v.z - this.z * v.y,
        this.z * v.x - this.x * v.z,
        this.x * v.y - this.y * v.x
    );
};

GameLib.D3.Vector3.prototype.negative = function () {
    this.x *= -1;
    this.y *= -1;
    this.z *= -1;
    return this;
};

GameLib.D3.Vector3.clockwise = function (u, v, w, viewPoint) {

    var normal = GameLib.D3.Vector3.normal(u, v, w);

    var uv = u.copy();

    var winding = normal.dot(uv.subtract(viewPoint));

    return (winding > 0);
};

GameLib.D3.Vector3.normal = function (u, v, w) {
    var vv = v.copy();
    var wv = w.copy();
    return vv.subtract(u).cross(wv.subtract(u));
};

GameLib.D3.Vector3.prototype.lookAt = function (at, up) {

    var lookAtMatrix = GameLib.D3.Matrix4.lookAt(this, at, up);

    this.multiply(lookAtMatrix);
};

GameLib.D3.Vector3.prototype.translate = function (v) {
    this.x += v.x;
    this.y += v.y;
    this.z += v.z;
    return this;
};

GameLib.D3.Vector3.prototype.squared = function () {
    return this.x * this.x + this.y * this.y + this.z * this.z;
};

GameLib.D3.Vector3.prototype.copy = function () {
    return new GameLib.D3.Vector3(
        this.x,
        this.y,
        this.z
    );
};

GameLib.D3.Vector3.prototype.lerp = function ( v, alpha ) {
    return new GameLib.D3.Vector3(
        this.x + ( v.x - this.x ) * alpha,
        this.y + ( v.y - this.y ) * alpha,
        this.z + ( v.z - this.z ) * alpha
    );
};

GameLib.D3.Vector3.prototype.multiply = function (s) {
    if (s instanceof GameLib.D3.Vector3) {
        this.x *= s.x;
        this.y *= s.y;
        this.z *= s.z;
    } else if (s instanceof GameLib.D3.Matrix4) {
        var x = s.rows[0].x * this.x + s.rows[0].y * this.y + s.rows[0].z * this.z;
        var y = s.rows[1].x * this.x + s.rows[1].y * this.y + s.rows[1].z * this.z;
        var z = s.rows[2].x * this.x + s.rows[2].y * this.y + s.rows[2].z * this.z;
        this.x = x;
        this.y = y;
        this.z = z;
    } else {
        console.log("functionality not implemented - please do this");
        throw new Error("not implemented");
    }
    return this;
};


GameLib.D3.Vector3.prototype.dot = function (v) {
    return (this.x * v.x) + (this.y * v.y) + (this.z * v.z);
};

GameLib.D3.Vector3.prototype.normalize = function () {

    var EPSILON = 0.000001;

    var v2 = this.squared();

    if (v2 < EPSILON) {
        return this; //do nothing for zero vector
    }

    var invLength = 1 / Math.sqrt(v2);

    this.x *= invLength;
    this.y *= invLength;
    this.z *= invLength;

    return this;
};