// Triangle class
// defines a Triangle shape

import javax.vecmath.*;

public class Triangle extends Shape {
    private Vector3f p0, p1, p2;    // three vertices make a triangle
    private Vector3f n0, n1, n2;    // normal at each vertex

    public Triangle() {
    }
    public Triangle(Vector3f _p0, Vector3f _p1, Vector3f _p2, Material mat) {
        p0 = new Vector3f(_p0);
        p1 = new Vector3f(_p1);
        p2 = new Vector3f(_p2);
        material = mat;
        Vector3f normal = new Vector3f();
        Vector3f v1 = new Vector3f();
        Vector3f v2 = new Vector3f();
        v1.sub(p1, p0);
        v2.sub(p2, p0);
        normal.cross(v1, v2);
        normal.normalize();             // compute default normal:
        n0 = new Vector3f(normal);      // the normal of the plane defined by the triangle
        n1 = new Vector3f(normal);
        n2 = new Vector3f(normal);
    }
    public Triangle(Vector3f _p0, Vector3f _p1, Vector3f _p2,
                    Vector3f _n0, Vector3f _n1, Vector3f _n2,
                    Material mat) {
        p0 = new Vector3f(_p0);
        p1 = new Vector3f(_p1);
        p2 = new Vector3f(_p2);
        material = mat;
        n0 = new Vector3f(_n0);     // the normal of the plane defined by the triangle
        n1 = new Vector3f(_n1);
        n2 = new Vector3f(_n2);
    }
    public HitRecord hit(Ray ray, float tmin, float tmax) {

        /* YOUR WORK HERE: complete the triangle's intersection routine
         * Normal should be computed by a bilinear interpolation from n0, n1 and n2
         * using the barycentric coordinates: alpha, beta, (1.0 - alpha - beta) */
        Vector3f o = ray.getOrigin();
        Vector3f d = ray.getDirection();

        Matrix3f matrix = new Matrix3f(-d.x, p1.x - p0.x, p2.x - p0.x, -d.y, p1.y - p0.y, p2.y - p0.y, -d.z, p1.z - p0.z, p2.z - p0.z);
        Vector3f finalcol = new Vector3f(o.x - p0.x, o.y - p0.y, o.z - p0.z);
        Matrix3f matrixT = new Matrix3f(matrix);
        matrixT.setColumn(0, finalcol);
        Matrix3f matrixB = new Matrix3f(matrix);
        matrixB.setColumn(1, finalcol);
        Matrix3f matrixG = new Matrix3f(matrix);
        matrixG.setColumn(2, finalcol);

        float det = matrix.determinant();
        if (det == 0) {
            return null;
        }
        float t = matrixT.determinant() / det;
        float beta = matrixB.determinant() / det;
        float gamma = matrixG.determinant() / det;
        float alpha = 1.0f - beta - gamma;
        if (t < tmin || t > tmax) {
            return null;
        }
        if (alpha < 0 || alpha > 1 || beta < 0 || beta > 1 || gamma < 0 || gamma > 1) {
            return null;
        }

        Vector3f p = ray.pointAt(t);
        HitRecord rec = new HitRecord();
        rec.pos = p;
        rec.t = t;
        rec.material = material;

        Vector3f scaledAlpha = new Vector3f(n0);
        scaledAlpha.scale(alpha);
        Vector3f scaledBeta = new Vector3f(n1);
        scaledBeta.scale(beta);
        Vector3f scaledGamma = new Vector3f(n2);
        scaledGamma.scale(gamma);

        rec.normal = new Vector3f();
        rec.normal.add(scaledAlpha);
        rec.normal.add(scaledBeta);
        rec.normal.add(scaledGamma);
        rec.normal.normalize();

        return rec;
    }
}