#include "HitTest.h"



float CrossZ(const Vector3& p0, const Vector3& p1, const Vector3& point)
{
    return (p1.x - p0.x) * (point.y - p0.y)
           - (p1.y - p0.y) * (point.x - p0.x);
}

std::optional<Sample> TriangleHitTest(const Vector3& fragPos, const VertexOut& v0, const VertexOut& v1, const VertexOut& v2)
{
    Vector3 weights;

    weights.x = CrossZ(v2.position, v1.position, fragPos);
    if ( weights.x > 0 )
        return std::nullopt;

    weights.y = CrossZ(v0.position, v2.position, fragPos);
    if ( weights.y > 0 )
        return std::nullopt;

    weights.z = CrossZ(v1.position, v0.position, fragPos);
    if ( weights.z > 0 )
        return std::nullopt;

    const float totalWeight{ weights.x + weights.y + weights.z };

    const float invTotalWeight{ 1.0f / totalWeight };
    const Vector3 normWeights{
            weights.x * invTotalWeight,
            weights.y * invTotalWeight,
            weights.z * invTotalWeight
    };

    const float depth =
            1 / (normWeights.x / v0.position.w +
                 normWeights.y / v1.position.w +
                 normWeights.z / v2.position.w);

    const Vector2 uv =
            v0.uv * depth * normWeights.x / v0.position.w +
            v1.uv * depth * normWeights.y / v1.position.w +
            v2.uv * depth * normWeights.z / v2.position.w;


    const float interpolatedDepth = 1 / (normWeights.x / v0.position.w + normWeights.y / v1.position.w + normWeights.z / v2.position.w);

    auto interpolate  =
            [&]<typename Type>(const Type& val0, const Type& val1, const Type& val2) -> Type
            {
                return (val0 / v0.position.w * normWeights.x +
                        val1 / v1.position.w * normWeights.y +
                        val2 / v2.position.w * normWeights.z) * interpolatedDepth;

            };

    //Invert the normal
    const Vector3 normal = interpolate(v0.normal, v1.normal, v2.normal).Normalized();
    const Vector3 tangent = interpolate(v0.tangent, v1.tangent, v2.tangent).Normalized();
    const Vector3 viewDir = interpolate(v0.viewDir, v1.viewDir, v2.viewDir).Normalized();

    return Sample{
            .uv = uv,
            .normal = normal,
            .tangent = tangent,
            .viewDirection = viewDir,
            .depth = depth,
            .weight = normWeights,
            .mesh = v0.mesh
    };
}