#include "camera.h"
#include "color.h"
#include "light.h"


// PRIVATE PROTOTYPES
static ColorF32 ComputeAmbientLight(
        Material &material, ColorF32 &intensity);

static ColorF32 ComputeDiffuseLight(
        Material &material, ColorF32 &intensity, Vertex &vert, Light &light);

static ColorF32 ComputeSpecularLight(
        Material &material, ColorF32 &intensity, Vertex &vert, Light &light,
        Camera &camera);


// PUBLIC FUNCTIONS
ColorF32 ComputeLight(
        Vertex &vert, Material &material, Light &light, Camera &camera)
{
    // Distance from light to vertex
    Vector direction = light.position - vert.position;
    float distance = VectorLength(direction);


    // Point light intensity is a function of the falloff factors and the distance
    ColorF32 intensity =
        (light.intensity * light.color)
        / (light.falloffConstant + light.falloffLinear * distance);


    // Compute ambient light
    ColorF32 ambientLight = ComputeAmbientLight(material, intensity);


    // Compute diffuse light
    ColorF32 diffuseLight = ComputeDiffuseLight(material, intensity, vert, light);


    // Compute specular light
    ColorF32 specularLight = ComputeSpecularLight(material, intensity, vert, light, camera);


    // Total light is sum of all lights
    ColorF32 result = ambientLight + diffuseLight + specularLight;


    return result;
}


// PRIVATE FUNCTIONS
static ColorF32 ComputeAmbientLight(
        Material &material, ColorF32 &intensity)
{
    // light = Kd * I
    ColorF32 result = material.ambient * intensity;


    return result;
}

static ColorF32 ComputeDiffuseLight(
        Material &material, ColorF32 &intensity, Vertex &vert, Light &light)
{
    // Vector from the light to the vertex
    Vector direction = light.position - vert.position;
    VectorNormalize(direction);
    float normalDotDirection = VectorDot(vert.normal, direction);


    // light = Kr * I * n.d
    ColorF32 result = material.diffuse * intensity * normalDotDirection;


    return result;
}

static ColorF32 ComputeSpecularLight(
        Material &material, ColorF32 &intensity, Vertex &vert, Light &light,
        Camera &camera)
{
    // Vector from the camera to the vertex
    Vector view = camera.position - vert.position;
    VectorNormalize(view);


    // Vector from the light to the vertex
    Vector direction = light.position - vert.position;
    VectorNormalize(direction);


    // Reflection vector of the light vector across the vertex normal
    float normalDotDirection = VectorDot(vert.normal, direction);
    Vector reflection = (2.0f * normalDotDirection * vert.normal) - direction;
    float reflectDotView = MAX(VectorDot(reflection, view), 0.0f);


    // light = Ks * I * (r.v)^sp
    ColorF32 result =
        material.specular * intensity * powf(reflectDotView, material.specularExp);


    return result;
}