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


// PRIVATE PROTOTYPES
static ColorF32 ComputeAmbientLight(
        ColorF32 surfaceReflectivity, ColorF32 lightIntensity);

static ColorF32 ComputeDiffuseLight(
        ColorF32 surfaceReflectivity, ColorF32 lightIntensity,
        Point &vertPosition, Vector &vertNormal,
        Point &lightPosition);


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


    // 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.ambient, intensity);


    // Compute diffuse light
    ColorF32 diffuseLight = ComputeDiffuseLight(
            material.diffuse, intensity,
            vert.point, vert.normal,
            light.position);


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


    return result;
}


// PRIVATE FUNCTIONS
static ColorF32 ComputeAmbientLight(
        ColorF32 surfaceReflectivity, ColorF32 lightIntensity)
{
    ColorF32 result;


    result = surfaceReflectivity * lightIntensity;


    return result;
}

static ColorF32 ComputeDiffuseLight(
        ColorF32 surfaceReflectivity, ColorF32 lightIntensity,
        Point &vertPosition, Vector &vertNormal,
        Point &lightPosition)
{
    // Light is a function of the position of the light source and the surface
    Vector direction = lightPosition - vertPosition;
    direction.Normalize();

    float dot = Vector::Dot(vertNormal, direction);

    ColorF32 result = surfaceReflectivity * lightIntensity * dot;


    return result;
}