#include "camera.h"
#include "color.h"
#include "engine.h"
#include "geometry.h"
#include "light.h"
#include "loader.h"
#include "matrix.h"
#include "transform.h"
#include "util.h"
#include "vec.h"
#include <cstring>
#include <cstdio>


// GLOBALS
static Mesh mesh;
static Camera camera;
static Light light;
static VertexList localVerts;
static VertexList transVerts;
static FaceList localFaces;
static FaceList transFaces;
static UVList uvs;
static MaterialList materials;
static TextureList textures;
static Matrix tPersp;
static Matrix tScreen;


// PRIVATE PROTOTYPES
static void CheckInputs(uint32_t input);
static void ComputeNormals(void);
static void ClearDepthBuffer(Engine_Buffer &buffer);
static void TransformToClipSpace(void);
static void TransformToScreenSpace(void);
static void LightMesh(void);


// PUBLIC FUNCTIONS
int Engine_Init(char *objFilename, char *mtlFilename)
{
    int result;


    result = ParseOBJ(objFilename, localVerts, localFaces, uvs);
    if (result < 0)
    {
        return -1;
    }


    result = ParseMTL(mtlFilename, materials, textures);
    if (result < 0)
    {
        return -1;
    }


    printf("Verts: %lu\n", localVerts.size);
    printf("Faces: %lu\n", localFaces.size);
    printf("Materials: %lu\n", materials.size);

    transVerts.size = localVerts.size;


    // Compute vertex and face normals for lighting calculation
    ComputeNormals();


    // Mesh configuration
    mesh.position.z = 50;
    mesh.position.y = -75;
    mesh.scale = 1.0f;


    // Light configuration
    light.position = Point(-100.0f, 200.0f, 0.0f);
    light.color = {1.0f, 1.0f, 1.0f, 1.0f};
    light.intensity = 2.0f;
    light.falloffConstant = 1.0f;
    light.falloffLinear = 0.001f;


    // Transformation matrices that do not change
    tPersp = Transform_Perspective(camera);
    tScreen = Transform_Screen(camera);


    return 0;
}

void Engine_Render(Engine_Buffer &buffer, uint32_t input)
{
    // Check for user input
    CheckInputs(input);


    // Clear the z-buffer
    ClearDepthBuffer(buffer);


    // Transform vertices to clip space
    TransformToClipSpace();


    // Clip near/far Z and cull backfaces
    ClipAndCull(transVerts, localFaces, transFaces, camera.position);


    // Light vertices and/or faces
    LightMesh();


    // Transform vertices to screen space
    TransformToScreenSpace();


    // Render
    RenderMesh(buffer, transFaces, transVerts, uvs, textures);
}

void Engine_Shutdown(void)
{
}


// PRIVATE FUNCTIONS
static void CheckInputs(uint32_t input)
{
    if (CHECK_BIT(input, TRANSLATE_X_POS))
    {
        light.position.x += 10;
    }
    else if (CHECK_BIT(input, TRANSLATE_X_NEG))
    {
        light.position.x -= 10;
    }

    if (CHECK_BIT(input, TRANSLATE_Z_POS))
    {
        light.position.z += 10;
    }
    else if (CHECK_BIT(input, TRANSLATE_Z_NEG))
    {
        light.position.z -= 10;
    }

    if (CHECK_BIT(input, TRANSLATE_Y_POS))
    {
        light.position.y += 10;
    }
    else if (CHECK_BIT(input, TRANSLATE_Y_NEG))
    {
        light.position.y -= 10;
    }

    if (CHECK_BIT(input, ROTATE_X_POS))
    {
        mesh.rotation.x += .10;
    }
    else if (CHECK_BIT(input, ROTATE_X_NEG))
    {
        mesh.rotation.x -= .10;
    }

    if (CHECK_BIT(input, ROTATE_Y_POS))
    {
        mesh.rotation.y += .10;
    }
    else if (CHECK_BIT(input, ROTATE_Y_NEG))
    {
        mesh.rotation.y -= .10;
    }

    if (CHECK_BIT(input, ROTATE_Z_POS))
    {
        mesh.rotation.z += .10;
    }
    else if (CHECK_BIT(input, ROTATE_Z_NEG))
    {
        mesh.rotation.z -= .10;
    }

    if (CHECK_BIT(input, SCALE_UP))
    {
        light.color.b = 0.0f;
        light.color.g = 0.0f;
        light.color.r = 1.0f;
    }
    else if (CHECK_BIT(input, SCALE_DOWN))
    {
        light.color.b = 1.0f;
        light.color.g = 1.0f;
        light.color.r = 1.0f;
    }
}


static void ComputeNormals(void)
{
    int vertexNormalCount[VERTEX_LIMIT] = {};

    for (size_t f = 0; f < localFaces.size; ++f)
    {
        size_t v0 = (size_t)localFaces.data[f].vertIndex[0];
        size_t v1 = (size_t)localFaces.data[f].vertIndex[1];
        size_t v2 = (size_t)localFaces.data[f].vertIndex[2];

        Point &p0 = localVerts.data[v0].point;
        Point &p1 = localVerts.data[v1].point;
        Point &p2 = localVerts.data[v2].point;

        Vector v01 = p1 - p0;
        Vector v02 = p2 - p0;

        Vector normal = VectorCross(v01, v02);

        // Add each vertex's normal to the sum for future averaging
        localVerts.data[v0].normal += normal;
        localVerts.data[v1].normal += normal;
        localVerts.data[v2].normal += normal;

        ++vertexNormalCount[v0];
        ++vertexNormalCount[v1];
        ++vertexNormalCount[v2];
    }

    for (size_t v = 0; v < localVerts.size; ++v)
    {
        if (vertexNormalCount[v] > 0)
        {
            // Compute the average normal for this vertex
            localVerts.data[v].normal /= vertexNormalCount[v];
            VectorNormalize(localVerts.data[v].normal);
        }
    }
}


static void ClearDepthBuffer(Engine_Buffer &buffer)
{
    memset(buffer.zbuffer, 0, sizeof(float) * (size_t)(buffer.width * buffer.height));
}


static void TransformToClipSpace(void)
{
    Matrix tTranslate = Transform_Translate(mesh.position);
    Matrix tRotate = Transform_Rotate(mesh.rotation);
    Matrix tScale = Transform_Scale(mesh.scale);
    Matrix tView = Transform_View(camera);

    for (size_t v = 0; v < localVerts.size; ++v)
    {
        transVerts.data[v].point =
            localVerts.data[v].point * tScale * tRotate * tTranslate * tView * tPersp;

        transVerts.data[v].normal =
            localVerts.data[v].normal * tScale * tRotate * tTranslate;
    }
}

static void TransformToScreenSpace(void)
{
    for (size_t v = 0; v < transVerts.size; ++v)
    {
        transVerts.data[v].point *= tScreen;
        transVerts.data[v].point.x /= transVerts.data[v].point.w;
        transVerts.data[v].point.y /= transVerts.data[v].point.w;
        transVerts.data[v].point.z /= transVerts.data[v].point.w;
    }
}

static void LightMesh(void)
{
    for (size_t f = 0; f < transFaces.size; ++f)
    {
        Face &face = transFaces.data[f];
        Material &material = materials.data[face.materialIndex];

        // Gouraud shading
        for (int i = 0; i < 3; ++i)
        {
            Vertex &vert = transVerts.data[face.vertIndex[i]];

            vert.color = ComputeLight(vert, material, light);
        }
    }
}