#include "camera.h"
#include "color.h"
#include "engine.h"
#include "geometry.h"
#include "light.h"
#include "loader.h"
#include "matrix.h"
#include "render.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 Matrix tPersp;
static Matrix tScreen;
static EngineMemory memory;


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


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


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


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


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

    memory.transVerts.size = memory.localVerts.size;


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


    // Mesh configuration
    mesh.position.z = 125;
    mesh.position.y = -125;
    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 EngineRender(EngineBuffer &buffer, uint32_t input)
{
    // Check for user input
    CheckInputs(input);


    // Clear the z-buffer
    ClearDepthBuffer();


    // Transform vertices to clip space
    TransformToClipSpace();


    // Clip near/far Z and cull backfaces
    ClipAndCull();


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


    // Transform vertices to screen space
    TransformToScreenSpace();


    // Render
    Render(buffer, memory);
}

void EngineShutdown(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)
{
    VertexList &verts = memory.localVerts;
    FaceList &faces = memory.localFaces;

    int vertexNormalCount[VERTEX_LIMIT] = {};

    for (size_t f = 0; f < faces.size; ++f)
    {
        Face &face = faces.data[f];

        Vertex &vert0 = verts.data[face.vertIndex[0]];
        Vertex &vert1 = verts.data[face.vertIndex[1]];
        Vertex &vert2 = verts.data[face.vertIndex[2]];


        Vector v01 = vert1.point - vert0.point;
        Vector v02 = vert2.point - vert0.point;

        Vector normal = VectorCross(v01, v02);

        // Add each vertex's normal to the sum for future averaging
        vert0.normal += normal;
        vert1.normal += normal;
        vert2.normal += normal;

        ++vertexNormalCount[face.vertIndex[0]];
        ++vertexNormalCount[face.vertIndex[1]];
        ++vertexNormalCount[face.vertIndex[2]];
    }

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


static void ClearDepthBuffer(void)
{
    memset(memory.zbuffer, 0, sizeof(memory.zbuffer));
}


static void TransformToClipSpace(void)
{
    VertexList &localVerts = memory.localVerts;
    VertexList &transVerts = memory.transVerts;

    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;
    }
}

void ClipAndCull(void)
{
    FaceList &localFaces = memory.localFaces;
    FaceList &transFaces = memory.transFaces;
    VertexList &verts = memory.transVerts;

    int faceIndex = 0;

    for (size_t f = 0; f < localFaces.size; ++f)
    {
        Face &face = localFaces.data[f];

        Point &p0 = verts.data[face.vertIndex[0]].point;
        Point &p1 = verts.data[face.vertIndex[1]].point;
        Point &p2 = verts.data[face.vertIndex[2]].point;

        // Ignore this face if its Z is outside the Z clip planes
        if ( (p0.z < -p0.w)
            || (p0.z > p0.w)
            || (p1.z < -p1.w)
            || (p1.z > p1.w)
            || (p2.z < -p2.w)
            || (p2.z > p2.w))
        {
            continue;
        }


        // Calculate the face's normal (inverted for Blender-compatibility)
        Vector v01 = p1 - p0;
        Vector v02 = p2 - p0;
        Vector normal = -VectorCross(v01, v02);

        // Eye vector to viewport
        Vector view = camera.position - p0;

        float dot = VectorDot(normal, view);

        // Not a backface; add it to the list
        if (dot < EPSILON_E3)
        {
            transFaces.data[faceIndex] = face;
            ++faceIndex;
            transFaces.size = (size_t)faceIndex;
        }
    }
}

static void TransformToScreenSpace(void)
{
    VertexList &verts = memory.transVerts;

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

static void LightMesh(void)
{
    VertexList &verts = memory.transVerts;
    FaceList &faces = memory.transFaces;
    MaterialList &materials = memory.materials;

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

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

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