#include "color.h"
#include "engine.h"
#include "geometry.h"
#include "render.h"
#include "util.h"


// MACROS
#define DrawPixel(buffer, width, color, x, y)\
{\
    buffer[width * y + x] = color;\
}


// STRUCTURES
struct BoundingBox
{
    BoundingBox(Point &v0, Point &v1, Point &v2)
    {
        yMin = MIN(v0.y, MIN(v1.y, v2.y));
        yMax = MAX(v0.y, MAX(v1.y, v2.y));

        xMin = MIN(v0.x, MIN(v1.x, v2.x));
        xMax = MAX(v0.x, MAX(v1.x, v2.x));
    }

    float yMin, yMax;
    float xMin, xMax;
};


// PUBLIC FUNCTIONS
void Render(EngineBuffer &buffer, EngineMemory &memory)
{
    FaceList &faces = memory.transFaces;
    VertexList &verts = memory.transVerts;
    TextureList &textures = memory.textures;
    UVList &uvs = memory.uvs;

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


        // Bounding box for barycentric calculations (top-left fill convention)
        BoundingBox box(p0, p1, p2);
        int yMin = (int)MAX(ceilf(box.yMin), 0);
        int yMax = (int)MIN(ceilf(box.yMax) - 1, buffer.height - 1);
        int xMin = (int)MAX(ceilf(box.xMin), 0);
        int xMax = (int)MIN(ceilf(box.xMax) - 1, buffer.width - 1);


        // Constants for this triangle used for barycentric calculations
        Vector v01 = p1 - p0;
        Vector v02 = p2 - p0;
        float dot0101 = VectorDot(v01, v01);
        float dot0102 = VectorDot(v01, v02);
        float dot0202 = VectorDot(v02, v02);


        // Iterate over the bounding box and determine if each point is in the triangle
        for (int y = yMin; y <= yMax; ++y)
        {
            for (int x = xMin; x <= xMax; ++x)
            {
                // Calculate the barycentric coordinate of this point
                Point p(x, y, 1.0f);
                Vector v0P = p - p0;
                float dot0P01 = VectorDot(v0P, v01);
                float dot0P02 = VectorDot(v0P, v02);
                float denomInv = 1.0f / ((dot0101 * dot0202) - (dot0102 * dot0102));
                float barycenter[3];
                barycenter[1] = (dot0202 * dot0P01 - dot0102 * dot0P02) * denomInv;
                barycenter[2] = (dot0101 * dot0P02 - dot0102 * dot0P01) * denomInv;
                barycenter[0] = 1.0f - barycenter[1] - barycenter[2];


                // Point is inside the triangle
                if ( (barycenter[0] >= 0.0f)
                        && (barycenter[1] >= 0.0f)
                        && (barycenter[2] >= 0.0f))
                {
                    // Interpolate 1/z for the z-buffer
                    float zInv =
                        1.0f /
                        ((barycenter[0] * p0.w)
                         + (barycenter[1] * p1.w)
                         + (barycenter[2] * p2.w));


                    // Compute pixel color if it's closer than what's in the z-buffer
                    if (zInv > memory.zbuffer[y][x])
                    {
                        // Update the depth buffer
                        memory.zbuffer[y][x] = zInv;


                        // Interpolate U and V of the texture for this point
                        Texture &texture = textures.data[faces.data[f].materialIndex];
                        UV &uv0 = uvs.data[face.uvIndex[0]];
                        UV &uv1 = uvs.data[face.uvIndex[1]];
                        UV &uv2 = uvs.data[face.uvIndex[2]];

                        float a = barycenter[0] * p1.w * p2.w;
                        float b = barycenter[1] * p0.w * p2.w;
                        float c = barycenter[2] * p0.w * p1.w;
                        float abc = 1.0f / (a + b + c);

                        float uInterp =
                            ((a * uv0.u) + (b * uv1.u) + (c * uv2.u))
                            * abc
                            * texture.width;

                        float vInterp =
                            ((a * uv0.v) + (b * uv1.v) + (c * uv2.v))
                            * abc
                            * texture.height;


                        // Bilinear filtering
                        unsigned int u = (unsigned int)uInterp;
                        unsigned int v = (unsigned int)vInterp;
                        float du = uInterp - u;
                        float dv = vInterp - v;
                        float duDiff = 1 - du;
                        float dvDiff = 1 - dv;

                        ColorU32 color =
                        {
                            (uint8_t)
                                (duDiff * dvDiff * texture.texels[v][u].b
                                 + du * dvDiff * texture.texels[v][u+1].b
                                 + du * dv * texture.texels[v+1][u+1].b
                                 + duDiff * dv * texture.texels[v+1][u].b),

                            (uint8_t)
                                (duDiff * dvDiff * texture.texels[v][u].g
                                 + du * dvDiff * texture.texels[v][u+1].g
                                 + du * dv * texture.texels[v+1][u+1].g
                                 + duDiff * dv * texture.texels[v+1][u].g),

                            (uint8_t)
                                (duDiff * dvDiff * texture.texels[v][u].r
                                 + du * dvDiff * texture.texels[v][u+1].r
                                 + du * dv * texture.texels[v+1][u+1].r
                                 + duDiff * dv * texture.texels[v+1][u].r),

                            (uint8_t)
                                (duDiff * dvDiff * texture.texels[v][u].a
                                 + du * dvDiff * texture.texels[v][u+1].a
                                 + du * dv * texture.texels[v+1][u+1].a
                                 + duDiff * dv * texture.texels[v+1][u].a)
                        };


                        // Perform Gouraud shading on the texture
                        ColorF32 &c0 = verts.data[face.vertIndex[0]].color;
                        ColorF32 &c1 = verts.data[face.vertIndex[1]].color;
                        ColorF32 &c2 = verts.data[face.vertIndex[2]].color;

                        ColorF32 shading =
                            (barycenter[0] * c0)
                            + (barycenter[1] * c1)
                            + (barycenter[2] * c2);


                        // Ensure no color channel exceeds max
                        ScaleColor(shading);


                        // Light the texture
                        color.b *= shading.b;
                        color.g *= shading.g;
                        color.r *= shading.r;


                        // Alpha blend the pixel
                        ColorU32 *pixel = (ColorU32*)&buffer.buffer[y*buffer.width+x];
                        float alpha = color.a / 255.0f;
                        float alphaDiff = 1.0f - alpha;

                        ColorU32 blended =
                        {
                            (uint8_t)((alpha * color.b) + (alphaDiff * pixel->b)),
                            (uint8_t)((alpha * color.g) + (alphaDiff * pixel->g)),
                            (uint8_t)((alpha * color.r) + (alphaDiff * pixel->r)),
                            (uint8_t)((alpha * color.a) + (alphaDiff * pixel->a))
                        };


                        // Draw
                        DrawPixel(buffer.buffer, buffer.width, blended.u32, x, y);
                    }
                }
            }
        }
    }
}