import derelict.sdl2.sdl;
import std.stdio;
import std.array;
import std.traits;
import std.math;
import std.datetime;

struct vec2 {
    float x, y;

    vec2 opBinary(string op, T)(T rhs) {
        static if(op == "+" || op == "-" || op == "*" || op == "/") {
            static if(is(T == vec2)) {
                mixin("return vec2(x $ rhs.x, y $ rhs.y);".replace("$", op));
            } else static if(isNumeric!T) {
                mixin("return vec2(x $ rhs, y $ rhs);".replace("$", op));
            } else {
                static assert(0, "Invalid use of operator: vec2 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
            }
        }
    }

    void opOpAssign(string op, T)(T rhs) {
        static if(op == "+" || op == "-" || op == "*" || op == "/") {
            static if(is(T == vec2)) {
                mixin("x $= rhs.x; y $= rhs.y;".replace("$", op));
            } else static if(isNumeric!T) {
                mixin("x $= rhs; y $= rhs;".replace("$", op));
            } else {
                static assert(0, "Invalid use of operator: vec2 " ~ op ~ "= " ~ fullyQualifiedName!T ~ ".");
            }
        }
    }
}

struct vec3 {
    float x, y, z;

    vec3 opBinary(string op, T)(T rhs) {
        static if(op == "+" || op == "-" || op == "*" || op == "/") {
            static if(is(T == vec3)) {
                mixin("return vec3(x $ rhs.x, y $ rhs.y, z $ rhs.z);".replace("$", op));
            } else static if(isNumeric!T) {
                mixin("return vec3(x $ rhs, y $ rhs, z $ rhs);".replace("$", op));
            } else {
                static assert(0, "Invalid use of operator: vec3 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
            }
        }
    }

    void opOpAssign(string op, T)(T rhs) {
        static if(op == "+" || op == "-" || op == "*" || op == "/") {
            static if(is(T == vec3)) {
                mixin("x $= rhs.x; y $= rhs.y; z $= rhs.z;".replace("$", op));
            } else static if(isNumeric!T) {
                mixin("x $= rhs; y $= rhs; z $= rhs;".replace("$", op));
            } else {
                static assert(0, "Invalid use of operator: vec3 " ~ op ~ "= " ~ fullyQualifiedName!T ~ ".");
            }
        }
    }
}

struct mat2 {
    float
        m0, m1,
        m2, m3;

    auto opBinary(string op, T)(T rhs) {
        static if(is(T == vec2)) {
            static if(op == "*") {
                return vec2(
                    m0 * rhs.x + m1 * rhs.y,
                    m2 * rhs.x + m3 * rhs.y);
            } else {
                static assert(0, "Invalid use of operator: mat2 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
            }
        } else {
            static assert(0, "Invalid use of operator: mat2 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
        }
    }
}

mat2 getRotMat2(float a) {
    return mat2(cos(a), -sin(a), sin(a), cos(a));
}

struct mat3 {
    float
        m0, m1, m2,
        m3, m4, m5,
        m6, m7, m8;

    auto opBinary(string op, T)(T rhs) {
        static if(is(T == vec3)) {
            static if(op == "*") {
                return vec3(
                    m0 * rhs.x + m1 * rhs.y + m2 * rhs.z,
                    m3 * rhs.x + m4 * rhs.y + m5 * rhs.z,
                    m6 * rhs.x + m7 * rhs.y + m8 * rhs.z);
            } else {
                static assert(0, "Invalid use of operator: mat2 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
            }
        } else {
            static assert(0, "Invalid use of operator: mat2 " ~ op ~ " " ~ fullyQualifiedName!T ~ ".");
        }
    }
}

mat3 getRotMat3X(float a) {
    return mat3(1,          0,          0,
                0,          cos(a),     -sin(a),
                0,          sin(a),     cos(a));
}

mat3 getRotMat3Y(float a) {
    return mat3(cos(a),     0,          sin(a),
                0,          1,          0,
                -sin(a),    0,          cos(a));
}

mat3 getRotMat3Z(float a) {
    return mat3(cos(a),     -sin(a),    0,
                sin(a),     cos(a),     0,
                0,          0,          1);
}

float length(vec2 v) {
    return sqrt(v.x ^^ 2 + v.y ^^ 2);
}

float length(vec3 v) {
    return sqrt(v.x ^^ 2 + v.y ^^ 2 + v.z ^^ 2);
}

vec2 normalize(vec2 v) {
    float len = length(v);
    return vec2(v.x/len, v.y/len);
}

vec3 normalize(vec3 v) {
    float len = length(v);
    return vec3(v.x/len, v.y/len, v.z/len);
}

struct HitInfo {
    float dist;
    vec3 color;
}

const vec3 circleColor = vec3(1., 0.5, 0.);
const float circleRad = 0.5;
const uint PIXEL_SIZE = 8;
const float EPSILON = 0.001;
const float MAX_DIST = 50;

HitInfo sphere(vec3 r, float rad) {
    return HitInfo(length(r) - rad, vec3(0, 1, 0));
}

HitInfo box(vec3 r, vec3 s) {
    return HitInfo(fmax(fmax(abs(r.x) - s.x, abs(r.y) - s.y), abs(r.z) - s.z), vec3(1, 0, 0));
}

HitInfo map(vec3 r) {
    auto h1 = sphere(r, 1);
    auto h2 = box(r, vec3(0.8, 0.8, 0.8));
    float d;
    if(h1.dist < h2.dist) {
        return h1;
    }
    return h2;
}

void main() {
    DerelictSDL2.load();
    SDL_Window* window = SDL_CreateWindow("SDL2/OpenGL Demo", 200, 200, PIXEL_SIZE*128, PIXEL_SIZE*72, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
    SDL_Surface* surface = SDL_GetWindowSurface(window);
    SDL_GLContext glcontext = SDL_GL_CreateContext(window);

    SDL_Event event;
    auto quit = false;

    auto start = Clock.currTime;
    uint frames = 0;

    while (!quit) {
        auto time = (cast(float)(Clock.currTime - start).total!"nsecs")/1000000000;
        while(SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                writefln("%s", frames/time);
                quit = true;
            }
        }

        auto res = vec2(surface.w/PIXEL_SIZE, surface.h/PIXEL_SIZE);
        for(auto x = 0; x < surface.w/PIXEL_SIZE; x++) {
            for(auto y = 0; y < surface.h/PIXEL_SIZE; y++) {
                auto coord = vec2(x, y);
                auto color = pixel(coord, res, time);
                ubyte r = cast(ubyte)(color.x * 255);
                ubyte g = cast(ubyte)(color.y * 255);
                ubyte b = cast(ubyte)(color.z * 255);
                SDL_Rect rect = SDL_Rect(x * PIXEL_SIZE, y * PIXEL_SIZE, PIXEL_SIZE, PIXEL_SIZE);
                SDL_FillRect(surface, &rect, r << 16 | g << 8 | b);
            }
        }
        frames++;
        SDL_UpdateWindowSurface(window);
    }
}

vec3 pixel(vec2 coord, vec2 res, float time) {
    vec2 uv = coord / res;
    uv.x *= res.x/res.y;
    uv.x -= res.x/res.y/2;
    uv.y -= 0.5;
    uv *= 2;

    // Rotation
    vec3 ro = vec3(0, 0, -2);
    ro = getRotMat3Y(time) * ro;
    ro = getRotMat3Z(time) * ro;
    ro = getRotMat3X(time) * ro;

    vec3 rd = normalize(vec3(uv.x, uv.y, 1));
    rd = getRotMat3Y(time) * rd;
    rd = getRotMat3Z(time) * rd;
    rd = getRotMat3X(time) * rd;

    // Raymarching
    float l = 0;
    for(uint i = 0; i < 100; i++) {
        vec3 r = ro + rd * l;
        auto hit = map(r);

        if(hit.dist <= EPSILON) {
            return hit.color;
        }

        if(l > MAX_DIST) {
            return vec3(0, 0, 0);
        }

        l = l + hit.dist;
    }

    return vec3(0, 0, 0);
}