import std::concat_strings;
import std::print;
import std::from_str;
import std::free_string;
import std::add_num_to_str;

///////////////////
/// SDL externs ///
///////////////////

// Helper struct for stack allocated const sized strings, because structs are
// easier to create uninit than arrays.
struct SDL_Window {}
struct SDL_Renderer {}
struct SDL_Texture {}
struct SDL_Event { type: u32, reserved: [u8; 124] }
struct SDL_FRect { x: f32, y: f32, w: f32, h: f32 }
struct SDL_Rect { x: i32, y: i32, w: i32, h: i32 }
extern fn SDL_malloc(size: u64) -> *u8;
extern fn SDL_Init(flags: u32) -> bool;
extern fn SDL_Quit();
extern fn SDL_CreateWindowAndRenderer(title: *char, width: i32, height: i32, flags: i32,
    window_out: &mut *SDL_Window, renderer_out: &mut *SDL_Renderer) -> bool;
extern fn SDL_Delay(ms: u32);
extern fn SDL_SetRenderDrawColor(renderer: *SDL_Renderer, r: u8, g: u8, b: u8, a: u8);
extern fn SDL_RenderClear(renderer: *SDL_Renderer);
extern fn SDL_RenderPresent(renderer: *SDL_Renderer);
extern fn SDL_HasEvent(event_type: u32) -> bool;
extern fn SDL_PollEvent(event: &mut SDL_Event) -> bool;
extern fn SDL_PumpEvents();
extern fn SDL_FlushEvents(min_type: u32, max_type: u32);
extern fn SDL_GetTicks() -> u64;
extern fn SDL_SetWindowTitle(window: *SDL_Window, title: *char) -> bool;
extern fn SDL_CreateTexture(renderer: *SDL_Renderer, 
    pixel_format: u32, texture_access: u32, width: u32, height: u32) -> *SDL_Texture;
extern fn SDL_RenderTexture(renderer: *SDL_Renderer,
    texture: *SDL_Texture, srcfrect: &SDL_FRect, dstfrect: &SDL_FRect) -> bool;
extern fn SDL_UpdateTexture(texture: *SDL_Texture, rect: &SDL_Rect, pixels: *u8, pitch: u32) -> bool;
extern fn SDL_GetError() -> *char;
extern fn SDL_GetWindowSize(window: *SDL_Window, w: &mut i32, h: &mut i32) -> bool;
extern fn SDL_rand(max_exclusive: u32) -> u32;
extern fn SDL_SetTextureScaleMode(texture: *SDL_Texture, scale_mode: i32) -> bool;
extern fn SDL_sqrtf(value: f32) -> f32;
extern fn SDL_randf() -> f32;
extern fn SDL_powf(value: f32, power: f32) -> f32;

// SDL error reporting helper
fn print_sdl_error(context: *char) {
    let mut message = from_str(context);

    let delim = from_str(": ");
    concat_strings(&mut message, delim);
    free_string(&delim);

    let error_msg = from_str(SDL_GetError());
    concat_strings(&mut message, error_msg);
    free_string(&error_msg);

    print(message);

    free_string(&message);
}

/////////////////////////////////
/// Main setup and frame loop ///
/////////////////////////////////

struct GameState {
    renderer: *SDL_Renderer,
    window: *SDL_Window,
    render_texture: *SDL_Texture,
    frame_counter: u32,
    last_fps_reset: u64,
    pixels: *u8,
    pixels_w: u32,
    pixels_h: u32,
    pixels_bpp: u32,
}

fn main() -> i32 {
    let SDL_INIT_VIDEO = 32;
    let SDL_WINDOW_RESIZABLE = 32;
    let SDL_PIXELFORMAT_RGBA8888 = 373694468;
    let SDL_PIXELFORMAT_ABGR8888 = 376840196;
    let SDL_PIXELFORMAT_RGB24 = 386930691;
    let SDL_PIXELFORMAT_BGR24 = 390076419;
    let SDL_PIXELFORMAT_RGB96_FLOAT = 454057996;
    let SDL_PIXELFORMAT_BGR96_FLOAT = 457203724;
    let SDL_TEXTUREACCESS_STREAMING = 1;
    let SDL_SCALEMODE_NEAREST = 0;
    let SDL_SCALEMODE_LINEAR = 1;
    let SDL_SCALEMODE_PIXELART = 2;

    let init_success = SDL_Init(SDL_INIT_VIDEO);
    if init_success == false {
        print_sdl_error("SDL init failed");
        return 1;
    }

    let mut window = SDL_malloc(1) as *SDL_Window;
    let mut renderer = SDL_malloc(1) as *SDL_Renderer;
    let gfx_init_success = SDL_CreateWindowAndRenderer(
        "graphical reid program", 640, 480, SDL_WINDOW_RESIZABLE,
        &mut window, &mut renderer
    );
    if gfx_init_success == false {
        print_sdl_error("SDL renderer and window creation failed");
        return 1;
    }

    let width = 320;
    let height = 240;
    let bpp = 4;
    let render_texture = SDL_CreateTexture(renderer, 
        SDL_PIXELFORMAT_ABGR8888, SDL_TEXTUREACCESS_STREAMING, width, height);
    SDL_SetTextureScaleMode(render_texture, SDL_SCALEMODE_NEAREST);

    let pixels_len = (width * height * bpp) as u64;
    let pixels = SDL_malloc(pixels_len);
    let mut game_state = GameState {
        renderer: renderer,
        window: window,
        render_texture: render_texture,
        frame_counter: 0,
        last_fps_reset: 0,
        pixels: pixels,
        pixels_w: width,
        pixels_h: height,
        pixels_bpp: bpp,
    };

    while frame_loop(&mut game_state) {}

    SDL_Quit();
    return 0;
}

fn frame_loop(game_state: &mut GameState) -> bool {
    let mut event = SDL_Event {};
    while (SDL_PollEvent(&mut event)) {
        if event.type == 256 { // SDL_EVENT_QUIT
            return false;
        }
    }

    let mut screen_width = 0;
    let mut screen_height = 0;
    SDL_GetWindowSize(*game_state.window, &mut screen_width, &mut screen_height);

    let renderer = *game_state.renderer;
    SDL_SetRenderDrawColor(renderer, 0, 50, 90, 255);
    SDL_RenderClear(renderer);

    let w = *game_state.pixels_w;
    let h = *game_state.pixels_h;
    let bpp = *game_state.pixels_bpp;
    for y in 0..h {
        for x in 0..w {
            render_pixel(x, y, game_state);
        }
    }

    let texture_area = SDL_Rect { x: 0, y: 0, w: w as i32, h: h as i32 };
    if SDL_UpdateTexture(*game_state.render_texture, &texture_area, *game_state.pixels as *u8, bpp * w) == false {
        print_sdl_error("UpdateTexture error");
    }
    let src = SDL_FRect { x: 0.0, y: 0.0, w: w as f32, h: h as f32 };
    let aspect_ratio = src.w / src.h;
    let scaled_width = screen_height as f32 * aspect_ratio;
    let dst = SDL_FRect { x: (screen_width as f32 - scaled_width) / 2.0, y: 0.0, w: scaled_width, h: screen_height as f32 };
    if SDL_RenderTexture(renderer, *game_state.render_texture, &src, &dst) == false {
        print_sdl_error("RenderTexture error");
    }

    SDL_RenderPresent(renderer);
    SDL_Delay(1);

    *game_state.frame_counter = *game_state.frame_counter + 1;
    let t = SDL_GetTicks();
    if (t - *game_state.last_fps_reset) >= 1000 {
        let mut title = from_str("graphical reid program ");
        add_num_to_str(&mut title, *game_state.frame_counter as u64);
        let fps_unit = from_str(" fps");
        concat_strings(&mut title, fps_unit);
        free_string(&fps_unit);
        SDL_SetWindowTitle(*game_state.window, title.inner);
        free_string(&title);
        *game_state.frame_counter = 0;
        *game_state.last_fps_reset = t;
    }

    return true;
}

fn render_pixel(x: u32, y: u32, game_state: &mut GameState) {
    let w = *game_state.pixels_w;
    let h = *game_state.pixels_h;
    let bpp = *game_state.pixels_bpp;

    let samples = 1;
    let old_sample_weight = 0.75;
    let new_sample_weight = 0.25 / samples as f32;
    let mut rgb = vec_mul_scalar(old_sample_weight, [
        srgb_to_linear(*game_state.pixels[(x + y * w) * bpp + 0]),
        srgb_to_linear(*game_state.pixels[(x + y * w) * bpp + 1]),
        srgb_to_linear(*game_state.pixels[(x + y * w) * bpp + 2])
    ]);
    for sample in 0..samples {
        rgb = vec_add(rgb, vec_mul_scalar(new_sample_weight, shade(x, y, *game_state.frame_counter, w, h)));
    }
    *game_state.pixels[(x + y * w) * bpp + 0] = linear_to_srgb(rgb[0]);
    *game_state.pixels[(x + y * w) * bpp + 1] = linear_to_srgb(rgb[1]);
    *game_state.pixels[(x + y * w) * bpp + 2] = linear_to_srgb(rgb[2]);
    *game_state.pixels[(x + y * w) * bpp + 3] = 255;
}


/////////////////
/// Rendering ///
/////////////////

struct Ray {
    origin: [f32; 3],
    direction: [f32; 3],
}

struct Material {
    // 0 = lambertian diffuse
    // 1 = mirror
    type: u32,
    // Generally the "color" of the surface (linear factors of how much of each
    // color channel this surface does not absorb), but the idea is that the
    // type governs what this means.
    linear_color: [f32; 3],
}

struct Hit {
    hit: bool,
    front_face: bool,
    distance: f32,
    normal: [f32; 3],
    position: [f32; 3],
    material: Material,
}

struct Sphere {
    center: [f32; 3],
    radius: f32,
    material: Material,
}

fn shade(x: u32, y: u32, t: u32, w: u32, h: u32) -> [f32; 3] {
    let jitter_x = SDL_randf() - 0.5;
    let jitter_y = SDL_randf() - 0.5;

    let pixel_scale = 1.0 / h as f32;
    let pixel_pos = [
        (x as f32 + jitter_x) * pixel_scale, 
        1.0 - (y as f32 + jitter_y) * pixel_scale,
        0.0 - 1.0
    ];
    let camera_pos = [w as f32 * 0.5f32 * pixel_scale, h as f32 * 0.5f32 * pixel_scale, 0.0f32];
    let dir = vec_normalize(vec_sub(pixel_pos, camera_pos));
    let ray = Ray { origin: camera_pos, direction: dir };
    let beige_lambertian = Material { type: 0, linear_color: [0.3, 0.2, 0.1] };
    let green_lambertian = Material { type: 0, linear_color: [0.1, 0.5, 0.06] };
    let greenish_mirror = Material { type: 1, linear_color: [0.9, 1.0, 0.95] };
    let spheres = [
        // Ground
        Sphere { center: vec_sub(camera_pos, [0.0, 100001.0, 0.0]), radius: 100000.0, material: beige_lambertian },
        // Centered unit sphere
        Sphere { center: vec_add(camera_pos, [0.0, 0.0, 0.0 - 5.0]), radius: 1.0, material: green_lambertian },
        // The unit sphere on the right
        Sphere { center: vec_add(camera_pos, [2.0, 0.0, 0.0 - 6.0]), radius: 1.0, material: greenish_mirror }
    ];
    return shade_world(ray, &spheres, 3);
}

fn shade_world(ray: Ray, spheres: &[Sphere; 3], bounces_left: u8) -> [f32; 3] {
    if bounces_left == 0 {
        return [0.0, 0.0, 0.0];
    }

    let ray_distance = 100.0;
    let mut closest_hit = Hit { hit: false, front_face: false, distance: ray_distance };
    for i in 0..3 {
        let sphere_hit = ray_sphere_closest_hit(ray, *spheres[i], [0.001, closest_hit.distance]);
        if sphere_hit.hit {
            closest_hit = sphere_hit;
        }
    }

    if closest_hit.hit {
        //return vec_mul_scalar(0.5, vec_add(closest_hit.normal, [1.0, 1.0, 1.0])); // normal
        //return vec_mul_scalar(closest_hit.distance / 10.0, [1.0, 1.0, 1.0]); // depth
        if closest_hit.material.type == 0 {
            let bounce_dir = vec_normalize(vec_add(closest_hit.normal, random_unit_vec()));
            let bounce_ray = Ray { origin: closest_hit.position, direction: bounce_dir };
            return vec_mul_componentwise(
                closest_hit.material.linear_color, 
                shade_world(bounce_ray, spheres, bounces_left - 1)
            );
        } else if closest_hit.material.type == 1 {
            let bounce_dir = vec_reflect(ray.direction, closest_hit.normal);
            let bounce_ray = Ray { origin: closest_hit.position, direction: bounce_dir };
            return vec_mul_componentwise(
                closest_hit.material.linear_color, 
                shade_world(bounce_ray, spheres, bounces_left - 1)
            );
        } else {
            return [1.0, 0.0, 1.0];
        }
    }

    return shade_sky(ray);
}

fn shade_sky(ray: Ray) -> [f32; 3] {
    let a = 0.5 * (ray.direction[1] + 1.0);
    return vec_add(
        vec_mul_scalar(1.0 - a, [1.0, 1.0, 1.0]),
        vec_mul_scalar(a, [0.5, 0.7, 1.0])
    );
}

// Returns the distance from the ray origin to the sphere, or -1.0 if the ray doesn't hit.
fn ray_sphere_closest_hit(ray: Ray, sphere: Sphere, interval: [f32; 2]) -> Hit {
    let to_sphere = vec_sub(sphere.center, ray.origin);
    let h = vec_dot(ray.direction, to_sphere);
    let c = vec_length_squared(to_sphere) - sphere.radius * sphere.radius;
    let discriminant = h * h - c;
    if discriminant < 0.0 {
        return Hit { hit: false };
    }

    let discriminant_sqrt = SDL_sqrtf(discriminant);
    let mut distance = h - discriminant_sqrt;
    if interval_surrounds(interval, distance) == false {
        distance = h - discriminant_sqrt;
        if interval_surrounds(interval, distance) == false {
            return Hit { hit: false };
        }
    }
    let hit_position = vec_add(ray.origin, vec_mul_scalar(distance, ray.direction));
    let mut front_face = true;
    let mut normal = vec_normalize(vec_sub(hit_position, sphere.center));
    if vec_dot(normal, ray.direction) > 0.0 {
        normal = vec_mul_scalar(0.0 - 1.0, normal);
        front_face = false;
    }

    return Hit {
        hit: true, 
        front_face: front_face,
        distance: distance,
        normal: normal,
        position: hit_position,
        material: sphere.material,
    };
}


//////////////////
/// Other math ///
//////////////////

fn clamp(min: f32, max: f32, value: f32) -> f32 {
    if value > max {
        return max;
    }
    if value < min {
        return min;
    }
    return value;
}

fn abs(f: f32) -> f32 {
    if f < 0.0 {
        return f * (0.0 - 1.0);
    }
    return f;
}

fn vec_add(lhs: [f32; 3], rhs: [f32; 3]) -> [f32; 3] {
    return [lhs[0] + rhs[0], lhs[1] + rhs[1], lhs[2] + rhs[2]];
}

fn vec_sub(lhs: [f32; 3], rhs: [f32; 3]) -> [f32; 3] {
    return [lhs[0] - rhs[0], lhs[1] - rhs[1], lhs[2] - rhs[2]];
}

fn vec_dot(lhs: [f32; 3], rhs: [f32; 3]) -> f32 {
    return lhs[0] * rhs[0] + lhs[1] * rhs[1] + lhs[2] * rhs[2];
}

fn vec_mul_componentwise(lhs: [f32; 3], rhs: [f32; 3]) -> [f32; 3] {
    return [lhs[0] * rhs[0], lhs[1] * rhs[1], lhs[2] * rhs[2]];
}

fn vec_mul_scalar(lhs: f32, rhs: [f32; 3]) -> [f32; 3] {
    return [lhs * rhs[0], lhs * rhs[1], lhs * rhs[2]];
}

fn vec_normalize(v: [f32; 3]) -> [f32; 3] {
    let len_reciprocal = 1.0f32 / SDL_sqrtf(vec_length_squared(v));
    return vec_mul_scalar(len_reciprocal, v);
}

fn vec_length_squared(v: [f32; 3]) -> f32 {
    return v[0] * v[0] + v[1] * v[1] + v[2] * v[2];
}

fn vec_abs(v: [f32; 3]) -> [f32; 3] {
    return [abs(v[0]), abs(v[1]), abs(v[2])];
}

fn vec_reflect(direction: [f32; 3], normal: [f32; 3]) -> [f32; 3] {
    return vec_sub(direction, vec_mul_scalar(2.0f32 * vec_dot(direction, normal), normal));
}

fn interval_surrounds(interval: [f32; 2], value: f32) -> bool {
    return (interval[0] < value) && (value < interval[1]);
}

fn random_unit_vec() -> [f32; 3] {
    let mut point = [
        SDL_randf() * 2.0f32 - 1.0f32,
        SDL_randf() * 2.0f32 - 1.0f32,
        SDL_randf() * 2.0f32 - 1.0f32
    ];
    let mut lensq = vec_length_squared(point);
    while lensq > 1.0 {
        point = [
            SDL_randf() * 2.0f32 - 1.0f32,
            SDL_randf() * 2.0f32 - 1.0f32,
            SDL_randf() * 2.0f32 - 1.0f32
        ];
        lensq = vec_length_squared(point);
    }
    let len_reciprocal = 1.0f32 / SDL_sqrtf(lensq);
    return vec_mul_scalar(len_reciprocal, point);
}

fn random_unit_vec_on_hemi(normal: [f32; 3]) -> [f32; 3] {
    let rand_vec = random_unit_vec();
    if vec_dot(rand_vec, normal) < 0.0f32 {
        return vec_mul_scalar(0.0f32 - 1.0f32, rand_vec);
    }
    return rand_vec;
}

fn linear_to_srgb(linear: f32) -> u8 {
    let mut floating_srgb = 0.0;
    if linear <= 0.0031308f32 {
        floating_srgb = 12.92f32 * linear;
    } else {
        floating_srgb = SDL_powf(linear as f32, 1.0 / 2.4) * 1.055f32 - 0.055f32;
    }
    let clamped = clamp(0.0, 1.0, floating_srgb);
    return (clamped * 255.999) as u8;
}

fn srgb_to_linear(srgb: u8) -> f32 {
    let floating_srgb = srgb as f32 / 255.0;
    if floating_srgb <= 0.04045f32 {
        return floating_srgb / 12.92f32;
    }
    return SDL_powf((floating_srgb as f32 + 0.055) / 1.055, 2.4);
}