const std = @import("std");
const sdl = @import("sdl");
const GameError = @import("game.zig").GameError;

window: *sdl.Window,
renderer: *sdl.Renderer,
device: *sdl.GPUDevice,
/// Only available while drawing
command_buffer: ?*sdl.GPUCommandBuffer,

shader_vert: *sdl.GPUShader,
shader_frag: *sdl.GPUShader,

vertex_buffer: *sdl.GPUBuffer,
depth_texture: *sdl.GPUTexture,
msaa_resolve: *sdl.GPUTexture,
pipeline: *sdl.GPUGraphicsPipeline,

to_resize: ?struct { u32, u32 } = null,

const Self = @This();
pub fn create() GameError!Self {
    // Init
    if (!sdl.Init(sdl.INIT_VIDEO | sdl.INIT_EVENTS)) return GameError.SdlError;

    // Window and Renderer
    var renderer: ?*sdl.Renderer = null;
    var window: ?*sdl.Window = null;

    if (!sdl.CreateWindowAndRenderer(
        "Spacefarer",
        1600,
        900,
        sdl.WINDOW_VULKAN | sdl.WINDOW_RESIZABLE,
        &window,
        &renderer,
    )) return GameError.SdlError;
    errdefer sdl.DestroyRenderer(renderer);
    errdefer sdl.DestroyWindow(window);

    if (!sdl.SetRenderVSync(renderer, sdl.RENDERER_VSYNC_ADAPTIVE)) return GameError.SdlError;

    // Device
    const device = sdl.CreateGPUDevice(
        sdl.GPU_SHADERFORMAT_SPIRV,
        @import("builtin").mode == .Debug,
        null,
    ) orelse return GameError.SdlError;
    errdefer sdl.DestroyGPUDevice(device);

    // Claim
    if (!sdl.ClaimWindowForGPUDevice(device, window)) return GameError.SdlError;
    errdefer sdl.ReleaseWindowFromGPUDevice(device, window);

    const shader_vert = try load_shader(
        device,
        "data/shaders/basic.vert",
        sdl.GPU_SHADERSTAGE_VERTEX,
    );
    errdefer sdl.ReleaseGPUShader(device, shader_vert);

    const shader_frag = try load_shader(
        device,
        "data/shaders/basic.frag",
        sdl.GPU_SHADERSTAGE_FRAGMENT,
    );
    errdefer sdl.ReleaseGPUShader(device, shader_frag);

    const vertex_buffer = sdl.CreateGPUBuffer(device, &.{
        .usage = sdl.GPU_BUFFERUSAGE_VERTEX,
        // 6 Vertices * 3 Coordinates * 4 Bytes
        .size = 6 * 3 * 4,
    }) orelse return GameError.SdlError;
    errdefer sdl.ReleaseGPUBuffer(device, vertex_buffer);

    const transfer_buffer = sdl.CreateGPUTransferBuffer(device, &.{
        .size = 6 * 3 * 4,
        .usage = sdl.GPU_TRANSFERBUFFERUSAGE_UPLOAD,
    }) orelse return GameError.SdlError;
    defer sdl.ReleaseGPUTransferBuffer(device, transfer_buffer);

    { // Filling up transfer buffer
        const mapped_buffer: [*c]f32 = @alignCast(@ptrCast(sdl.MapGPUTransferBuffer(device, transfer_buffer, false) orelse return GameError.SdlError));
        defer sdl.UnmapGPUTransferBuffer(device, transfer_buffer);
        std.mem.copyForwards(f32, mapped_buffer[0 .. 6 * 3], &[6 * 3]f32{
            // Triangle 1
            -1.0, 0.0,  0.0,
            0.0,  1.0,  0.0,
            1.0,  -1.0, 1.0,
            // Triangle 2
            1.0,  0.0,  0.0,
            0.0,  -1.0, 0.0,
            -1.0, 1.0,  1.0,
        });
    }

    { // Copying data over from transfer buffer to vertex buffer
        const command_buffer = sdl.AcquireGPUCommandBuffer(device) orelse return GameError.SdlError;
        const copy_pass = sdl.BeginGPUCopyPass(command_buffer) orelse return GameError.SdlError;

        sdl.UploadToGPUBuffer(copy_pass, &.{ .transfer_buffer = transfer_buffer }, &.{
            .size = 6 * 3 * 4,
            .buffer = vertex_buffer,
        }, false);

        sdl.EndGPUCopyPass(copy_pass);
        if (!sdl.SubmitGPUCommandBuffer(command_buffer)) return GameError.SdlError;
    }

    const target_format = sdl.GetGPUSwapchainTextureFormat(device, window);
    if (target_format == sdl.GPU_TEXTUREFORMAT_INVALID) return GameError.SdlError;

    // TODO: Clean
    var window_width: c_int = 1;
    var window_height: c_int = 1;
    if (!sdl.GetWindowSizeInPixels(window, &window_width, &window_height)) return GameError.SdlError;

    const depth_texture = try create_depth_texture(device, @intCast(window_width), @intCast(window_height));
    errdefer sdl.ReleaseGPUTexture(device, depth_texture);

    const msaa_resolve = try create_texture(device, @intCast(window_width), @intCast(window_height), target_format);
    errdefer sdl.ReleaseGPUTexture(device, msaa_resolve);

    const pipeline = sdl.CreateGPUGraphicsPipeline(device, &.{
        .vertex_shader = shader_vert,
        .fragment_shader = shader_frag,
        .vertex_input_state = .{
            .vertex_buffer_descriptions = &.{
                .slot = 0,
                // 3 Coordinates * 4 Bytes
                .pitch = 3 * 4,
                .input_rate = sdl.GPU_VERTEXINPUTRATE_VERTEX,
            },
            .num_vertex_buffers = 1,
            .vertex_attributes = &sdl.GPUVertexAttribute{
                .offset = 0,
                .location = 0,
                .format = sdl.GPU_VERTEXELEMENTFORMAT_FLOAT3,
                .buffer_slot = 0,
            },
            .num_vertex_attributes = 1,
        },
        .primitive_type = sdl.GPU_PRIMITIVETYPE_TRIANGLELIST,
        .rasterizer_state = .{
            .cull_mode = sdl.GPU_CULLMODE_BACK,
            .fill_mode = sdl.GPU_FILLMODE_FILL,
            .front_face = sdl.GPU_FRONTFACE_CLOCKWISE,
        },
        .multisample_state = .{
            .sample_count = sdl.GPU_SAMPLECOUNT_4,
        },
        .depth_stencil_state = .{
            .compare_op = sdl.GPU_COMPAREOP_LESS,
            .enable_depth_test = true,
            .enable_depth_write = true,
        },
        .target_info = .{
            .depth_stencil_format = sdl.GPU_TEXTUREFORMAT_D16_UNORM,
            .color_target_descriptions = &sdl.GPUColorTargetDescription{
                .format = target_format,
                .blend_state = .{
                    .enable_blend = true,
                    .alpha_blend_op = sdl.GPU_BLENDOP_ADD,
                    .color_blend_op = sdl.GPU_BLENDOP_ADD,
                    .color_write_mask = sdl.GPU_COLORCOMPONENT_R | sdl.GPU_COLORCOMPONENT_G | sdl.GPU_COLORCOMPONENT_B | sdl.GPU_COLORCOMPONENT_A,
                    .src_alpha_blendfactor = sdl.GPU_BLENDFACTOR_ONE,
                    .src_color_blendfactor = sdl.GPU_BLENDFACTOR_SRC_ALPHA,
                    .dst_alpha_blendfactor = sdl.GPU_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
                    .dst_color_blendfactor = sdl.GPU_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
                },
            },
            .num_color_targets = 1,
            .has_depth_stencil_target = true,
        },
    }) orelse return GameError.SdlError;
    errdefer sdl.ReleaseGPUGraphicsPipeline(pipeline);

    return .{
        .window = window.?,
        .renderer = renderer.?,
        .device = device,
        .command_buffer = null,
        .shader_vert = shader_vert,
        .shader_frag = shader_frag,
        .vertex_buffer = vertex_buffer,
        .depth_texture = depth_texture,
        .msaa_resolve = msaa_resolve,
        .pipeline = pipeline,
    };
}

pub fn destroy(self: *Self) void {
    sdl.ReleaseWindowFromGPUDevice(self.device, self.window);
    sdl.DestroyRenderer(self.renderer);
    sdl.DestroyWindow(self.window);

    sdl.ReleaseGPUGraphicsPipeline(self.device, self.pipeline);
    sdl.ReleaseGPUTexture(self.device, self.msaa_resolve);
    sdl.ReleaseGPUTexture(self.device, self.depth_texture);
    sdl.ReleaseGPUBuffer(self.device, self.vertex_buffer);

    sdl.ReleaseGPUShader(self.device, self.shader_vert);
    sdl.ReleaseGPUShader(self.device, self.shader_frag);

    if (self.command_buffer != null) {
        _ = sdl.CancelGPUCommandBuffer(self.command_buffer);
        self.command_buffer = null;
    }
    sdl.DestroyGPUDevice(self.device);
}

pub fn begin_draw(self: *Self) GameError!void {
    self.command_buffer = sdl.AcquireGPUCommandBuffer(self.device) orelse return GameError.SdlError;
    if (self.to_resize) |new_size| {
        try self.reset_textures(new_size[0], new_size[1]);
        self.to_resize = null;
    }
}

pub fn draw_debug(self: *Self) GameError!void {
    var render_target: ?*sdl.GPUTexture = null;
    var width: u32 = 0;
    var height: u32 = 0;
    if (!sdl.WaitAndAcquireGPUSwapchainTexture(self.command_buffer, self.window, &render_target, &width, &height)) return GameError.SdlError;
    // Hidden
    if (render_target == null) return;

    const render_pass = sdl.BeginGPURenderPass(self.command_buffer, &.{
        .clear_color = .{ .r = 0.0, .g = 0.0, .b = 1.0, .a = 1.0 },
        .cycle = false,
        .load_op = sdl.GPU_LOADOP_CLEAR,
        .store_op = sdl.GPU_STOREOP_RESOLVE,
        // .store_op = sdl.GPU_STOREOP_STORE,
        .resolve_texture = render_target,
        .mip_level = 0,
        .texture = self.msaa_resolve,
    }, 1, &.{
        .clear_depth = 1.0,
        .load_op = sdl.GPU_LOADOP_CLEAR,
        .store_op = sdl.GPU_STOREOP_DONT_CARE,
        .stencil_load_op = sdl.GPU_STOREOP_DONT_CARE,
        .stencil_store_op = sdl.GPU_STOREOP_DONT_CARE,
        .texture = self.depth_texture,
    }) orelse return GameError.SdlError;

    sdl.BindGPUGraphicsPipeline(render_pass, self.pipeline);
    sdl.BindGPUVertexBuffers(render_pass, 0, &.{ .offset = 0, .buffer = self.vertex_buffer }, 1);
    sdl.DrawGPUPrimitives(render_pass, 6, 1, 0, 0);

    sdl.EndGPURenderPass(render_pass);
}

pub fn end_draw(self: *Self) GameError!void {
    defer self.command_buffer = null;
    if (!sdl.SubmitGPUCommandBuffer(self.command_buffer)) return GameError.SdlError;
}

fn load_shader(device: *sdl.GPUDevice, path: []const u8, stage: c_uint) GameError!*sdl.GPUShader {
    const file = std.fs.cwd().openFile(path, .{}) catch return GameError.OSError;
    defer file.close();

    const code = file.readToEndAllocOptions(std.heap.c_allocator, 1024 * 1024 * 1024, null, @alignOf(u8), 0) catch return GameError.OSError;
    defer std.heap.c_allocator.free(code);

    return sdl.CreateGPUShader(device, &.{
        .code = code,
        .code_size = code.len,
        .entrypoint = "main",
        .format = sdl.GPU_SHADERFORMAT_SPIRV,
        .stage = stage,
    }) orelse return GameError.SdlError;
}

fn create_depth_texture(device: *sdl.GPUDevice, width: u32, height: u32) GameError!*sdl.GPUTexture {
    return sdl.CreateGPUTexture(device, &.{
        .format = sdl.GPU_TEXTUREFORMAT_D16_UNORM,
        .layer_count_or_depth = 1,
        .width = width,
        .height = height,
        .num_levels = 1,
        .sample_count = sdl.GPU_SAMPLECOUNT_4,
        .usage = sdl.GPU_TEXTUREUSAGE_DEPTH_STENCIL_TARGET,
    }) orelse return GameError.SdlError;
}

fn create_texture(device: *sdl.GPUDevice, width: u32, height: u32, format: c_uint) GameError!*sdl.GPUTexture {
    return sdl.CreateGPUTexture(device, &.{
        .format = format,
        .layer_count_or_depth = 1,
        .width = width,
        .height = height,
        .num_levels = 1,
        .sample_count = sdl.GPU_SAMPLECOUNT_4,
        .usage = sdl.GPU_TEXTUREUSAGE_COLOR_TARGET,
    }) orelse return GameError.SdlError;
}

fn reset_textures(self: *Self, width: u32, height: u32) GameError!void {
    sdl.ReleaseGPUTexture(self.device, self.depth_texture);
    self.depth_texture = try create_depth_texture(self.device, width, height);

    const target_format = sdl.SDL_GetGPUSwapchainTextureFormat(self.device, self.window);

    sdl.ReleaseGPUTexture(self.device, self.msaa_resolve);
    self.msaa_resolve = try create_texture(self.device, width, height, target_format);
}

pub fn resize(self: *Self, width: u32, height: u32) void {
    self.to_resize = .{ width, height };
}