const std = @import("std");
const testing = std.testing;

const glfw = @import("glfw");
const gpu = @import("gpu");
const util = @import("util.zig");
const c = @import("c.zig").c;

/// For now, this contains nothing. In the future, this will include application configuration that
/// can only be specified at compile-time.
pub const AppConfig = struct {};

pub const VSyncMode = enum {
    /// Potential screen tearing.
    /// No synchronization with monitor, render frames as fast as possible.
    none,

    /// No tearing, synchronizes rendering with monitor refresh rate, rendering frames when ready.
    ///
    /// Tries to stay one frame ahead of the monitor, so when it's ready for the next frame it is
    /// already prepared.
    double,

    /// No tearing, synchronizes rendering with monitor refresh rate, rendering frames when ready.
    ///
    /// Tries to stay two frames ahead of the monitor, so when it's ready for the next frame it is
    /// already prepared.
    triple,
};

/// Application options that can be configured at init time.
pub const Options = struct {
    /// The title of the window.
    title: [*:0]const u8 = "Mach engine",

    /// The width of the window.
    width: u32 = 640,

    /// The height of the window.
    height: u32 = 480,

    /// Monitor synchronization modes.
    vsync: VSyncMode = .double,

    /// GPU features required by the application.
    required_features: ?[]gpu.Feature = null,

    /// GPU limits required by the application.
    required_limits: ?gpu.Limits = null,

    /// Whether the application has a preference for low power or high performance GPU.
    power_preference: gpu.PowerPreference = .none,
};

/// Default GLFW error handling callback
fn glfwErrorCallback(error_code: glfw.Error, description: [:0]const u8) void {
    std.debug.print("glfw: {}: {s}\n", .{ error_code, description });
}

/// A Mach application.
///
/// The Context type is your own data type which can later be accessed via app.context from within
/// the frame function you pass to run().
pub fn App(comptime Context: type, comptime config: AppConfig) type {
    _ = config;
    return struct {
        context: Context,
        device: gpu.Device,
        window: glfw.Window,
        backend_type: gpu.Adapter.BackendType,
        allocator: std.mem.Allocator,
        swap_chain: ?gpu.SwapChain,
        swap_chain_format: gpu.Texture.Format,

        /// The amount of time (in seconds) that has passed since the last frame was rendered.
        ///
        /// For example, if you are animating a cube which should rotate 360 degrees every second,
        /// instead of writing (360.0 / 60.0) and assuming the frame rate is 60hz, write
        /// (360.0 * app.delta_time)
        delta_time: f64 = 0,
        delta_time_ns: u64 = 0,

        // Internals
        native_instance: gpu.NativeInstance,
        surface: ?gpu.Surface,
        current_desc: gpu.SwapChain.Descriptor,
        target_desc: gpu.SwapChain.Descriptor,
        timer: std.time.Timer,

        const Self = @This();

        pub fn init(allocator: std.mem.Allocator, context: Context, options: Options) !Self {
            const backend_type = try util.detectBackendType(allocator);

            glfw.setErrorCallback(glfwErrorCallback);
            try glfw.init(.{});

            // Create the test window and discover adapters using it (esp. for OpenGL)
            var hints = util.glfwWindowHintsForBackend(backend_type);
            hints.cocoa_retina_framebuffer = true;
            const window = try glfw.Window.create(
                options.width,
                options.height,
                options.title,
                null,
                null,
                hints,
            );

            const backend_procs = c.machDawnNativeGetProcs();
            c.dawnProcSetProcs(backend_procs);

            const instance = c.machDawnNativeInstance_init();
            var native_instance = gpu.NativeInstance.wrap(c.machDawnNativeInstance_get(instance).?);

            // Discover e.g. OpenGL adapters.
            try util.discoverAdapters(instance, window, backend_type);

            // Request an adapter.
            //
            // TODO: It would be nice if we could use gpu_interface.waitForAdapter here, however the webgpu.h
            // API does not yet have a way to specify what type of backend you want (vulkan, opengl, etc.)
            // In theory, I suppose we shouldn't need to and Dawn should just pick the best adapter - but in
            // practice if Vulkan is not supported today waitForAdapter/requestAdapter merely generates an error.
            //
            // const gpu_interface = native_instance.interface();
            // const backend_adapter = switch (gpu_interface.waitForAdapter(&.{
            //     .power_preference = .high_performance,
            // })) {
            //     .adapter => |v| v,
            //     .err => |err| {
            //         std.debug.print("mach: failed to get adapter: error={} {s}\n", .{ err.code, err.message });
            //         std.process.exit(1);
            //     },
            // };
            const adapters = c.machDawnNativeInstance_getAdapters(instance);
            var dawn_adapter: ?c.MachDawnNativeAdapter = null;
            var i: usize = 0;
            while (i < c.machDawnNativeAdapters_length(adapters)) : (i += 1) {
                const adapter = c.machDawnNativeAdapters_index(adapters, i);
                const properties = c.machDawnNativeAdapter_getProperties(adapter);
                const found_backend_type = @intToEnum(gpu.Adapter.BackendType, c.machDawnNativeAdapterProperties_getBackendType(properties));
                if (found_backend_type == backend_type) {
                    dawn_adapter = adapter;
                    break;
                }
            }
            if (dawn_adapter == null) {
                std.debug.print("mach: no matching adapter found for {s}", .{@tagName(backend_type)});
                std.debug.print("-> maybe try GPU_BACKEND=opengl ?\n", .{});
                std.process.exit(1);
            }
            std.debug.assert(dawn_adapter != null);
            const backend_adapter = gpu.NativeInstance.fromWGPUAdapter(c.machDawnNativeAdapter_get(dawn_adapter.?).?);

            // Print which adapter we are going to use.
            const props = backend_adapter.properties;
            std.debug.print("mach: found {s} backend on {s} adapter: {s}, {s}\n", .{
                gpu.Adapter.backendTypeName(props.backend_type),
                gpu.Adapter.typeName(props.adapter_type),
                props.name,
                props.driver_description,
            });

            const device = switch (backend_adapter.waitForDevice(&.{
                .required_features = options.required_features,
                .required_limits = options.required_limits,
            })) {
                .device => |v| v,
                .err => |err| {
                    // TODO: return a proper error type
                    std.debug.print("mach: failed to get device: error={} {s}\n", .{ err.code, err.message });
                    std.process.exit(1);
                },
            };

            var framebuffer_size = try window.getFramebufferSize();

            // If targeting OpenGL, we can't use the newer WGPUSurface API. Instead, we need to use the
            // older Dawn-specific API. https://bugs.chromium.org/p/dawn/issues/detail?id=269&q=surface&can=2
            const use_legacy_api = backend_type == .opengl or backend_type == .opengles;
            var descriptor: gpu.SwapChain.Descriptor = undefined;
            var swap_chain: ?gpu.SwapChain = null;
            var swap_chain_format: gpu.Texture.Format = undefined;
            var surface: ?gpu.Surface = null;
            if (!use_legacy_api) {
                swap_chain_format = .bgra8_unorm;
                descriptor = .{
                    .label = "basic swap chain",
                    .usage = .{ .render_attachment = true },
                    .format = swap_chain_format,
                    .width = framebuffer_size.width,
                    .height = framebuffer_size.height,
                    .present_mode = switch (options.vsync) {
                        .none => .immediate,
                        .double => .fifo,
                        .triple => .mailbox,
                    },
                    .implementation = 0,
                };
                surface = util.createSurfaceForWindow(
                    &native_instance,
                    window,
                    comptime util.detectGLFWOptions(),
                );
            } else {
                const binding = c.machUtilsCreateBinding(@enumToInt(backend_type), @ptrCast(*c.GLFWwindow, window.handle), @ptrCast(c.WGPUDevice, device.ptr));
                if (binding == null) {
                    @panic("failed to create Dawn backend binding");
                }
                descriptor = std.mem.zeroes(gpu.SwapChain.Descriptor);
                descriptor.implementation = c.machUtilsBackendBinding_getSwapChainImplementation(binding);
                swap_chain = device.nativeCreateSwapChain(null, &descriptor);

                swap_chain_format = @intToEnum(gpu.Texture.Format, @intCast(u32, c.machUtilsBackendBinding_getPreferredSwapChainTextureFormat(binding)));
                swap_chain.?.configure(
                    swap_chain_format,
                    .{ .render_attachment = true },
                    framebuffer_size.width,
                    framebuffer_size.height,
                );
            }

            device.setUncapturedErrorCallback(&util.printUnhandledErrorCallback);
            return Self{
                .context = context,
                .device = device,
                .window = window,
                .backend_type = backend_type,
                .allocator = allocator,

                .native_instance = native_instance,
                .surface = surface,
                .swap_chain = swap_chain,
                .swap_chain_format = swap_chain_format,
                .timer = try std.time.Timer.start(),
                .current_desc = descriptor,
                .target_desc = descriptor,
            };
        }

        const Funcs = struct {
            // Run once per frame
            frame: fn (app: *Self, ctx: Context) error{OutOfMemory}!void,
            // Run once at the start, and whenever the swapchain is recreated
            resize: ?fn (app: *Self, ctx: Context, width: u32, height: u32) error{OutOfMemory}!void = null,
        };

        pub fn run(app: *Self, funcs: Funcs) !void {
            if (app.swap_chain != null and funcs.resize != null) {
                try funcs.resize.?(app, app.context, app.current_desc.width, app.current_desc.height);
            }
            while (!app.window.shouldClose()) {
                try glfw.pollEvents();

                app.delta_time_ns = app.timer.lap();
                app.delta_time = @intToFloat(f64, app.delta_time_ns) / @intToFloat(f64, std.time.ns_per_s);

                var framebuffer_size = try app.window.getFramebufferSize();
                app.target_desc.width = framebuffer_size.width;
                app.target_desc.height = framebuffer_size.height;

                if (app.swap_chain == null or !app.current_desc.equal(&app.target_desc)) {
                    const use_legacy_api = app.surface == null;
                    if (!use_legacy_api) {
                        app.swap_chain = app.device.nativeCreateSwapChain(app.surface, &app.target_desc);
                    } else app.swap_chain.?.configure(
                        app.swap_chain_format,
                        .{ .render_attachment = true },
                        app.target_desc.width,
                        app.target_desc.height,
                    );
                    if (funcs.resize) |f| {
                        try f(app, app.context, app.target_desc.width, app.target_desc.height);
                    }
                    app.current_desc = app.target_desc;
                }

                try funcs.frame(app, app.context);
            }
        }
    };
}

test "glfw_basic" {
    _ = Options;
    _ = App;
    glfw.basicTest() catch unreachable;
}