const std = @import("std");
const core = @import("mach-core");
const gpu = core.gpu;

const zm = @import("zmath");
const vec = zm.f32x4;
const Mat = zm.Mat;

pub const App = @This();

app_timer: core.Timer,
title_timer: core.Timer,

pipeline: *gpu.RenderPipeline,
mvp_uniform_buffer: *gpu.Buffer,
mvp_bind_group: *gpu.BindGroup,

pub fn init(app: *App) !void {
    try core.init(.{});

    const shader_module = core.device.createShaderModuleWGSL("shader.wgsl", @embedFile("shader.wgsl"));
    defer shader_module.release();

    const blend = gpu.BlendState{};
    const color_target = gpu.ColorTargetState{
        .format = core.descriptor.format,
        .blend = &blend,
        .write_mask = gpu.ColorWriteMaskFlags.all,
    };
    const fragment = gpu.FragmentState.init(.{
        .module = shader_module,
        .entry_point = "frag_main",
        .targets = &.{color_target},
    });
    const pipeline_descriptor = gpu.RenderPipeline.Descriptor{
        .vertex = gpu.VertexState{
            .module = shader_module,
            .entry_point = "vertex_main",
        },
        .fragment = &fragment,
    };

    app.app_timer = try core.Timer.start();
    app.title_timer = try core.Timer.start();

    app.pipeline = core.device.createRenderPipeline(&pipeline_descriptor);

    app.mvp_uniform_buffer = core.device.createBuffer(&.{
        .usage = .{ .copy_dst = true, .uniform = true },
        .size = @sizeOf(zm.Mat),
        .mapped_at_creation = .false,
    });

    app.mvp_bind_group = core.device.createBindGroup(
        &gpu.BindGroup.Descriptor.init(.{
            .layout = app.pipeline.getBindGroupLayout(0),
            .entries = &.{
                gpu.BindGroup.Entry.buffer(0, app.mvp_uniform_buffer, 0, @sizeOf(zm.Mat)),
            },
        }),
    );
}

pub fn deinit(app: *App) void {
    defer core.deinit();
    defer app.pipeline.release();
    defer app.mvp_uniform_buffer.release();
    defer app.mvp_bind_group.release();
}

pub fn update(app: *App) !bool {
    var iter = core.pollEvents();
    while (iter.next()) |event| {
        switch (event) {
            .close => return true,
            else => {},
        }
    }

    // Set up a view matrix from the camera transform.
    // This moves everything to be relative to the camera.
    // TODO: Actually implement camera transform instead of hardcoding a look-at matrix.
    // const view_matrix = zm.inverse(app.camera_transform);
    const time = app.app_timer.read();
    const x = @cos(time * std.math.tau / 10);
    const y = @sin(time * std.math.tau / 10);
    const view_matrix = zm.lookAtLh(vec(x, y, -2, 1), vec(0, 0, 0, 1), vec(0, 1, 0, 1));

    // Set up a projection matrix using the size of the window.
    // The perspective projection will make things further away appear smaller.
    const width: f32 = @floatFromInt(core.descriptor.width);
    const height: f32 = @floatFromInt(core.descriptor.height);
    const field_of_view = std.math.degreesToRadians(f32, 45.0);
    const proj_matrix = zm.perspectiveFovLh(field_of_view, width / height, 0.1, 10);

    const view_proj_matrix = zm.mul(view_matrix, proj_matrix);

    // Get back buffer texture to render to.
    const back_buffer_view = core.swap_chain.getCurrentTextureView().?;
    defer back_buffer_view.release();
    // Once rendering is done (hence `defer`), swap back buffer to the front to display.
    defer core.swap_chain.present();

    const color_attachment = gpu.RenderPassColorAttachment{
        .view = back_buffer_view,
        .clear_value = std.mem.zeroes(gpu.Color),
        .load_op = .clear,
        .store_op = .store,
    };
    const render_pass_info = gpu.RenderPassDescriptor.init(.{
        .color_attachments = &.{color_attachment},
    });

    // Create a `WGPUCommandEncoder` which provides an interface for recording GPU commands.
    const encoder = core.device.createCommandEncoder(null);
    defer encoder.release();

    encoder.writeBuffer(app.mvp_uniform_buffer, 0, &[_]zm.Mat{zm.transpose(view_proj_matrix)});

    {
        const pass = encoder.beginRenderPass(&render_pass_info);
        defer pass.release();
        defer pass.end();

        pass.setPipeline(app.pipeline);
        pass.setBindGroup(0, app.mvp_bind_group, &.{});

        // Draw three triangles with the help of a specialized shader.
        pass.draw(9, 1, 0, 0);
    }

    // Finish recording commands, creating a `WGPUCommandBuffer`.
    var command = encoder.finish(null);
    defer command.release();

    // Submit the command(s) to the GPU.
    core.queue.submit(&.{command});

    // Update the window title to show FPS and input frequency.
    if (app.title_timer.read() >= 1.0) {
        app.title_timer.reset();
        try core.printTitle("Triangle [ {d}fps ] [ Input {d}hz ]", .{ core.frameRate(), core.inputRate() });
    }

    return false;
}