use crate::gpu::Gpu;

#[repr(C, align(16))]
#[derive(Copy, Clone, Debug, PartialEq, bytemuck::Pod, bytemuck::Zeroable)]
pub struct ChromeInstance {
    pub rect_xywh_px: [f32; 4],
    pub fill_premul_rgba: [f32; 4],
    pub border_premul_rgba: [f32; 4],
    pub thickness_radius_px: [f32; 2],
    pub(crate) pad: [f32; 2],
}

impl ChromeInstance {
    #[must_use]
    pub const fn new(
        rect_xywh_px: [f32; 4],
        fill_premul_rgba: [f32; 4],
        border_premul_rgba: [f32; 4],
        thickness_radius_px: [f32; 2],
    ) -> Self {
        Self {
            rect_xywh_px,
            fill_premul_rgba,
            border_premul_rgba,
            thickness_radius_px,
            pad: [0.0, 0.0],
        }
    }
}

const INSTANCE_STRIDE: u64 = core::mem::size_of::<ChromeInstance>() as u64;
const INITIAL_INSTANCE_CAP: u64 = 256;

#[repr(C, align(16))]
#[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
struct ChromeFrame {
    viewport_px: [f32; 2],
    pad: [f32; 2],
}

const FRAME_SIZE: u64 = core::mem::size_of::<ChromeFrame>() as u64;

pub struct ChromePipeline {
    device: wgpu::Device,
    queue: wgpu::Queue,
    pipeline: wgpu::RenderPipeline,
    uniform_buffer: wgpu::Buffer,
    bind_group: wgpu::BindGroup,
    instance_buffer: wgpu::Buffer,
    instance_capacity: u64,
}

impl ChromePipeline {
    #[must_use]
    pub fn new(gpu: &Gpu, color_format: wgpu::TextureFormat) -> Self {
        let device = gpu.device().clone();
        let queue = gpu.queue().clone();
        let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
            label: Some("bone-render:chrome-shader"),
            source: wgpu::ShaderSource::Wgsl(include_str!("chrome.wgsl").into()),
        });
        let bind_group_layout = device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: Some("bone-render:chrome-bgl"),
            entries: &[wgpu::BindGroupLayoutEntry {
                binding: 0,
                visibility: wgpu::ShaderStages::VERTEX_FRAGMENT,
                ty: wgpu::BindingType::Buffer {
                    ty: wgpu::BufferBindingType::Uniform,
                    has_dynamic_offset: false,
                    min_binding_size: wgpu::BufferSize::new(FRAME_SIZE),
                },
                count: None,
            }],
        });
        let pipeline_layout = device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
            label: Some("bone-render:chrome-layout"),
            bind_group_layouts: &[Some(&bind_group_layout)],
            immediate_size: 0,
        });
        let pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
            label: Some("bone-render:chrome-pipeline"),
            layout: Some(&pipeline_layout),
            vertex: wgpu::VertexState {
                module: &shader,
                entry_point: Some("vs"),
                compilation_options: wgpu::PipelineCompilationOptions::default(),
                buffers: &[wgpu::VertexBufferLayout {
                    array_stride: INSTANCE_STRIDE,
                    step_mode: wgpu::VertexStepMode::Instance,
                    attributes: &INSTANCE_ATTRS,
                }],
            },
            fragment: Some(wgpu::FragmentState {
                module: &shader,
                entry_point: Some("fs"),
                compilation_options: wgpu::PipelineCompilationOptions::default(),
                targets: &[Some(wgpu::ColorTargetState {
                    format: color_format,
                    blend: Some(wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING),
                    write_mask: wgpu::ColorWrites::ALL,
                })],
            }),
            primitive: wgpu::PrimitiveState {
                topology: wgpu::PrimitiveTopology::TriangleList,
                strip_index_format: None,
                front_face: wgpu::FrontFace::Ccw,
                cull_mode: None,
                polygon_mode: wgpu::PolygonMode::Fill,
                conservative: false,
                unclipped_depth: false,
            },
            depth_stencil: None,
            multisample: wgpu::MultisampleState::default(),
            multiview_mask: None,
            cache: None,
        });
        let uniform_buffer = device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("bone-render:chrome-uniform"),
            size: FRAME_SIZE,
            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });
        let bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
            label: Some("bone-render:chrome-bg"),
            layout: &bind_group_layout,
            entries: &[wgpu::BindGroupEntry {
                binding: 0,
                resource: uniform_buffer.as_entire_binding(),
            }],
        });
        let instance_buffer = create_instance_buffer(&device, INITIAL_INSTANCE_CAP);
        Self {
            device,
            queue,
            pipeline,
            uniform_buffer,
            bind_group,
            instance_buffer,
            instance_capacity: INITIAL_INSTANCE_CAP,
        }
    }

    pub fn draw(
        &mut self,
        encoder: &mut wgpu::CommandEncoder,
        color_view: &wgpu::TextureView,
        viewport_px: [f32; 2],
        instances: &[ChromeInstance],
    ) {
        if instances.is_empty() {
            return;
        }
        let frame = ChromeFrame {
            viewport_px,
            pad: [0.0, 0.0],
        };
        self.queue
            .write_buffer(&self.uniform_buffer, 0, bytemuck::bytes_of(&frame));
        let needed = instances.len() as u64;
        if needed > self.instance_capacity {
            let new_cap = needed.next_power_of_two().max(self.instance_capacity * 2);
            self.instance_buffer = create_instance_buffer(&self.device, new_cap);
            self.instance_capacity = new_cap;
        }
        self.queue
            .write_buffer(&self.instance_buffer, 0, bytemuck::cast_slice(instances));
        let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
            label: Some("bone-render:chrome-pass"),
            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                view: color_view,
                resolve_target: None,
                depth_slice: None,
                ops: wgpu::Operations {
                    load: wgpu::LoadOp::Load,
                    store: wgpu::StoreOp::Store,
                },
            })],
            depth_stencil_attachment: None,
            timestamp_writes: None,
            occlusion_query_set: None,
            multiview_mask: None,
        });
        pass.set_pipeline(&self.pipeline);
        pass.set_bind_group(0, &self.bind_group, &[]);
        let used_bytes = needed * INSTANCE_STRIDE;
        pass.set_vertex_buffer(0, self.instance_buffer.slice(0..used_bytes));
        let Ok(count) = u32::try_from(needed) else {
            panic!("chrome instance count {needed} exceeds u32::MAX");
        };
        pass.draw(0..6, 0..count);
    }
}

fn create_instance_buffer(device: &wgpu::Device, capacity: u64) -> wgpu::Buffer {
    device.create_buffer(&wgpu::BufferDescriptor {
        label: Some("bone-render:chrome-instances"),
        size: capacity * INSTANCE_STRIDE,
        usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
        mapped_at_creation: false,
    })
}

impl core::fmt::Debug for ChromePipeline {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("ChromePipeline").finish_non_exhaustive()
    }
}

const INSTANCE_ATTRS: [wgpu::VertexAttribute; 4] = wgpu::vertex_attr_array![
    0 => Float32x4,
    1 => Float32x4,
    2 => Float32x4,
    3 => Float32x2,
];
