use bevy::{
    ecs::system::{lifetimeless::SRes, SystemParamItem},
    prelude::*,
    render::{
        render_asset::{PrepareAssetError, RenderAsset, RenderAssets},
        render_resource::{Buffer, BufferDescriptor, BufferUsages, Extent3d, TextureFormat},
        renderer::RenderDevice, texture::GpuImage,
    },
};

/// Render-world version of HeadlessRenderSource
pub struct GpuHeadlessRenderSource {
    pub(crate) buffer: Buffer,
    pub(crate) source_handle: Handle<Image>,
    pub(crate) source_size: Extent3d,
    pub(crate) bytes_per_row: u32,
    pub(crate) padded_bytes_per_row: u32,
    pub(crate) format: TextureFormat,
}

/// Headless render source. Contains a handle to the render texture which will be copied
/// from.
#[derive(Asset, Reflect, Clone, Default)]
pub struct HeadlessRenderSource(pub Handle<Image>);

impl RenderAsset for GpuHeadlessRenderSource {
    type SourceAsset = HeadlessRenderSource;
    type Param = (SRes<RenderDevice>, SRes<RenderAssets<GpuImage>>);

    fn prepare_asset(
        source_asset: Self::SourceAsset,
        (device, images): &mut SystemParamItem<Self::Param>,
    ) -> Result<Self, PrepareAssetError<Self::SourceAsset>> {
        let Some(gpu_image) = images.get(source_asset.0.id()) else {
            warn!("Failed to get GPU image");
            return Err(PrepareAssetError::RetryNextUpdate(source_asset));
        };

        let size = gpu_image.texture.size();
        let format = gpu_image.texture_format;
        let bytes_per_row =
            (size.width / format.block_dimensions().0) * format.block_copy_size(None).unwrap();
        let padded_bytes_per_row =
            RenderDevice::align_copy_bytes_per_row(bytes_per_row as usize) as u32;

        Ok(GpuHeadlessRenderSource {
            buffer: device.create_buffer(&BufferDescriptor {
                label: Some("framebuffer_extract_buffer"),
                size: (size.height * padded_bytes_per_row) as u64,
                usage: BufferUsages::COPY_DST | BufferUsages::MAP_READ,
                mapped_at_creation: false,
            }),
            source_handle: source_asset.0.clone(),
            source_size: size,
            bytes_per_row,
            padded_bytes_per_row,
            format,
        })
    }
    
}