use bevy::{
    core_pipeline::Transparent3d,
    ecs::system::{lifetimeless::*, SystemParamItem},
    pbr::{
        DrawMesh, MeshPipeline, MeshPipelineKey, MeshUniform, SetMeshBindGroup,
        SetMeshViewBindGroup,
    },
    prelude::*,
    reflect::TypeUuid,
    render::{
        camera::PerspectiveCameraBundle,
        render_asset::{PrepareAssetError, RenderAsset, RenderAssetPlugin, RenderAssets},
        render_component::ExtractComponentPlugin,
        render_phase::{
            AddRenderCommand, DrawFunctions, EntityRenderCommand, RenderCommandResult, RenderPhase,
            SetItemPipeline, TrackedRenderPass,
        },
        render_resource::*,
        renderer::RenderDevice,
        view::{ExtractedView, Msaa},
        RenderApp, RenderStage,
    },
};
use crevice::std140::{AsStd140, Std140};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(CustomMaterialPlugin)
        .add_startup_system(setup)
        .run();
}

/// set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<CustomMaterial>>,
) {
    // cube
    commands.spawn().insert_bundle((
        meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
        Transform::from_xyz(0.0, 0.5, 0.0),
        GlobalTransform::default(),
        Visibility::default(),
        ComputedVisibility::default(),
        materials.add(CustomMaterial {
            color: Color::GREEN,
        }),
    ));

    // camera
    commands.spawn_bundle(PerspectiveCameraBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..Default::default()
    });
}

#[derive(Debug, Clone, TypeUuid)]
#[uuid = "4ee9c363-1124-4113-890e-199d81b00281"]
pub struct CustomMaterial {
    color: Color,
}

#[derive(Clone)]
pub struct GpuCustomMaterial {
    _buffer: Buffer,
    bind_group: BindGroup,
}

impl RenderAsset for CustomMaterial {
    type ExtractedAsset = CustomMaterial;
    type PreparedAsset = GpuCustomMaterial;
    type Param = (SRes<RenderDevice>, SRes<CustomPipeline>);
    fn extract_asset(&self) -> Self::ExtractedAsset {
        self.clone()
    }

    fn prepare_asset(
        extracted_asset: Self::ExtractedAsset,
        (render_device, custom_pipeline): &mut SystemParamItem<Self::Param>,
    ) -> Result<Self::PreparedAsset, PrepareAssetError<Self::ExtractedAsset>> {
        let color = Vec4::from_slice(&extracted_asset.color.as_linear_rgba_f32());
        let buffer = render_device.create_buffer_with_data(&BufferInitDescriptor {
            contents: color.as_std140().as_bytes(),
            label: None,
            usage: BufferUsages::UNIFORM | BufferUsages::COPY_DST,
        });
        let bind_group = render_device.create_bind_group(&BindGroupDescriptor {
            entries: &[BindGroupEntry {
                binding: 0,
                resource: buffer.as_entire_binding(),
            }],
            label: None,
            layout: &custom_pipeline.material_layout,
        });

        Ok(GpuCustomMaterial {
            _buffer: buffer,
            bind_group,
        })
    }
}
pub struct CustomMaterialPlugin;

impl Plugin for CustomMaterialPlugin {
    fn build(&self, app: &mut App) {
        app.add_asset::<CustomMaterial>()
            .add_plugin(ExtractComponentPlugin::<Handle<CustomMaterial>>::default())
            .add_plugin(RenderAssetPlugin::<CustomMaterial>::default());
        app.sub_app(RenderApp)
            .add_render_command::<Transparent3d, DrawCustom>()
            .init_resource::<CustomPipeline>()
            .init_resource::<SpecializedPipelines<CustomPipeline>>()
            .add_system_to_stage(RenderStage::Queue, queue_custom);
    }
}

pub struct CustomPipeline {
    mesh_pipeline: MeshPipeline,
    material_layout: BindGroupLayout,
    shader: Handle<Shader>,
}

impl SpecializedPipeline for CustomPipeline {
    type Key = MeshPipelineKey;

    fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor {
        let mut descriptor = self.mesh_pipeline.specialize(key);
        descriptor.fragment.as_mut().unwrap().shader = self.shader.clone();
        descriptor.layout = Some(vec![
            self.mesh_pipeline.view_layout.clone(),
            self.material_layout.clone(),
            self.mesh_pipeline.mesh_layout.clone(),
        ]);
        descriptor
    }
}

impl FromWorld for CustomPipeline {
    fn from_world(world: &mut World) -> Self {
        let asset_server = world.get_resource::<AssetServer>().unwrap();
        // Watch for changes, allowing for hot shader reloading
        // Try changing custom_material.wgsl while the app is running!
        asset_server.watch_for_changes().unwrap();

        let render_device = world.get_resource::<RenderDevice>().unwrap();
        let material_layout = render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
            entries: &[BindGroupLayoutEntry {
                binding: 0,
                visibility: ShaderStages::FRAGMENT,
                ty: BindingType::Buffer {
                    ty: BufferBindingType::Uniform,
                    has_dynamic_offset: false,
                    min_binding_size: BufferSize::new(Vec4::std140_size_static() as u64),
                },
                count: None,
            }],
            label: None,
        });

        CustomPipeline {
            mesh_pipeline: world.get_resource::<MeshPipeline>().unwrap().clone(),
            shader: asset_server.load("shaders/custom_material.wgsl"),
            material_layout,
        }
    }
}

#[allow(clippy::too_many_arguments)]
pub fn queue_custom(
    transparent_3d_draw_functions: Res<DrawFunctions<Transparent3d>>,
    materials: Res<RenderAssets<CustomMaterial>>,
    custom_pipeline: Res<CustomPipeline>,
    mut pipeline_cache: ResMut<RenderPipelineCache>,
    mut specialized_pipelines: ResMut<SpecializedPipelines<CustomPipeline>>,
    msaa: Res<Msaa>,
    material_meshes: Query<(Entity, &Handle<CustomMaterial>, &MeshUniform), With<Handle<Mesh>>>,
    mut views: Query<(&ExtractedView, &mut RenderPhase<Transparent3d>)>,
) {
    let draw_custom = transparent_3d_draw_functions
        .read()
        .get_id::<DrawCustom>()
        .unwrap();
    let key = MeshPipelineKey::from_msaa_samples(msaa.samples);
    for (view, mut transparent_phase) in views.iter_mut() {
        let view_matrix = view.transform.compute_matrix();
        let view_row_2 = view_matrix.row(2);
        for (entity, material_handle, mesh_uniform) in material_meshes.iter() {
            if materials.contains_key(material_handle) {
                transparent_phase.add(Transparent3d {
                    entity,
                    pipeline: specialized_pipelines.specialize(
                        &mut pipeline_cache,
                        &custom_pipeline,
                        key,
                    ),
                    draw_function: draw_custom,
                    distance: view_row_2.dot(mesh_uniform.transform.col(3)),
                });
            }
        }
    }
}

type DrawCustom = (
    SetItemPipeline,
    SetMeshViewBindGroup<0>,
    SetCustomMaterialBindGroup,
    SetMeshBindGroup<2>,
    DrawMesh,
);

struct SetCustomMaterialBindGroup;
impl EntityRenderCommand for SetCustomMaterialBindGroup {
    type Param = (
        SRes<RenderAssets<CustomMaterial>>,
        SQuery<Read<Handle<CustomMaterial>>>,
    );
    fn render<'w>(
        _view: Entity,
        item: Entity,
        (materials, query): SystemParamItem<'w, '_, Self::Param>,
        pass: &mut TrackedRenderPass<'w>,
    ) -> RenderCommandResult {
        let material_handle = query.get(item).unwrap();
        let material = materials.into_inner().get(material_handle).unwrap();
        pass.set_bind_group(1, &material.bind_group, &[]);
        RenderCommandResult::Success
    }
}