use bevy::{
    asset::LoadState,
    prelude::*,
    reflect::TypeUuid,
    render::{
        render_asset::RenderAssets,
        render_resource::{
            AsBindGroup, AsBindGroupError, BindGroupDescriptor, BindGroupEntry, BindGroupLayout,
            BindGroupLayoutDescriptor, BindGroupLayoutEntry, BindingResource, BindingType,
            OwnedBindingResource, PreparedBindGroup, SamplerBindingType, ShaderRef, ShaderStages,
            TextureSampleType, TextureViewDimension,
        },
        renderer::RenderDevice,
        texture::FallbackImage,
    },
};

/// This example illustrates how to create a texture for use with a `texture_2d_array<f32>` shader
/// uniform variable.
fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(MaterialPlugin::<ArrayTextureMaterial>::default())
        .add_startup_system(setup)
        .add_system(create_array_texture)
        .run();
}

struct LoadingTexture {
    is_loaded: bool,
    handle: Handle<Image>,
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    // Start loading the texture.
    commands.insert_resource(LoadingTexture {
        is_loaded: false,
        handle: asset_server.load("textures/array_texture.png"),
    });

    // light
    commands.spawn_bundle(PointLightBundle {
        point_light: PointLight {
            intensity: 3000.0,
            ..Default::default()
        },
        transform: Transform::from_xyz(-3.0, 2.0, -1.0),
        ..Default::default()
    });
    commands.spawn_bundle(PointLightBundle {
        point_light: PointLight {
            intensity: 3000.0,
            ..Default::default()
        },
        transform: Transform::from_xyz(3.0, 2.0, 1.0),
        ..Default::default()
    });

    // camera
    commands.spawn_bundle(Camera3dBundle {
        transform: Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::new(1.5, 0.0, 0.0), Vec3::Y),
        ..Default::default()
    });
}

fn create_array_texture(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut loading_texture: ResMut<LoadingTexture>,
    mut images: ResMut<Assets<Image>>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ArrayTextureMaterial>>,
) {
    if loading_texture.is_loaded
        || asset_server.get_load_state(loading_texture.handle.clone()) != LoadState::Loaded
    {
        return;
    }
    loading_texture.is_loaded = true;
    let image = images.get_mut(&loading_texture.handle).unwrap();

    // Create a new array texture asset from the loaded texture.
    let array_layers = 4;
    image.reinterpret_stacked_2d_as_array(array_layers);

    // Spawn some cubes using the array texture
    let mesh_handle = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));
    let material_handle = materials.add(ArrayTextureMaterial {
        array_texture: loading_texture.handle.clone(),
    });
    for x in -5..=5 {
        commands.spawn_bundle(MaterialMeshBundle {
            mesh: mesh_handle.clone(),
            material: material_handle.clone(),
            transform: Transform::from_xyz(x as f32 + 0.5, 0.0, 0.0),
            ..Default::default()
        });
    }
}

#[derive(Debug, Clone, TypeUuid)]
#[uuid = "9c5a0ddf-1eaf-41b4-9832-ed736fd26af3"]
struct ArrayTextureMaterial {
    array_texture: Handle<Image>,
}

impl Material for ArrayTextureMaterial {
    fn fragment_shader() -> ShaderRef {
        "shaders/array_texture.wgsl".into()
    }
}

impl AsBindGroup for ArrayTextureMaterial {
    type Data = ();

    fn as_bind_group(
        &self,
        layout: &BindGroupLayout,
        render_device: &RenderDevice,
        images: &RenderAssets<Image>,
        _fallback_image: &FallbackImage,
    ) -> Result<PreparedBindGroup<Self>, AsBindGroupError> {
        let image = images
            .get(&self.array_texture)
            .ok_or(AsBindGroupError::RetryNextUpdate)?;
        let bind_group = render_device.create_bind_group(&BindGroupDescriptor {
            entries: &[
                BindGroupEntry {
                    binding: 0,
                    resource: BindingResource::TextureView(&image.texture_view),
                },
                BindGroupEntry {
                    binding: 1,
                    resource: BindingResource::Sampler(&image.sampler),
                },
            ],
            label: Some("array_texture_material_bind_group"),
            layout,
        });

        Ok(PreparedBindGroup {
            bind_group,
            bindings: vec![
                OwnedBindingResource::TextureView(image.texture_view.clone()),
                OwnedBindingResource::Sampler(image.sampler.clone()),
            ],
            data: (),
        })
    }

    fn bind_group_layout(render_device: &RenderDevice) -> BindGroupLayout {
        render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
            entries: &[
                // Array Texture
                BindGroupLayoutEntry {
                    binding: 0,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Texture {
                        multisampled: false,
                        sample_type: TextureSampleType::Float { filterable: true },
                        view_dimension: TextureViewDimension::D2Array,
                    },
                    count: None,
                },
                // Array Texture Sampler
                BindGroupLayoutEntry {
                    binding: 1,
                    visibility: ShaderStages::FRAGMENT,
                    ty: BindingType::Sampler(SamplerBindingType::Filtering),
                    count: None,
                },
            ],
            label: None,
        })
    }
}