use bevy::{
    image::{ImageArrayLayout, ImageLoaderSettings},
    mesh::MeshTag,
    prelude::*,
    reflect::TypePath,
    render::render_resource::AsBindGroup,
    shader::ShaderRef,
};

/// This example uses a shader source file from the assets subdirectory.
const SHADER_ASSET_PATH: &str = "shaders/array_texture.wgsl";

/// Corresponds to the number of layers in the array texture.
const TEXTURE_COUNT: u32 = 4;

fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins,
            MaterialPlugin::<ArrayTextureMaterial>::default(),
        ))
        .add_systems(Startup, setup)
        .add_systems(Update, update_mesh_tags)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ArrayTextureMaterial>>,
    asset_server: Res<AssetServer>,
) {
    // Load the texture.
    let array_texture = asset_server
        .load_builder()
        .with_settings(|settings: &mut ImageLoaderSettings| {
            settings.array_layout = Some(ImageArrayLayout::RowCount {
                rows: TEXTURE_COUNT,
            });
        })
        .load("textures/array_texture.png");

    // light
    commands.spawn((
        DirectionalLight::default(),
        Transform::from_xyz(3.0, 2.0, 1.0).looking_at(Vec3::ZERO, Vec3::Y),
    ));

    // camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::new(1.5, 0.0, 0.0), Vec3::Y),
    ));

    // Spawn some cubes using the array texture.
    let mesh_handle = meshes.add(Cuboid::default());
    let material_handle = materials.add(ArrayTextureMaterial { array_texture });
    for x in -5..=5 {
        commands.spawn((
            Mesh3d(mesh_handle.clone()),
            MeshMaterial3d(material_handle.clone()),
            // Pass a different mesh tag to allow selecting different layers of
            // the array texture in the shader.
            MeshTag(x as u32 % TEXTURE_COUNT),
            Transform::from_xyz(x as f32 + 0.5, 0.0, 0.0),
        ));
    }
}

fn update_mesh_tags(time: Res<Time>, mut query: Query<&mut MeshTag>, mut timer: Local<Timer>) {
    // Initialize the timer on the first run.
    if timer.duration().is_zero() {
        *timer = Timer::from_seconds(1.5, TimerMode::Repeating);
    }

    timer.tick(time.delta());
    if timer.just_finished() {
        for mut tag in query.iter_mut() {
            // Cycle through the texture layers to demonstrate that we can
            // select different layers of the array texture at runtime.
            tag.0 = (tag.0 + 1) % TEXTURE_COUNT;
        }
    }
}

#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
struct ArrayTextureMaterial {
    #[texture(0, dimension = "2d_array")]
    #[sampler(1)]
    array_texture: Handle<Image>,
}

impl Material for ArrayTextureMaterial {
    fn fragment_shader() -> ShaderRef {
        SHADER_ASSET_PATH.into()
    }
}

#import bevy_pbr::{
    forward_io::VertexOutput,
    mesh_functions,
    mesh_view_bindings::view,
    pbr_types::{STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT, PbrInput, pbr_input_new},
    pbr_functions as fns,
    pbr_bindings,
}
#import bevy_core_pipeline::tonemapping::tone_mapping

@group(#{MATERIAL_BIND_GROUP}) @binding(0) var my_array_texture: texture_2d_array<f32>;
@group(#{MATERIAL_BIND_GROUP}) @binding(1) var my_array_texture_sampler: sampler;

@fragment
fn fragment(
    @builtin(front_facing) is_front: bool,
    mesh: VertexOutput,
) -> @location(0) vec4<f32> {
    // Determine which layer of the array texture to sample from based on the
    // mesh tag which originates from the MeshTag component on the entity.
    let layer = mesh_functions::get_tag(mesh.instance_index);

    // Prepare a 'processed' StandardMaterial by sampling all textures to resolve
    // the material members
    var pbr_input: PbrInput = pbr_input_new();

    pbr_input.material.base_color = textureSample(my_array_texture, my_array_texture_sampler, mesh.uv, layer);
#ifdef VERTEX_COLORS
    pbr_input.material.base_color = pbr_input.material.base_color * mesh.color;
#endif

    let double_sided = (pbr_input.material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u;

    pbr_input.frag_coord = mesh.position;
    pbr_input.world_position = mesh.world_position;
    pbr_input.world_normal = fns::prepare_world_normal(
        mesh.world_normal,
        double_sided,
        is_front,
    );

    pbr_input.is_orthographic = view.clip_from_view[3].w == 1.0;

    pbr_input.N = normalize(pbr_input.world_normal);

#ifdef VERTEX_TANGENTS
    let Nt = textureSampleBias(pbr_bindings::normal_map_texture, pbr_bindings::normal_map_sampler, mesh.uv, view.mip_bias).rgb;
    let TBN = fns::calculate_tbn_mikktspace(mesh.world_normal, mesh.world_tangent);
    pbr_input.N = fns::apply_normal_mapping(
        pbr_input.material.flags,
        TBN,
        double_sided,
        is_front,
        Nt,
    );
#endif

    pbr_input.V = fns::calculate_view(mesh.world_position, pbr_input.is_orthographic);

    return tone_mapping(fns::apply_pbr_lighting(pbr_input), view.color_grading);
}