//! This example illustrates how to create a texture for use with a `texture_2d_array<f32>` shader
//! uniform variable.

use bevy::{
    asset::LoadState,
    prelude::*,
    reflect::TypePath,
    render::render_resource::{AsBindGroup, ShaderRef},
};

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

#[derive(Resource)]
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(DirectionalLightBundle {
        transform: Transform::from_xyz(3.0, 2.0, 1.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..Default::default()
    });

    // camera
    commands.spawn(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.load_state(loading_texture.handle.id()) != 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(Cuboid::default());
    let material_handle = materials.add(ArrayTextureMaterial {
        array_texture: loading_texture.handle.clone(),
    });
    for x in -5..=5 {
        commands.spawn(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(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 {
        "shaders/array_texture.wgsl".into()
    }
}

#import bevy_pbr::{
    forward_io::VertexOutput,
    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(2) @binding(0) var my_array_texture: texture_2d_array<f32>;
@group(2) @binding(1) var my_array_texture_sampler: sampler;

@fragment
fn fragment(
    @builtin(front_facing) is_front: bool,
    mesh: VertexOutput,
) -> @location(0) vec4<f32> {
    let layer = i32(mesh.world_position.x) & 0x3;

    // 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);
}