//! A shader that samples a texture with view-independent UV coordinates.

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

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

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

#[derive(Component)]
struct MainCamera;

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut custom_materials: ResMut<Assets<CustomMaterial>>,
    mut standard_materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        Mesh3d(meshes.add(Plane3d::default().mesh().size(5.0, 5.0))),
        MeshMaterial3d(standard_materials.add(Color::srgb(0.3, 0.5, 0.3))),
    ));
    commands.spawn((PointLight::default(), Transform::from_xyz(4.0, 8.0, 4.0)));

    commands.spawn((
        Mesh3d(meshes.add(Cuboid::default())),
        MeshMaterial3d(custom_materials.add(CustomMaterial {
            texture: asset_server.load(
                "models/FlightHelmet/FlightHelmet_Materials_LensesMat_OcclusionRoughMetal.png",
            ),
        })),
        Transform::from_xyz(0.0, 0.5, 0.0),
    ));

    // camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(4.0, 2.5, 4.0).looking_at(Vec3::ZERO, Vec3::Y),
        MainCamera,
    ));
}

fn rotate_camera(mut cam_transform: Single<&mut Transform, With<MainCamera>>, time: Res<Time>) {
    cam_transform.rotate_around(
        Vec3::ZERO,
        Quat::from_axis_angle(Vec3::Y, 45f32.to_radians() * time.delta_secs()),
    );
    cam_transform.look_at(Vec3::ZERO, Vec3::Y);
}

#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
struct CustomMaterial {
    #[texture(0)]
    #[sampler(1)]
    texture: Handle<Image>,
}

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

#import bevy_pbr::{
    mesh_view_bindings::view,
    forward_io::VertexOutput,
    utils::coords_to_viewport_uv,
}

@group(2) @binding(0) var texture: texture_2d<f32>;
@group(2) @binding(1) var texture_sampler: sampler;

@fragment
fn fragment(
    mesh: VertexOutput,
) -> @location(0) vec4<f32> {
    let viewport_uv = coords_to_viewport_uv(mesh.position.xy, view.viewport);
    let color = textureSample(texture, texture_sampler, viewport_uv);
    return color;
}