//! A shader and a material that uses it.

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

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

/// set up a simple 3D scene
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<CustomMaterial>>,
    asset_server: Res<AssetServer>,
) {
    // cube
    commands.spawn(MaterialMeshBundle {
        mesh: meshes.add(Cuboid::default()),
        transform: Transform::from_xyz(0.0, 0.5, 0.0),
        material: materials.add(CustomMaterial {
            color: LinearRgba::BLUE,
            color_texture: Some(asset_server.load("branding/icon.png")),
            alpha_mode: AlphaMode::Blend,
        }),
        ..default()
    });

    // camera
    commands.spawn(Camera3dBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..default()
    });
}

// This struct defines the data that will be passed to your shader
#[derive(Asset, TypePath, AsBindGroup, Debug, Clone)]
struct CustomMaterial {
    #[uniform(0)]
    color: LinearRgba,
    #[texture(1)]
    #[sampler(2)]
    color_texture: Option<Handle<Image>>,
    alpha_mode: AlphaMode,
}

/// The Material trait is very configurable, but comes with sensible defaults for all methods.
/// You only need to implement functions for features that need non-default behavior. See the Material api docs for details!
impl Material for CustomMaterial {
    fn fragment_shader() -> ShaderRef {
        "shaders/custom_material.wgsl".into()
    }

    fn alpha_mode(&self) -> AlphaMode {
        self.alpha_mode
    }
}

#import bevy_pbr::forward_io::VertexOutput
// we can import items from shader modules in the assets folder with a quoted path
#import "shaders/custom_material_import.wgsl"::COLOR_MULTIPLIER

@group(2) @binding(0) var<uniform> material_color: vec4<f32>;
@group(2) @binding(1) var material_color_texture: texture_2d<f32>;
@group(2) @binding(2) var material_color_sampler: sampler;

@fragment
fn fragment(
    mesh: VertexOutput,
) -> @location(0) vec4<f32> {
    return material_color * textureSample(material_color_texture, material_color_sampler, mesh.uv) * COLOR_MULTIPLIER;
}