//! A shader that uses the GLSL shading language.

use bevy::{
    prelude::*,
    reflect::TypePath,
    render::render_resource::{AsBindGroup, ShaderRef},
    sprite::{AlphaMode2d, Material2d, Material2dPlugin},
    window::PrimaryWindow,
};

const SHADER_ASSET_PATH: &str = "shaders/default.wgsl";

fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins,
            Material2dPlugin::<CustomMaterial>::default(),
        ))
        .add_systems(Startup, setup)
        .add_systems(Update, resize_fullscreen_quad)
        .run();
}

/// set up a simple 2D-screen-like surface
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<CustomMaterial>>,
    primary_window: Single<&Window, With<PrimaryWindow>>,
) {
    // camera
    commands.spawn(Camera2d);

    // quad that fills the whole window
    let size = Vec2::new(
        primary_window.resolution.width(),
        primary_window.resolution.height(),
    );

    commands.spawn((
        Mesh2d(meshes.add(Rectangle::default())),
        MeshMaterial2d(materials.add(CustomMaterial {})),
        Transform::from_scale(Vec3::new(size.x, size.y, 1.0)),
        FullscreenQuad,
    ));
}

/// Marker component for the fullscreen quad so we can update it on window resize
#[derive(Component)]
struct FullscreenQuad;

/// Update fullscreen quad transforms when the primary window is resized.
fn resize_fullscreen_quad(
    primary_window: Single<&Window, With<PrimaryWindow>>,
    mut transform: Single<&mut Transform, With<FullscreenQuad>>,
) {
    let size = Vec2::new(
        primary_window.resolution.width(),
        primary_window.resolution.height(),
    );
    transform.scale = Vec3::new(size.x, size.y, 1.0);
}

// This is the struct that will be passed to your shader
#[derive(Asset, TypePath, AsBindGroup, Clone)]
struct CustomMaterial {}

/// The Material2d 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 Material2d api docs for details!
impl Material2d for CustomMaterial {
    fn fragment_shader() -> ShaderRef {
        SHADER_ASSET_PATH.into()
    }

    fn alpha_mode(&self) -> AlphaMode2d {
        AlphaMode2d::Opaque
    }
}