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

use bevy::{
    pbr::{MaterialPipeline, MaterialPipelineKey},
    prelude::*,
    reflect::TypePath,
    render::{
        mesh::MeshVertexBufferLayoutRef,
        render_resource::{
            AsBindGroup, RenderPipelineDescriptor, ShaderRef, SpecializedMeshPipelineError,
        },
    },
};

/// This example uses shader source files from the assets subdirectory
const VERTEX_SHADER_ASSET_PATH: &str = "shaders/custom_material.vert";
const FRAGMENT_SHADER_ASSET_PATH: &str = "shaders/custom_material.frag";

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((
        Mesh3d(meshes.add(Cuboid::default())),
        MeshMaterial3d(materials.add(CustomMaterial {
            color: LinearRgba::BLUE,
            color_texture: Some(asset_server.load("branding/icon.png")),
            alpha_mode: AlphaMode::Blend,
        })),
        Transform::from_xyz(0.0, 0.5, 0.0),
    ));

    // camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
    ));
}

// This is the struct that will be passed to your shader
#[derive(Asset, TypePath, AsBindGroup, 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!
/// When using the GLSL shading language for your shader, the specialize method must be overridden.
impl Material for CustomMaterial {
    fn vertex_shader() -> ShaderRef {
        VERTEX_SHADER_ASSET_PATH.into()
    }

    fn fragment_shader() -> ShaderRef {
        FRAGMENT_SHADER_ASSET_PATH.into()
    }

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

    // Bevy assumes by default that vertex shaders use the "vertex" entry point
    // and fragment shaders use the "fragment" entry point (for WGSL shaders).
    // GLSL uses "main" as the entry point, so we must override the defaults here
    fn specialize(
        _pipeline: &MaterialPipeline<Self>,
        descriptor: &mut RenderPipelineDescriptor,
        _layout: &MeshVertexBufferLayoutRef,
        _key: MaterialPipelineKey<Self>,
    ) -> Result<(), SpecializedMeshPipelineError> {
        descriptor.vertex.entry_point = "main".into();
        descriptor.fragment.as_mut().unwrap().entry_point = "main".into();
        Ok(())
    }
}

#version 450

layout(location = 0) in vec3 Vertex_Position;
layout(location = 1) in vec3 Vertex_Normal;
layout(location = 2) in vec2 Vertex_Uv;

layout(location = 0) out vec2 v_Uv;

layout(set = 0, binding = 0) uniform CameraViewProj {
    mat4 clip_from_world;
    // Other attributes exist that can be described here.
    // See full definition in: crates/bevy_render/src/view/view.wgsl
    // Attributes added here must be in the same order as they are defined
    // in view.wgsl, and they must be contiguous starting from the top to
    // ensure they have the same layout.
    //
    // Needing to maintain this mapping yourself is one of the harder parts of using
    // GLSL with Bevy. WGSL provides a much better user experience! 
} camera_view;

struct Mesh {
    mat3x4 Model;
    mat4 InverseTransposeModel;
    uint flags;
};

#ifdef PER_OBJECT_BUFFER_BATCH_SIZE
layout(set = 1, binding = 0) uniform Mesh Meshes[#{PER_OBJECT_BUFFER_BATCH_SIZE}];
#else
layout(set = 1, binding = 0) readonly buffer _Meshes {
    Mesh Meshes[];
};
#endif // PER_OBJECT_BUFFER_BATCH_SIZE

mat4 affine_to_square(mat3x4 affine) {
    return transpose(mat4(
        affine[0],
        affine[1],
        affine[2],
        vec4(0.0, 0.0, 0.0, 1.0)
    ));
}

void main() {
    v_Uv = Vertex_Uv;
    gl_Position = camera_view.clip_from_world
        * affine_to_square(Meshes[gl_InstanceIndex].Model)
        * vec4(Vertex_Position, 1.0);
}

#version 450
layout(location = 0) in vec2 v_Uv;

layout(location = 0) out vec4 o_Target;

layout(set = 2, binding = 0) uniform vec4 CustomMaterial_color;

layout(set = 2, binding = 1) uniform texture2D CustomMaterial_texture;
layout(set = 2, binding = 2) uniform sampler CustomMaterial_sampler;

// wgsl modules can be imported and used in glsl
// FIXME - this doesn't work any more ...
// #import bevy_pbr::pbr_functions as PbrFuncs

void main() {
    // o_Target = PbrFuncs::tone_mapping(Color * texture(sampler2D(CustomMaterial_texture,CustomMaterial_sampler), v_Uv));
    o_Target = CustomMaterial_color * texture(sampler2D(CustomMaterial_texture,CustomMaterial_sampler), v_Uv);
}