//! Demonstrates parallax-corrected cubemap reflections.

use core::f32;

use bevy::{
    camera::Hdr,
    camera_controller::free_camera::{FreeCamera, FreeCameraPlugin},
    light::ParallaxCorrection,
    prelude::*,
};

use crate::widgets::{WidgetClickEvent, WidgetClickSender};

#[path = "../helpers/widgets.rs"]
mod widgets;

/// A marker component for the inner rotating reflective cube.
#[derive(Clone, Component)]
struct InnerCube;

/// The brightness of the cubemap.
///
/// Since the cubemap image was baked in Blender, which uses a different
/// exposure setting than that of Bevy, we need this factor in order to make the
/// exposure of the baked image match ours.
const ENVIRONMENT_MAP_INTENSITY: f32 = 100.0;

const OUTER_CUBE_URL: &str =
    "https://github.com/bevyengine/bevy_asset_files/raw/main/pccm_example/outer_cube.glb#Scene0";
const ENV_DIFFUSE_URL: &str =
    "https://github.com/bevyengine/bevy_asset_files/raw/main/pccm_example/env_diffuse.ktx2";
const ENV_SPECULAR_URL: &str =
    "https://github.com/bevyengine/bevy_asset_files/raw/main/pccm_example/env_specular.ktx2";

/// The current value of user-customizable settings for this demo.
#[derive(Resource, Default)]
struct AppStatus {
    /// Whether parallax correction is enabled.
    pccm_enabled: PccmEnableStatus,
}

/// Whether parallax correction is enabled.
#[derive(Clone, Copy, PartialEq, Default)]
enum PccmEnableStatus {
    /// Parallax correction is enabled.
    #[default]
    Enabled,
    /// Parallax correction is disabled.
    Disabled,
}

/// The example entry point.
fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins.set(WindowPlugin {
                primary_window: Some(Window {
                    title: "Bevy Parallax-Corrected Cubemaps Example".into(),
                    ..default()
                }),
                ..default()
            }),
            FreeCameraPlugin,
        ))
        .init_resource::<AppStatus>()
        .add_message::<WidgetClickEvent<PccmEnableStatus>>()
        .add_systems(Startup, setup)
        .add_systems(Update, widgets::handle_ui_interactions::<PccmEnableStatus>)
        .add_systems(
            Update,
            (handle_pccm_enable_change, update_radio_buttons)
                .after(widgets::handle_ui_interactions::<PccmEnableStatus>),
        )
        .run();
}

/// Creates the initial scene.
fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // Spawn the glTF scene.
    commands.spawn(WorldAssetRoot(asset_server.load(OUTER_CUBE_URL)));

    spawn_camera(&mut commands);
    spawn_inner_cube(&mut commands, &mut meshes, &mut materials);
    spawn_reflection_probe(&mut commands, &asset_server);
    spawn_buttons(&mut commands);
}

/// Spawns the camera.
fn spawn_camera(commands: &mut Commands) {
    commands.spawn((
        Camera3d::default(),
        FreeCamera::default(),
        Transform::from_xyz(0.0, 0.0, 4.0).looking_at(Vec3::new(0.0, -2.5, 0.0), Dir3::Y),
        Hdr,
    ));
}

/// Spawns the inner reflective cube in the scene.
fn spawn_inner_cube(
    commands: &mut Commands,
    meshes: &mut Assets<Mesh>,
    materials: &mut Assets<StandardMaterial>,
) {
    let cube_mesh = meshes.add(
        Cuboid {
            half_size: Vec3::new(5.0, 1.0, 2.0),
        }
        .mesh()
        .build()
        .with_duplicated_vertices()
        .with_computed_flat_normals(),
    );
    let cube_material = materials.add(StandardMaterial {
        base_color: Color::WHITE,
        metallic: 1.0,
        reflectance: 1.0,
        perceptual_roughness: 0.0,
        ..default()
    });

    commands.spawn((
        Mesh3d(cube_mesh),
        MeshMaterial3d(cube_material),
        Transform::from_xyz(0.0, -4.0, -2.5),
        InnerCube,
    ));
}

/// Spawns the reflection probe (i.e. cubemap reflection) in the center of the scene.
fn spawn_reflection_probe(commands: &mut Commands, asset_server: &AssetServer) {
    let diffuse_map = asset_server.load(ENV_DIFFUSE_URL);
    let specular_map = asset_server.load(ENV_SPECULAR_URL);
    commands.spawn((
        LightProbe::default(),
        EnvironmentMapLight {
            diffuse_map,
            specular_map,
            intensity: ENVIRONMENT_MAP_INTENSITY,
            ..default()
        },
        // HACK: slightly larger than 10.0 to avoid z-fighting from the outer cube
        // faces being partially inside and partially outside the light probe influence
        // volume. We should have a smooth falloff probe transition option at some point.
        Transform::from_scale(Vec3::splat(10.01)),
    ));
}

/// Spawns the buttons at the bottom of the screen.
fn spawn_buttons(commands: &mut Commands) {
    commands.spawn((
        widgets::main_ui_node(),
        children![widgets::option_buttons(
            "Parallax Correction",
            &[
                (PccmEnableStatus::Enabled, "On"),
                (PccmEnableStatus::Disabled, "Off"),
            ],
        )],
    ));
}

/// Handles a change to the parallax correction setting UI.
fn handle_pccm_enable_change(
    mut commands: Commands,
    light_probe_query: Query<Entity, With<LightProbe>>,
    mut app_status: ResMut<AppStatus>,
    mut messages: MessageReader<WidgetClickEvent<PccmEnableStatus>>,
) {
    let Some(light_probe_entity) = light_probe_query.iter().next() else {
        return;
    };

    for message in messages.read() {
        // The UI message contains the `PccmEnableStatus` value that the user
        // selected.
        app_status.pccm_enabled = **message;

        // Add the appropriate variant of the `ParallaxCorrection` component.
        match **message {
            PccmEnableStatus::Enabled => {
                commands
                    .entity(light_probe_entity)
                    .insert(ParallaxCorrection::Auto);
            }
            PccmEnableStatus::Disabled => {
                commands
                    .entity(light_probe_entity)
                    .insert(ParallaxCorrection::None);
            }
        }
    }
}

/// Updates the state of the UI at the bottom of the screen to reflect the
/// current application settings.
fn update_radio_buttons(
    mut widgets_query: Query<(
        Entity,
        Option<&mut BackgroundColor>,
        Has<Text>,
        &WidgetClickSender<PccmEnableStatus>,
    )>,
    app_status: Res<AppStatus>,
    mut text_ui_writer: TextUiWriter,
) {
    for (entity, maybe_bg_color, has_text, sender) in &mut widgets_query {
        // The `sender` value contains the `PccmEnableStatus` that the user
        // selected.
        let selected = app_status.pccm_enabled == **sender;

        if let Some(mut bg_color) = maybe_bg_color {
            widgets::update_ui_radio_button(&mut bg_color, selected);
        }
        if has_text {
            widgets::update_ui_radio_button_text(entity, &mut text_ui_writer, selected);
        }
    }
}
