//! Plays animations from a skinned glTF.

use std::{f32::consts::PI, time::Duration};

use bevy::{pbr::CascadeShadowConfigBuilder, prelude::*};

const FOX_PATH: &str = "models/animated/Fox.glb";

fn main() {
    App::new()
        .insert_resource(AmbientLight {
            color: Color::WHITE,
            brightness: 2000.,
            ..default()
        })
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, setup_scene_once_loaded)
        .run();
}

#[derive(Resource)]
struct Animations {
    graph_handle: Handle<AnimationGraph>,
    index: AnimationNodeIndex,
}

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut graphs: ResMut<Assets<AnimationGraph>>,
) {
    // Build the animation graph
    let (graph, index) = AnimationGraph::from_clip(
        // We specifically want the "walk" animation, which is the first one.
        asset_server.load(GltfAssetLabel::Animation(0).from_asset(FOX_PATH)),
    );

    // Keep our animation graph in a Resource so that it can be inserted onto
    // the correct entity once the scene actually loads.
    let graph_handle = graphs.add(graph);
    commands.insert_resource(Animations {
        graph_handle: graph_handle.clone(),
        index,
    });

    // Camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(100.0, 100.0, 150.0).looking_at(Vec3::new(0.0, 20.0, 0.0), Vec3::Y),
    ));

    // Plane
    commands.spawn((
        Mesh3d(meshes.add(Plane3d::default().mesh().size(500000.0, 500000.0))),
        MeshMaterial3d(materials.add(Color::srgb(0.3, 0.5, 0.3))),
    ));

    // Light
    commands.spawn((
        Transform::from_rotation(Quat::from_euler(EulerRot::ZYX, 0.0, 1.0, -PI / 4.)),
        DirectionalLight {
            shadows_enabled: true,
            ..default()
        },
        CascadeShadowConfigBuilder {
            first_cascade_far_bound: 200.0,
            maximum_distance: 400.0,
            ..default()
        }
        .build(),
    ));

    // Fox
    commands.spawn((
        SceneRoot(asset_server.load(GltfAssetLabel::Scene(0).from_asset(FOX_PATH))),
        AnimationGraphHandle(graph_handle),
    ));
}

// Once the scene is loaded, start the animation
fn setup_scene_once_loaded(
    mut commands: Commands,
    animations: Res<Animations>,
    mut players: Query<(Entity, &mut AnimationPlayer), Added<AnimationPlayer>>,
) {
    for (entity, mut player) in &mut players {
        let mut transitions = AnimationTransitions::new();

        // Make sure to start the animation via the `AnimationTransitions`
        // component. The `AnimationTransitions` component wants to manage all
        // the animations and will get confused if the animations are started
        // directly via the `AnimationPlayer`.
        transitions
            .play(&mut player, animations.index, Duration::ZERO)
            .repeat();

        commands
            .entity(entity)
            .insert(transitions)
            .insert(AnimationGraphHandle(animations.graph_handle.clone()));
    }
}