//! Simple benchmark to test rendering many point lights.
//! Run with `WGPU_SETTINGS_PRIO=webgl2` to restrict to uniform buffers and max 256 lights.

use std::f64::consts::PI;

use bevy::{
    diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
    math::{DVec2, DVec3},
    pbr::{ExtractedPointLight, GlobalLightMeta},
    prelude::*,
    render::{camera::ScalingMode, Render, RenderApp, RenderSet},
    window::{PresentMode, WindowPlugin, WindowResolution},
};
use rand::{thread_rng, Rng};

fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins.set(WindowPlugin {
                primary_window: Some(Window {
                    resolution: WindowResolution::new(1920.0, 1080.0)
                        .with_scale_factor_override(1.0),
                    title: "many_lights".into(),
                    present_mode: PresentMode::AutoNoVsync,
                    ..default()
                }),
                ..default()
            }),
            FrameTimeDiagnosticsPlugin,
            LogDiagnosticsPlugin::default(),
            LogVisibleLights,
        ))
        .add_systems(Startup, setup)
        .add_systems(Update, (move_camera, print_light_count))
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    warn!(include_str!("warning_string.txt"));

    const LIGHT_RADIUS: f32 = 0.3;
    const LIGHT_INTENSITY: f32 = 5.0;
    const RADIUS: f32 = 50.0;
    const N_LIGHTS: usize = 100_000;

    commands.spawn(PbrBundle {
        mesh: meshes.add(
            Mesh::try_from(shape::Icosphere {
                radius: RADIUS,
                subdivisions: 9,
            })
            .unwrap(),
        ),
        material: materials.add(StandardMaterial::from(Color::WHITE)),
        transform: Transform::from_scale(Vec3::NEG_ONE),
        ..default()
    });

    let mesh = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));
    let material = materials.add(StandardMaterial {
        base_color: Color::PINK,
        ..default()
    });

    // NOTE: This pattern is good for testing performance of culling as it provides roughly
    // the same number of visible meshes regardless of the viewing angle.
    // NOTE: f64 is used to avoid precision issues that produce visual artifacts in the distribution
    let golden_ratio = 0.5f64 * (1.0f64 + 5.0f64.sqrt());
    let mut rng = thread_rng();
    for i in 0..N_LIGHTS {
        let spherical_polar_theta_phi = fibonacci_spiral_on_sphere(golden_ratio, i, N_LIGHTS);
        let unit_sphere_p = spherical_polar_to_cartesian(spherical_polar_theta_phi);
        commands.spawn(PointLightBundle {
            point_light: PointLight {
                range: LIGHT_RADIUS,
                intensity: LIGHT_INTENSITY,
                color: Color::hsl(rng.gen_range(0.0..360.0), 1.0, 0.5),
                ..default()
            },
            transform: Transform::from_translation((RADIUS as f64 * unit_sphere_p).as_vec3()),
            ..default()
        });
    }

    // camera
    match std::env::args().nth(1).as_deref() {
        Some("orthographic") => commands.spawn(Camera3dBundle {
            projection: OrthographicProjection {
                scale: 20.0,
                scaling_mode: ScalingMode::FixedHorizontal(1.0),
                ..default()
            }
            .into(),
            ..default()
        }),
        _ => commands.spawn(Camera3dBundle::default()),
    };

    // add one cube, the only one with strong handles
    // also serves as a reference point during rotation
    commands.spawn(PbrBundle {
        mesh,
        material,
        transform: Transform {
            translation: Vec3::new(0.0, RADIUS, 0.0),
            scale: Vec3::splat(5.0),
            ..default()
        },
        ..default()
    });
}

// NOTE: This epsilon value is apparently optimal for optimizing for the average
// nearest-neighbor distance. See:
// http://extremelearning.com.au/how-to-evenly-distribute-points-on-a-sphere-more-effectively-than-the-canonical-fibonacci-lattice/
// for details.
const EPSILON: f64 = 0.36;
fn fibonacci_spiral_on_sphere(golden_ratio: f64, i: usize, n: usize) -> DVec2 {
    DVec2::new(
        PI * 2. * (i as f64 / golden_ratio),
        (1.0 - 2.0 * (i as f64 + EPSILON) / (n as f64 - 1.0 + 2.0 * EPSILON)).acos(),
    )
}

fn spherical_polar_to_cartesian(p: DVec2) -> DVec3 {
    let (sin_theta, cos_theta) = p.x.sin_cos();
    let (sin_phi, cos_phi) = p.y.sin_cos();
    DVec3::new(cos_theta * sin_phi, sin_theta * sin_phi, cos_phi)
}

// System for rotating the camera
fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
    let mut camera_transform = camera_query.single_mut();
    let delta = time.delta_seconds() * 0.15;
    camera_transform.rotate_z(delta);
    camera_transform.rotate_x(delta);
}

// System for printing the number of meshes on every tick of the timer
fn print_light_count(time: Res<Time>, mut timer: Local<PrintingTimer>, lights: Query<&PointLight>) {
    timer.0.tick(time.delta());

    if timer.0.just_finished() {
        info!("Lights: {}", lights.iter().len());
    }
}

struct LogVisibleLights;

impl Plugin for LogVisibleLights {
    fn build(&self, app: &mut App) {
        let Ok(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app.add_systems(Render, print_visible_light_count.in_set(RenderSet::Prepare));
    }
}

// System for printing the number of meshes on every tick of the timer
fn print_visible_light_count(
    time: Res<Time>,
    mut timer: Local<PrintingTimer>,
    visible: Query<&ExtractedPointLight>,
    global_light_meta: Res<GlobalLightMeta>,
) {
    timer.0.tick(time.delta());

    if timer.0.just_finished() {
        info!(
            "Visible Lights: {}, Rendered Lights: {}",
            visible.iter().len(),
            global_light_meta.entity_to_index.len()
        );
    }
}

struct PrintingTimer(Timer);

impl Default for PrintingTimer {
    fn default() -> Self {
        Self(Timer::from_seconds(1.0, TimerMode::Repeating))
    }
}