//! Expression example.
//!
//! This example demonstrate how to customize the behavior of modifiers by
//! creating complex expressions assigned to their input(s).
//!
//! The entire effect, including the animation, runs on the GPU exclusively. The
//! acceleration varies based on the simulation time by building an expression
//! based on [`ExprWriter::time()`] then assigned to the [`AccelModifier`].

use bevy::{
    core_pipeline::{bloom::Bloom, tonemapping::Tonemapping},
    prelude::*,
};
use bevy_hanabi::prelude::*;

mod utils;
use utils::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let app_exit = utils::make_test_app("expr")
        .add_systems(Startup, setup)
        .run();
    app_exit.into_result()
}

fn setup(mut commands: Commands, mut effects: ResMut<Assets<EffectAsset>>) {
    commands.spawn((
        Transform::from_translation(Vec3::new(3., 12., 20.)).looking_at(Vec3::Y * 5., Vec3::Y),
        Camera3d::default(),
        Camera {
            hdr: true,
            clear_color: Color::BLACK.into(),
            ..default()
        },
        Tonemapping::None,
        Bloom::default(),
    ));

    let mut color_gradient = Gradient::new();
    color_gradient.add_key(0.0, Vec4::new(4.0, 4.0, 4.0, 1.0));
    color_gradient.add_key(0.7, Vec4::new(0.0, 0.0, 4.0, 1.0));
    color_gradient.add_key(1.0, Vec4::new(0.0, 0.0, 0.0, 0.0));

    let mut size_gradient = Gradient::new();
    size_gradient.add_key(0.3, Vec3::new(0.2, 0.02, 1.0));
    size_gradient.add_key(1.0, Vec3::ZERO);

    let writer = ExprWriter::new();

    let age = writer.lit(0.).expr();
    let init_age = SetAttributeModifier::new(Attribute::AGE, age);

    // Give a bit of variation by randomizing the lifetime per particle
    let lifetime = writer.lit(2.5).uniform(writer.lit(3.5)).expr();
    let init_lifetime = SetAttributeModifier::new(Attribute::LIFETIME, lifetime);

    // Create some whirlwind effect by adding some radial acceleration pointing at
    // the origin (0,0,0) and some upward acceleration (alongside Y). The proportion
    // of radial acceleration varies based on the simulation time.
    let pos = writer.attr(Attribute::POSITION);
    let zero = writer.lit(Vec3::ZERO);
    let radial = (pos - zero).normalized();
    let vertical = writer.lit(Vec3::Y * 4.);
    let anim = writer.time().sin() * writer.lit(6.) - writer.lit(6.);
    let accel = radial * anim + vertical;
    let update_accel = AccelModifier::new(accel.expr());

    let init_pos = SetPositionCircleModifier {
        center: writer.lit(Vec3::ZERO).expr(),
        axis: writer.lit(Vec3::Y).expr(),
        radius: writer.lit(4.).expr(),
        dimension: ShapeDimension::Surface,
    };

    let init_vel = SetVelocityTangentModifier {
        origin: writer.lit(Vec3::ZERO).expr(),
        axis: writer.lit(Vec3::Y).expr(),
        speed: writer.lit(3.).expr(),
    };

    let effect = effects.add(
        EffectAsset::new(32768, Spawner::rate(500.0.into()), writer.finish())
            .with_name("whirlwind")
            .init(init_pos)
            .init(init_age)
            .init(init_lifetime)
            .init(init_vel)
            .update(update_accel)
            .render(ColorOverLifetimeModifier {
                gradient: color_gradient,
            })
            .render(SizeOverLifetimeModifier {
                gradient: size_gradient,
                screen_space_size: false,
            })
            .render(OrientModifier::new(OrientMode::AlongVelocity)),
    );

    commands.spawn((
        Name::new("whirlwind"),
        ParticleEffectBundle {
            effect: ParticleEffect::new(effect),
            transform: Transform::IDENTITY,
            ..Default::default()
        },
    ));
}