bevy 0.20.0

//! Demonstrates implementing a cooldown in UI.
//!
//! You might want a system like this for abilities, buffs or consumables.
//! We create four food buttons to eat with 2, 1, 10, and 4 seconds cooldown.

use bevy::{
    color::palettes::tailwind::{SLATE_400, SLATE_50},
    image::TextureAtlasTemplate,
    prelude::*,
    ui_widgets::{Activate, Button},
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(
            Update,
            animate_cooldowns.run_if(any_with_component::<ActiveCooldown>),
        )
        .add_observer(on_activate_start_cooldown)
        .run();
}

fn setup(mut commands: Commands, mut texture_atlas_layouts: ResMut<Assets<TextureAtlasLayout>>) {
    let layout = TextureAtlasLayout::from_grid(UVec2::splat(64), 7, 7, None, None);
    let texture_atlas_layout = texture_atlas_layouts.add(layout);

    commands.spawn(Camera2d);

    // The food items
    commands.spawn_scene(bsn! {
        Node {
            width: percent(100),
            height: percent(100),
            align_items: AlignItems::Center,
            justify_content: JustifyContent::Center,
            column_gap: px(15),
        }
        Children [
            { food_items_scene_list(texture_atlas_layout) }
        ]
    });

    // Status text
    commands.spawn_scene(bsn! {
        Node {
            position_type: PositionType::Absolute,
            top: px(12),
            left: px(12),
        }
        Children [
            Text("*Click some food to eat it*")
        ]
    });
}

// Returns the scene list of food items.
fn food_items_scene_list(texture_atlas_layout: Handle<TextureAtlasLayout>) -> impl SceneList {
    let foods = [
        FoodItem {
            name: "an apple",
            cooldown: 2.,
            index: 2,
        },
        FoodItem {
            name: "a burger",
            cooldown: 1.,
            index: 23,
        },
        FoodItem {
            name: "chocolate",
            cooldown: 10.,
            index: 32,
        },
        FoodItem {
            name: "cherries",
            cooldown: 4.,
            index: 41,
        },
    ];

    foods
        .into_iter()
        .map(|food| {
            build_ability(
                food,
                "textures/food_kenney.png".into(),
                texture_atlas_layout.clone(),
            )
        })
        .collect::<Vec<_>>()
}

struct FoodItem {
    name: &'static str,
    cooldown: f32,
    index: usize,
}

// Returns a scene of this food item as a button.
fn build_ability(
    food: FoodItem,
    texture: String,
    layout: Handle<TextureAtlasLayout>,
) -> impl Scene {
    let FoodItem {
        name,
        cooldown,
        index,
    } = food;

    // Every food item is a button with a child node.
    // The child node's height will be animated to be at 100% at the beginning
    // of a cooldown, effectively graying out the whole button, and then getting smaller over time.
    bsn! {
        Node {
            width: px(80),
            height: px(80),
            flex_direction: FlexDirection::ColumnReverse,
        }
        BackgroundColor(SLATE_400)
        Button
        ImageNode {
            image: texture,
            texture_atlas: texture_atlas_template(layout, index),
        }
        Cooldown(Timer::from_seconds(cooldown, TimerMode::Once))
        Name(name)
        Children [
            Node {
                width: percent(100),
                height: percent(0),
            }
            BackgroundColor({SLATE_50.with_alpha(0.5)})
        ]
    }
}

// Ensure the texture_atlas in the ImageNode can be set correctly.
fn texture_atlas_template(
    layout: Handle<TextureAtlasLayout>,
    index: usize,
) -> TextureAtlasTemplate {
    TextureAtlasTemplate {
        layout: layout.into(),
        index,
    }
}

#[derive(Component, Clone, Default)]
struct Cooldown(Timer);

#[derive(Component)]
#[component(storage = "SparseSet")]
struct ActiveCooldown;

/// Observer that starts the cooldown whenever a food item button is activated.
fn on_activate_start_cooldown(
    event: On<Activate>,
    mut commands: Commands,
    mut interaction_query: Query<
        (Entity, &mut Cooldown, &Name, Option<&ActiveCooldown>),
        With<Button>,
    >,
    mut text: Query<&mut Text>,
) -> Result {
    if let Ok((entity, mut cooldown, name, on_cooldown)) = interaction_query.get_mut(event.entity) {
        if on_cooldown.is_none() {
            cooldown.0.reset();
            commands.entity(entity).insert(ActiveCooldown);
            **text.single_mut()? = format!("You ate {name}");
        } else {
            **text.single_mut()? = format!(
                "You can eat {name} again in {} seconds.",
                cooldown.0.remaining_secs().ceil()
            );
        }
    }

    Ok(())
}

fn animate_cooldowns(
    time: Res<Time>,
    mut commands: Commands,
    buttons: Query<(Entity, &mut Cooldown, &Children), With<ActiveCooldown>>,
    mut nodes: Query<&mut Node>,
) -> Result {
    for (entity, mut timer, children) in buttons {
        timer.0.tick(time.delta());
        let cooldown = children.first().ok_or("No child")?;
        if timer.0.just_finished() {
            commands.entity(entity).remove::<ActiveCooldown>();
            nodes.get_mut(*cooldown)?.height = percent(0);
        } else {
            nodes.get_mut(*cooldown)?.height = percent((1. - timer.0.fraction()) * 100.);
        }
    }

    Ok(())
}