Proof-of-concept for fuel change event handling

Added a `FuelChanged` event which is to be used to trigger Observers
watching for a machine's fuel level change.

I've written a slapdash observer to emit these events when the cutting
machine's big red button is pressed. That observer *must* be replaced
because of how it feeds the machine ID into the UI (it only works when
there is exactly 1 CuttingMachine, which won't be the case).

The dummy machines are missing their machine components. I've added the
`CuttingMachine` component to the cutting machine just to test the event
passing.

src/game/mod.rs

@@ -34,4 +34,7 @@ pub mod consumables {
 
   #[derive(Component)]
   pub struct Fuel(u32);
+
+  #[derive(Event)]
+  pub struct FuelChanged;
 }

src/main.rs

@@ -1,9 +1,10 @@
-use bevy::{color::palettes::css::GREEN, prelude::*, window::WindowResolution};
+use bevy::{color::palettes::css::*, prelude::*, window::WindowResolution};
 use bevy_inspector_egui::{bevy_egui::EguiPlugin, quick::WorldInspectorPlugin};
 
 use crate::{
-  game::machines::{CuttingMachine, RotatingMachine},
+  game::machines::{CuttingMachine, FlippingMachine, RotatingMachine, TransposingMachine},
   resources::UiTheme,
+  widgets::SpawnUi,
 };
 
 mod assets;
@@ -24,7 +25,7 @@ fn main() {
     .add_plugins(EguiPlugin::default())
     .add_plugins(WorldInspectorPlugin::new())
     .add_plugins(widgets::GameUiPlugin)
-    .add_systems(Startup, (setup, assets::load_assets, dummy_machine))
+    .add_systems(Startup, (setup, assets::load_assets, dummy_machines))
     .run();
 }
 
@@ -39,26 +40,51 @@ fn despawn<T: Component>(mut commands: Commands, to_despawn: Query<Entity, With<
   }
 }
 
-fn dummy_machine(
-  mut commands: Commands,
-  // mut meshes: ResMut<Assets<Mesh>>,
-  // mut materials: ResMut<Assets<ColorMaterial>>,
-) {
+/// Dev tool for spawning dummy entities. I'm developing their UIs by hooking
+/// up to these while the TileMap gets ready.
+fn dummy_machines(mut commands: Commands) {
+  // Spawn a dummy Cutting Machine
+  commands
+    .spawn((
+      CuttingMachine,
+      Sprite::from_color(RED, Vec2::splat(40.0)),
+      Transform::from_translation(Vec3::new(-40.0, 40.0, 0.0)),
+      Pickable::default(),
+    ))
+    .observe(spawn_machine_ui::<CuttingMachine>);
+
   commands
     .spawn((
       Sprite::from_color(GREEN, Vec2::splat(40.0)),
-      // WARN: Mesh picking is not part of the `DefaultPlugins` plugin collection!
-      // (but sprite picking is!)
-
-      // Mesh2d(meshes.add(Rectangle::new(25., 25.))),
-      // MeshMaterial2d(materials.add(ColorMaterial::from_color(GREEN))),
-      Transform::default(),
+      Transform::from_translation(Vec3::new(40.0, 40.0, 0.0)),
       Pickable::default(),
     ))
-    .observe(
-      |event: Trigger<Pointer<Click>>, commands: Commands, theme: Res<UiTheme>| {
-        let entity = event.target;
-        CuttingMachine::spawn_ui(commands, theme);
-      },
-    );
+    .observe(spawn_machine_ui::<RotatingMachine>);
+
+  // TODO: The other observers, once they have a spawner struct & impl.
+  commands
+    .spawn((
+      Sprite::from_color(PURPLE, Vec2::splat(40.)),
+      Transform::from_translation(Vec3::new(-40.0, -40.0, 0.0)),
+      Pickable::default(),
+    ))
+    .observe(spawn_machine_ui::<FlippingMachine>);
+
+  commands
+    .spawn((
+      Sprite::from_color(DARK_ORANGE, Vec2::splat(40.)),
+      Transform::from_translation(Vec3::new(40.0, -40.0, 0.0)),
+      Pickable::default(),
+    ))
+    .observe(spawn_machine_ui::<TransposingMachine>);
+}
+
+fn spawn_machine_ui<M: SpawnUi>(
+  event: Trigger<Pointer<Click>>,
+  commands: Commands,
+  theme: Res<UiTheme>,
+) {
+  let _entity = event.target;
+  // TODO: Hook up the Fuel component (and spawn one so that I can)
+  M::spawn_ui(commands, theme);
 }

src/widgets/fuel_gauge.rs

@@ -0,0 +1,32 @@
+use bevy::{color::palettes::css::*, prelude::*, ui::Val::*};
+
+use crate::game::consumables::{Fuel, FuelChanged};
+
+#[derive(Component)]
+#[require(Label)]
+pub struct FuelGauge(Entity);
+
+impl FuelGauge {
+  /// Default bundle for a machine's fuel gauge widget. Give it the ID of the
+  /// machine whose info it is displaying.
+  pub fn bundle(target: Entity) -> impl Bundle {
+    (
+      FuelGauge(target),
+      Node {
+        min_width: Px(20.0),
+        min_height: Px(10.0),
+        ..default()
+      },
+      BackgroundColor(GREEN.into()),
+      Text::new("Fuel: "),
+      children![TextSpan::new("<n>"),],
+    )
+  }
+
+  pub fn detect_fuel_change(event: Trigger<FuelChanged>) {
+    dbg!(format!(
+      "Detected fuel change on entity ID: {}",
+      event.target()
+    ));
+  }
+}

src/widgets/machines.rs

@@ -1,25 +1,18 @@
-use bevy::{color::palettes::css::*, prelude::*, ui::Val::*};
+use bevy::{color::palettes::css::*, prelude::*};
 
 use crate::{
-  game::machines::*,
+  game::{consumables::FuelChanged, machines::*},
   resources::UiTheme,
-  widgets::{BigRedButton, machine_ui_base},
+  widgets::{BigRedButton, SpawnUi, fuel_gauge::FuelGauge, machine_ui_base},
 };
 
-impl CuttingMachine {
-  pub fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+impl SpawnUi for CuttingMachine {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
     let base_entity = machine_ui_base(&mut commands, "Cutting Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
       // Left panel. For fuel or machine stats or whatever.
-      commands.spawn((
-        Node {
-          padding: UiRect::all(Px(10.0)),
-          ..default()
-        },
-        BackgroundColor(GREEN.into()),
-        Pickable::default(),
-        children![(Text::new("Uses: <n>"), TextColor(BLACK.into()),)],
-      ));
+      // TODO: Pass along target machine, not the UI's root entity.
+      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
 
       // Center panel (placeholder for the Card view)
       commands.spawn((
@@ -43,7 +36,20 @@ impl CuttingMachine {
           Pickable::default(),
         ))
         .with_children(|cmds| {
-          let _button_cmds = cmds.spawn(BigRedButton::bundle("CUT"));
+          let mut button_cmds = cmds.spawn(BigRedButton::bundle("CUT"));
+          button_cmds.observe(
+            |trigger: Trigger<Pointer<Click>>,
+             mut com: Commands,
+             q: Single<(Entity, &CuttingMachine)>| {
+              dbg!("Cut button pressed. Triggering a FuelChanged event");
+
+              // Feed through the target machine, once the SpawnUi trait is updated
+              // to require it gets here in the first place.
+
+              let cutting_machine = q.0;
+              com.trigger_targets(FuelChanged, cutting_machine);
+            },
+          );
           // TODO: Attach on-press observer so this machine can do something
           // in response to that button being pressed
         });
@@ -51,19 +57,11 @@ impl CuttingMachine {
   }
 }
 
-impl RotatingMachine {
-  pub fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+impl SpawnUi for RotatingMachine {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
     let base_entity = machine_ui_base(&mut commands, "Rotating Machine", &theme);
     commands.entity(base_entity).with_children(|commands| {
-      commands.spawn((
-        Node {
-          padding: UiRect::all(Px(10.0)),
-          ..Default::default()
-        },
-        BackgroundColor(GREEN.into()),
-        Pickable::default(),
-        children![(Text::new("Uses: <n>"), TextColor(BLACK.into()))],
-      ));
+      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
 
       // Center panel (placeholder for input-output rotation)
       commands.spawn((
@@ -93,3 +91,73 @@ impl RotatingMachine {
     });
   }
 }
+
+impl SpawnUi for FlippingMachine {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+    let base_entity = machine_ui_base(&mut commands, "Flipping Machine", &theme);
+    commands.entity(base_entity).with_children(|commands| {
+      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+
+      // Center panel (placeholder)
+      commands.spawn((
+        Node::default(),
+        BackgroundColor(BLUE.into()),
+        Pickable::default(),
+        children![
+          Text::new("Card Flipping placeholder"),
+          TextColor(MAGENTA.into()),
+        ],
+      ));
+
+      // Right panel go button
+      commands
+        .spawn((
+          Node {
+            align_items: AlignItems::End,
+            ..Default::default()
+          },
+          BackgroundColor(DARK_GRAY.into()),
+          Pickable::default(),
+        ))
+        .with_children(|cmds| {
+          let _button_cmds = cmds.spawn(BigRedButton::bundle("FLIP"));
+          // TODO: Attach on-press observer to the button.
+        });
+    });
+  }
+}
+
+impl SpawnUi for TransposingMachine {
+  fn spawn_ui(mut commands: Commands, theme: Res<UiTheme>) {
+    let base_entity = machine_ui_base(&mut commands, "Transposing Machine", &theme);
+    commands.entity(base_entity).with_children(|commands| {
+      commands.spawn(FuelGauge::bundle(Entity::PLACEHOLDER));
+
+      // Center panel (placeholder)
+      commands.spawn((
+        Node::default(),
+        BackgroundColor(BLUE.into()),
+        Pickable::default(),
+        children![
+          Text::new("Card Transposition placeholder"),
+          TextColor(MAGENTA.into()),
+        ],
+      ));
+
+      // Right panel go button
+      commands
+        .spawn((
+          Node {
+            align_items: AlignItems::End,
+            ..Default::default()
+          },
+          BackgroundColor(DARK_GRAY.into()),
+          Pickable::default(),
+        ))
+        .with_children(|cmds| {
+          let _button_cmds = cmds.spawn(BigRedButton::bundle("SWAP"));
+          // TODO: Attach on-press observer to the button.
+        });
+    });
+  }
+}

src/widgets/mod.rs

@@ -1,10 +1,11 @@
 //! Catch-all location for UI bits
 
+mod fuel_gauge;
 pub mod machines;
 
 use bevy::{color::palettes::css::*, prelude::*, ui::Val::*};
 
-use crate::resources::UiTheme;
+use crate::{resources::UiTheme, widgets::fuel_gauge::FuelGauge};
 
 /// Plugin to set up systems & resources for the custom UI elements
 ///
@@ -24,10 +25,19 @@ impl Plugin for GameUiPlugin {
       .add_observer(BigRedButton::button_hover_start)
       .add_observer(BigRedButton::button_hover_stop)
       .add_observer(BigRedButton::button_press_start)
-      .add_observer(BigRedButton::button_press_stop);
+      .add_observer(BigRedButton::button_press_stop)
+      .add_observer(FuelGauge::detect_fuel_change);
   }
 }
 
+/// Anything that can spawn a themed UI should impl this trait.
+///
+/// This exists mainly so that I can write generic functions and have the *compiler*
+/// expand the code for me, instead of doing it by hand.
+pub trait SpawnUi {
+  fn spawn_ui(commands: Commands, theme: Res<UiTheme>);
+}
+
 /// The base panel for the machines that manipulate the room cards.
 ///
 /// This function is not a valid Bevy System because of how the Commands struct