backpack implementation (#15)

src/backpack/mod.rs

@@ -0,0 +1,38 @@
+mod backpack_ui;
+
+use crate::heads_ui::HEAD_COUNT;
+use bevy::prelude::*;
+
+pub use backpack_ui::BackpackAction;
+
+#[derive(Clone, Copy, Debug)]
+pub struct BackpackHead {
+    pub head: usize,
+    pub health: f32,
+}
+
+#[derive(Resource, Default)]
+pub struct Backpack {
+    pub heads: Vec<BackpackHead>,
+}
+
+#[derive(Event)]
+pub struct BackbackSwapEvent(pub usize);
+
+pub fn plugin(app: &mut App) {
+    app.add_plugins(backpack_ui::plugin);
+
+    app.add_systems(Startup, setup);
+}
+
+fn setup(mut commands: Commands) {
+    commands.insert_resource(Backpack {
+        heads: (0usize..HEAD_COUNT)
+            .into_iter()
+            .map(|i| BackpackHead {
+                head: i,
+                health: 1.,
+            })
+            .collect(),
+    });
+}