feat(health): added damage event and vulnerable structs

src/health/event.rs

@@ -0,0 +1,22 @@
+use bevy::prelude::*;
+
+use crate::health::Health;
+
+/// Event that is called on entities when they should recieve damage
+#[derive(EntityEvent)]
+pub struct Damage {
+    entity: Entity,
+    damage: usize
+}
+
+/// Marker-component that marks entity for an automatic damage handling
+#[derive(Component)]
+#[require(Health)]
+pub struct Vulnerable;
+
+/// Damages every vulnerable health components.
+pub(super) fn damage_vulnerable_system(event: On<Damage>, mut health_query: Query<&mut Health,With<Vulnerable>>) {
+    if let Ok(mut health) = health_query.get_mut(event.entity) {
+        health.damage(event.damage);
+    }
+}

src/health/mod.rs

@@ -1,9 +1,75 @@
 use bevy::prelude::*;
 
+use event::damage_vulnerable_system;
+
+pub use event::{Damage,Vulnerable};
+
+pub mod event;
+
+/// Health plugin provides systems to handle health modifications and events
 pub struct HealthPlugin;
 
 impl Plugin for HealthPlugin {
     fn build(&self, app: &mut App) {
-        //todo!()
+        app.add_systems(PostUpdate,cleanup_killed).add_observer(damage_vulnerable_system);
+    }
+}
+
+/// Component that holds health points and max health points of entity
+#[derive(Component)]
+pub struct Health {
+    health: usize,
+    max_health: usize,
+}
+
+impl Default for Health {
+    fn default() -> Self {
+        Self { health: 1, max_health: 1 }
+    }
+}
+
+impl Health {
+    /// Create new health component with set 'health' and 'max_health'.
+    pub fn new(health: usize, max_health: usize) -> Self {
+        Self {
+            health,
+            max_health
+        }
+    }
+    /// Create new health component from max health.
+    pub fn from_max(max_health: usize) -> Self {
+        Self {
+            health: max_health,
+            max_health
+        }
+    }
+
+    /// Substract 'damage' amount of health points from component with boundary check.
+    pub fn damage(&mut self, damage: usize) {
+        self.health = if damage > self.health {0} else {self.health - damage};
+    }
+    /// Add 'heal' amount of health points to component with max health as a boundary.
+    pub fn heal_no_overheal(&mut self, heal: usize) {
+        self.health = if self.health + heal > self.max_health {self.max_health} else {self.health + heal};
+    }
+    /// Add 'heal' amount of health points to component with usize::MAX as a boundary.
+    pub fn heal_with_overheal(&mut self, heal: usize) {
+        self.health = if usize::MAX-heal < self.health {usize::MAX} else {self.health + heal};
+    }
+    pub fn get_health(&self) -> usize {
+        self.health
+    }
+}
+
+/// Marker component that marks entity to NOT be despawned at the end of frame when health reaches zero
+#[derive(Component)]
+#[require(Health)]
+pub struct Unkillable;
+
+fn cleanup_killed(mut commands: Commands, query: Query<(Entity, &Health), Without<Unkillable>>) {
+    for (entity, health) in query {
+        if health.health == 0 {
+            commands.entity(entity).despawn();
+        }
     }
 }