Add chasing system

src/components.rs

@@ -35,3 +35,6 @@ pub struct WantsToAttack {
     pub attacker: Entity,
     pub victim: Entity,
 }
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct ChasingPlayer;

src/map.rs

@@ -38,4 +38,50 @@ impl Map {
             Some(map_idx(point.x, point.y))
         }
     }
+
+    fn valid_exit(&self, loc: Point, delta: Point) -> Option<usize> {
+        let destination = loc + delta;
+        if self.in_bounds(destination) && self.can_enter_tile(destination) {
+            let idx = self.point2d_to_index(destination);
+            Some(idx)
+        } else {
+            None
+        }
+    }
+}
+
+impl Algorithm2D for Map {
+    fn dimensions(&self) -> Point {
+        Point::new(SCREEN_WIDTH, SCREEN_HEIGHT)
+    }
+
+    fn in_bounds(&self, point: Point) -> bool {
+        self.in_bounds(point)
+    }
+}
+
+impl BaseMap for Map {
+    fn get_available_exits(&self, idx: usize) -> SmallVec<[(usize, f32); 10]> {
+        let mut exits = SmallVec::new();
+        let location = self.index_to_point2d(idx);
+
+        if let Some(idx) = self.valid_exit(location, Point::new(-1, 0)) {
+            exits.push((idx, 1.0));
+        }
+        if let Some(idx) = self.valid_exit(location, Point::new(1, 0)) {
+            exits.push((idx, 1.0));
+        }
+        if let Some(idx) = self.valid_exit(location, Point::new(0, -1)) {
+            exits.push((idx, 1.0));
+        }
+        if let Some(idx) = self.valid_exit(location, Point::new(0, 1)) {
+            exits.push((idx, 1.0));
+        }
+
+        exits
+    }
+
+    fn get_pathing_distance(&self, idx1: usize, idx2: usize) -> f32 {
+        DistanceAlg::Pythagoras.distance2d(self.index_to_point2d(idx1), self.index_to_point2d(idx2))
+    }
 }

src/spawner.rs

@@ -29,7 +29,7 @@ pub fn spawn_monster(ecs: &mut World, rng: &mut RandomNumberGenerator, pos: Poin
             color: ColorPair::new(WHITE, BLACK),
             glyph,
         },
-        MovingRandomly,
+        ChasingPlayer,
         Health {
             current: hp,
             max: hp,

src/systems/mod.rs

@@ -1,3 +1,4 @@
+mod chasing;
 mod combat;
 mod end_turn;
 mod entity_render;
@@ -37,6 +38,7 @@ pub fn build_player_scheduler() -> Schedule {
 
 pub fn build_monster_scheduler() -> Schedule {
     Schedule::builder()
+        .add_system(chasing::chasing_system())
         .add_system(random_move::random_move_system())
         .flush()
         .add_system(combat::combat_system())