Add chasing system

src/systems/chasing.rs

@@ -0,0 +1,60 @@
+use crate::prelude::*;
+
+#[system]
+#[read_component(Point)]
+#[read_component(ChasingPlayer)]
+#[read_component(Health)]
+#[read_component(Player)]
+pub fn chasing(#[resource] map: &Map, ecs: &SubWorld, commands: &mut CommandBuffer) {
+    let mut movers = <(Entity, &Point, &ChasingPlayer)>::query();
+    let mut positions = <(Entity, &Point, &Health)>::query();
+    let mut player = <(&Point, &Player)>::query();
+    let player_pos = player.iter(ecs).next().unwrap().0;
+    let player_idx = map_idx(player_pos.x, player_pos.y);
+    let search_targets = vec![player_idx];
+    let dijkstra_map = DijkstraMap::new(SCREEN_WIDTH, SCREEN_HEIGHT, &search_targets, map, 1024.0);
+
+    movers.iter(ecs).for_each(|(entity, pos, _)| {
+        let idx = map_idx(pos.x, pos.y);
+        if let Some(destination) = DijkstraMap::find_lowest_exit(&dijkstra_map, idx, map) {
+            let distance = DistanceAlg::Pythagoras.distance2d(*pos, *player_pos);
+            let destination = if distance > 1.2 {
+                map.index_to_point2d(destination)
+            } else {
+                *player_pos
+            };
+
+            let mut attacked = false;
+            positions
+                .iter(ecs)
+                .filter(|(_, target_pos, _)| **target_pos == destination)
+                .for_each(|(victim, _, _)| {
+                    if ecs
+                        .entry_ref(*victim)
+                        .unwrap()
+                        .get_component::<Player>()
+                        .is_ok()
+                    {
+                        commands.push((
+                            (),
+                            WantsToAttack {
+                                attacker: *entity,
+                                victim: *victim,
+                            },
+                        ));
+                        attacked = true;
+                    }
+                });
+
+            if !attacked {
+                commands.push((
+                    (),
+                    WantsToMove {
+                        entity: *entity,
+                        destination,
+                    },
+                ));
+            }
+        }
+    })
+}