server: Add slime attacks

server/src/implementation/entities/mobs/slime/abstract-slime.ts

@@ -1,6 +1,6 @@
 import { Mob } from "../mob";
 import { EventEmitter2 } from "@nestjs/event-emitter";
-import { EntityMoveEvent } from "updater/updater.event";
+import { EntityAttackEvent, EntityMoveEvent } from "updater/updater.event";
 import { EntityType } from "../../entity";
 import { WorldService } from "world/world.service";
 import { distance, projectDistance } from "utils/coordinates";
@@ -14,7 +14,10 @@ import { Direction } from "../../creature";
 export abstract class AbstractSlime extends Mob {
   static readonly MAX_HP: number;
   static readonly MAX_SPEED: number;
-  readonly ATTACK_DISTANCE: number;
+  protected readonly ATTACK_DISTANCE: number;
+  protected readonly ATTACK_COOLDOWN: number = 1;  // in seconds
+
+  protected lastAttackAt: number = 0;  // The last tick the slime attacked
 
   constructor(type: EntityType, x: number, y: number, hp: number, speed: number) {
     super(type, x, y, hp);
@@ -26,12 +29,16 @@ export abstract class AbstractSlime extends Mob {
    *
    * Moves the slime every few ticks
    * @param tick The current game tick
-   * @param serverService A reference to the server service
+   * @param world A reference to the world service
    * @param eventEmitter A reference to the event emitter
    */
   public override tick(tick: number, world: WorldService, eventEmitter: EventEmitter2): void {
     super.tick(tick, world, eventEmitter);
     eventEmitter.emit("entity.move", this.move(WorldService.MS_PER_TICK / 1000, world));
+
+    // Attack
+    const attack = this.tryAttack(tick, world);
+    if (attack) eventEmitter.emit("entity.attack", attack);
   }
 
   /**
@@ -44,8 +51,8 @@ export abstract class AbstractSlime extends Mob {
   public move(time: number, world: WorldService): EntityMoveEvent {
     let target = world.getClosestEntity(this.x, this.y, EntityType.PLAYER) ?? this;
     const dist = distance(this.x, this.y, target.x, target.y);
-    if (dist <= this.ATTACK_DISTANCE) target = this;  // If close enough for attack, don't move closer
-    
+    if (dist <= this.ATTACK_DISTANCE) target = this; // Don't move closer
+
     this.isMoving = target != this;
 
     const maxDist = Math.min(time * this.speed); // Maximum distance the slime can move in this move
@@ -54,6 +61,25 @@ export abstract class AbstractSlime extends Mob {
     return this.moveTo(x, y);
   }
 
+  /**
+   * Attempt to attack the nearest player
+   * 
+   * @param tick The current game tick
+   * @param world A reference to the world service
+   * @returns An event representing the attack, or null if the slime is not attacking
+   */
+  public tryAttack(tick: number, world: WorldService): EntityAttackEvent | null {
+    if (this.isMoving) return null;
+    if ((tick - this.lastAttackAt)*WorldService.MS_PER_TICK/1000 < this.ATTACK_COOLDOWN) return null;
+
+    const target = world.getClosestEntity(this.x, this.y, EntityType.PLAYER);
+    if (target && distance(this.x, this.y, target.x, target.y) <= this.ATTACK_DISTANCE) {
+      this.lastAttackAt = tick;
+      return { id: this.id };
+    }
+    return null;
+  }
+
   /**
    * Override the default getDirTo method for the horizontally moving slime
    *