use ticks instead of Date when retreating for determinism (#208)

src/core/execution/RetreatExecution.ts

@@ -1,13 +1,13 @@
 import { Execution, Game, Player, PlayerID } from "../game/Game";
 
-const cancelDelay = 2;
+const cancelDelay = 20;
 
 export class RetreatExecution implements Execution {
   private active = true;
   private retreatOrdered = false;
   private player: Player;
-  private executionDateInSecs = new Date().getTime() / 1000 + cancelDelay;
-
+  private startTick: number;
+  private mg: Game;
   constructor(
     private playerID: PlayerID,
     private attackID: string,
@@ -18,19 +18,19 @@ export class RetreatExecution implements Execution {
       console.warn(`RetreatExecution: player ${this.player.id()} not found`);
       return;
     }
+    this.mg = mg;
 
     this.player = mg.player(this.playerID);
+    this.startTick = mg.ticks();
   }
 
   tick(ticks: number): void {
-    const nowInSecs = new Date().getTime() / 1000;
-
     if (!this.retreatOrdered) {
       this.player.orderRetreat(this.attackID);
       this.retreatOrdered = true;
     }
 
-    if (nowInSecs >= this.executionDateInSecs) {
+    if (this.mg.ticks() >= this.startTick + cancelDelay) {
       this.player.executeRetreat(this.attackID);
       this.active = false;
     }