Add path cache (#763)

Based on #753

Co-authored-by: Scott Anderson <662325+scottanderson@users.noreply.github.com>

src/core/execution/TradeShipExecution.ts

@@ -98,6 +98,19 @@ export class TradeShipExecution implements Execution {
       }
     }
 
+    const cachedNextTile = this._dstPort.cacheGet(this.tradeShip.tile());
+    if (cachedNextTile !== undefined) {
+      if (
+        this.mg.isWater(cachedNextTile) &&
+        this.mg.isShoreline(cachedNextTile)
+      ) {
+        this.tradeShip.setSafeFromPirates();
+      }
+      this.tradeShip.move(cachedNextTile);
+      this.tilesTraveled++;
+      return;
+    }
+
     const result = this.pathFinder.nextTile(
       this.tradeShip.tile(),
       this._dstPort.tile(),
@@ -112,6 +125,7 @@ export class TradeShipExecution implements Execution {
         this.tradeShip.move(this.tradeShip.tile());
         break;
       case PathFindResultType.NextTile:
+        this._dstPort.cachePut(this.tradeShip.tile(), result.tile);
         // Update safeFromPirates status
         if (this.mg.isWater(result.tile) && this.mg.isShoreline(result.tile)) {
           this.tradeShip.setSafeFromPirates();

src/core/game/Game.ts

@@ -370,6 +370,9 @@ export interface Unit {
 
   // Updates
   toUpdate(): UnitUpdate;
+
+  cachePut(from: TileRef, to: TileRef): void; // ports only
+  cacheGet(from: TileRef): TileRef | undefined; // ports only
 }
 
 export interface TerraNullius {

src/core/game/UnitImpl.ts

@@ -28,6 +28,7 @@ export class UnitImpl implements Unit {
   private _detonationDst: TileRef | undefined = undefined; // Only for nukes
   private _warshipTarget: Unit | undefined = undefined;
   private _cooldownDuration: number | undefined = undefined;
+  private _pathCache: Map<TileRef, TileRef> = new Map();
 
   constructor(
     private _type: UnitType,
@@ -53,6 +54,13 @@ export class UnitImpl implements Unit {
         : 0;
   }
 
+  cachePut(from: TileRef, to: TileRef): void {
+    this._pathCache.set(from, to);
+  }
+  cacheGet(from: TileRef): TileRef | undefined {
+    return this._pathCache.get(from);
+  }
+
   id() {
     return this._id;
   }