Multi src astar (#594)

## Description:
Samples border shore tiles and uses multi-a* for determining the
transport ship spawn cell.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

<DISCORD USERNAME>
evan

---------

Co-authored-by: evan <openfrontio@gmail.com>

src/core/pathfinding/SerialAStar.ts

@@ -4,29 +4,42 @@ import { GameMap, TileRef } from "../game/GameMap";
 import { AStar, PathFindResultType } from "./AStar";
 
 export class SerialAStar implements AStar {
-  private fwdOpenSet: PriorityQueue<{ tile: TileRef; fScore: number }>;
-  private bwdOpenSet: PriorityQueue<{ tile: TileRef; fScore: number }>;
+  private fwdOpenSet: PriorityQueue<{
+    tile: TileRef;
+    fScore: number;
+  }>;
+
+  private bwdOpenSet: PriorityQueue<{
+    tile: TileRef;
+    fScore: number;
+  }>;
+
   private fwdCameFrom: Map<TileRef, TileRef>;
   private bwdCameFrom: Map<TileRef, TileRef>;
   private fwdGScore: Map<TileRef, number>;
   private bwdGScore: Map<TileRef, number>;
   private meetingPoint: TileRef | null;
   public completed: boolean;
+  private sources: TileRef[];
+  private closestSource: TileRef;
 
   constructor(
-    private src: TileRef,
+    src: TileRef | TileRef[],
     private dst: TileRef,
-    private canMove: (t: TileRef) => boolean,
     private iterations: number,
     private maxTries: number,
     private gameMap: GameMap,
   ) {
-    this.fwdOpenSet = new PriorityQueue<{ tile: TileRef; fScore: number }>(
-      (a, b) => a.fScore - b.fScore,
-    );
-    this.bwdOpenSet = new PriorityQueue<{ tile: TileRef; fScore: number }>(
-      (a, b) => a.fScore - b.fScore,
-    );
+    this.fwdOpenSet = new PriorityQueue<{
+      tile: TileRef;
+      fScore: number;
+    }>((a, b) => a.fScore - b.fScore);
+
+    this.bwdOpenSet = new PriorityQueue<{
+      tile: TileRef;
+      fScore: number;
+    }>((a, b) => a.fScore - b.fScore);
+
     this.fwdCameFrom = new Map<TileRef, TileRef>();
     this.bwdCameFrom = new Map<TileRef, TileRef>();
     this.fwdGScore = new Map<TileRef, number>();
@@ -34,13 +47,32 @@ export class SerialAStar implements AStar {
     this.meetingPoint = null;
     this.completed = false;
 
-    // Initialize forward search
-    this.fwdGScore.set(src, 0);
-    this.fwdOpenSet.enqueue({ tile: src, fScore: this.heuristic(src, dst) });
+    this.sources = Array.isArray(src) ? src : [src];
+    this.closestSource = this.findClosestSource(dst);
 
-    // Initialize backward search
+    // Initialize forward search with source point(s)
+    this.sources.forEach((startPoint) => {
+      this.fwdGScore.set(startPoint, 0);
+      this.fwdOpenSet.enqueue({
+        tile: startPoint,
+        fScore: this.heuristic(startPoint, dst),
+      });
+    });
+
+    // Initialize backward search from destination
     this.bwdGScore.set(dst, 0);
-    this.bwdOpenSet.enqueue({ tile: dst, fScore: this.heuristic(dst, src) });
+    this.bwdOpenSet.enqueue({
+      tile: dst,
+      fScore: this.heuristic(dst, this.findClosestSource(dst)),
+    });
+  }
+
+  private findClosestSource(tile: TileRef): TileRef {
+    return this.sources.reduce((closest, source) =>
+      this.heuristic(tile, source) < this.heuristic(tile, closest)
+        ? source
+        : closest,
+    );
   }
 
   compute(): PathFindResultType {
@@ -60,8 +92,9 @@ export class SerialAStar implements AStar {
 
       // Process forward search
       const fwdCurrent = this.fwdOpenSet.dequeue()!.tile;
+
+      // Check if we've found a meeting point
       if (this.bwdGScore.has(fwdCurrent)) {
-        // We found a meeting point!
         this.meetingPoint = fwdCurrent;
         this.completed = true;
         return PathFindResultType.Completed;
@@ -71,8 +104,9 @@ export class SerialAStar implements AStar {
 
       // Process backward search
       const bwdCurrent = this.bwdOpenSet.dequeue()!.tile;
+
+      // Check if we've found a meeting point
       if (this.fwdGScore.has(bwdCurrent)) {
-        // We found a meeting point!
         this.meetingPoint = bwdCurrent;
         this.completed = true;
         return PathFindResultType.Completed;
@@ -89,8 +123,8 @@ export class SerialAStar implements AStar {
   private expandTileRef(current: TileRef, isForward: boolean) {
     for (const neighbor of this.gameMap.neighbors(current)) {
       if (
-        neighbor != (isForward ? this.dst : this.src) &&
-        !this.canMove(neighbor)
+        neighbor != (isForward ? this.dst : this.closestSource) &&
+        !this.gameMap.isWater(neighbor)
       )
         continue;
 
@@ -106,21 +140,22 @@ export class SerialAStar implements AStar {
         gScore.set(neighbor, tentativeGScore);
         const fScore =
           tentativeGScore +
-          this.heuristic(neighbor, isForward ? this.dst : this.src);
+          this.heuristic(neighbor, isForward ? this.dst : this.closestSource);
         openSet.enqueue({ tile: neighbor, fScore: fScore });
       }
     }
   }
 
   private heuristic(a: TileRef, b: TileRef): number {
-    // TODO use wrapped
     try {
       return (
-        1.1 * Math.abs(this.gameMap.x(a) - this.gameMap.x(b)) +
-        Math.abs(this.gameMap.y(a) - this.gameMap.y(b))
+        1.1 *
+        (Math.abs(this.gameMap.x(a) - this.gameMap.x(b)) +
+          Math.abs(this.gameMap.y(a) - this.gameMap.y(b)))
       );
     } catch {
       consolex.log("uh oh");
+      return 0;
     }
   }
 
@@ -130,6 +165,7 @@ export class SerialAStar implements AStar {
     // Reconstruct path from start to meeting point
     const fwdPath: TileRef[] = [this.meetingPoint];
     let current = this.meetingPoint;
+
     while (this.fwdCameFrom.has(current)) {
       current = this.fwdCameFrom.get(current)!;
       fwdPath.unshift(current);
@@ -137,6 +173,7 @@ export class SerialAStar implements AStar {
 
     // Reconstruct path from meeting point to goal
     current = this.meetingPoint;
+
     while (this.bwdCameFrom.has(current)) {
       current = this.bwdCameFrom.get(current)!;
       fwdPath.push(current);