Disallow piece placement when piece is not connected to adjacent piece or exit

interface/constants/Pieces.ts

@@ -294,7 +294,7 @@ const T_JUNCTION_ROAD: Piece = new Piece({
     },
     {
       startPoint: Direction.WEST,
-      type: TrackType.RAIL,
+      type: TrackType.ROAD,
     },
   ],
 });

interface/types/Cell.ts

@@ -1,10 +1,12 @@
 import { CellType } from "../constants/CellType";
-import { Direction } from "../constants/Direction";
+import { Direction, directions } from "../constants/Direction";
 import { ExitType } from "../constants/ExitType";
 import { PieceId, pieceMap } from "../constants/Pieces";
+import { TrackType } from "../constants/TrackType";
 import { Exit } from "./Exit";
 import { ExternalNode } from "./ExternalNode";
 import { InternalNode } from "./InternalNode";
+import { Piece } from "./Piece";
 import { PlacedPiece } from "./PlacedPiece";
 
 export class Cell {
@@ -33,45 +35,72 @@ export class Cell {
 
   public placePiece(pieceId: PieceId) {
     if (this.placedPiece !== undefined) return;
-    const piece = pieceMap[pieceId];
-    const connectionTypes = Array.from(piece.tracks).flatMap((track) => {
-      const directions =
-        track.joinedPoints.secondPoint instanceof InternalNode
-          ? [track.joinedPoints.firstPoint]
-          : [track.joinedPoints.firstPoint, track.joinedPoints.secondPoint];
-      return directions.map((direction) => {
-        return { direction: direction, type: track.type };
-      });
-    });
-    connectionTypes.forEach(({ direction, type }) => {
-      const adjacentPoint = this.getNodeAt(direction).traverseBorder();
-      if (adjacentPoint instanceof Exit) {
-        if (
-          adjacentPoint.type !== ExitType.AMBIVALENT &&
-          adjacentPoint.type.toString() !== type.toString()
-        ) {
-          throw Error(
-            `Unable to place piece, invalid border at direction ${direction}`,
-          );
-        }
-      } else {
-        if (adjacentPoint.cell.placedPiece !== undefined) {
-          const adjacentTrack =
-            adjacentPoint.cell.placedPiece.piece.findTrackForDirection(
-              adjacentPoint.direction,
-            );
-          if (adjacentTrack !== undefined && adjacentTrack.type !== type) {
-            throw Error(
-              `Unable to place piece next to another due to conflicting track types at ${direction}`,
-            );
-          }
-        }
-      }
-    });
+    const piece: Piece = pieceMap[pieceId];
+
+    this.validatePiecePlacement(piece);
 
     this.placedPiece = {
       piece: piece.toPlacedPiece(this),
       id: pieceId,
     };
   }
+
+  private validatePiecePlacement(piece: Piece) {
+    const hasAnyConnection = Array.from(piece.tracks)
+      .map((track) => {
+        const trackExternalNodes = [
+          this.getNodeAt(track.joinedPoints.firstPoint),
+        ];
+        if (!(track.joinedPoints.secondPoint instanceof InternalNode)) {
+          trackExternalNodes.push(
+            this.getNodeAt(track.joinedPoints.secondPoint),
+          );
+        }
+        return {
+          trackExternalNodes: trackExternalNodes,
+          trackType: track.type,
+        };
+      })
+      .some(({ trackExternalNodes, trackType }) => {
+        let isTrackConnected: boolean = false;
+        trackExternalNodes
+          .filter((node) => node.traverseBorder() instanceof Exit)
+          .forEach((node) => {
+            const exitType = (node.traverseBorder() as Exit).type;
+            isTrackConnected = true;
+            if (
+              exitType !== ExitType.AMBIVALENT &&
+              exitType.toString() !== trackType.toString()
+            ) {
+              throw Error(
+                `Unable to place piece, invalid exit type at direction ${node.direction}`,
+              );
+            }
+          });
+
+        trackExternalNodes
+          .filter((node) => node.traverseBorder() instanceof ExternalNode)
+          .forEach((node) => {
+            const adjacentExternalNode = node.traverseBorder() as ExternalNode;
+            const adjacentTrack =
+              adjacentExternalNode.cell.placedPiece?.piece.findTrackForDirection(
+                adjacentExternalNode.direction,
+              );
+            if (adjacentTrack !== undefined) {
+              isTrackConnected = true;
+              if (adjacentTrack.type !== trackType) {
+                throw Error(
+                  `Unable to place piece next to another due to conflicting track types at ${node.direction}`,
+                );
+              }
+            }
+          });
+
+        return isTrackConnected;
+      });
+
+    if (!hasAnyConnection) {
+      throw Error("No adjacent exit or piece available to connect to");
+    }
+  }
 }