fix the canMove function to cover a edge-case

packages/game-engine/src/board.test.ts

@@ -58,7 +58,7 @@ describe('Board', () => {
     expect(hasTile(board, { value: 2 })).toBe(false)
   })
 
-  it('The board can move if there is at least one empty cell', () => {
+  it('The board can move if there is at least one reachable empty cell', () => {
     let board = createEmptyBoard(3)
     board = setCell(board, { x: 0, y: 0 }, { value: 2 })
     board = setCell(board, { x: 1, y: 0 }, { value: 4 })
@@ -146,6 +146,28 @@ describe('Board', () => {
     expect(canMove(board)).toBe(false)
   })
 
+  it('The board cannot move if there are unreachable cells', () => {
+    let board = createEmptyBoard(3)
+    board = setCell(board, { x: 0, y: 0 }, { obstacle: true })
+    board = setCell(board, { x: 1, y: 0 }, { value: 2 })
+    board = setCell(board, { x: 2, y: 0 }, { value: 1 })
+    board = setCell(board, { x: 0, y: 1 }, { obstacle: true })
+    board = setCell(board, { x: 1, y: 1 }, { obstacle: true })
+    board = setCell(board, { x: 2, y: 1 }, { value: 2 })
+    board = setCell(board, { x: 0, y: 2 }, null)
+    board = setCell(board, { x: 1, y: 2 }, { obstacle: true })
+    board = setCell(board, { x: 2, y: 2 }, { value: 1 })
+
+    // prettier-ignore
+    expect(boardToMatrix(board)).toEqual([
+      ['X' , 2   , 1],
+      ['X' , 'X' , 2],
+      [null, 'X' , 1],
+    ])
+
+    expect(canMove(board)).toBe(false)
+  })
+
   it('Finds the farthest empty tile on the right', () => {
     let board = createEmptyBoard(6)
     const t1 = {

packages/game-engine/src/board.ts

@@ -170,19 +170,13 @@ export const hasTile = (board: Board, tile: Tile): boolean =>
  * @param board the board to check
  * @returns true if the board can move in any direction, false otherwise
  */
-export const canMove = (board: Board): boolean => {
-  // if there are empty cells, we can move
-  if (hasEmpty(board)) {
-    return true
-  }
-
-  // if there are adjacent cells with the same value, we can move
-  const directions: Array<Direction> = ['up', 'down', 'left', 'right']
-  return directions.some(direction => {
+export const canMove = (board: Board): boolean =>
+  (['up', 'down', 'left', 'right'] as const).some(direction => {
+    // try to move the board
     const newBoard = move(board, direction)
-    return hasEmpty(newBoard)
+    // if the board changed, we can move
+    return !isBoardEqual(board, newBoard)
   })
-}
 
 /**
  * Finds the farthest position in a given direction
@@ -244,13 +238,6 @@ export const isEmpty = (cell: Tile | Obstacle | null): cell is null =>
 export const isObstacle = (cell: Tile | Obstacle | null): cell is Obstacle =>
   cell !== null && 'obstacle' in cell && cell.obstacle === true
 
-/**
- * Checks if the board has empty cells
- * @param board the board to check
- * @returns true if the board has emptycells, false otherwise
- */
-const hasEmpty = (board: Board): boolean => board.grid.some(isEmpty)
-
 /**
  * Checks if two cells are equal
  * @param cell1 the first cell to compare