From 75c0351d446eefb6a5729dcedf66e5f32814d70b Mon Sep 17 00:00:00 2001
From: tiennm99 <tiennm99@outlook.com>
Date: Tue, 7 Apr 2026 20:53:10 +0700
Subject: [PATCH] feat: add board generation, remaining tiles, and shuffle

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/game/board.ts        | 91 ++++++++++++++++++++++++++++++++++++++++
 tests/game/board.test.ts | 91 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 182 insertions(+)
 create mode 100644 src/game/board.ts
 create mode 100644 tests/game/board.test.ts

diff --git a/src/game/board.ts b/src/game/board.ts
new file mode 100644
index 0000000..d05fc24
--- /dev/null
+++ b/src/game/board.ts
@@ -0,0 +1,91 @@
+import { Board, Difficulty, TileData, Point } from "../types";
+import { DIFFICULTY_CONFIGS } from "./constants";
+import { getEmojisForDifficulty } from "./emoji";
+
+let nextTileId = 0;
+
+export function createBoard(difficulty: Difficulty): Board {
+  const config = DIFFICULTY_CONFIGS[difficulty];
+  const { rows, cols } = config;
+  const emojis = getEmojisForDifficulty(difficulty);
+
+  // Create pairs
+  const tiles: TileData[] = [];
+  nextTileId = 0;
+  for (const emoji of emojis) {
+    tiles.push({ emoji, id: nextTileId++ });
+    tiles.push({ emoji, id: nextTileId++ });
+  }
+
+  // Fisher-Yates shuffle
+  for (let i = tiles.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [tiles[i], tiles[j]] = [tiles[j], tiles[i]];
+  }
+
+  // Place into grid
+  const board: Board = [];
+  let idx = 0;
+  for (let r = 0; r < rows; r++) {
+    const row: (TileData | null)[] = [];
+    for (let c = 0; c < cols; c++) {
+      row.push(tiles[idx++]);
+    }
+    board.push(row);
+  }
+
+  return board;
+}
+
+export function getRemainingTiles(board: Board): { tile: TileData; pos: Point }[] {
+  const result: { tile: TileData; pos: Point }[] = [];
+  for (let r = 0; r < board.length; r++) {
+    for (let c = 0; c < board[r].length; c++) {
+      const cell = board[r][c];
+      if (cell !== null) {
+        result.push({ tile: cell, pos: { row: r, col: c } });
+      }
+    }
+  }
+  return result;
+}
+
+export function shuffleBoard(board: Board): Board {
+  const rows = board.length;
+  const cols = board[0].length;
+
+  const tiles: TileData[] = [];
+  const occupiedPositions: Point[] = [];
+  const emptyPositions: Point[] = [];
+
+  for (let r = 0; r < rows; r++) {
+    for (let c = 0; c < cols; c++) {
+      if (board[r][c] !== null) {
+        tiles.push(board[r][c]!);
+        occupiedPositions.push({ row: r, col: c });
+      } else {
+        emptyPositions.push({ row: r, col: c });
+      }
+    }
+  }
+
+  // Fisher-Yates shuffle the tiles
+  for (let i = tiles.length - 1; i > 0; i--) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [tiles[i], tiles[j]] = [tiles[j], tiles[i]];
+  }
+
+  // Create new board with nulls
+  const newBoard: Board = [];
+  for (let r = 0; r < rows; r++) {
+    newBoard.push(new Array(cols).fill(null));
+  }
+
+  // Place shuffled tiles back into occupied positions
+  for (let i = 0; i < tiles.length; i++) {
+    const pos = occupiedPositions[i];
+    newBoard[pos.row][pos.col] = tiles[i];
+  }
+
+  return newBoard;
+}
diff --git a/tests/game/board.test.ts b/tests/game/board.test.ts
new file mode 100644
index 0000000..8191c4f
--- /dev/null
+++ b/tests/game/board.test.ts
@@ -0,0 +1,91 @@
+import { describe, it, expect } from "vitest";
+import { createBoard, getRemainingTiles, shuffleBoard } from "../../src/game/board";
+
+describe("createBoard", () => {
+  it("creates a board with correct dimensions for easy", () => {
+    const board = createBoard("easy");
+    expect(board.length).toBe(4);
+    expect(board[0].length).toBe(6);
+  });
+
+  it("creates a board with correct dimensions for medium", () => {
+    const board = createBoard("medium");
+    expect(board.length).toBe(6);
+    expect(board[0].length).toBe(8);
+  });
+
+  it("creates a board with correct dimensions for hard", () => {
+    const board = createBoard("hard");
+    expect(board.length).toBe(8);
+    expect(board[0].length).toBe(10);
+  });
+
+  it("every tile has a matching pair", () => {
+    const board = createBoard("easy");
+    const emojiCounts = new Map<string, number>();
+    for (const row of board) {
+      for (const cell of row) {
+        if (cell) {
+          emojiCounts.set(cell.emoji, (emojiCounts.get(cell.emoji) ?? 0) + 1);
+        }
+      }
+    }
+    for (const [, count] of emojiCounts) {
+      expect(count).toBe(2);
+    }
+  });
+
+  it("all tiles have unique ids", () => {
+    const board = createBoard("medium");
+    const ids = new Set<number>();
+    for (const row of board) {
+      for (const cell of row) {
+        if (cell) {
+          expect(ids.has(cell.id)).toBe(false);
+          ids.add(cell.id);
+        }
+      }
+    }
+  });
+});
+
+describe("getRemainingTiles", () => {
+  it("returns all tiles from a full board", () => {
+    const board = createBoard("easy");
+    const remaining = getRemainingTiles(board);
+    expect(remaining.length).toBe(24);
+  });
+
+  it("excludes null cells", () => {
+    const board = createBoard("easy");
+    board[0][0] = null;
+    board[0][1] = null;
+    const remaining = getRemainingTiles(board);
+    expect(remaining.length).toBe(22);
+  });
+});
+
+describe("shuffleBoard", () => {
+  it("preserves tile count after shuffle", () => {
+    const board = createBoard("easy");
+    board[0][0] = null;
+    board[0][1] = null;
+    const shuffled = shuffleBoard(board);
+    const remaining = getRemainingTiles(shuffled);
+    expect(remaining.length).toBe(22);
+  });
+
+  it("keeps null positions as occupied cells and vice versa", () => {
+    const board = createBoard("easy");
+    board[0][0] = null;
+    board[1][2] = null;
+    const shuffled = shuffleBoard(board);
+    let nullCount = 0;
+    for (const row of shuffled) {
+      for (const cell of row) {
+        if (cell === null) nullCount++;
+      }
+    }
+    expect(nullCount).toBe(2);
+  });
+});