let board = [];
let score = 0;

// --- Audio setup ---
const audio = {
  bg: new Audio("bgmusic.mp3"),
  pop: new Audio("pop.mp3"),
  merge: new Audio("merge.wav")
};

// lower default volumes
audio.bg.volume = 0.25;
audio.pop.volume = 0.9;
audio.merge.volume = 0.9;
audio.bg.loop = true;

// try to play background music; may be blocked until user interaction
function tryPlayBg() {
  audio.bg.play().catch(() => {
    // autoplay blocked — will try again on first user keypress or click
    const unlock = () => {
      audio.bg.play().catch(() => {});
      window.removeEventListener("keydown", unlock);
      window.removeEventListener("click", unlock);
    };
    window.addEventListener("keydown", unlock, { once: true });
    window.addEventListener("click", unlock, { once: true });
  });
}

// --- DOM ready: setup board and initial tiles ---
document.addEventListener("DOMContentLoaded", () => {
  setupBoard();
  addNewTile();
  addNewTile();
  tryPlayBg();

  // keyboard controls (also used to unlock audio)
  document.addEventListener("keydown", handleKey);
});

// ----------------------------
// SETUP BOARD (render tiles ONCE)
// ----------------------------
function setupBoard() {
  board = [];
  score = 0;
  updateScore();

  const container = document.getElementById("board");
  if (!container) {
    console.error("Board element not found (#board).");
    return;
  }

  // empty container and create fixed 4x4 cells
  container.innerHTML = "";
  for (let r = 0; r < 4; r++) {
    board[r] = [];
    for (let c = 0; c < 4; c++) {
      board[r][c] = 0;
      const tile = document.createElement("div");
      tile.id = `${r}-${c}`;
      tile.className = "tile"; // base class only
      // ensure box sizing not influenced by text nodes
      tile.style.boxSizing = "border-box";
      container.appendChild(tile);
    }
  }
}

// ----------------------------
// UPDATE UI FOR SINGLE TILE
// ----------------------------
function updateTile(row, col, num) {
  const tile = document.getElementById(`${row}-${col}`);
  if (!tile) return;

  // reset classes to base
  tile.className = "tile";

  // force reflow to allow re-adding 'new' animation class reliably
  void tile.offsetWidth;

  if (num > 0) {
    tile.textContent = num;
    // add tile class for color (expects classes like tile-2, tile-4, ...)
    tile.classList.add("tile-" + num);

    // make numbers visually white-neon glow if desired:
    // ensure text is centered by CSS; no inline style needed
  } else {
    tile.textContent = "";
  }
}

// updates entire board DOM from board array
function refreshBoard() {
  for (let r = 0; r < 4; r++) {
    for (let c = 0; c < 4; c++) {
      updateTile(r, c, board[r][c]);
    }
  }
  updateScore();
}

// ----------------------------
// SCORE UI
// ----------------------------
function updateScore() {
  const el = document.getElementById("score");
  if (el) el.textContent = score;
}

// ----------------------------
// ADD NEW TILE (value 2, play pop sound + animation)
// ----------------------------
function addNewTile() {
  const empty = [];
  for (let r = 0; r < 4; r++) {
    for (let c = 0; c < 4; c++) {
      if (board[r][c] === 0) empty.push({ r, c });
    }
  }

  if (empty.length === 0) return false;

  const spot = empty[Math.floor(Math.random() * empty.length)];
  board[spot.r][spot.c] = 2;

  const tile = document.getElementById(`${spot.r}-${spot.c}`);
  if (tile) {
    tile.classList.add("new");
    // play pop sound
    playSound(audio.pop);
    // remove 'new' class after animation completes to keep DOM tidy
    tile.addEventListener("animationend", function handler() {
      tile.classList.remove("new");
      tile.removeEventListener("animationend", handler);
    });
    // update text/color
    updateTile(spot.r, spot.c, 2);
  } else {
    // fallback
    updateTile(spot.r, spot.c, 2);
  }
  return true;
}

// helper to play sound safely
function playSound(soundObj) {
  try {
    soundObj.currentTime = 0;
    soundObj.play().catch(() => {
      // suppressed (autoplay or other)
    });
  } catch (e) { /* ignore */ }
}

// ----------------------------
// INPUT HANDLING
// ----------------------------
function handleKey(e) {
  let moved = false;
  if (e.key === "ArrowLeft") moved = moveLeft();
  else if (e.key === "ArrowRight") moved = moveRight();
  else if (e.key === "ArrowUp") moved = moveUp();
  else if (e.key === "ArrowDown") moved = moveDown();

  if (moved) {
    // after a successful move: add tile, refresh board, play bg or unlock
    addNewTile();
    refreshBoard();
  }
}

// ---------- MOVE HELPERS ----------
function filterZero(row) {
  return row.filter(n => n !== 0);
}

function slide(row) {
  // row is an array of length 4
  row = filterZero(row);
  let mergedThisMove = false;

  for (let i = 0; i < row.length - 1; i++) {
    if (row[i] === row[i + 1]) {
      row[i] = row[i] * 2;
      // play merge sound and vibrate
      playSound(audio.merge);
      if (navigator.vibrate) navigator.vibrate(30);

      score += row[i];
      row[i + 1] = 0;
      mergedThisMove = true;
    }
  }

  row = filterZero(row);
  while (row.length < 4) row.push(0);
  return { row, merged: mergedThisMove };
}

// Compare arrays helper
function arraysEqual(a, b) {
  return a.length === b.length && a.every((v, i) => v === b[i]);
}

function moveLeft() {
  let moved = false;
  for (let r = 0; r < 4; r++) {
    const { row: newRow } = slide(board[r]);
    if (!arraysEqual(newRow, board[r])) moved = true;
    board[r] = newRow;
  }
  if (moved) updateAfterMove();
  return moved;
}

function moveRight() {
  let moved = false;
  for (let r = 0; r < 4; r++) {
    let reversed = [...board[r]].reverse();
    const { row: slid } = slide(reversed);
    let newRow = slid.reverse();
    if (!arraysEqual(newRow, board[r])) moved = true;
    board[r] = newRow;
  }
  if (moved) updateAfterMove();
  return moved;
}

function moveUp() {
  let moved = false;
  for (let c = 0; c < 4; c++) {
    const col = [board[0][c], board[1][c], board[2][c], board[3][c]];
    const { row: newCol } = slide(col);
    for (let r = 0; r < 4; r++) {
      if (board[r][c] !== newCol[r]) moved = true;
      board[r][c] = newCol[r];
    }
  }
  if (moved) updateAfterMove();
  return moved;
}

function moveDown() {
  let moved = false;
  for (let c = 0; c < 4; c++) {
    const col = [board[3][c], board[2][c], board[1][c], board[0][c]];
    const { row: slid } = slide(col);
    const newCol = slid.reverse();
    for (let r = 0; r < 4; r++) {
      if (board[r][c] !== newCol[r]) moved = true;
      board[r][c] = newCol[r];
    }
  }
  if (moved) updateAfterMove();
  return moved;
}

function updateAfterMove() {
  // update all tiles now (this keeps sizes stable)
  refreshBoard();
  // update score DOM
  updateScore();
  // small debounce is not required—moves are sequential
}

// ----------------------------
// RESTART & HOME
// ----------------------------
function restartGame() {
  setupBoard();
  addNewTile();
  addNewTile();
  refreshBoard();
}

function goHome() {
  // stops music to prevent continuing on homepage
  try { audio.bg.pause(); audio.bg.currentTime = 0; } catch (e) {}
  window.location.href = "Homepage.html";
}

// ----------------------------
// OPTIONAL: touch swipe for mobile
// ----------------------------
let touchStartX = 0;
let touchStartY = 0;
document.addEventListener("touchstart", function (e) {
  const t = e.touches[0];
  touchStartX = t.clientX;
  touchStartY = t.clientY;
}, { passive: true });

document.addEventListener("touchend", function (e) {
  const t = e.changedTouches[0];
  const dx = t.clientX - touchStartX;
  const dy = t.clientY - touchStartY;
  if (Math.abs(dx) > Math.abs(dy) && Math.abs(dx) > 30) {
    if (dx > 0) moveRight() && addNewTile() && refreshBoard();
    else moveLeft() && addNewTile() && refreshBoard();
  } else if (Math.abs(dy) > 30) {
    if (dy > 0) moveDown() && addNewTile() && refreshBoard();
    else moveUp() && addNewTile() && refreshBoard();
  }
}, { passive: true });

/* End of file */