document.addEventListener('keydown', e => {
if (!gameRunning) return;
switch(e.key) {
case 'ArrowUp':
case 'w':
case 'W':
if (direction !== 'down') nextDirection = 'up';
break;
case 'ArrowDown':
case 's':
case 'S':
if (direction !== 'up') nextDirection = 'down';
break;
case 'ArrowLeft':
case 'a':
case 'A':
if (direction !== 'right') nextDirection = 'left';
break;
case 'ArrowRight':
case 'd':
case 'D':
if (direction !== 'left') nextDirection = 'right';
break;
case ' ':
pauseGame();
break;
}
});