def opponent_engine(board, randomness, depth):
    if random.random() < randomness:               # random mode
        return random.choice(legal_moves(board))
    best_move = None                                 # minimax mode: try every move,
    best_score = float("-inf")                       # keep the one with the best score
    for move in legal_moves(board):
        score = minimax(apply_move(board, move), depth - 1, my_turn=False)
        if score > best_score:
            best_move, best_score = move, score
    return best_move