<dependencies>
    <dependency>
        <groupId>commons-codec</groupId>
        <artifactId>commons-codec</artifactId>
        <version>1.15</version>
    </dependency>
</dependencies>

import java.nio.ByteBuffer;
import java.time.Instant;
import org.apache.commons.codec.binary.Base32;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class OtpService {

    private static final int TIME_STEP = 30; // 時間步長（秒）
    private static final int OTP_LENGTH = 6; // OTP 長度
    private static final int MAX_ATTEMPTS = 5; // 最大嘗試次數(shù)
    private static final long BLOCK_DURATION = 300_000; // 封鎖時間（毫秒）

    private final ConcurrentHashMap<String, AtomicInteger> attemptCounter = new ConcurrentHashMap<>();
    private final ConcurrentHashMap<String, Long> blockedUsers = new ConcurrentHashMap<>();

    // 生成 TOTP
    public String generateTOTP(String secret) throws Exception {
        long timeIndex = Instant.now().getEpochSecond() / TIME_STEP;
        return generateOtp(secret, timeIndex);
    }

    // 驗(yàn)證 TOTP
    public boolean validateTOTP(String secret, String otp, String userId) throws Exception {
        if (isBlocked(userId)) {
            System.out.println("User is temporarily blocked: " + userId);
            return false;
        }

        long timeIndex = Instant.now().getEpochSecond() / TIME_STEP;

        // 在驗(yàn)證窗口內(nèi)檢查 OTP
        for (int i = -1; i <= 1; i++) {
            String generatedOtp = generateOtp(secret, timeIndex + i);
            if (generatedOtp.equals(otp)) {
                resetAttempts(userId);
                return true;
            }
        }

        recordFailedAttempt(userId);
        return false;
    }

    private String generateOtp(String secret, long timeIndex) throws Exception {
        // 解碼 Base32 密鑰
        Base32 base32 = new Base32();
        byte[] keyBytes = base32.decode(secret);

        // 轉(zhuǎn)換時間索引為字節(jié)數(shù)組
        byte[] timeBytes = ByteBuffer.allocate(8).putLong(timeIndex).array();

        // 使用 HMAC-SHA1 生成哈希
        Mac mac = Mac.getInstance("HmacSHA1");
        SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "HmacSHA1");
        mac.init(keySpec);
        byte[] hash = mac.doFinal(timeBytes);

        // 提取動態(tài)偏移量
        int offset = hash[hash.length - 1] & 0x0F;
        int binary = ((hash[offset] & 0x7F) << 24) | ((hash[offset + 1] & 0xFF) << 16)
                | ((hash[offset + 2] & 0xFF) << 8) | (hash[offset + 3] & 0xFF);

        // 生成 OTP
        int otp = binary % (int) Math.pow(10, OTP_LENGTH);
        return String.format("%0" + OTP_LENGTH + "d", otp);
    }

    private void recordFailedAttempt(String userId) {
        attemptCounter.putIfAbsent(userId, new AtomicInteger(0));
        int attempts = attemptCounter.get(userId).incrementAndGet();

        if (attempts >= MAX_ATTEMPTS) {
            blockedUsers.put(userId, System.currentTimeMillis());
            System.out.println("User blocked due to multiple failed attempts: " + userId);
        }
    }

    private void resetAttempts(String userId) {
        attemptCounter.remove(userId);
        blockedUsers.remove(userId);
    }

    private boolean isBlocked(String userId) {
        Long blockTime = blockedUsers.get(userId);
        if (blockTime == null) {
            return false;
        }

        if (System.currentTimeMillis() - blockTime > BLOCK_DURATION) {
            blockedUsers.remove(userId);
            return false;
        }
        return true;
    }
}

public class OtpServiceTest {
    public static void main(String[] args) throws Exception {
        OtpService otpService = new OtpService();

        // 使用 Base32 編碼密鑰
        String secret = "JBSWY3DPEHPK3PXP";
        String userId = "user123";

        // 生成 OTP
        String otp = otpService.generateTOTP(secret);
        System.out.println("Generated OTP: " + otp);

        // 嘗試驗(yàn)證 OTP
        for (int i = 0; i < 7; i++) {
            boolean isValid = otpService.validateTOTP(secret, otp, userId);
            System.out.println("Attempt " + (i + 1) + ": Is OTP valid: " + isValid);
        }
    }
}