<?php

namespace App\Core;

use Exception;
use RuntimeException;

/**
 * 库内敏感字段 AES-256-CBC 加解密
 * 密文格式：nl_ase_256_ + base64(iv + ciphertext)
 * 密钥派生：hash('sha256', ENCRYPT_KEY, true) → 32 字节
 * 读取时兼容历史前缀 ***（迁移期）
 */
class DatabaseEncryptor
{
    /** 新密文前缀（入库统一用这个） */
    public const PREFIX = 'nl_ase_256_';

    /** 历史密文前缀（仅解密兼容） */
    public const LEGACY_PREFIX = '***';

    private string $cipherMethod = 'AES-256-CBC';

    private string $secretKey;

    private int $ivLength;

    /**
     * @param string $key 来自 config('nl.encrypt_key') / env ENCRYPT_KEY
     */
    public function __construct(string $key)
    {
        $key = trim($key);
        if ($key === '') {
            throw new RuntimeException('AES 加密密钥未配置（请设置 ENCRYPT_KEY）');
        }
        $this->secretKey = hash('sha256', $key, true);
        $ivLength = openssl_cipher_iv_length($this->cipherMethod);
        if ($ivLength === false) {
            throw new RuntimeException('不支持的加密算法：' . $this->cipherMethod);
        }
        $this->ivLength = $ivLength;
    }

    /**
     * 加密后入库；空串不加密，已是密文则原样返回避免二次加密
     *
     * @param string|null $data 明文
     * @throws Exception
     */
    public function encrypt($data): string
    {
        if ($data === null || $data === '') {
            return '';
        }
        $data = (string) $data;
        if (self::isEncrypted($data)) {
            return $data;
        }
        $iv = openssl_random_pseudo_bytes($this->ivLength);
        if ($iv === false) {
            throw new RuntimeException('生成 IV 失败');
        }
        $encryptedData = openssl_encrypt($data, $this->cipherMethod, $this->secretKey, OPENSSL_RAW_DATA, $iv);
        if ($encryptedData === false) {
            throw new RuntimeException('加密失败：' . (openssl_error_string() ?: 'unknown'));
        }
        return self::PREFIX . base64_encode($iv . $encryptedData);
    }

    /**
     * 从库内密文解密；无已知前缀视为明文原样返回
     *
     * @param string|null $base64EncodedEncryptedData 库内值
     * @throws Exception
     */
    public function decrypt($base64EncodedEncryptedData): string
    {
        if ($base64EncodedEncryptedData === null || $base64EncodedEncryptedData === '') {
            return '';
        }
        $base64EncodedEncryptedData = (string) $base64EncodedEncryptedData;
        $prefix = self::detectPrefix($base64EncodedEncryptedData);
        if ($prefix === null) {
            return $base64EncodedEncryptedData;
        }
        $payload = substr($base64EncodedEncryptedData, strlen($prefix));
        $decodedData = base64_decode($payload, true);
        if ($decodedData === false) {
            throw new RuntimeException('Base64 解码失败');
        }
        if (strlen($decodedData) <= $this->ivLength) {
            throw new RuntimeException('密文长度非法');
        }
        $iv = substr($decodedData, 0, $this->ivLength);
        $encryptedData = substr($decodedData, $this->ivLength);
        $decryptedData = openssl_decrypt($encryptedData, $this->cipherMethod, $this->secretKey, OPENSSL_RAW_DATA, $iv);
        if ($decryptedData === false) {
            throw new RuntimeException('解密失败：' . (openssl_error_string() ?: 'unknown'));
        }
        return $decryptedData;
    }

    /**
     * 是否已是库内密文（含历史前缀）
     */
    public static function isEncrypted(?string $value): bool
    {
        return self::detectPrefix($value) !== null;
    }

    /**
     * 识别密文前缀；新前缀优先
     */
    public static function detectPrefix(?string $value): ?string
    {
        if (!is_string($value) || $value === '') {
            return null;
        }
        if (str_starts_with($value, self::PREFIX)) {
            return self::PREFIX;
        }
        if (str_starts_with($value, self::LEGACY_PREFIX)) {
            return self::LEGACY_PREFIX;
        }
        return null;
    }
}