package com.sshmanager.service;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

import javax.crypto.Cipher;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;
import java.util.Base64;

@Service
public class EncryptionService {

    private static final int GCM_IV_LENGTH = 12;
    private static final int GCM_TAG_LENGTH = 128;
    private static final String ALGORITHM = "AES/GCM/NoPadding";

    private final byte[] keyBytes;

    public EncryptionService(@Value("${sshmanager.encryption-key}") String base64Key) {
        this.keyBytes = Base64.getDecoder().decode(base64Key);
        if (keyBytes.length != 32) {
            throw new IllegalArgumentException("Encryption key must be 32 bytes (256 bits)");
        }
    }

    public String encrypt(String plainText) {
        if (plainText == null || plainText.isEmpty()) {
            return null;
        }
        try {
            byte[] iv = new byte[GCM_IV_LENGTH];
            new SecureRandom().nextBytes(iv);

            SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
            GCMParameterSpec gcmSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);

            Cipher cipher = Cipher.getInstance(ALGORITHM);
            cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmSpec);
            byte[] encrypted = cipher.doFinal(plainText.getBytes(StandardCharsets.UTF_8));

            byte[] combined = new byte[iv.length + encrypted.length];
            System.arraycopy(iv, 0, combined, 0, iv.length);
            System.arraycopy(encrypted, 0, combined, iv.length, encrypted.length);

            return Base64.getEncoder().encodeToString(combined);
        } catch (Exception e) {
            throw new RuntimeException("Encryption failed", e);
        }
    }

    public String decrypt(String encryptedText) {
        if (encryptedText == null || encryptedText.isEmpty()) {
            return null;
        }
        try {
            byte[] combined = Base64.getDecoder().decode(encryptedText);
            byte[] iv = new byte[GCM_IV_LENGTH];
            byte[] encrypted = new byte[combined.length - GCM_IV_LENGTH];
            System.arraycopy(combined, 0, iv, 0, iv.length);
            System.arraycopy(combined, iv.length, encrypted, 0, encrypted.length);

            SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
            GCMParameterSpec gcmSpec = new GCMParameterSpec(GCM_TAG_LENGTH, iv);

            Cipher cipher = Cipher.getInstance(ALGORITHM);
            cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmSpec);
            byte[] decrypted = cipher.doFinal(encrypted);

            return new String(decrypted, StandardCharsets.UTF_8);
        } catch (Exception e) {
            throw new RuntimeException("Decryption failed", e);
        }
    }
}