package at.gv.egiz.eaaf.core.impl.credential.inline;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URI;
import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.PrivateKey;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Arrays;
import java.util.Base64;
import java.util.Objects;

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.openssl.PEMKeyPair;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;

import at.gv.egiz.eaaf.core.exceptions.EaafConfigurationException;
import at.gv.egiz.eaaf.core.impl.utils.FileUtils;
import lombok.extern.slf4j.Slf4j;

/**
 * Convenience class to load keys and certificates in PEM-format into a
 * {@link KeyStore} by providing the file paths.
 */
@Slf4j
public class InlineKeyStoreBuilder {
  private final KeyStore keyStore;
  private final ResourceLoader loader;
  private final URI configRootDir;

  /**
   * Create a new instance.
   *
   * @param type                the type of the KeyStore to be built, e.g.
   *                            "PKCS12"
   * @param configRootDirectory Root directory for configuration
   * @param resourceLoader      Spring ResourceLoader
   * @throws GeneralSecurityException if the empty KeyStore object could not be
   *                                  created
   * @throws IOException              if the empty KeyStore object could not be
   *                                  created
   */
  public InlineKeyStoreBuilder(String type, ResourceLoader resourceLoader,
      URI configRootDirectory)
      throws GeneralSecurityException, IOException {
    loader = resourceLoader;
    configRootDir = configRootDirectory;

    keyStore = KeyStore.getInstance(type);
    keyStore.load(null, null);

  }

  /**
   * Sets a key entry, i.e. build a key store.
   *
   * @param privateKeyFile   the path to the private key file
   * @param certificateFiles the paths to the certificate files
   * @throws GeneralSecurityException   if a file could not be parsed
   * @throws IOException                if a file could not be read
   * @throws EaafConfigurationException if a file could not be found
   */
  public void setKeyEntry(String privateKeyFile, String[] certificateFiles)
      throws GeneralSecurityException, IOException, EaafConfigurationException {
    final X509Certificate[] certificates = readCertificates(certificateFiles);
    final PrivateKey privateKey = readPrivateKey(privateKeyFile);
    keyStore.setKeyEntry("keyEntry", privateKey, new char[0], certificates);

  }

  /**
   * Sets certificate entries, i.e. build a trust store.
   *
   * @param certificateFiles the path to the certificate files
   * @throws GeneralSecurityException if a file could not be parsed
   */
  public void setCertificateEntries(String[] certificateFiles) throws GeneralSecurityException {

    final X509Certificate[] certificates = readCertificates(certificateFiles);

    for (int i = 0; i < certificates.length; i++) {
      keyStore.setCertificateEntry("certificateEntry" + i, certificates[i]);
    }
  }

  /**
   * Sets a secret key, i.e. builds a keystore.
   *
   * @param secret the secret encoded as a Base64 string
   * @throws KeyStoreException if the secret key could not be added to the store
   */
  public void setSecretEntry(final String secret) throws KeyStoreException {
    final byte[] decodedKey = Base64.getDecoder().decode(secret);
    final SecretKey key = new SecretKeySpec(decodedKey, 0, decodedKey.length, "AES");
    keyStore.setEntry("secret", new KeyStore.SecretKeyEntry(key),
        new KeyStore.PasswordProtection(new char[] {}));
  }

  public KeyStore getKeyStore() {
    return keyStore;
  }

  private X509Certificate[] readCertificates(String[] certificateFiles) throws CertificateException {
    final CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");

    return Arrays.stream(certificateFiles).map(certificateFile -> {
      try (InputStream is = readResourceFromFile(certificateFile)) {
        return (X509Certificate) certificateFactory.generateCertificate(is);

      } catch (CertificateException | IOException | EaafConfigurationException e) {
        log.error("Failed to load certificate file {}.", certificateFile, e);
        return null;

      }
    }).filter(Objects::nonNull).toArray(X509Certificate[]::new);
  }

  private PrivateKey readPrivateKey(String filePath) throws IOException, EaafConfigurationException {
    try (
        Reader fileReader = new InputStreamReader(
            readResourceFromFile(filePath), StandardCharsets.UTF_8);
        PEMParser pemParser = new PEMParser(fileReader)) {

      final Object object = pemParser.readObject();
      final JcaPEMKeyConverter converter = new JcaPEMKeyConverter();

      if (object instanceof PrivateKeyInfo) {
        return converter.getPrivateKey((PrivateKeyInfo) object);

      } else if (object instanceof PEMKeyPair) {
        return converter.getKeyPair((PEMKeyPair) object).getPrivate();

      } else {
        throw new IllegalArgumentException("Unsupported object: " + object.getClass());

      }
    }
  }

  private InputStream readResourceFromFile(String filePath) throws IOException, EaafConfigurationException {
    final String absKeyStorePath = FileUtils.makeAbsoluteUrl(filePath, configRootDir);
    log.debug("Use filepath from config: {}", absKeyStorePath);
    Resource ressource = loader.getResource(absKeyStorePath);

    if (!ressource.exists()) {
      throw new EaafConfigurationException("internal.keystore.15",
          new Object[] { "RessourceLoader does NOT find File at: " + ressource.getURI() });

    }

    return ressource.getInputStream();

  }
}