/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package org.apache.commons.net.util;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.Socket;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.Principal;
import java.security.PrivateKey;
import java.security.cert.Certificate;
import java.security.cert.X509Certificate;
import java.util.Enumeration;

import javax.net.ssl.KeyManager;
import javax.net.ssl.X509ExtendedKeyManager;

import org.apache.commons.net.io.Util;

/**
 * General KeyManager utilities
 * <p>
 * How to use with a client certificate:
 * <pre>
 * KeyManager km = KeyManagerUtils.createClientKeyManager("JKS",
 *     "/path/to/privatekeystore.jks","storepassword",
 *     "privatekeyalias", "keypassword");
 * FTPSClient cl = new FTPSClient();
 * cl.setKeyManager(km);
 * cl.connect(...);
 * </pre>
 * If using the default store type and the key password is the same as the
 * store password, these parameters can be omitted. <br>
 * If the desired key is the first or only key in the keystore, the keyAlias parameter
 * can be omitted, in which case the code becomes:
 * <pre>
 * KeyManager km = KeyManagerUtils.createClientKeyManager(
 *     "/path/to/privatekeystore.jks","storepassword");
 * FTPSClient cl = new FTPSClient();
 * cl.setKeyManager(km);
 * cl.connect(...);
 * </pre>
 *
 * @since 3.0
 */
public final class KeyManagerUtils {

    private static final String DEFAULT_STORE_TYPE = KeyStore.getDefaultType();

    private KeyManagerUtils(){
        // Not instantiable
    }

    /**
     * Create a client key manager which returns a particular key.
     * Does not handle server keys.
     *
     * @param ks the keystore to use
     * @param keyAlias the alias of the key to use, may be {@code null} in which case the first key entry alias is used
     * @param keyPass the password of the key to use
     * @return the customised KeyManager
     * @throws GeneralSecurityException if there is a problem creating the keystore
     */
    public static KeyManager createClientKeyManager(KeyStore ks, String keyAlias, String keyPass)
        throws GeneralSecurityException
    {
        ClientKeyStore cks = new ClientKeyStore(ks, keyAlias != null ? keyAlias : findAlias(ks), keyPass);
        return new X509KeyManager(cks);
    }

    /**
     * Create a client key manager which returns a particular key.
     * Does not handle server keys.
     *
     * @param storeType the type of the keyStore, e.g. "JKS"
     * @param storePath the path to the keyStore
     * @param storePass the keyStore password
     * @param keyAlias the alias of the key to use, may be {@code null} in which case the first key entry alias is used
     * @param keyPass the password of the key to use
     * @return the customised KeyManager
     * @throws GeneralSecurityException if there is a problem creating the keystore
     * @throws IOException if there is a problem creating the keystore
     */
    public static KeyManager createClientKeyManager(
            String storeType, File storePath, String storePass, String keyAlias, String keyPass)
        throws IOException, GeneralSecurityException
    {
        KeyStore ks = loadStore(storeType, storePath, storePass);
        return createClientKeyManager(ks, keyAlias, keyPass);
    }

    /**
     * Create a client key manager which returns a particular key.
     * Does not handle server keys.
     * Uses the default store type and assumes the key password is the same as the store password
     *
     * @param storePath the path to the keyStore
     * @param storePass the keyStore password
     * @param keyAlias the alias of the key to use, may be {@code null} in which case the first key entry alias is used
     * @return the customised KeyManager
     * @throws IOException if there is a problem creating the keystore
     * @throws GeneralSecurityException if there is a problem creating the keystore
     */
    public static KeyManager createClientKeyManager(File storePath, String storePass, String keyAlias)
        throws IOException, GeneralSecurityException
    {
        return createClientKeyManager(DEFAULT_STORE_TYPE, storePath, storePass, keyAlias, storePass);
    }

    /**
     * Create a client key manager which returns a particular key.
     * Does not handle server keys.
     * Uses the default store type and assumes the key password is the same as the store password.
     * The key alias is found by searching the keystore for the first private key entry
     *
     * @param storePath the path to the keyStore
     * @param storePass the keyStore password
     * @return the customised KeyManager
     * @throws IOException if there is a problem creating the keystore
     * @throws GeneralSecurityException if there is a problem creating the keystore
     */
    public static KeyManager createClientKeyManager(File storePath, String storePass)
        throws IOException, GeneralSecurityException
    {
        return createClientKeyManager(DEFAULT_STORE_TYPE, storePath, storePass, null, storePass);
    }

    private static KeyStore loadStore(String storeType, File storePath, String storePass)
        throws KeyStoreException,  IOException, GeneralSecurityException {
        KeyStore ks = KeyStore.getInstance(storeType);
        FileInputStream stream = null;
        try {
            stream = new FileInputStream(storePath);
            ks.load(stream, storePass.toCharArray());
        } finally {
            Util.closeQuietly(stream);
        }
        return ks;
    }

    private static String findAlias(KeyStore ks) throws KeyStoreException {
        Enumeration<String> e = ks.aliases();
        while(e.hasMoreElements()) {
            String entry = e.nextElement();
            if (ks.isKeyEntry(entry)) {
                return entry;
            }
        }
        throw new KeyStoreException("Cannot find a private key entry");
    }

    private static class ClientKeyStore {

        private final X509Certificate[] certChain;
        private final PrivateKey key;
        private final String keyAlias;

        ClientKeyStore(KeyStore ks, String keyAlias, String keyPass) throws GeneralSecurityException
        {
            this.keyAlias = keyAlias;
            this.key = (PrivateKey) ks.getKey(this.keyAlias, keyPass.toCharArray());
            Certificate[] certs = ks.getCertificateChain(this.keyAlias);
            X509Certificate[] X509certs = new X509Certificate[certs.length];
            for (int i=0; i < certs.length; i++) {
                X509certs[i] = (X509Certificate) certs[i];
            }
            this.certChain = X509certs;
        }

        final X509Certificate[] getCertificateChain() {
            return this.certChain;
        }

        final PrivateKey getPrivateKey() {
            return this.key;
        }

        final String getAlias() {
            return this.keyAlias;
        }
    }

    private static class X509KeyManager extends X509ExtendedKeyManager  {

        private final ClientKeyStore keyStore;

        X509KeyManager(final ClientKeyStore keyStore) {
            this.keyStore = keyStore;
        }

        // Call sequence: 1
//        @Override
        public String chooseClientAlias(String[] keyType, Principal[] issuers,
                Socket socket) {
            return keyStore.getAlias();
        }

        // Call sequence: 2
//        @Override
        public X509Certificate[] getCertificateChain(String alias) {
            return keyStore.getCertificateChain();
        }

//        @Override
        public String[] getClientAliases(String keyType, Principal[] issuers) {
            return new String[]{ keyStore.getAlias()};
        }

        // Call sequence: 3
//        @Override
        public PrivateKey getPrivateKey(String alias) {
            return keyStore.getPrivateKey();
        }

//        @Override
        public String[] getServerAliases(String keyType, Principal[] issuers) {
            return null;
        }

//        @Override
        public String chooseServerAlias(String keyType, Principal[] issuers, Socket socket) {
            return null;
        }

    }

}
