/*
 *  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.ahc.auth;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class AuthPolicy {
    private static final HashMap SCHEMES = new HashMap();
    private static final ArrayList SCHEME_LIST = new ArrayList();

    /**
     * The key used to look up the list of IDs of supported {@link AuthScheme
     * authentication schemes} in their order of preference. The scheme IDs are
     * stored in a {@link java.util.Collection} as {@link java.lang.String}s.
     * <p/>
     * <p/>
     * If several schemes are returned in the <tt>WWW-Authenticate</tt>
     * or <tt>Proxy-Authenticate</tt> header, this parameter defines which
     * {@link AuthScheme authentication schemes} takes precedence over others.
     * The first item in the collection represents the most preferred
     * {@link AuthScheme authentication scheme}, the last item represents the ID
     * of the least preferred one.
     * </p>
     *
     */
    public static final String AUTH_SCHEME_PRIORITY = "http.auth.scheme-priority";

    /**
     * The NTLM scheme is a proprietary Microsoft Windows Authentication
     * protocol (considered to be the most secure among currently supported
     * authentication schemes).
     */
    public static final String NTLM = "NTLM";

    /**
     * Digest authentication scheme as defined in RFC2617.
     */
    public static final String DIGEST = "Digest";

    /**
     * Basic authentication scheme as defined in RFC2617 (considered inherently
     * insecure, but most widely supported)
     */
    public static final String BASIC = "Basic";

    static {
        AuthPolicy.registerAuthScheme(NTLM, NTLMScheme.class);
        AuthPolicy.registerAuthScheme(DIGEST, DigestScheme.class);
        AuthPolicy.registerAuthScheme(BASIC, BasicScheme.class);
    }

    /**
     * Log object.
     */
    private static final Logger LOG = LoggerFactory.getLogger(AuthPolicy.class);

    /**
     * Registers a class implementing an {@link AuthScheme authentication scheme} with
     * the given identifier. If a class with the given ID already exists it will be overridden.
     * This ID is the same one used to retrieve the {@link AuthScheme authentication scheme}
     * from {@link #getAuthScheme(String)}.
     * <p/>
     * <p/>
     * Please note that custom authentication preferences, if used, need to be updated accordingly
     * for the new {@link AuthScheme authentication scheme} to take effect.
     * </p>
     *
     * @param id    the identifier for this scheme
     * @param clazz the class to register
     * @see #getAuthScheme(String)
     * @see #AUTH_SCHEME_PRIORITY
     */
    public static synchronized void registerAuthScheme(final String id, Class clazz) {
        if (id == null) {
            throw new IllegalArgumentException("Id may not be null");
        }
        if (clazz == null) {
            throw new IllegalArgumentException("Authentication scheme class may not be null");
        }
        SCHEMES.put(id.toLowerCase(), clazz);
        SCHEME_LIST.add(id.toLowerCase());
    }

    /**
     * Unregisters the class implementing an {@link AuthScheme authentication scheme} with
     * the given ID.
     *
     * @param id the ID of the class to unregister
     */
    public static synchronized void unregisterAuthScheme(final String id) {
        if (id == null) {
            throw new IllegalArgumentException("Id may not be null");
        }
        SCHEMES.remove(id.toLowerCase());
        SCHEME_LIST.remove(id.toLowerCase());
    }

    /**
     * Gets the {@link AuthScheme authentication scheme} with the given ID.
     *
     * @param id the {@link AuthScheme authentication scheme} ID
     * @return {@link AuthScheme authentication scheme}
     * @throws IllegalStateException if a scheme with the ID cannot be found
     */
    public static synchronized AuthScheme getAuthScheme(final String id)
        throws IllegalStateException {

        if (id == null) {
            throw new IllegalArgumentException("Id may not be null");
        }
        Class clazz = (Class)SCHEMES.get(id.toLowerCase());
        if (clazz != null) {
            try {
                return (AuthScheme)clazz.newInstance();
            } catch (Exception e) {
                LOG.error("Error initializing authentication scheme: " + id, e);
                throw new IllegalStateException(id +
                    " authentication scheme implemented by " +
                    clazz.getName() + " could not be initialized");
            }
        } else {
            throw new IllegalStateException("Unsupported authentication scheme " + id);
        }
    }

    /**
     * Returns a list containing all registered {@link AuthScheme authentication
     * schemes} in their default order.
     *
     * @return {@link AuthScheme authentication scheme}
     */
    public static synchronized List getDefaultAuthPrefs() {
        return (List)SCHEME_LIST.clone();
    }
}