/*
 * Copyright (c) 2006, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.net.httpserver;

import java.nio.charset.Charset;
import java.util.Base64;
import java.util.Objects;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * BasicAuthenticator provides an implementation of HTTP Basic
 * authentication. It is an abstract class and must be extended
 * to provide an implementation of {@link #checkCredentials(String,String)}
 * which is called to verify each incoming request.
 */
public abstract class BasicAuthenticator extends Authenticator {

    protected final String realm;
    protected final Charset charset;
    private final boolean isUTF8;

    /**
     * Creates a BasicAuthenticator for the given HTTP realm.
     * The Basic authentication credentials (username and password) are decoded
     * using the platform's {@link Charset#defaultCharset() default character set}.
     *
     * @param realm The HTTP Basic authentication realm
     * @throws NullPointerException if realm is {@code null}
     * @throws IllegalArgumentException if realm is an empty string
     */
    public BasicAuthenticator (String realm) {
        this(realm, Charset.defaultCharset());
    }

    /**
     * Creates a BasicAuthenticator for the given HTTP realm and using the
     * given {@link Charset} to decode the Basic authentication credentials
     * (username and password).
     *
     * @apiNote {@code UTF-8} is the recommended charset because its usage is
     * communicated to the client, and therefore more likely to be used also
     * by the client.
     *
     * @param realm The HTTP Basic authentication realm
     * @param charset The Charset to decode incoming credentials from the client
     * @throws NullPointerException if realm or charset are {@code null}
     * @throws IllegalArgumentException if realm is an empty string
     */
    public BasicAuthenticator (String realm, Charset charset) {
        Objects.requireNonNull(charset);
        if (realm.isEmpty()) // implicit NPE check
            throw new IllegalArgumentException("realm must not be empty");
        this.realm = realm;
        this.charset = charset;
        this.isUTF8 = charset.equals(UTF_8);
    }

    /**
     * returns the realm this BasicAuthenticator was created with
     * @return the authenticator's realm string.
     */
    public String getRealm () {
        return realm;
    }

    public Result authenticate (HttpExchange t)
    {
        Headers rmap = t.getRequestHeaders();
        /*
         * look for auth token
         */
        String auth = rmap.getFirst ("Authorization");
        if (auth == null) {
            Headers map = t.getResponseHeaders();
            var authString = "Basic realm=" + "\"" + realm + "\"" +
                (isUTF8 ? " charset=\"UTF-8\"" : "");
            map.set ("WWW-Authenticate", authString);
            return new Authenticator.Retry (401);
        }
        int sp = auth.indexOf (' ');
        if (sp == -1 || !auth.substring(0, sp).equals ("Basic")) {
            return new Authenticator.Failure (401);
        }
        byte[] b = Base64.getDecoder().decode(auth.substring(sp+1));
        String userpass = new String (b, charset);
        int colon = userpass.indexOf (':');
        String uname = userpass.substring (0, colon);
        String pass = userpass.substring (colon+1);

        if (checkCredentials (uname, pass)) {
            return new Authenticator.Success (
                new HttpPrincipal (
                    uname, realm
                )
            );
        } else {
            /* reject the request again with 401 */

            Headers map = t.getResponseHeaders();
            map.set ("WWW-Authenticate", "Basic realm=" + "\""+realm+"\"");
            return new Authenticator.Failure(401);
        }
    }

    /**
     * called for each incoming request to verify the
     * given name and password in the context of this
     * Authenticator's realm. Any caching of credentials
     * must be done by the implementation of this method
     * @param username the username from the request
     * @param password the password from the request
     * @return <code>true</code> if the credentials are valid,
     *    <code>false</code> otherwise.
     */
    public abstract boolean checkCredentials (String username, String password);
}