/*
 * Copyright (c) 2009, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.jvnet.libpam;

import static com.sun.jna.Native.POINTER_SIZE;
import static java.util.logging.Level.FINE;
import static org.jvnet.libpam.impl.CLibrary.libc;
import static org.jvnet.libpam.impl.PAMLibrary.PAM_CONV_ERR;
import static org.jvnet.libpam.impl.PAMLibrary.PAM_PROMPT_ECHO_OFF;
import static org.jvnet.libpam.impl.PAMLibrary.PAM_SUCCESS;
import static org.jvnet.libpam.impl.PAMLibrary.PAM_USER;
import static org.jvnet.libpam.impl.PAMLibrary.libpam;

import java.util.Set;
import java.util.logging.Logger;

import org.jvnet.libpam.impl.CLibrary.Passwd;
import org.jvnet.libpam.impl.PAMLibrary.pam_conv;
import org.jvnet.libpam.impl.PAMLibrary.pam_conv.PamCallback;
import org.jvnet.libpam.impl.PAMLibrary.pam_handle_t;
import org.jvnet.libpam.impl.PAMLibrary.pam_message;
import org.jvnet.libpam.impl.PAMLibrary.pam_response;

import com.sun.jna.Pointer;
import com.sun.jna.ptr.PointerByReference;

/**
 * PAM authenticator.
 *
 * <p>
 * Instances are thread unsafe and non reentrant. An instance cannot be reused to authenticate multiple users.
 *
 * <p>
 * For an overview of PAM programming, refer to the following resources:
 *
 * <ul>
 * <li><a href="http://www.netbsd.org/docs/guide/en/chap-pam.html">NetBSD PAM programming guide</a>
 * <li><a href="http://www.kernel.org/pub/linux/libs/pam/">Linux PAM</a>
 * </ul>
 *
 * @author Kohsuke Kawaguchi
 */
public class PAM {

    private static final Logger LOGGER = Logger.getLogger(PAM.class.getName());

    private pam_handle_t pht;
    private int ret;

    /**
     * Temporarily stored to pass a value from {@link #authenticate(String, String)} to {@link pam_conv}.
     */
    private String password;

    /**
     * Creates a new authenticator.
     *
     * @param serviceName PAM service name. This corresponds to the service name that shows up in the PAM configuration,
     */
    public PAM(String serviceName) throws PAMException {
        pam_conv conv = new pam_conv(new PamCallback() {
            @Override
            public int callback(int num_msg, Pointer msg, Pointer resp, Pointer pointer) {
                if (LOGGER.isLoggable(FINE)) {
                    LOGGER.fine("pam_conv num_msg=" + num_msg);
                }
                if (password == null) {
                    return PAM_CONV_ERR;
                }

                // allocates pam_response[num_msg]. the caller will free this
                Pointer m = libc.calloc(pam_response.SIZE, num_msg);
                resp.setPointer(0, m);

                for (int i = 0; i < num_msg; i++) {
                    pam_message pm = new pam_message(msg.getPointer(POINTER_SIZE * i));
                    if (LOGGER.isLoggable(FINE)) {
                        LOGGER.fine(pm.msg_style + ":" + pm.msg);
                    }
                    if (pm.msg_style == PAM_PROMPT_ECHO_OFF) {
                        pam_response r = new pam_response(m.share(pam_response.SIZE * i));
                        r.setResp(password);
                        r.write(); // write to (*resp)[i]
                    }
                }

                return PAM_SUCCESS;
            }
        });

        PointerByReference phtr = new PointerByReference();
        check(libpam.pam_start(serviceName, null, conv, phtr), "pam_start failed");
        pht = new pam_handle_t(phtr.getValue());
    }

    private void check(int ret, String msg) throws PAMException {
        this.ret = ret;
        if (ret != 0) {
            if (pht != null) {
                throw new PAMException(msg + " : " + libpam.pam_strerror(pht, ret));
            } else {
                throw new PAMException(msg);
            }
        }
    }

    /**
     * Authenticate the user with a password.
     *
     * @return Upon a successful authentication, return information about the user.
     * @throws PAMException If the authentication fails.
     */
    public UnixUser authenticate(String username, String password) throws PAMException {
        this.password = password;
        try {
            check(libpam.pam_set_item(pht, PAM_USER, username), "pam_set_item failed");
            check(libpam.pam_authenticate(pht, 0), "pam_authenticate failed");
            check(libpam.pam_setcred(pht, 0), "pam_setcred failed");
            // several different error code seem to be used to represent authentication failures
//            check(libpam.pam_acct_mgmt(pht,0),"pam_acct_mgmt failed");

            PointerByReference r = new PointerByReference();
            check(libpam.pam_get_item(pht, PAM_USER, r), "pam_get_item failed");
            String userName = r.getValue().getString(0);
            Passwd pwd = libc.getpwnam(userName);
            if (pwd == null) {
                throw new PAMException("Authentication succeeded but no user information is available");
            }
            return new UnixUser(userName, pwd);
        } finally {
            this.password = null;
        }
    }

    /**
     * Returns the groups a user belongs to
     *
     * @param username
     * @return Set of group names
     * @throws PAMException
     * @deprecated Pointless and ugly convenience method.
     */
    @Deprecated
    public Set<String> getGroupsOfUser(String username) throws PAMException {
        return new UnixUser(username).getGroups();
    }

    /**
     * After a successful authentication, call this method to obtain the effective user name. This can be different from the
     * user name that you passed to the {@link #authenticate(String, String)} method.
     */

    /**
     * Performs an early disposal of the object, instead of letting this GC-ed. Since PAM may hold on to native resources
     * that don't put pressure on Java GC, doing this is a good idea.
     *
     * <p>
     * This method is called by {@link #finalize()}, too, so it's not required to call this method explicitly, however.
     */
    public void dispose() {
        if (pht != null) {
            libpam.pam_end(pht, ret);
            pht = null;
        }
    }

    @Override
    protected void finalize() throws Throwable {
        super.finalize();
        dispose();
    }


}