/*
 * (C) Copyright 2010 Nuxeo SA (http://nuxeo.com/) and others.
 *
 * Licensed 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.
 *
 * Contributors:
 *     Nuxeo - initial API and implementation
 */

package org.nuxeo.ecm.platform.login;

import java.security.Principal;
import java.security.acl.Group;
import java.util.Enumeration;
import java.util.Vector;

/**
 * This class implements a group of principals.
 *
 * @author Satish Dharmaraj
 */
public class GroupImpl implements Group {
    private Vector<Principal> groupMembers = new Vector<>(50, 100);

    private String group;

    /**
     * Constructs a Group object with no members.
     *
     * @param groupName the name of the group
     */
    public GroupImpl(String groupName) {
        this.group = groupName;
    }

    /**
     * adds the specified member to the group.
     *
     * @param user The principal to add to the group.
     * @return true if the member was added - false if the member could not be added.
     */
    @Override
    public boolean addMember(Principal user) {
        if (groupMembers.contains(user)) {
            return false;
        }

        // do not allow groups to be added to itself.
        if (group.equals(user.toString())) {
            throw new IllegalArgumentException();
        }

        groupMembers.addElement(user);
        return true;
    }

    /**
     * Removes the specified member from the group.
     *
     * @param user The principal to remove from the group.
     * @return true if the principal was removed false if the principal was not a member
     */
    @Override
    public boolean removeMember(Principal user) {
        return groupMembers.removeElement(user);
    }

    /**
     * returns the enumeration of the members in the group.
     */
    @Override
    public Enumeration<? extends Principal> members() {
        return groupMembers.elements();
    }

    /**
     * This function returns true if the group passed matches the group represented in this interface.
     *
     * @param obj the group to compare this group to.
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof Group)) {
            return false;
        }
        Group other = (Group) obj;
        return group.equals(other.toString());
    }

    // equals(Group) for compatibility
    public boolean equals(Group other) {
        return equals((Object) other);
    }

    /**
     * Prints a stringified version of the group.
     */
    @Override
    public String toString() {
        return group;
    }

    /**
     * return a hashcode for the principal.
     */
    @Override
    public int hashCode() {
        return group.hashCode();
    }

    /**
     * returns true if the passed principal is a member of the group.
     *
     * @param member The principal whose membership must be checked for.
     * @return true if the principal is a member of this group, false otherwise
     */
    @Override
    public boolean isMember(Principal member) {

        //
        // if the member is part of the group (common case), return true.
        // if not, recursively search depth first in the group looking for the
        // principal.
        //
        if (groupMembers.contains(member)) {
            return true;
        } else {
            Vector<Group> alreadySeen = new Vector<>(10);
            return isMemberRecurse(member, alreadySeen);
        }
    }

    /**
     * return the name of the principal.
     */
    @Override
    public String getName() {
        return group;
    }

    //
    // This function is the recursive search of groups for this
    // implementation of the Group. The search proceeds building up
    // a vector of already seen groups. Only new groups are considered,
    // thereby avoiding loops.
    //
    boolean isMemberRecurse(Principal member, Vector<Group> alreadySeen) {
        Enumeration<? extends Principal> e = members();
        while (e.hasMoreElements()) {
            boolean mem = false;
            Principal p = e.nextElement();

            // if the member is in this collection, return true
            if (p.equals(member)) {
                return true;
            } else if (p instanceof GroupImpl) {
                //
                // if not recurse if the group has not been checked already.
                // Can call method in this package only if the object is an
                // instance of this class. Otherwise call the method defined
                // in the interface. (This can lead to a loop if a mixture of
                // implementations form a loop, but we live with this improbable
                // case rather than clutter the interface by forcing the
                // implementation of this method.)
                //
                GroupImpl g = (GroupImpl) p;
                alreadySeen.addElement(this);
                if (!alreadySeen.contains(g)) {
                    mem = g.isMemberRecurse(member, alreadySeen);
                }
            } else if (p instanceof Group) {
                Group g = (Group) p;
                if (!alreadySeen.contains(g)) {
                    mem = g.isMember(member);
                }
            }

            if (mem) {
                return mem;
            }
        }
        return false;
    }
}