hazelcast-master/hazelcast/src/main/java/com/hazelcast/internal/partition/membergroup/BackupSafeMemberGroupFactory.java
/*
 * Copyright (c) 2008-2023, Hazelcast, Inc. All Rights Reserved.
 *
 * 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.
 */

package com.hazelcast.internal.partition.membergroup;

import com.hazelcast.cluster.Member;
import com.hazelcast.spi.partitiongroup.MemberGroup;

import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

abstract class BackupSafeMemberGroupFactory implements MemberGroupFactory {

    @Override
    public final Collection<MemberGroup> createMemberGroups(Collection<? extends Member> members) {
        Collection<MemberGroup> groups = createInternalMemberGroups(members);
        if (groups.size() == 1 && members.size() > 1) {
            // If there are more than one members and just one group
            // then split members into two groups to guarantee at least the first backup.
            MemberGroup group1 = groups.iterator().next();
            MemberGroup group2 = new DefaultMemberGroup();
            int sizePerGroup = group1.size() / 2;

            Iterator<Member> iter = group1.iterator();
            while (group2.size() < sizePerGroup && iter.hasNext()) {
                group2.addMember(iter.next());
                iter.remove();
            }
            groups.add(group2);
        }
        return groups;
    }

    protected abstract Set<MemberGroup> createInternalMemberGroups(Collection<? extends Member> allMembers);

}
