/*

 * Copyright (c) 2015, 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.

 *

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

import java.lang.management.GarbageCollectorMXBean;

import java.lang.management.ManagementFactory;

import java.util.Arrays;

import java.util.Objects;

/**

 * Helper class with enum representation of GC types.

 */

public final class GCTypes {

    private static <T extends GCType> T getCurrentGCType(Class<T> type) {

        return ManagementFactory.getGarbageCollectorMXBeans().stream()

                .map(bean -> getGCTypeByName(type, bean.getName()))

                .filter(Objects::nonNull)

                .findFirst()

                .orElse(null);

    }

    private static <T extends GCType> T getGCTypeByName(Class<T> type, String name) {

        return Arrays.stream(type.getEnumConstants())

                .filter(e -> e.getGCName().equals(name))

                .findFirst()

                .orElse(null);

    }

    private static <T extends GCType> GarbageCollectorMXBean getGCBeanByType(Class<T> type) {

        return ManagementFactory.getGarbageCollectorMXBeans().stream()

                .filter(bean -> Arrays.stream(type.getEnumConstants())

                        .filter(enumName -> enumName.getGCName().equals(bean.getName()))

                        .findFirst()

                        .isPresent()

                )

                .findFirst()

                .orElse(null);

    }

    /**

     * Helper interface used by GCTypes static methods

     * to get gcTypeName field of *GCType classes.

     */

    private interface GCType {

        String getGCName();

    }

    public static enum YoungGCType implements GCType {

        DefNew("Copy"),

        ParNew("ParNew"),

        PSNew("PS Scavenge"),

        G1("G1 Young Generation");

        @Override

        public String getGCName() {

            return gcTypeName;

        }

        private final String gcTypeName;

        private YoungGCType(String name) {

            gcTypeName = name;

        }

        public static YoungGCType getYoungGCType() {

            return GCTypes.getCurrentGCType(YoungGCType.class);

        }

        public static GarbageCollectorMXBean getYoungGCBean() {

            return GCTypes.getGCBeanByType(YoungGCType.class);

        }

    }

    public static enum OldGCType implements GCType {

        Serial("MarkSweepCompact"),

        CMS("ConcurrentMarkSweep"),

        PSOld("PS MarkSweep"),

        G1("G1 Old Generation");

        private final String gcTypeName;

        private OldGCType(String name) {

            gcTypeName = name;

        }

        public static OldGCType getOldGCType() {

            return GCTypes.getCurrentGCType(OldGCType.class);

        }

        @Override

        public String getGCName() {

            return gcTypeName;

        }

    }

}