/*
 * Copyright (c) 2005, 2019, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package java.io;

import java.util.*;

import jdk.internal.access.SharedSecrets;

/**
 * This class holds a set of filenames to be deleted on VM exit through a shutdown hook.
 * A set is used both to prevent double-insertion of the same file as well as offer
 * quick removal.
 */

class DeleteOnExitHook {
    private static class OrderCount {
        long order;
        int count;
    }
    private static long nextOrder;
    private static HashMap<String, OrderCount> files = new HashMap<>();
    static {
        // DeleteOnExitHook must be the last shutdown hook to be invoked.
        // Application shutdown hooks may add the first file to the
        // delete on exit list and cause the DeleteOnExitHook to be
        // registered during shutdown in progress. So set the
        // registerShutdownInProgress parameter to true.
        SharedSecrets.getJavaLangAccess()
            .registerShutdownHook(2 /* Shutdown hook invocation order */,
                true /* register even if shutdown in progress */,
                new Runnable() {
                    public void run() {
                       runHooks();
                    }
                }
        );
    }

    private DeleteOnExitHook() {}

    static synchronized void deleteOnExit(String file) {
        if(files == null) {
            // DeleteOnExitHook is running. Too late to add a file
            throw new IllegalStateException("Shutdown in progress");
        }

        OrderCount oc = files.computeIfAbsent(file, f -> new OrderCount());
        oc.order = nextOrder++;
        oc.count++;
    }

    static synchronized void cancelDeleteOnExit(String file) {
        if(files != null) {
            files.compute(file, (f, oc) -> {
                if (oc == null) {
                    throw new IllegalStateException(
                        "Unbalanced cancelDeleteOnExit for missing deleteOnExit");
                }
                return --oc.count <= 0 ? null : oc;
            });
        }
    }

    static void runHooks() {
        HashMap<String, OrderCount> theFiles;

        synchronized (DeleteOnExitHook.class) {
            theFiles = files;
            files = null;
        }

        theFiles
            .entrySet()
            .stream()
            // last registered -> first deleted
            .sorted(Comparator.comparing(e -> -e.getValue().order))
            .map(e -> new File(e.getKey()))
            .forEach(File::delete);
    }
}