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/*
 * This code is based on OpenJDK source file(s) which contain the following copyright notice:
 *
 * ------
 * Copyright (c) 2001, 2021, 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
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 * This file may contain additional modifications which are Copyright (c) Red Hat and other
 * contributors.
 */

package java.lang;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.concurrent.ConcurrentHashMap;

import org.qbicc.rt.annotation.Tracking;
import org.qbicc.runtime.main.InitialHeap;

/**
 * Implementation of String.intern(); pulled to a separate class because
 * we can't define nested classes as part of a patch.
 */
@Tracking("src/java.base/share/native/libjava/String.c")
class StringSupport {
    private static final ReferenceQueue REF_QUEUE = new ReferenceQueue<>();
    private static final ConcurrentHashMap INTERNED = new ConcurrentHashMap<>();

    static String intern(String candidate) {
        // First look to see if there is a build-time interned String
        int btIndex = Arrays.binarySearch(InitialHeap.internedStrings, candidate);
        if (btIndex >=0) {
            return InitialHeap.internedStrings[btIndex];
        }

        // No build-time interned String; fallback to runtime interning
        byte coder = candidate.coder();
        byte[] bytes = candidate.value();
        int hc = candidate.hashCode();
        Key key = new Key(bytes, coder, hc);
        for (;;) {
            Ref strRef = INTERNED.get(key);
            if (strRef == null) {
                INTERNED.putIfAbsent(key, new Ref(key, candidate, REF_QUEUE));
            } else {
                String existing = strRef.get();
                if (existing != null) {
                    cleanQueue();
                    return existing;
                }
                if (INTERNED.replace(key, strRef, new Ref(key, candidate, REF_QUEUE))) {
                    cleanQueue();
                    return candidate;
                }
            }
        }
    }

    private static void cleanQueue() {
        Ref item;
        while ((item = (Ref) REF_QUEUE.poll()) != null) {
            INTERNED.remove(item.key, item);
        }
    }

    static final class Ref extends WeakReference {
        final Key key;

        Ref(final Key key, final String referent, final ReferenceQueue q) {
            super(referent, q);
            this.key = key;
        }
    }

    static final class Key {
        private final byte[] bytes;
        private final byte coder;
        private final int hashCode;

        Key(final byte[] bytes, final byte coder, final int hashCode) {
            this.bytes = bytes;
            this.coder = coder;
            this.hashCode = hashCode;
        }

        public boolean equals(final Object other) {
            return other instanceof Key key && equals(key);
        }

        boolean equals(final Key other) {
            return this == other || other != null && hashCode == other.hashCode && coder == other.coder && Arrays.equals(bytes, other.bytes);
        }

        public int hashCode() {
            return hashCode;
        }
    }
}