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/*
 * Copyright 2013 Samppa Saarela
 *
 * 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 org.javersion.util;

import javax.annotation.concurrent.NotThreadSafe;

@NotThreadSafe
public final class UpdateContext implements Merger {

    private static final class UncommittedContext {

        private int expectedUpdates;

        private Merger merger;

        private int change = 0;

        UncommittedContext(int expectedUpdates, Merger merger) {
            this.expectedUpdates = expectedUpdates;
            this.merger = merger;
        }

        int getChangeAndReset() {
            try {
                return change;
            } finally {
                change = 0;
            }
        }

        void insert(T newEntry) {
            change = 1;
            if (merger != null) {
                merger.insert(newEntry);
            }
        }

        boolean merge(T oldEntry, T newEntry) {
            return merger == null ? true : merger.merge(oldEntry, newEntry);
        }

        void delete(T oldEntry) {
            change = -1;
            if (merger != null) {
                merger.delete(oldEntry);
            }
        }

    }

    private UncommittedContext context;

    public UpdateContext() {
        this(1, null);
    }

    public UpdateContext(int expectedUpdates) {
        this(expectedUpdates, null);
    }

    public UpdateContext(int expectedUpdates, Merger merger) {
        this.context = new UncommittedContext<>(expectedUpdates, merger);
    }

    public void merger(Merger merger) {
        context.merger = merger;
    }

    public int expectedUpdates() {
        return context.expectedUpdates;
    }

    public void commit() {
        this.context = null;
    }

    public boolean isCommitted() {
        return context == null;
    }

    public boolean isSameAs(UpdateContext other) {
        return this.context != null && this.context == other.context;
    }

    public void validate() {
        if (isCommitted()) {
            throw new IllegalStateException("This update is already committed");
        }
    }

    public boolean hasChanged() {
        return context.change != 0;
    }

    public int getChangeAndReset() {
        return context.getChangeAndReset();
    }

    @Override
    public void insert(T newEntry) {
        context.insert(newEntry);
    }

    @Override
    public boolean merge(T oldEntry, T newEntry) {
        return context.merge(oldEntry, newEntry);
    }

    @Override
    public void delete(T oldEntry) {
        context.delete(oldEntry);
    }
}