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/**
 * Copyright (C) 2013 Microsoft Corporation
 *
 * 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.microsoft.reef.io.storage.ram;

import com.microsoft.reef.io.Accumulator;
import com.microsoft.reef.io.Spool;

import javax.inject.Inject;
import java.util.ArrayList;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;

/**
 * A SpoolFile implementation that is backed by RAM.
 * 
 * It uses an ArrayList to store the objects in. 
 */
public final class RamSpool implements Spool {

    private boolean canAppend = true;
    private boolean canGetAccumulator = true;
    private final List backingStore = new ArrayList();
    
    @Inject
    public RamSpool(RamStorageService ramStore) {
    }

    @Override
    public Iterator iterator() {
        canAppend = false;
        return backingStore.iterator();
    }

    @Override
    public Accumulator accumulator() {
        if (!canGetAccumulator) {
            throw new UnsupportedOperationException("Can only getAccumulator() once!");
        }
        canGetAccumulator = false;
        return new Accumulator() {
            @Override
            public void add(T datum) {
                if (!canAppend) {
                    throw new ConcurrentModificationException("Attempt to append after creating iterator!");
                }
                backingStore.add(datum);
            }

            @Override
            public void close() {
                canAppend = false;
            }
        };
    }
}