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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.flink.runtime.state;

import org.apache.flink.api.common.state.MapState;

import java.util.Collections;
import java.util.Iterator;
import java.util.Map;

/**
 * Simple wrapper map state that exposes empty state properly as an empty map.
 *
 * @param  The type of keys in the map state.
 * @param  The type of values in the map state.
 */
class UserFacingMapState implements MapState {

    private final MapState originalState;

    private final Map emptyState = Collections.emptyMap();

    UserFacingMapState(MapState originalState) {
        this.originalState = originalState;
    }

    // ------------------------------------------------------------------------

    @Override
    public V get(K key) throws Exception {
        return originalState.get(key);
    }

    @Override
    public void put(K key, V value) throws Exception {
        originalState.put(key, value);
    }

    @Override
    public void putAll(Map value) throws Exception {
        originalState.putAll(value);
    }

    @Override
    public void clear() {
        originalState.clear();
    }

    @Override
    public void remove(K key) throws Exception {
        originalState.remove(key);
    }

    @Override
    public boolean contains(K key) throws Exception {
        return originalState.contains(key);
    }

    @Override
    public Iterable> entries() throws Exception {
        Iterable> original = originalState.entries();
        return original != null ? original : emptyState.entrySet();
    }

    @Override
    public Iterable keys() throws Exception {
        Iterable original = originalState.keys();
        return original != null ? original : emptyState.keySet();
    }

    @Override
    public Iterable values() throws Exception {
        Iterable original = originalState.values();
        return original != null ? original : emptyState.values();
    }

    @Override
    public Iterator> iterator() throws Exception {
        Iterator> original = originalState.iterator();
        return original != null ? original : emptyState.entrySet().iterator();
    }

    @Override
    public boolean isEmpty() throws Exception {
        return originalState.isEmpty();
    }
}