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/*
* SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
*
* SPDX-License-Identifier: EPL-2.0
*/
package tools.refinery.store.map;
import java.util.Iterator;
import java.util.Map;
public final class Cursors {
private Cursors() {
throw new IllegalStateException("This is a static utility class and should not be instantiated directly");
}
public static <K, V> Cursor<K, V> empty() {
return new Empty<>();
}
public static <K, V> Cursor<K, V> singleton(K key, V value) {
return new Singleton<>(key, value);
}
public static <K, V> Cursor<K, V> of(Iterator<Map.Entry<K, V>> iterator) {
return new IteratorBasedCursor<>(iterator);
}
public static <K, V> Cursor<K, V> of(Map<K, V> map) {
return of(map.entrySet().iterator());
}
private static class Empty<K, V> implements Cursor<K, V> {
private boolean terminated = false;
@Override
public K getKey() {
return null;
}
@Override
public V getValue() {
return null;
}
@Override
public boolean isTerminated() {
return terminated;
}
@Override
public boolean move() {
terminated = true;
return false;
}
}
private static class Singleton<K, V> implements Cursor<K, V> {
private State state = State.INITIAL;
private final K key;
private final V value;
public Singleton(K key, V value) {
this.key = key;
this.value = value;
}
@Override
public K getKey() {
if (state == State.STARTED) {
return key;
}
return null;
}
@Override
public V getValue() {
if (state == State.STARTED) {
return value;
}
return null;
}
@Override
public boolean isTerminated() {
return state == State.TERMINATED;
}
@Override
public boolean move() {
if (state == State.INITIAL) {
state = State.STARTED;
return true;
}
state = State.TERMINATED;
return false;
}
private enum State {
INITIAL,
STARTED,
TERMINATED
}
}
}
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