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Provides common utility functions
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/*
 * Copyright (c) CQSE GmbH
 *
 * 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.conqat.lib.commons.collections;

import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.conqat.lib.commons.test.IndexValueClass;

/**
 * Special implementation of a {@link Set} of {@link String}s, which allows storing strings in a
 * case-insensitive manner. Two strings which only differ in case are handled as equal and can thus
 * occur just once in the set (the first string added to the set is retained).
 * 
 * It also allows accessing the case-sensitive representation of a string that was stored utilizing
 * the {@link #get(String)} method. I.e. storing string "A" in the set and calling set.get("a") will
 * return the original representation "A".
 * 
 * This class does not inherit from {@link AbstractSet} or {@link AbstractCollection} as most
 * provided operations have higher performance directly using the hash map instead of the iterator
 * implementations. Moreover, comparison in {@link AbstractCollection} is performed with equals and
 * the {@link CaseInsensitiveStringSet} violates this contract as it requires comparison after
 * normalization with {@link #getMappingKey(String)}.
 */
@IndexValueClass(containedInBackup = true)
public class CaseInsensitiveStringSet implements Set {

	/**
	 * Mapping from case-insensitive lower-cased strings to case-sensitive ones.
	 */
	private Map caseInsensitiveMapping = new HashMap<>();

	/** Constructor. */
	public CaseInsensitiveStringSet() {
		// default constructor.
	}

	/** Constructor. */
	public CaseInsensitiveStringSet(Collection strings) {
		addAll(strings);
	}

	/**
	 * Returns the case-sensitive representation of the given string, as it was stored with the call to
	 * {@link #add(String)} or null if the string is not stored in the {@link Set}.
	 */
	public String get(String string) {
		return caseInsensitiveMapping.get(getMappingKey(string));
	}

	/**
	 * Converts the string to a case-insensitive mapping key. This is lower-cased string representation.
	 */
	private static String getMappingKey(String string) {
		if (string == null) {
			return null;
		}
		return string.toLowerCase();
	}

	/** {@inheritDoc} */
	@Override
	public int size() {
		return caseInsensitiveMapping.size();
	}

	/** {@inheritDoc} */
	@Override
	public boolean isEmpty() {
		return caseInsensitiveMapping.isEmpty();
	}

	/** {@inheritDoc} */
	@Override
	public boolean contains(Object o) {
		if (o instanceof String) {
			String mappingKey = getMappingKey((String) o);
			return caseInsensitiveMapping.containsKey(mappingKey);
		}
		return false;
	}

	/** {@inheritDoc} */
	@Override
	public Iterator iterator() {
		return caseInsensitiveMapping.values().iterator();
	}

	/** {@inheritDoc} */
	@Override
	public Object[] toArray() {
		return caseInsensitiveMapping.values().toArray();
	}

	/** {@inheritDoc} */
	@Override
	public  T[] toArray(T[] a) {
		return caseInsensitiveMapping.values().toArray(a);
	}

	/** {@inheritDoc} */
	@Override
	public boolean add(String e) {
		if (!contains(e)) {
			caseInsensitiveMapping.put(getMappingKey(e), e);
			return true;
		}
		return false;
	}

	/** {@inheritDoc} */
	@Override
	public boolean remove(Object o) {
		if (o instanceof String) {
			return caseInsensitiveMapping.remove(getMappingKey((String) o)) != null;
		}
		return false;
	}

	/** {@inheritDoc} */
	@Override
	public boolean containsAll(Collection c) {
		for (Object o : c) {
			if (!contains(o)) {
				return false;
			}
		}
		return true;
	}

	/** {@inheritDoc} */
	@Override
	public boolean addAll(Collection c) {
		boolean setChanged = false;
		for (String s : c) {
			setChanged |= add(s);
		}
		return setChanged;
	}

	/** {@inheritDoc} */
	@Override
	public boolean retainAll(Collection c) {
		boolean setChanged = false;

		CaseInsensitiveStringSet retain = new CaseInsensitiveStringSet();
		for (Object toRetain : c) {
			if (toRetain instanceof String) {
				retain.add((String) toRetain);
			}
		}

		List keys = new ArrayList<>(caseInsensitiveMapping.keySet());

		for (String string : keys) {
			if (!retain.contains(string)) {
				setChanged |= remove(string);
			}
		}

		return setChanged;
	}

	/** {@inheritDoc} */
	@Override
	public boolean removeAll(Collection c) {
		boolean setChanged = false;
		for (Object o : c) {
			setChanged |= remove(o);
		}

		return setChanged;
	}

	/** {@inheritDoc} */
	@Override
	public void clear() {
		caseInsensitiveMapping.clear();
	}

	/** {@inheritDoc} */
	@Override
	public String toString() {
		return caseInsensitiveMapping.values().toString();
	}
}