/*-------------------------------------------------------------------------+
|                                                                          |
| Copyright 2005-2011 the ConQAT Project                                   |
|                                                                          |
| 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;

/**
 * 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).
 * <p>
 * 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".
 * <p>
 * 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)}.
 */
public class CaseInsensitiveStringSet implements Set<String> {

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

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

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

        /**
         * Returns the case-sensitive representation of the given string, as it was
         * stored with the call to {@link #add(String)} or <code>null</code> 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<String> iterator() {
                return caseInsensitiveMapping.values().iterator();
        }

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

        /** {@inheritDoc} */
        @Override
        public <T> 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<? extends String> 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<String> keys = new ArrayList<String>(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();
        }

}