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/* This file is part of the OWL API.
 * The contents of this file are subject to the LGPL License, Version 3.0.
 * Copyright 2014, The University of Manchester
 * 
 * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License along with this program.  If not, see http://www.gnu.org/licenses/.
 *
 * Alternatively, the contents of this file may be used under the terms of the Apache License, Version 2.0 in which case, the provisions of the Apache License Version 2.0 are applicable instead of those above.
 * 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.semanticweb.owlapi.util;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicInteger;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import org.semanticweb.owlapi.model.OWLObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author Matthew Horridge, The University Of Manchester, Bio-Health Informatics Group
 * @since 2.0.0
 */
public class CollectionFactory {

    private static final String MISBEHAVING_TRIPLE_COMPARATOR =
        "Misbehaving triple comparator, leaving triples unsorted";
    private static final String COMPARISON_METHOD =
        "Comparison method violates its general contract!";
    private static final Logger LOGGER = LoggerFactory.getLogger(CollectionFactory.class.getName());
    private static final AtomicInteger EXPECTEDTHREADS = new AtomicInteger(1);

    /**
     * Sort the input collection; if the ordering is unstable and an error is thrown (due to the use
     * of TimSort in JDK 1.7 and newer), catch it and leave the collection unsorted. NOTE: use this
     * method if ordering is desirable but not necessary.
     * 
     * @param  list type
     * @param toReturn list to sort
     */
    public static > void sortOptionallyComparables(
        @Nonnull List toReturn) {
        try {
            Collections.sort(toReturn);
        } catch (IllegalArgumentException e) {
            // catch possible sorting misbehaviour
            if (!e.getMessage().contains(COMPARISON_METHOD)) {
                throw e;
            }
            // otherwise print a warning and leave the list unsorted
            LOGGER.warn(MISBEHAVING_TRIPLE_COMPARATOR, e);
        }
    }

    /**
     * Sort the input collection; if the ordering is unstable and an error is thrown (due to the use
     * of TimSort in JDK 1.7 and newer), catch it and leave the collection unsorted. NOTE: use this
     * method if ordering is desirable but not necessary.
     * 
     * @param toReturn list to sort
     */
    public static void sortOptionally(@Nonnull List toReturn) {
        try {
            Collections.sort(toReturn);
        } catch (IllegalArgumentException e) {
            // catch possible sorting misbehaviour
            if (!e.getMessage().contains(COMPARISON_METHOD)) {
                throw e;
            }
            // otherwise print a warning and leave the list unsorted
            LOGGER.warn(MISBEHAVING_TRIPLE_COMPARATOR, e);
        }
    }

    /**
     * Sort a copy of the input collection; if the ordering is unstable and an error is thrown (due
     * to the use of TimSort in JDK 1.7 and newer), catch it and leave the collection unsorted.
     * NOTE: use this method if ordering is desirable but not necessary.
     * 
     * @param toReturn collection to sort
     * @param  list type
     * @return sorted copy of the input, if no errors are raised. Copy of the original otherwise.
     */
    @Nonnull
    public static > List sortOptionallyComparables(
        @Nonnull Collection toReturn) {
        List list = new ArrayList<>(toReturn);
        try {
            Collections.sort(list);
        } catch (IllegalArgumentException e) {
            // catch possible sorting misbehaviour
            if (!e.getMessage().contains(COMPARISON_METHOD)) {
                throw e;
            }
            // otherwise print a warning and leave the list unsorted
            LOGGER.warn(MISBEHAVING_TRIPLE_COMPARATOR, e);
        }
        return list;
    }

    /**
     * Sort a copy of the input collection; if the ordering is unstable and an error is thrown (due
     * to the use of TimSort in JDK 1.7 and newer), catch it and leave the collection unsorted.
     * NOTE: use this method if ordering is desirable but not necessary.
     * 
     * @param toReturn collection to sort
     * @param  list type
     * @return sorted copy of the input, if no errors are raised. Copy of the original otherwise.
     */
    @Nonnull
    public static  List sortOptionally(@Nonnull Collection toReturn) {
        List list = new ArrayList<>(toReturn);
        try {
            Collections.sort(list);
        } catch (IllegalArgumentException e) {
            // catch possible sorting misbehaviour
            if (!e.getMessage().contains(COMPARISON_METHOD)) {
                throw e;
            }
            // otherwise print a warning and leave the list unsorted
            LOGGER.warn(MISBEHAVING_TRIPLE_COMPARATOR, e);
        }
        return list;
    }

    /**
     * Wrapper for Collections.emptySet() to allow nullity annotations.
     * 
     * @param  set type
     * @return empty set
     */
    @Nonnull
    public static  Set emptySet() {
        return Collections.emptySet();
    }

    /**
     * @param value the number of expected threads that will update threadsafe collections; useful
     *        for increasing the concurrency in ConcurrentHashMap instances created by this factory
     */
    public static void setExpectedThreads(int value) {
        EXPECTEDTHREADS.set(value);
    }

    /**
     * @return The current number of expected updating threads.
     */
    public static int getExpectedThreads() {
        return EXPECTEDTHREADS.get();
    }

    /**
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    public static  Set createSet() {
        // TODO large number of sets stay very small, wasting space
        return new HashSet<>();
    }

    /**
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    public static  Set createLinkedSet() {
        // TODO large number of sets stay very small, wasting space
        return new LinkedHashSet<>();
    }

    /**
     * @return fresh non threadsafe list
     * @param  axiom type
     */
    @Nonnull
    public static  List createList() {
        return new ArrayList<>();
    }

    /**
     * @return fresh threadsafe list
     * @param  content type
     */
    @Nonnull
    public static  List createSyncList() {
        return new CopyOnWriteArrayList<>();
    }

    /**
     * @param i iterable
     * @return list from iterable
     * @param  type
     */
    @Nonnull
    public static  List list(Iterable i) {
        List l = new ArrayList<>();
        for (T t : i) {
            l.add(t);
        }
        return l;
    }

    /**
     * @param i iterable
     * @return list from iterable
     * @param  type
     */
    @Nonnull
    @SafeVarargs
    public static  List list(T... i) {
        List l = new ArrayList<>();
        for (T t : i) {
            l.add(t);
        }
        return l;
    }

    /**
     * @param i iterable
     * @return list from iterable
     * @param  type
     */
    @Nonnull
    public static  List list(T i) {
        return Collections.singletonList(i);
    }

    /**
     * @return empty list
     * @param  type
     */
    @Nonnull
    public static  List emptyList() {
        return Collections.emptyList();
    }

    /**
     * @param c values to add to the set
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    public static  Set createSet(@Nonnull Collection c) {
        return new HashSet<>(c);
    }

    /**
     * @param initialCapacity initial capacity for the new set
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    public static  Set createSet(int initialCapacity) {
        return new HashSet<>(initialCapacity);
    }

    /**
     * @return fresh map
     * @param  key type
     * @param  value type
     */
    @Nonnull
    public static  Map createMap() {
        return new HashMap<>();
    }

    /**
     * @return a new weak HashMap wrapped as a synchronized map
     * @param  key type
     * @param  value type
     */
    public static  Map> createSyncWeakMap() {
        return Collections.synchronizedMap(new WeakHashMap>());
    }

    /**
     * @param elements values to add to the set
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    @SafeVarargs
    public static  Set createSet(@Nonnull T... elements) {
        return new HashSet<>(list(elements));
    }

    /**
     * @param element value to add to the set
     * @return fresh non threadsafe set
     * @param  axiom type
     */
    @Nonnull
    public static  Set createSet(@Nonnull T element) {
        Set result = createSet();
        result.add(element);
        return result;
    }

    /**
     * @return fresh threadsafe set
     * @param  set type
     */
    @Nonnull
    public static  Set createSyncSet() {
        ConcurrentHashMap internalMap = createSyncMap();
        return Collections.newSetFromMap(internalMap);
    }

    /**
     * @return fresh threadsafe HashMap
     * @param  key type
     * @param  value type
     */
    @Nonnull
    public static  ConcurrentHashMap createSyncMap() {
        return new ConcurrentHashMap<>(16, 0.75F, EXPECTEDTHREADS.get());
    }

    /**
     * @param source the collection to lazily copy
     * @return a lazy defensive copy for source; the source collection will not be copied until a
     *         method that modifies the collection gets called, e.g., add(), addAll()
     * @param  axiom type
     */
    @Nonnull
    public static  Set getCopyOnRequestSet(Collection source) {
        return getCopyOnRequestSetFromMutableCollection(source);
    }

    /**
     * @param source source collection
     * @return copy on request that builds a list from the input set
     * @param  axiom type
     */
    @Nonnull
    public static  Set getCopyOnRequestSetFromMutableCollection(
        @Nullable Collection source) {
        if (source == null || source.isEmpty()) {
            return emptySet();
        }
        return new ConditionalCopySet<>(source, true);
    }

    /**
     * @param source the source collection
     * @return copy on request that does not build a list immediately
     * @param  axiom type
     */
    @Nonnull
    public static  Set getCopyOnRequestSetFromImmutableCollection(
        @Nullable Collection source) {
        if (source == null || source.isEmpty()) {
            return emptySet();
        }
        return new ConditionalCopySet<>(source, false);
    }

    /**
     * a set implementation that uses a delegate collection for all read-only operations and makes a
     * copy if changes are attempted. Useful for cheap defensive copies: no costly rehashing on the
     * original collection is made unless changes are attempted. Changes are not mirrored back to
     * the original collection, although changes to the original set BEFORE changes to the copy are
     * reflected in the copy. If the source collection is not supposed to change, then this
     * collection behaves just like a regular defensive copy; if the source collection can change,
     * then this collection should be built from a cheap copy of the original collection. For
     * example, if the source collection is a set, it can be copied into a list; the cost of the
     * copy operation from set to list is approximately 1/3 of the cost of copying into a new
     * HashSet. This is not efficient if the most common operations performed on the copy are
     * contains() or containsAll(), since they are more expensive for lists wrt sets; a counter for
     * these calls is maintained by the collection, so if a large number of contains/containsAll
     * calls takes place, the delegate is turned into a regular set. This implementation is not
     * threadsafe even if the source set is: there is no lock during the copy, and the new set is
     * not threadsafe.
     * 
     * @param  the type contained
     */
    public static class ConditionalCopySet implements Set {

        private static final int MAXCONTAINS = 10;
        private boolean copyDone = false;
        protected Collection delegate;
        private int containsCounter = 0;

        /**
         * @param source initial elements
         * @param listCopy true if a copy must be made
         */
        public ConditionalCopySet(@Nonnull Collection source, boolean listCopy) {
            if (listCopy) {
                delegate = new ArrayList<>(source);
            } else {
                delegate = source;
            }
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (this == obj) {
                return true;
            }
            if (obj instanceof ConditionalCopySet) {
                return delegate.containsAll(((ConditionalCopySet) obj).delegate)
                    && ((ConditionalCopySet) obj).delegate.containsAll(delegate);
            }
            if (obj instanceof Collection) {
                return delegate.containsAll((Collection) obj)
                    && ((Collection) obj).containsAll(delegate);
            }
            return false;
        }

        @Override
        public int hashCode() {
            return delegate.hashCode();
        }

        @Override
        public String toString() {
            return delegate.toString();
        }

        @Override
        public boolean add(T e) {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
            return delegate.add(e);
        }

        @Override
        public boolean addAll(Collection c) {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
            return delegate.addAll(c);
        }

        @Override
        public void clear() {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>();
            }
            delegate.clear();
        }

        @Override
        public boolean contains(Object o) {
            containsCounter++;
            if (containsCounter >= MAXCONTAINS && !copyDone) {
                checkDelegate();
            }
            return delegate.contains(o);
        }

        private void checkDelegate() {
            // many calls to contains, inefficient if the delegate is not a
            // set
            if (!(delegate instanceof Set)) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
        }

        @Override
        public boolean containsAll(Collection c) {
            containsCounter++;
            if (containsCounter >= MAXCONTAINS && !copyDone) {
                checkDelegate();
            }
            return delegate.containsAll(c);
        }

        @Override
        public boolean isEmpty() {
            return delegate.isEmpty();
        }

        @Nonnull
        @Override
        public Iterator iterator() {
            return delegate.iterator();
        }

        @Override
        public boolean remove(Object o) {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
            return delegate.remove(o);
        }

        @Override
        public boolean removeAll(Collection c) {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
            return delegate.removeAll(c);
        }

        @Override
        public boolean retainAll(Collection c) {
            if (!copyDone) {
                copyDone = true;
                delegate = new LinkedHashSet<>(delegate);
            }
            return delegate.retainAll(c);
        }

        @Override
        public int size() {
            return delegate.size();
        }

        @Nonnull
        @Override
        public Object[] toArray() {
            return delegate.toArray();
        }

        @Nonnull
        @Override
        public  Type[] toArray(Type[] a) {
            return delegate.toArray(a);
        }
    }
}




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