/*
 * Copyright (c) 2018 Goldman Sachs and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v. 1.0 which accompany this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 */

package org.eclipse.collections.impl.factory;

import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;

import org.eclipse.collections.api.LazyIterable;
import org.eclipse.collections.api.block.function.Function2;
import org.eclipse.collections.api.block.predicate.Predicate;
import org.eclipse.collections.api.block.procedure.Procedure2;
import org.eclipse.collections.api.factory.set.FixedSizeSetFactory;
import org.eclipse.collections.api.factory.set.ImmutableSetFactory;
import org.eclipse.collections.api.factory.set.MutableSetFactory;
import org.eclipse.collections.api.set.MutableSet;
import org.eclipse.collections.api.tuple.Pair;
import org.eclipse.collections.impl.block.factory.Comparators;
import org.eclipse.collections.impl.set.fixed.FixedSizeSetFactoryImpl;
import org.eclipse.collections.impl.set.immutable.ImmutableSetFactoryImpl;
import org.eclipse.collections.impl.set.mutable.MultiReaderMutableSetFactory;
import org.eclipse.collections.impl.set.mutable.MutableSetFactoryImpl;
import org.eclipse.collections.impl.set.mutable.SetAdapter;
import org.eclipse.collections.impl.set.mutable.UnifiedSet;
import org.eclipse.collections.impl.tuple.Tuples;
import org.eclipse.collections.impl.utility.ArrayIterate;
import org.eclipse.collections.impl.utility.Iterate;
import org.eclipse.collections.impl.utility.LazyIterate;

Set algebra operations are available in this class as static utility.

Most operations are non-destructive, i.e. no input sets are modified during execution.
The exception is operations ending in "Into." These accept the target collection of
the final calculation as the first parameter.
 Some effort is made to return a SortedSet if any input set is sorted, but this is not guaranteed (e.g., this will not be the case for collections proxied by Hibernate). When in doubt, specify the target collection explicitly with the "Into" version. This class should be used to create instances of MutableSet, ImmutableSet and FixedSizeSet 

Mutable Examples:
MutableSet<String> emptySet = Sets.mutable.empty();
MutableSet<String> setWith = Sets.mutable.with("a", "b", "c");
MutableSet<String> setOf = Sets.mutable.of("a", "b", "c");

Immutable Examples:
ImmutableSet<String> emptySet = Sets.immutable.empty();
ImmutableSet<String> setWith = Sets.immutable.with("a", "b", "c");
ImmutableSet<String> setOf = Sets.immutable.of("a", "b", "c");

FixedSize Examples:
FixedSizeList<String> emptySet = Sets.fixedSize.empty();
FixedSizeList<String> setWith = Sets.fixedSize.with("a", "b", "c");
FixedSizeList<String> setOf = Sets.fixedSize.of("a", "b", "c");

/**
 * Set algebra operations are available in this class as static utility.
 * <p>
 * Most operations are non-destructive, i.e. no input sets are modified during execution.
 * The exception is operations ending in "Into." These accept the target collection of
 * the final calculation as the first parameter.
 * <p>
 * Some effort is made to return a {@code SortedSet} if any input set is sorted, but
 * this is not guaranteed (e.g., this will not be the case for collections proxied by
 * Hibernate). When in doubt, specify the target collection explicitly with the "Into"
 * version.
 *
 * This class should be used to create instances of MutableSet, ImmutableSet and FixedSizeSet
 * <p>
 * Mutable Examples:
 *
 * <pre>
 * MutableSet&lt;String&gt; emptySet = Sets.mutable.empty();
 * MutableSet&lt;String&gt; setWith = Sets.mutable.with("a", "b", "c");
 * MutableSet&lt;String&gt; setOf = Sets.mutable.of("a", "b", "c");
 * </pre>
 *
 * Immutable Examples:
 *
 * <pre>
 * ImmutableSet&lt;String&gt; emptySet = Sets.immutable.empty();
 * ImmutableSet&lt;String&gt; setWith = Sets.immutable.with("a", "b", "c");
 * ImmutableSet&lt;String&gt; setOf = Sets.immutable.of("a", "b", "c");
 * </pre>
 *
 * FixedSize Examples:
 *
 * <pre>
 * FixedSizeList&lt;String&gt; emptySet = Sets.fixedSize.empty();
 * FixedSizeList&lt;String&gt; setWith = Sets.fixedSize.with("a", "b", "c");
 * FixedSizeList&lt;String&gt; setOf = Sets.fixedSize.of("a", "b", "c");
 * </pre>
 */
@SuppressWarnings("ConstantNamingConvention")
public final class Sets
{
    public static final ImmutableSetFactory immutable = ImmutableSetFactoryImpl.INSTANCE;
    public static final FixedSizeSetFactory fixedSize = FixedSizeSetFactoryImpl.INSTANCE;
    public static final MutableSetFactory mutable = MutableSetFactoryImpl.INSTANCE;
    public static final MutableSetFactory multiReader = MultiReaderMutableSetFactory.INSTANCE;

    private static final Predicate<Set<?>> INSTANCE_OF_SORTED_SET_PREDICATE = SortedSet.class::isInstance;

    private static final Predicate<Set<?>> HAS_NON_NULL_COMPARATOR = set -> ((SortedSet<?>) set).comparator() != null;

    private Sets()
    {
        throw new AssertionError("Suppress default constructor for noninstantiability");
    }

    
Since:
9.0./**
     * @since 9.0.
     */
    public static <T> MutableSet<T> adapt(Set<T> list)
    {
        return SetAdapter.adapt(list);
    }

    public static <E> MutableSet<E> union(
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return unionInto(newSet(setA, setB), setA, setB);
    }

    public static <E, R extends Set<E>> R unionInto(
            R targetSet,
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return setA.size() > setB.size() ? fillSet(targetSet, Sets.addAllProcedure(), setA, setB)
                : fillSet(targetSet, Sets.addAllProcedure(), setB, setA);
    }

    public static <E> MutableSet<E> unionAll(Set<? extends E>... sets)
    {
        return unionAllInto(newSet(sets), sets);
    }

    public static <E, R extends Set<E>> R unionAllInto(
            R targetSet,
            Set<? extends E>... sets)
    {
        Arrays.sort(sets, 0, sets.length, Comparators.descendingCollectionSizeComparator());
        return fillSet(targetSet, Sets.addAllProcedure(), sets);
    }

    public static <E> MutableSet<E> intersect(
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return intersectInto(newSet(setA, setB), setA, setB);
    }

    public static <E, R extends Set<E>> R intersectInto(
            R targetSet,
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return setA.size() < setB.size() ? fillSet(targetSet, Sets.retainAllProcedure(), setA, setB)
                : fillSet(targetSet, Sets.retainAllProcedure(), setB, setA);
    }

    public static <E> MutableSet<E> intersectAll(Set<? extends E>... sets)
    {
        return intersectAllInto(newSet(sets), sets);
    }

    public static <E, R extends Set<E>> R intersectAllInto(
            R targetSet,
            Set<? extends E>... sets)
    {
        Arrays.sort(sets, 0, sets.length, Comparators.ascendingCollectionSizeComparator());
        return fillSet(targetSet, Sets.retainAllProcedure(), sets);
    }

    public static <E> MutableSet<E> difference(
            Set<? extends E> minuendSet,
            Set<? extends E> subtrahendSet)
    {
        return differenceInto(newSet(minuendSet, subtrahendSet), minuendSet, subtrahendSet);
    }

    public static <E, R extends Set<E>> R differenceInto(
            R targetSet,
            Set<? extends E> minuendSet,
            Set<? extends E> subtrahendSet)
    {
        return fillSet(targetSet, Sets.removeAllProcedure(), minuendSet, subtrahendSet);
    }

    public static <E> MutableSet<E> differenceAll(Set<? extends E>... sets)
    {
        return differenceAllInto(newSet(sets), sets);
    }

    public static <E, R extends Set<E>> R differenceAllInto(
            R targetSet,
            Set<? extends E>... sets)
    {
        return fillSet(targetSet, Sets.removeAllProcedure(), sets);
    }

    public static <E> MutableSet<E> symmetricDifference(
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return symmetricDifferenceInto(newSet(setA, setB), setA, setB);
    }

    public static <E, R extends Set<E>> R symmetricDifferenceInto(
            R targetSet,
            Set<? extends E> setA,
            Set<? extends E> setB)
    {
        return unionInto(
                targetSet,
                differenceInto(newSet(setA, setB), setA, setB),
                differenceInto(newSet(setA, setB), setB, setA));
    }

    public static <E> boolean isSubsetOf(
            Set<? extends E> candidateSubset,
            Set<? extends E> candidateSuperset)
    {
        return candidateSubset.size() <= candidateSuperset.size()
                && candidateSuperset.containsAll(candidateSubset);
    }

    public static <E> boolean isProperSubsetOf(
            Set<? extends E> candidateSubset,
            Set<? extends E> candidateSuperset)
    {
        return candidateSubset.size() < candidateSuperset.size()
                && candidateSuperset.containsAll(candidateSubset);
    }

    private static <E> MutableSet<E> newSet(Set<? extends E>... sets)
    {
        Comparator<? super E> comparator = extractComparator(sets);
        if (comparator != null)
        {
            // TODO: this should return a SortedSetAdapter once implemented
            return SetAdapter.adapt(new TreeSet<>(comparator));
        }
        return UnifiedSet.newSet();
    }

    private static <E> Comparator<? super E> extractComparator(Set<? extends E>... sets)
    {
        Collection<Set<? extends E>> sortedSetCollection = ArrayIterate.select(sets, INSTANCE_OF_SORTED_SET_PREDICATE);
        if (sortedSetCollection.isEmpty())
        {
            return null;
        }
        SortedSet<E> sortedSetWithComparator = (SortedSet<E>) Iterate.detect(sortedSetCollection, HAS_NON_NULL_COMPARATOR);
        if (sortedSetWithComparator != null)
        {
            return sortedSetWithComparator.comparator();
        }
        return Comparators.safeNullsLow(Comparators.naturalOrder());
    }

    private static <E, R extends Set<E>> R fillSet(
            R targetSet,
            Procedure2<Set<? extends E>, R> procedure,
            Set<? extends E>... sets)
    {
        targetSet.addAll(sets[0]);
        for (int i = 1; i < sets.length; i++)
        {
            procedure.value(sets[i], targetSet);
        }
        return targetSet;
    }

    private static <E, R extends Set<E>> Procedure2<Set<? extends E>, R> addAllProcedure()
    {
        return (argumentSet, targetSet) -> targetSet.addAll(argumentSet);
    }

    private static <E, R extends Set<E>> Procedure2<Set<? extends E>, R> retainAllProcedure()
    {
        return (argumentSet, targetSet) -> targetSet.retainAll(argumentSet);
    }

    private static <E, R extends Set<E>> Procedure2<Set<? extends E>, R> removeAllProcedure()
    {
        return (argumentSet, targetSet) -> targetSet.removeAll(argumentSet);
    }

    public static <T> MutableSet<MutableSet<T>> powerSet(Set<T> set)
    {
        MutableSet<MutableSet<T>> seed = UnifiedSet.newSetWith(UnifiedSet.newSet());
        return Iterate.injectInto(seed, set, (accumulator, element) -> Sets.union(accumulator, accumulator.collect(innerSet -> innerSet.toSet().with(element))));
    }

    public static <A, B> LazyIterable<Pair<A, B>> cartesianProduct(Set<A> set1, Set<B> set2)
    {
        return Sets.cartesianProduct(set1, set2, Tuples::pair);
    }

    public static <A, B, C> LazyIterable<C> cartesianProduct(Set<A> set1, Set<B> set2, Function2<A, B, C> function)
    {
        return LazyIterate.flatCollect(set1, first -> LazyIterate.collect(set2, second -> function.value(first, second)));
    }
}