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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package org.graalvm.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.IntFunction;
import java.util.function.Predicate;
import java.util.function.Supplier;


This class contains utility methods for commonly used functional patterns for collections.

/**
 * This class contains utility methods for commonly used functional patterns for collections.
 */
public final class CollectionsUtil {

    private CollectionsUtil() {
    }

    
Concatenates two iterables into a single iterable. The iterator exposed by the returned iterable does not support Iterator.remove() even if the input iterables do. 
Throws:
/**
     * Concatenates two iterables into a single iterable. The iterator exposed by the returned
     * iterable does not support {@link Iterator#remove()} even if the input iterables do.
     *
     * @throws NullPointerException if {@code a} or {@code b} is {@code null}
     */
    public static <T> Iterable<T> concat(Iterable<T> a, Iterable<T> b) {
        List<Iterable<T>> l = Arrays.asList(a, b);
        return concat(l);
    }

    
Concatenates multiple iterables into a single iterable. The iterator exposed by the returned iterable does not support Iterator.remove() even if the input iterables do. 
Throws:
/**
     * Concatenates multiple iterables into a single iterable. The iterator exposed by the returned
     * iterable does not support {@link Iterator#remove()} even if the input iterables do.
     *
     * @throws NullPointerException if {@code iterables} or any of its elements are {@code null}
     */
    public static <T> Iterable<T> concat(List<Iterable<T>> iterables) {
        for (Iterable<T> iterable : iterables) {
            Objects.requireNonNull(iterable);
        }
        return new Iterable<T>() {
            @Override
            public Iterator<T> iterator() {
                if (iterables.size() == 0) {
                    return Collections.emptyIterator();
                }
                return new Iterator<T>() {
                    Iterator<Iterable<T>> cursor = iterables.iterator();
                    Iterator<T> currentIterator = cursor.next().iterator();

                    private void advance() {
                        while (!currentIterator.hasNext() && cursor.hasNext()) {
                            currentIterator = cursor.next().iterator();
                        }
                    }

                    @Override
                    public boolean hasNext() {
                        advance();
                        return currentIterator.hasNext();
                    }

                    @Override
                    public T next() {
                        advance();
                        return currentIterator.next();
                    }
                };
            }

        };
    }

    
Returns whether all elements in inputs match predicate. May not evaluate predicate on all elements if not necessary for determining the result. If inputs is empty then true is returned and predicate is not evaluated. 
Returns:true if either all elements in inputs match predicate or inputs is empty, otherwise false.
/**
     * Returns whether all elements in {@code inputs} match {@code predicate}. May not evaluate
     * {@code predicate} on all elements if not necessary for determining the result. If
     * {@code inputs} is empty then {@code true} is returned and {@code predicate} is not evaluated.
     *
     * @return {@code true} if either all elements in {@code inputs} match {@code predicate} or
     *         {@code inputs} is empty, otherwise {@code false}.
     */
    public static <T> boolean allMatch(T[] inputs, Predicate<T> predicate) {
        return allMatch(Arrays.asList(inputs), predicate);
    }

    
Returns whether all elements in inputs match predicate. May not evaluate predicate on all elements if not necessary for determining the result. If inputs is empty then true is returned and predicate is not evaluated. 
Returns:true if either all elements in inputs match predicate or inputs is empty, otherwise false.
/**
     * Returns whether all elements in {@code inputs} match {@code predicate}. May not evaluate
     * {@code predicate} on all elements if not necessary for determining the result. If
     * {@code inputs} is empty then {@code true} is returned and {@code predicate} is not evaluated.
     *
     * @return {@code true} if either all elements in {@code inputs} match {@code predicate} or
     *         {@code inputs} is empty, otherwise {@code false}.
     */
    public static <T> boolean allMatch(Iterable<T> inputs, Predicate<T> predicate) {
        for (T t : inputs) {
            if (!predicate.test(t)) {
                return false;
            }
        }
        return true;
    }

    
Returns whether any elements in inputs match predicate. May not evaluate predicate on all elements if not necessary for determining the result. If inputs is empty then false is returned and predicate is not evaluated. 
Returns:true if any elements in inputs match predicate, otherwise false.
/**
     * Returns whether any elements in {@code inputs} match {@code predicate}. May not evaluate
     * {@code predicate} on all elements if not necessary for determining the result. If
     * {@code inputs} is empty then {@code false} is returned and {@code predicate} is not
     * evaluated.
     *
     * @return {@code true} if any elements in {@code inputs} match {@code predicate}, otherwise
     *         {@code false}.
     */
    public static <T> boolean anyMatch(T[] inputs, Predicate<T> predicate) {
        return anyMatch(Arrays.asList(inputs), predicate);
    }

    
Returns whether any elements in inputs match predicate. May not evaluate predicate on all elements if not necessary for determining the result. If inputs is empty then false is returned and predicate is not evaluated. 
Returns:true if any elements in inputs match predicate, otherwise false.
/**
     * Returns whether any elements in {@code inputs} match {@code predicate}. May not evaluate
     * {@code predicate} on all elements if not necessary for determining the result. If
     * {@code inputs} is empty then {@code false} is returned and {@code predicate} is not
     * evaluated.
     *
     * @return {@code true} if any elements in {@code inputs} match {@code predicate}, otherwise
     *         {@code false}.
     */
    public static <T> boolean anyMatch(Iterable<T> inputs, Predicate<T> predicate) {
        for (T t : inputs) {
            if (predicate.test(t)) {
                return true;
            }
        }
        return false;
    }

    
Returns a new list consisting of the elements in inputs that match predicate. 
Returns:the new list.
/**
     * Returns a new list consisting of the elements in {@code inputs} that match {@code predicate}.
     *
     * @return the new list.
     */
    public static <T> List<T> filterToList(List<T> inputs, Predicate<? super T> predicate) {
        return filterToList(inputs, predicate, ArrayList::new);
    }

    
Appends elements of inputs that match predicate to the list generated by listGenerator. 
Returns:the list generated by listGenerator.
/**
     * Appends elements of {@code inputs} that match {@code predicate} to the list generated by
     * {@code listGenerator}.
     *
     * @return the list generated by {@code listGenerator}.
     */
    public static <T> List<T> filterToList(List<T> inputs, Predicate<? super T> predicate, Supplier<List<T>> listGenerator) {
        List<T> resultList = listGenerator.get();
        for (T t : inputs) {
            if (predicate.test(t)) {
                resultList.add(t);
            }
        }
        return resultList;
    }

    
Filters inputs with predicate, applies mapper and adds them in the array provided by arrayGenerator. 
Returns:the array provided by arrayGenerator.
/**
     * Filters {@code inputs} with {@code predicate}, applies {@code mapper} and adds them in the
     * array provided by {@code arrayGenerator}.
     *
     * @return the array provided by {@code arrayGenerator}.
     */
    public static <T, R> R[] filterAndMapToArray(T[] inputs, Predicate<? super T> predicate, Function<? super T, ? extends R> mapper, IntFunction<R[]> arrayGenerator) {
        List<R> resultList = new ArrayList<>();
        for (T t : inputs) {
            if (predicate.test(t)) {
                resultList.add(mapper.apply(t));
            }
        }
        return resultList.toArray(arrayGenerator.apply(resultList.size()));
    }

    
Applies mapper on the elements in inputs and adds them in the array provided by arrayGenerator. 
Returns:the array provided by arrayGenerator.
/**
     * Applies {@code mapper} on the elements in {@code inputs} and adds them in the array provided
     * by {@code arrayGenerator}.
     *
     * @return the array provided by {@code arrayGenerator}.
     */
    public static <T, R> R[] mapToArray(T[] inputs, Function<? super T, ? extends R> mapper, IntFunction<R[]> arrayGenerator) {
        return mapToArray(Arrays.asList(inputs), mapper, arrayGenerator);
    }

    
Applies mapper on the elements in inputs and adds them in the array provided by arrayGenerator. 
Returns:the array provided by arrayGenerator.
/**
     * Applies {@code mapper} on the elements in {@code inputs} and adds them in the array provided
     * by {@code arrayGenerator}.
     *
     * @return the array provided by {@code arrayGenerator}.
     */
    public static <T, R> R[] mapToArray(Collection<T> inputs, Function<? super T, ? extends R> mapper, IntFunction<R[]> arrayGenerator) {
        R[] result = arrayGenerator.apply(inputs.size());
        int idx = 0;
        for (T t : inputs) {
            result[idx++] = mapper.apply(t);
        }
        return result;
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(T[] inputs, Function<? super T, ? extends R> mapper, String delimiter) {
        return mapAndJoin(Arrays.asList(inputs), mapper, delimiter, "", "");
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter and starting with prefix. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter} and starting with {@code prefix}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(T[] inputs, Function<? super T, ? extends R> mapper, String delimiter, String prefix) {
        return mapAndJoin(Arrays.asList(inputs), mapper, delimiter, prefix, "");
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter and starting with prefix and ending with suffix. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter} and starting with {@code prefix} and ending with {@code suffix}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(T[] inputs, Function<? super T, ? extends R> mapper, String delimiter, String prefix, String suffix) {
        return mapAndJoin(Arrays.asList(inputs), mapper, delimiter, prefix, suffix);
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(Iterable<T> inputs, Function<? super T, ? extends R> mapper, String delimiter) {
        return mapAndJoin(inputs, mapper, delimiter, "", "");
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter and starting with prefix. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter} and starting with {@code prefix}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(Iterable<T> inputs, Function<? super T, ? extends R> mapper, String delimiter, String prefix) {
        return mapAndJoin(inputs, mapper, delimiter, prefix, "");
    }

    
Applies mapper on the elements in inputs, and joins them together separated by delimiter and starting with prefix and ending with suffix. 
Returns:a new String that is composed from inputs.
/**
     * Applies {@code mapper} on the elements in {@code inputs}, and joins them together separated
     * by {@code delimiter} and starting with {@code prefix} and ending with {@code suffix}.
     *
     * @return a new String that is composed from {@code inputs}.
     */
    public static <T, R> String mapAndJoin(Iterable<T> inputs, Function<? super T, ? extends R> mapper, String delimiter, String prefix, String suffix) {
        StringBuilder strb = new StringBuilder();
        String sep = "";
        for (T t : inputs) {
            strb.append(sep).append(prefix).append(mapper.apply(t)).append(suffix);
            sep = delimiter;
        }
        return strb.toString();
    }

}