/*
 * Copyright 2002-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.util;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

/**
 * Miscellaneous collection utility methods.
 * Mainly for internal use within the framework.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Arjen Poutsma
 * @since 1.1.3
 */
public abstract class CollectionUtils {

        /**
         * Return {@code true} if the supplied Collection is {@code null} or empty.
         * Otherwise, return {@code false}.
         * @param collection the Collection to check
         * @return whether the given Collection is empty
         */
        public static boolean isEmpty(Collection<?> collection) {
                return (collection == null || collection.isEmpty());
        }

        /**
         * Return {@code true} if the supplied Map is {@code null} or empty.
         * Otherwise, return {@code false}.
         * @param map the Map to check
         * @return whether the given Map is empty
         */
        public static boolean isEmpty(Map<?, ?> map) {
                return (map == null || map.isEmpty());
        }

        /**
         * Convert the supplied array into a List. A primitive array gets converted
         * into a List of the appropriate wrapper type.
         * <p><b>NOTE:</b> Generally prefer the standard {@link Arrays#asList} method.
         * This {@code arrayToList} method is just meant to deal with an incoming Object
         * value that might be an {@code Object[]} or a primitive array at runtime.
         * <p>A {@code null} source value will be converted to an empty List.
         * @param source the (potentially primitive) array
         * @return the converted List result
         * @see ObjectUtils#toObjectArray(Object)
         * @see Arrays#asList(Object[])
         */
        @SuppressWarnings("rawtypes")
        public static List arrayToList(Object source) {
                return Arrays.asList(ObjectUtils.toObjectArray(source));
        }

        /**
         * Merge the given array into the given Collection.
         * @param array the array to merge (may be {@code null})
         * @param collection the target Collection to merge the array into
         */
        @SuppressWarnings("unchecked")
        public static <E> void mergeArrayIntoCollection(Object array, Collection<E> collection) {
                if (collection == null) {
                        throw new IllegalArgumentException("Collection must not be null");
                }
                Object[] arr = ObjectUtils.toObjectArray(array);
                for (Object elem : arr) {
                        collection.add((E) elem);
                }
        }

        /**
         * Merge the given Properties instance into the given Map,
         * copying all properties (key-value pairs) over.
         * <p>Uses {@code Properties.propertyNames()} to even catch
         * default properties linked into the original Properties instance.
         * @param props the Properties instance to merge (may be {@code null})
         * @param map the target Map to merge the properties into
         */
        @SuppressWarnings("unchecked")
        public static <K, V> void mergePropertiesIntoMap(Properties props, Map<K, V> map) {
                if (map == null) {
                        throw new IllegalArgumentException("Map must not be null");
                }
                if (props != null) {
                        for (Enumeration<?> en = props.propertyNames(); en.hasMoreElements();) {
                                String key = (String) en.nextElement();
                                Object value = props.get(key);
                                if (value == null) {
                                        // Allow for defaults fallback or potentially overridden accessor...
                                        value = props.getProperty(key);
                                }
                                map.put((K) key, (V) value);
                        }
                }
        }


        /**
         * Check whether the given Iterator contains the given element.
         * @param iterator the Iterator to check
         * @param element the element to look for
         * @return {@code true} if found, {@code false} otherwise
         */
        public static boolean contains(Iterator<?> iterator, Object element) {
                if (iterator != null) {
                        while (iterator.hasNext()) {
                                Object candidate = iterator.next();
                                if (ObjectUtils.nullSafeEquals(candidate, element)) {
                                        return true;
                                }
                        }
                }
                return false;
        }

        /**
         * Check whether the given Enumeration contains the given element.
         * @param enumeration the Enumeration to check
         * @param element the element to look for
         * @return {@code true} if found, {@code false} otherwise
         */
        public static boolean contains(Enumeration<?> enumeration, Object element) {
                if (enumeration != null) {
                        while (enumeration.hasMoreElements()) {
                                Object candidate = enumeration.nextElement();
                                if (ObjectUtils.nullSafeEquals(candidate, element)) {
                                        return true;
                                }
                        }
                }
                return false;
        }

        /**
         * Check whether the given Collection contains the given element instance.
         * <p>Enforces the given instance to be present, rather than returning
         * {@code true} for an equal element as well.
         * @param collection the Collection to check
         * @param element the element to look for
         * @return {@code true} if found, {@code false} otherwise
         */
        public static boolean containsInstance(Collection<?> collection, Object element) {
                if (collection != null) {
                        for (Object candidate : collection) {
                                if (candidate == element) {
                                        return true;
                                }
                        }
                }
                return false;
        }

        /**
         * Return {@code true} if any element in '{@code candidates}' is
         * contained in '{@code source}'; otherwise returns {@code false}.
         * @param source the source Collection
         * @param candidates the candidates to search for
         * @return whether any of the candidates has been found
         */
        public static boolean containsAny(Collection<?> source, Collection<?> candidates) {
                if (isEmpty(source) || isEmpty(candidates)) {
                        return false;
                }
                for (Object candidate : candidates) {
                        if (source.contains(candidate)) {
                                return true;
                        }
                }
                return false;
        }

        /**
         * Return the first element in '{@code candidates}' that is contained in
         * '{@code source}'. If no element in '{@code candidates}' is present in
         * '{@code source}' returns {@code null}. Iteration order is
         * {@link Collection} implementation specific.
         * @param source the source Collection
         * @param candidates the candidates to search for
         * @return the first present object, or {@code null} if not found
         */
        @SuppressWarnings("unchecked")
        public static <E> E findFirstMatch(Collection<?> source, Collection<E> candidates) {
                if (isEmpty(source) || isEmpty(candidates)) {
                        return null;
                }
                for (Object candidate : candidates) {
                        if (source.contains(candidate)) {
                                return (E) candidate;
                        }
                }
                return null;
        }

        /**
         * Find a single value of the given type in the given Collection.
         * @param collection the Collection to search
         * @param type the type to look for
         * @return a value of the given type found if there is a clear match,
         * or {@code null} if none or more than one such value found
         */
        @SuppressWarnings("unchecked")
        public static <T> T findValueOfType(Collection<?> collection, Class<T> type) {
                if (isEmpty(collection)) {
                        return null;
                }
                T value = null;
                for (Object element : collection) {
                        if (type == null || type.isInstance(element)) {
                                if (value != null) {
                                        // More than one value found... no clear single value.
                                        return null;
                                }
                                value = (T) element;
                        }
                }
                return value;
        }

        /**
         * Find a single value of one of the given types in the given Collection:
         * searching the Collection for a value of the first type, then
         * searching for a value of the second type, etc.
         * @param collection the collection to search
         * @param types the types to look for, in prioritized order
         * @return a value of one of the given types found if there is a clear match,
         * or {@code null} if none or more than one such value found
         */
        public static Object findValueOfType(Collection<?> collection, Class<?>[] types) {
                if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
                        return null;
                }
                for (Class<?> type : types) {
                        Object value = findValueOfType(collection, type);
                        if (value != null) {
                                return value;
                        }
                }
                return null;
        }

        /**
         * Determine whether the given Collection only contains a single unique object.
         * @param collection the Collection to check
         * @return {@code true} if the collection contains a single reference or
         * multiple references to the same instance, {@code false} otherwise
         */
        public static boolean hasUniqueObject(Collection<?> collection) {
                if (isEmpty(collection)) {
                        return false;
                }
                boolean hasCandidate = false;
                Object candidate = null;
                for (Object elem : collection) {
                        if (!hasCandidate) {
                                hasCandidate = true;
                                candidate = elem;
                        }
                        else if (candidate != elem) {
                                return false;
                        }
                }
                return true;
        }

        /**
         * Find the common element type of the given Collection, if any.
         * @param collection the Collection to check
         * @return the common element type, or {@code null} if no clear
         * common type has been found (or the collection was empty)
         */
        public static Class<?> findCommonElementType(Collection<?> collection) {
                if (isEmpty(collection)) {
                        return null;
                }
                Class<?> candidate = null;
                for (Object val : collection) {
                        if (val != null) {
                                if (candidate == null) {
                                        candidate = val.getClass();
                                }
                                else if (candidate != val.getClass()) {
                                        return null;
                                }
                        }
                }
                return candidate;
        }

        /**
         * Marshal the elements from the given enumeration into an array of the given type.
         * Enumeration elements must be assignable to the type of the given array. The array
         * returned will be a different instance than the array given.
         */
        public static <A, E extends A> A[] toArray(Enumeration<E> enumeration, A[] array) {
                ArrayList<A> elements = new ArrayList<A>();
                while (enumeration.hasMoreElements()) {
                        elements.add(enumeration.nextElement());
                }
                return elements.toArray(array);
        }

        /**
         * Adapt an {@link Enumeration} to an {@link Iterator}.
         * @param enumeration the original {@code Enumeration}
         * @return the adapted {@code Iterator}
         */
        @SuppressWarnings("unchecked")
        public static <E> Iterator<E> toIterator(Enumeration<E> enumeration) {
                return (enumeration != null ? new EnumerationIterator<E>(enumeration) : Collections.EMPTY_SET.iterator());
        }

        /**
         * Adapt a {@code Map<K, List<V>>} to an {@code MultiValueMap<K, V>}.
         * @param map the original map
         * @return the multi-value map
         * @since 3.1
         */
        public static <K, V> MultiValueMap<K, V> toMultiValueMap(Map<K, List<V>> map) {
                return new MultiValueMapAdapter<K, V>(map);
        }

        /**
         * Return an unmodifiable view of the specified multi-value map.
         * @param  map the map for which an unmodifiable view is to be returned.
         * @return an unmodifiable view of the specified multi-value map.
         * @since 3.1
         */
        @SuppressWarnings("unchecked")
        public static <K, V> MultiValueMap<K, V> unmodifiableMultiValueMap(MultiValueMap<? extends K, ? extends V> map) {
                Assert.notNull(map, "'map' must not be null");
                Map<K, List<V>> result = new LinkedHashMap<K, List<V>>(map.size());
                for (Map.Entry<? extends K, ? extends List<? extends V>> entry : map.entrySet()) {
                        List<? extends V> values = Collections.unmodifiableList(entry.getValue());
                        result.put(entry.getKey(), (List<V>) values);
                }
                Map<K, List<V>> unmodifiableMap = Collections.unmodifiableMap(result);
                return toMultiValueMap(unmodifiableMap);
        }


        /**
         * Iterator wrapping an Enumeration.
         */
        private static class EnumerationIterator<E> implements Iterator<E> {

                private final Enumeration<E> enumeration;

                public EnumerationIterator(Enumeration<E> enumeration) {
                        this.enumeration = enumeration;
                }

                @Override
                public boolean hasNext() {
                        return this.enumeration.hasMoreElements();
                }

                @Override
                public E next() {
                        return this.enumeration.nextElement();
                }

                @Override
                public void remove() throws UnsupportedOperationException {
                        throw new UnsupportedOperationException("Not supported");
                }
        }


        /**
         * Adapts a Map to the MultiValueMap contract.
         */
        @SuppressWarnings("serial")
        private static class MultiValueMapAdapter<K, V> implements MultiValueMap<K, V>, Serializable {

                private final Map<K, List<V>> map;

                public MultiValueMapAdapter(Map<K, List<V>> map) {
                        Assert.notNull(map, "'map' must not be null");
                        this.map = map;
                }

                @Override
                public void add(K key, V value) {
                        List<V> values = this.map.get(key);
                        if (values == null) {
                                values = new LinkedList<V>();
                                this.map.put(key, values);
                        }
                        values.add(value);
                }

                @Override
                public V getFirst(K key) {
                        List<V> values = this.map.get(key);
                        return (values != null && !values.isEmpty() ? values.get(0) : null);
                }

                @Override
                public void set(K key, V value) {
                        List<V> values = new LinkedList<V>();
                        values.add(value);
                        this.map.put(key, values);
                }

                @Override
                public void setAll(Map<K, V> values) {
                        for (Entry<K, V> entry : values.entrySet()) {
                                set(entry.getKey(), entry.getValue());
                        }
                }

                @Override
                public Map<K, V> toSingleValueMap() {
                        LinkedHashMap<K, V> singleValueMap = new LinkedHashMap<K,V>(this.map.size());
                        for (Entry<K, List<V>> entry : map.entrySet()) {
                                List<V> values = entry.getValue();
                                if (values != null && !values.isEmpty()) {
                                        singleValueMap.put(entry.getKey(), values.get(0));
                                }
                        }
                        return singleValueMap;
                }

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

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

                @Override
                public boolean containsKey(Object key) {
                        return this.map.containsKey(key);
                }

                @Override
                public boolean containsValue(Object value) {
                        return this.map.containsValue(value);
                }

                @Override
                public List<V> get(Object key) {
                        return this.map.get(key);
                }

                @Override
                public List<V> put(K key, List<V> value) {
                        return this.map.put(key, value);
                }

                @Override
                public List<V> remove(Object key) {
                        return this.map.remove(key);
                }

                @Override
                public void putAll(Map<? extends K, ? extends List<V>> map) {
                        this.map.putAll(map);
                }

                @Override
                public void clear() {
                        this.map.clear();
                }

                @Override
                public Set<K> keySet() {
                        return this.map.keySet();
                }

                @Override
                public Collection<List<V>> values() {
                        return this.map.values();
                }

                @Override
                public Set<Entry<K, List<V>>> entrySet() {
                        return this.map.entrySet();
                }

                @Override
                public boolean equals(Object other) {
                        return (this == other || this.map.equals(other));
                }

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

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

}