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package com.sap.it.commons.tools;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

public final class CollectionTools {
    /**
     * Private constructor to avoid instantiation of this class.
     */
    private CollectionTools() {
    }

    /**
     * Returns the the initialCapacity value for creating a (Hash-)Map that can
     * store elements without reallocation.
     * 
     * @param elements
     *            number of elements to be stored.
     * 
     * @return the initialCapacity value for the Map constructor.
     */
    public static int computeMapInitialSize(int elements) {
        return Math.max((int) (elements / 0.75) + 1, 16);
    }

    /**
     * Return the first element of a collection. If the collection is empty null
     * is returned.
     * 
     * @param collection
     * @return the first element or {@code null}.
     */
    public static  T firstOf(Collection collection) {
        if (collection == null || collection.isEmpty()) {
            return null;
        }

        if (collection instanceof List) {
            return ((List) collection).get(0);
        } else {
            return collection.iterator().next();
        }
    }

    /**
     * Return if a collection at least contains one element.
     * 
     * @param collection
     * @return true if the collection is neither empty nor null.
     */
    public static boolean hasContent(Collection collection) {
        return collection != null && !collection.isEmpty();
    }

    /**
     * Return if a collection is null or empty.
     * 
     * @param collection
     * @return true if the collection is empty or null.
     */
    public static boolean isEmpty(Collection collection) {
        return collection == null || collection.isEmpty();
    }

    /**
     * Cluster a collection into part of size elements. If last part has
     * potentially less than size elements.
     * 
     * @param collection
     *            collection to cluster
     * @param clusterSize
     *            maximum elements per cluster
     * @return allays a collection is returned. Containing no elements if the
     *         collection input parameter was null or an empty collection.
     */
    public static  Collection> cluster(Collection collection, int clusterSize) {
        if (clusterSize <= 0) {
            throw new IllegalArgumentException("clusterSize must be greater than 0");
        }
        if (isEmpty(collection)) {
            return Collections.emptyList();
        }

        List> res = new ArrayList>();
        Iterator it = collection.iterator();
        while (it.hasNext()) {
            ArrayList part = new ArrayList();
            int cnt = clusterSize;

            do {
                part.add(it.next());
            } while ((--cnt > 0) && it.hasNext());
            res.add(part);
        }
        return res;
    }

    public static String asString(Collection collection, String separator, String collectionEmptyValue, boolean skipNullValues) {
        if (CollectionTools.isEmpty(collection)) {
            return collectionEmptyValue;
        }

        final StringBuilder sb = new StringBuilder();
        for (Object o : collection) {
            if (skipNullValues && o == null) {
                continue;
            }
            if (sb.length() > 0) {
                sb.append(separator);
            }
            sb.append(o);
        }

        if (skipNullValues && sb.length() == 0) {
            return collectionEmptyValue;
        }

        return sb.toString();
    }

    public static String asString(Collection collection, String separator, String collectionEmptyValue) {
        return asString(collection, separator, collectionEmptyValue, false);
    }

    public static String asString(Collection collection, String separator) {
        return asString(collection, separator, StringTools.EMPTY_STRING);
    }

    public static > T nullify(T data) {
        return data == null || data.isEmpty() ? null : data;
    }

    @SuppressWarnings("rawtypes")
    public static Iterator EMPTY_ITERATOR = new Iterator() {
        @Override
        public boolean hasNext() {
            return false;
        }

        @Override
        public Object next() {
            throw new NoSuchElementException();
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    };

    @SuppressWarnings("unchecked")
    public static  Iterator emptyIterator() {
        return (Iterator) EMPTY_ITERATOR;
    }

    @SuppressWarnings("rawtypes")
    public static Iterable EMPTY_ITERABLE = new Iterable() {
        @Override
        public Iterator iterator() {
            return emptyIterator();
        }
    };

    @SuppressWarnings("unchecked")
    public static final  Iterable emptyIterable() {
        return (Iterable) EMPTY_ITERABLE;
    }

    public static final  boolean addAll(Collection collection, Iterator iterator) {
        boolean res = false;
        while (iterator.hasNext()) {
            res |= collection.add(iterator.next());
        }
        return res;
    }

    public static final  boolean addAll(Collection collection, Iterable iterable) {
        boolean res = false;
        for (E o : iterable) {
            res |= collection.add(o);
        }
        return res;
    }
}