/*
 * Java Genetic Algorithm Library (jenetics-5.1.0).
 * Copyright (c) 2007-2019 Franz Wilhelmstötter
 *
 * 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.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.util;

import java.util.List;

/**
 * This sorting methods doesn't sort a given array directly, instead
 * an index lookup array is returned which allows to access the array in
 * an sorted order.
 *
 * <pre>{@code
 * final double[] array = new Random().doubles(100).toArray();
 * final int[] proxy = ProxySorter.sort(array);
 *
 * // 'Classical' array sort.
 * final double[] sorted = array.clone();
 * Arrays.sort(sorted);
 *
 * // Iterating the array in ascending order.
 * for (int i = 0; i < array.length; ++i) {
 *     assert sorted[i] == array[proxy[i]];
 * }
 * }</pre>
 *
 * The minimal requirement of the proxy-sorter will be an access function and
 * the number of elements you want to sort.
 * <pre>{@code
 * final IntFunction<String> access = ...;
 * final int length = 100;
 * final int[] proxy = ProxySorter.sort(
 *     access, length,
 *     (a, i, j) -> a.apply(i).compareTo(a.apply(j))
 * );
 * }</pre>
 * @apiNote
 * The most general sorting method is {@link #sort(Object, int, Comparator)}.
 * All other sorting methods can be created with this method.
 *
 * @see #sort(Object, int, Comparator)
 * @see Comparator
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 5.1
 * @since 5.1
 */
public final class ProxySorter {

        /**
         * The comparator used for comparing two array elements at the specified
         * indexes.
         * <pre>{@code
         * final ProxySorter.Comparator<double[]> comparator =
         *     (a, i, j) -> Double.compare(a[i], a[j]);
         * }</pre>
         * The example above shows how to create a comparator for {@code double[]}
         * arrays.
         *
         * @see ProxySorter#sort(Object, int, Comparator)
         * @see ProxySorter
         *
         * @param <T> the array type, e.g. {@code int[]}, {@code double[]} or
         *            {@code Seq<String>}
         *
         * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
         * @version 5.1
         * @since 5.1
         */
        @FunctionalInterface
        public static interface Comparator<T> {

                /**
                 * Compares the two array elements, specified by its indices, for order.
                 * Returns a negative integer, zero, or a positive integer as the first
                 * argument is less than, equal to, or greater than the second.
                 *
                 * @see java.util.Comparator#compare(Object, Object)
                 *
                 * @param array the array where the two comparing elements are fetched
                 * @param i the index of the first array element
                 * @param j the index of the second array element
                 * @return a negative integer, zero, or a positive integer as the first
                 *         argument is less than, equal to, or greater than the second.
                 * @throws NullPointerException if an argument is null and this
                 *         comparator does not permit null arguments
                 */
                public int compare(final T array, final int i, final int j);

                /**
                 * Returns a comparator that imposes the reverse ordering of this
                 * comparator.
                 *
                 * @return a comparator that imposes the reverse ordering of this
                 *         comparator.
                 */
                public default Comparator<T> reversed() {
                        return (a, i, j) -> compare(a, j, i);
                }

        }

        private ProxySorter() {
        }

        /**
         * Sorting the given array by creating an index lookup array. The original
         * array is not touched and the returned array can then be used for
         * iterating the array in ascending order.
         *
         * <pre>{@code
         * final double[] array = ...;
         * final int[] sorted = ProxySorter.sort(
         *     array, array.length,
         *     (a, i, j) -> Doubler.compare(a[i], a[j])
         * );
         * for (int i : sorted) {
         *     System.out.println(array[i]);
         * }
         * }</pre>
         *
         * @param array the array which is sorted
         * @param length the array length
         * @param comparator the array element comparator
         * @param <T> the array type
         * @return the sorted index array
         * @throws NullPointerException if one of the array is {@code null}
         */
        public static <T> int[] sort(
                final T array,
                final int length,
                final Comparator<? super T> comparator
        ) {
                return TimProxySorter.sort(array, length, comparator);
        }


        /* *************************************************************************
         * Derived sorting methods.
         * ************************************************************************/

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static int[] sort(final int[] array) {
                return sort(array, array.length, ProxySorter::compare);
        }

        private static int compare(final int[] a, final int i, final int j) {
                return Integer.compare(a[i], a[j]);
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static int[] sort(final long[] array) {
                return sort(array, array.length, ProxySorter::compare);
        }

        private static int compare(final long[] a, final int i, final int j) {
                return Long.compare(a[i], a[j]);
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static int[] sort(final double[] array) {
                return sort(array, array.length, ProxySorter::compare);
        }

        private static int compare(final double[] a, final int i, final int j) {
                return Double.compare(a[i], a[j]);
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @param comparator the array element comparator
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <T> int[] sort(
                final T[] array,
                final java.util.Comparator<? super T> comparator
        ) {
                return sort(
                        array, array.length,
                        (a, i, j) -> comparator.compare(a[i], a[j])
                );
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static <T extends Comparable<? super T>> int[] sort(final T[] array) {
                return sort(
                        array, array.length,
                        (a, i, j) -> a[i].compareTo(a[j])
                );
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @param comparator the array element comparator
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <T> int[] sort(
                final Seq<? extends T> array,
                final java.util.Comparator<? super T> comparator
        ) {
                return sort(
                        array, array.size(),
                        (a, i, j) -> comparator.compare(a.get(i), a.get(j))
                );
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static <T extends Comparable<? super T>>
        int[] sort(final Seq<? extends T> array) {
                return sort(
                        array, array.size(),
                        (a, i, j) -> a.get(i).compareTo(a.get(j))
                );
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @param comparator the array element comparator
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <T> int[] sort(
                final List<? extends T> array,
                final java.util.Comparator<? super T> comparator
        ) {
                return sort(
                        array, array.size(),
                        (a, i, j) -> comparator.compare(a.get(i), a.get(j))
                );
        }

        /**
         * Sorting the given array by creating an index lookup array.
         *
         * @see #sort(Object, int, Comparator)
         *
         * @param <T> the array element type
         * @param array the array to sort
         * @return the <em>sorted</em> index lookup array
         * @throws NullPointerException if the array is {@code null}
         */
        public static <T extends Comparable<? super T>>
        int[] sort(final List<? extends T> array) {
                return sort(
                        array, array.size(),
                        (a, i, j) -> a.get(i).compareTo(a.get(j))
                );
        }

        /* *************************************************************************
         * Some helper methods.
         * ************************************************************************/

        /**
         * Create an initial indexes array of the given {@code length}.
         *
         * @param length the length of the indexes array
         * @return the initialized indexes array
         */
        static int[] indexes(final int length) {
                return init(new int[length]);
        }

        /**
         * Initializes the given {@code indexes} array.
         *
         * @param indexes the indexes array to initialize
         * @return the initialized indexes array
         * @throws NullPointerException if the given {@code indexes} array is
         *         {@code null}
         */
        static int[] init(final int[] indexes) {
                for (int i = 0; i < indexes.length; ++i) {
                        indexes[i] = i;
                }
                return indexes;
        }

}