/Obtics/Collections/ObservableEnumerable.ThenByDescending.cs

using System;

using System.Collections.Generic;

using Obtics.Values;

using System.Linq;



namespace Obtics.Collections

{

    public static partial class ObservableEnumerable

    {

        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order according to a key.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        public static IObservableOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IObservableOrderedEnumerable<TSource> source, Func<TSource, TKey> keySelector)

        { return ThenByDescending(source, keySelector, Comparer<TKey>.Default); }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order by using a given comparer.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element.</param>

        /// <param name="comparer">An <see cref="IComparer{TKey}"/> used to compare key values.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        public static IObservableOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IObservableOrderedEnumerable<TSource> source, Func<TSource, TKey> keySelector, IComparer<TKey> comparer)

        {

            if (source == null)

                return null;



            return source.CreateOrderedEnumerable(keySelector, comparer, true);

        }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order according to a key dynamicaly.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element. It returns an <see cref="IValueProvider{TKey}"/> whose <typeparamref name="TKey"/> Value property gives the key to order the given element by.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        public static IObservableOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IObservableOrderedEnumerable<TSource> source, Func<TSource, IValueProvider<TKey>> keySelector)

        { return ThenByDescending(source, keySelector, Comparer<TKey>.Default); }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order dynamicaly by using a given comparer.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element.</param>

        /// <param name="comparer">An <see cref="IComparer{TKey}"/> used to compare key values. It returns an <see cref="IValueProvider{TKey}"/> whose <typeparamref name="TKey"/> Value property gives the key to order the given element by.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        public static IObservableOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IObservableOrderedEnumerable<TSource> source, Func<TSource, IValueProvider<TKey>> keySelector, IComparer<TKey> comparer)

        {

            if (source == null)

                return null;



            return source.CreateOrderedEnumerable(keySelector, comparer, true);

        }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order according to a key.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element.</param>

        /// <returns>An <see cref="IOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        /// <remarks>The result of this method will only be reactive and observable if source is in fact an <see cref="IObservableOrderedEnumerable{TSource}"/>.</remarks>

        public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IOrderedEnumerable<TSource> source, Func<TSource, TKey> keySelector)

        { return ThenByDescending(source, keySelector, Comparer<TKey>.Default); }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order by using a given comparer.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element.</param>

        /// <param name="comparer">An <see cref="IComparer{TKey}"/> used to compare key values.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        /// <remarks>The result of this method will only be reactive and observable if source is in fact an <see cref="IObservableOrderedEnumerable{TSource}"/>.</remarks>

        public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IOrderedEnumerable<TSource> source, Func<TSource, TKey> keySelector, IComparer<TKey> comparer)

        {

            if (source == null || keySelector == null || comparer == null )

                return null;



            var asObservable = source as IObservableOrderedEnumerable<TSource>;



            return asObservable != null ? asObservable.CreateOrderedEnumerable(keySelector, comparer, true) : source.CreateOrderedEnumerable(keySelector, comparer, true);

        }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order according to a key dynamicaly.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element. It returns an <see cref="IValueProvider{TKey}"/> whose <typeparamref name="TKey"/> Value property gives the key to order the given element by.</param>

        /// <returns>An <see cref="IOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        /// <remarks>The result of this method will only be reactive and observable if source is in fact an <see cref="IObservableOrderedEnumerable{TSource}"/>.</remarks>

        public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IOrderedEnumerable<TSource> source, Func<TSource, IValueProvider<TKey>> keySelector)

        { return ThenByDescending(source, keySelector, Comparer<TKey>.Default); }



        /// <summary>

        /// Performs a subsequent ordering of the elements in a sequence in descending order dynamicaly by using a given comparer.

        /// </summary>

        /// <typeparam name="TSource">The type of the elements of the sequence.</typeparam>

        /// <typeparam name="TKey">The type of the key.</typeparam>

        /// <param name="source">An <see cref="IObservableOrderedEnumerable{TSource}"/> that contains elements to sort.</param>

        /// <param name="keySelector">A function to extract a key from each element. It returns an <see cref="IValueProvider{TKey}"/> whose <typeparamref name="TKey"/> Value property gives the key to order the given element by.</param>

        /// <param name="comparer">An <see cref="IComparer{TKey}"/> used to compare key values.</param>

        /// <returns>An <see cref="IObservableOrderedEnumerable{TSource}"/>, whose elements are sorted according to a key, or null when either <paramref name="source"/> or <paramref name="keySelector"/> is null.</returns>

        /// <remarks>The result of this method will only be reactive and observable if source is in fact an <see cref="IObservableOrderedEnumerable{TSource}"/>.</remarks>

        public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IOrderedEnumerable<TSource> source, Func<TSource, IValueProvider<TKey>> keySelector, IComparer<TKey> comparer)

        {

            if (source == null || keySelector == null || comparer == null)

                return null;



            var asObservable = source as IObservableOrderedEnumerable<TSource>;



            return asObservable != null ? asObservable.CreateOrderedEnumerable(keySelector, comparer, true) : source.CreateOrderedEnumerable(FuncExtender<TSource>.Extend(keySelector, (i, ks) => ks(i).Value), comparer, true);

        }

    }

}