Examples/GerstITS.Examples.Logic/Shared/Search/Sorting/SortingProvider.cs

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using GerstITS.Common;
using GerstITS.Search;

namespace GerstITS.Examples.Logic.Shared.Search.Sorting
{
    internal class SortingProvider : ISortingProvider
    {
        #region ISortingProvider

        public bool CanSort<TItem>(IQueryable<TItem> query)
        {
            return typeof(TItem).IsAssignableTo(typeof(ISortable));
        }

        public IQueryable<TItem> Sort<TItem>(IQueryable<TItem> query, ISorting sorting)
        {
            var propertyInfo = typeof(TItem).GetProperties()
                                            .SingleOrDefault(i => string.Equals(i.Name, sorting.SortBy, StringComparison.InvariantCultureIgnoreCase));

            if (!CanSort(query) || propertyInfo.IsNull())
                return query;

            var sortExpression = CreateSortExpression<TItem>(propertyInfo);

            return (sorting.SortDirection == SortingDirections.Ascending
                    ? query.OrderBy(sortExpression)
                    : query.OrderByDescending(sortExpression))
                .AsQueryable();
        }

        #endregion

        #region Methods

        private static Expression<Func<TItem, object>> CreateSortExpression<TItem>(MemberInfo propertyInfo)
        {
            var parameterExpression = Expression.Parameter(typeof(TItem), "x");
            var propertyExpression = Expression.Property(parameterExpression, propertyInfo.Name);
            var convertExpression = Expression.Convert(propertyExpression, typeof(object));

            return Expression.Lambda<Func<TItem, object>>(convertExpression, parameterExpression);
        } 
        
        #endregion
    }
}