PagedListExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using MongoDB.Driver;

namespace PagedList
{
	/// <summary>
	/// Container for extension methods designed to simplify the creation of instances of <see cref="PagedList{T}"/>.
	/// </summary>
	public static class MongoPagedListExtensions
	{
		/// <summary>
		/// Creates a subset of this collection of objects that can be individually accessed by index and containing metadata about the collection of objects the subset was created from.
		/// </summary>
		/// <typeparam name="T">The type of object the collection should contain.</typeparam>
		/// <param name="superset">The collection of objects to be divided into subsets. If the collection implements <see cref="IQueryable{T}"/>, it will be treated as such.</param>
		/// <param name="pageNumber">The one-based index of the subset of objects to be contained by this instance.</param>
		/// <param name="pageSize">The maximum size of any individual subset.</param>
		/// <returns>A subset of this collection of objects that can be individually accessed by index and containing metadata about the collection of objects the subset was created from.</returns>
		/// <seealso cref="PagedList{T}"/>
        public static IPagedList<T> ToPagedList<T>(this MongoCursor<T> superset, int pageNumber, int pageSize)
		{
			return new PagedList<T>(superset, pageNumber, pageSize);
		}


		/// <summary>
		/// Splits a collection of objects into n pages with an (for example, if I have a list of 45 shoes and say 'shoes.Split(5)' I will now have 4 pages of 10 shoes and 1 page of 5 shoes.
		/// </summary>
		/// <typeparam name="T">The type of object the collection should contain.</typeparam>
		/// <param name="superset">The collection of objects to be divided into subsets.</param>
		/// <param name="numberOfPages">The number of pages this collection should be split into.</param>
		/// <returns>A subset of this collection of objects, split into n pages.</returns>
        public static IEnumerable<IEnumerable<T>> Split<T>(this MongoCursor<T> superset, int numberOfPages)
		{
			return superset
				.Select((item, index) => new { index, item })
				.GroupBy(x => x.index % numberOfPages)
				.Select(x => x.Select(y => y.item));
		}

		/// <summary>
		/// Splits a collection of objects into an unknown number of pages with n items per page (for example, if I have a list of 45 shoes and say 'shoes.Partition(10)' I will now have 4 pages of 10 shoes and 1 page of 5 shoes.
		/// </summary>
		/// <typeparam name="T">The type of object the collection should contain.</typeparam>
		/// <param name="superset">The collection of objects to be divided into subsets.</param>
		/// <param name="pageSize">The maximum number of items each page may contain.</param>
		/// <returns>A subset of this collection of objects, split into pages of maximum size n.</returns>
        public static IEnumerable<IEnumerable<T>> Partition<T>(this MongoCursor<T> superset, int pageSize)
		{
			if (superset.Count() < pageSize)
				yield return superset;
			else
			{
				var numberOfPages = Math.Ceiling(superset.Count() / (double)pageSize);
				for (var i = 0; i < numberOfPages; i++)
					yield return superset.Skip(pageSize * i).Take(pageSize);				
			}
		}
	}
}