#region (c)2009 Lokad - New BSD license

// Copyright (c) Lokad 2009 
// Company: http://www.lokad.com
// This code is released under the terms of the new BSD licence

#endregion

using System;
using System.Collections.Generic;
using System.Linq;

namespace Shared.Util
{
	/// <summary>
	/// Helper class with shortcut methods for managing enumerations.
	/// Useful for inlining object generation in tests
	/// </summary>
	public static class Range
	{
		/// <summary> Returns empty enumerator </summary>
		/// <typeparam name="T">type of the item to enumerate</typeparam>
		/// <returns>singleton instance of the empty enumerator</returns>
		public static IEnumerable<T> Empty<T>()
		{
			return Enumerable.Empty<T>();
		}

		/// <summary>
		/// returns enumeration from 0 with <paramref name="count"/> numbers
		/// </summary>
		/// <param name="count">Number of items to create</param>
		/// <returns>enumerable</returns>
		public static IEnumerable<int> Create(int count)
		{
			return Enumerable.Range(0, count);
		}


		/// <summary>
		/// Creates sequence of the integral numbers within the specified range
		/// </summary>
		/// <param name="start">The value of the first integer in sequence.</param>
		/// <param name="count">The number of values in the sequence.</param>
		/// <returns>sequence of the integral numbers within the specified range</returns>
		public static IEnumerable<int> Create(int start, int count)
		{
			return Enumerable.Range(start, count);
		}

		/// <summary>
		/// Creates sequence that consists of a repeated value.
		/// </summary>
		/// <typeparam name="TResult">The type of the value to repeat.</typeparam>
		/// <param name="item">The value to repeat.</param>
		/// <param name="count">The number of times to repeat.</param>
		/// <returns>sequence that consists of a repeated value</returns>
		public static IEnumerable<TResult> Repeat<TResult>(TResult item, int count)
		{
			return Enumerable.Repeat(item, count);
		}


		/// <summary>
		/// Creates the generator to iterate from 1 to <see cref="int.MaxValue"/>.
		/// </summary>
		/// <typeparam name="T">type of the item to generate</typeparam>
		/// <param name="generator">The generator.</param>
		/// <returns>new enumerator</returns>
		public static IEnumerable<T> Create<T>(Func<int, T> generator)
		{
			for (int i = 0; i < int.MaxValue; i++)
			{
				yield return generator(i);
			}
			throw new InvalidOperationException("Generator has reached the end");
		}

		/// <summary>
		/// Creates the enumerable using the provided generator.
		/// </summary>
		/// <typeparam name="T"></typeparam>
		/// <param name="count">The count.</param>
		/// <param name="generator">The generator.</param>
		/// <returns>enumerable instance</returns>
		public static IEnumerable<T> Create<T>(int count, Func<int, T> generator)
		{
			for (int i = 0; i < count; i++)
			{
				yield return generator(i);
			}
		}

		/// <summary>
		/// Creates the enumerable using the provided generator.
		/// </summary>
		/// <typeparam name="T"></typeparam>
		/// <param name="count">The count.</param>
		/// <param name="generator">The generator.</param>
		/// <returns>enumerable instance</returns>
		public static IEnumerable<T> Create<T>(int count, Func<T> generator)
		{
			for (int i = 0; i < count; i++)
			{
				yield return generator();
			}
		}

		/// <summary>
		/// Creates the array populated with the provided generator
		/// </summary>
		/// <typeparam name="TValue">The type of the value.</typeparam>
		/// <param name="count">The count.</param>
		/// <param name="generator">The generator.</param>
		/// <returns>array</returns>
		public static TValue[] Array<TValue>(int count, Func<int, TValue> generator)
		{
			if (generator == null) throw new ArgumentNullException("generator");

			var array = new TValue[count];
			for (int i = 0; i < array.Length; i++)
			{
				array[i] = generator(i);
			}

			return array;
		}

		/// <summary>
		/// Creates the array of integers
		/// </summary>
		/// <param name="count">The count.</param>
		/// <returns></returns>
		public static int[] Array(int count)
		{
			var array = new int[count];
			for (int i = 0; i < array.Length; i++)
			{
				array[i] = i;
			}
			return array;
		}
	}
}