using System.Collections.Generic;

namespace BitStrap
{
	public static class StringHelper
	{
		private class IndexComparer : IEqualityComparer<Index>
		{
			public bool Equals(Index x, Index y)
			{
				return x.Equals(y);
			}

			public int GetHashCode(Index x)
			{
				return x.GetHashCode();
			}
		}

		private struct Index
		{
			public readonly int number;

			public readonly string format;

			private readonly int hashCode;

			public Index(string format, int number)
			{
				this.number = number;
				this.format = format;
				hashCode = number * format.GetHashCode();
			}

			public bool Equals(Index other)
			{
				return number == other.number && format == other.format;
			}

			public override int GetHashCode()
			{
				return hashCode;
			}

			public string GetString()
			{
				return string.Format(format, number);
			}
		}

		private static Dictionary<Index, string> stringTable = new Dictionary<Index, string>(new IndexComparer());

		public static string Format(string format, int number)
		{
			Index key = new Index(format, number);
			if (!stringTable.ContainsKey(key))
			{
				stringTable[key] = key.GetString();
			}
			return stringTable[key];
		}

		public static string ToStringSmart(this int n, string format = "{0}")
		{
			return Format(format, n);
		}
	}
}