case-insensitive string.Replace C#

ReplaceString.cs

//// http://stackoverflow.com/a/244933/84852

public static string ReplaceString(string str, string oldValue, string newValue, StringComparison comparison)
		{
			if (string.IsNullOrEmpty(oldValue))
			{
				throw new ArgumentNullException("oldValue");
			}

			StringBuilder sb = new StringBuilder();

			int previousIndex = 0;
			int index = str.IndexOf(oldValue, comparison);

			while (index != -1)
			{
				sb.Append(str.Substring(previousIndex, index - previousIndex));
				sb.Append(newValue);
				index += oldValue.Length;

				previousIndex = index;
				index = str.IndexOf(oldValue, index, comparison);
			}

			sb.Append(str.Substring(previousIndex));

			return sb.ToString();
		}

StringExtension.cs

	public static class StringExtension
	{
		public static string Replace(this string str, string oldValue, string newValue, StringComparison comparison)
		{
			if (string.IsNullOrEmpty(oldValue))
			{
				throw new ArgumentNullException("oldValue");
			}

			StringBuilder sb = new StringBuilder();

			int previousIndex = 0;
			int index = str.IndexOf(oldValue, comparison);

			while (index != -1)
			{
				sb.Append(str.Substring(previousIndex, index - previousIndex));
				sb.Append(newValue);
				index += oldValue.Length;

				previousIndex = index;
				index = str.IndexOf(oldValue, index, comparison);
			}

			sb.Append(str.Substring(previousIndex));

			return sb.ToString();
		}
	}