using System;
using System.IO;
using System.Text;

namespace CUP_POD_Mail_Reader.Common
{
	/// <summary>
	/// Utility to help reading bytes and strings of a <see cref="Stream"/>
	/// </summary>
	internal static class StreamUtility
	{
		/// <summary>
		/// Read a line from the stream.
		/// A line is interpreted as all the bytes read until a CRLF or LF is encountered.<br/>
		/// CRLF pair or LF is not included in the string.
		/// </summary>
		/// <param name="stream">The stream from which the line is to be read</param>
		/// <returns>A line read from the stream returned as a byte array or <see langword="null"/> if no bytes were readable from the stream</returns>
		/// <exception cref="ArgumentNullException">If <paramref name="stream"/> is <see langword="null"/></exception>
		public static byte[] ReadLineAsBytes(Stream stream)
		{
			if(stream == null)
				throw new ArgumentNullException("stream");

			using (MemoryStream memoryStream = new MemoryStream())
			{
				while (true)
				{
					int justRead = stream.ReadByte();
					if (justRead == -1 && memoryStream.Length > 0)
						break;

					// Check if we started at the end of the stream we read from
					// and we have not read anything from it yet
					if (justRead == -1 && memoryStream.Length == 0)
						return null;

					char readChar = (char)justRead;

					// Do not write \r or \n
					if (readChar != '\r' && readChar != '\n')
						memoryStream.WriteByte((byte)justRead);

					// Last point in CRLF pair
					if (readChar == '\n')
						break;
				}

				return memoryStream.ToArray();
			}
		}

		/// <summary>
		/// Read a line from the stream. <see cref="ReadLineAsBytes"/> for more documentation.
		/// </summary>
		/// <param name="stream">The stream to read from</param>
		/// <returns>A line read from the stream or <see langword="null"/> if nothing could be read from the stream</returns>
		/// <exception cref="ArgumentNullException">If <paramref name="stream"/> is <see langword="null"/></exception>
		public static string ReadLineAsAscii(Stream stream)
		{
			byte[] readFromStream = ReadLineAsBytes(stream);
			return readFromStream != null ? Encoding.ASCII.GetString(readFromStream) : null;
		}
	}
}