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

namespace S22.Sasl.Mechanisms.Srp {
	/// <summary>
	/// Adds extension methods to the BinaryReader class to simplify the
	/// deserialization of SRP messages.
	/// </summary>
	internal static class BinaryReaderExtensions {
		/// <summary>
		/// Reads an unsigned integer value from the underlying stream,
		/// optionally using big endian byte ordering.
		/// </summary>
		/// <param name="reader">Extension method for BinaryReader.</param>
		/// <param name="bigEndian">Set to true to interpret the integer value
		/// as big endian value.</param>
		/// <returns>The 32-byte unsigned integer value read from the underlying
		/// stream.</returns>
		public static uint ReadUInt32(this BinaryReader reader, bool bigEndian) {
			if (!bigEndian)
				return reader.ReadUInt32();
			int ret = 0;
			ret |= (reader.ReadByte() << 24);
			ret |= (reader.ReadByte() << 16);
			ret |= (reader.ReadByte() <<  8);
			ret |= (reader.ReadByte() <<  0);
			return (uint) ret;
		}

		/// <summary>
		/// Reads an unsigned short value from the underlying stream, optionally
		/// using big endian byte ordering.
		/// </summary>
		/// <param name="reader">Extension method for BinaryReader.</param>
		/// <param name="bigEndian">Set to true to interpret the short value
		/// as big endian value.</param>
		/// <returns>The 16-byte unsigned short value read from the underlying
		/// stream.</returns>
		public static ushort ReadUInt16(this BinaryReader reader, bool bigEndian) {
			if (!bigEndian)
				return reader.ReadUInt16();
			int ret = 0;
			ret |= (reader.ReadByte() << 8);
			ret |= (reader.ReadByte() << 0);
			return (ushort) ret;
		}

		/// <summary>
		/// Reads a "multi-precision integer" from this instance.
		/// </summary>
		/// <param name="reader">Extension method for the BinaryReader class.</param>
		/// <returns>An instance of the Mpi class decoded from the bytes read
		/// from the underlying stream.</returns>
		public static Mpi ReadMpi(this BinaryReader reader) {
			ushort length = reader.ReadUInt16(true);
			byte[] data = reader.ReadBytes(length);

			return new Mpi(data);
		}

		/// <summary>
		/// Reads an "octet-sequence" from this instance.
		/// </summary>
		/// <param name="reader">Extension method for the BinaryReader class.</param>
		/// <returns>An instance of the OctetSequence class decoded from the bytes
		/// read from the underlying stream.</returns>
		public static OctetSequence ReadOs(this BinaryReader reader) {
			byte length = reader.ReadByte();
			byte[] data = reader.ReadBytes(length);

			return new OctetSequence(data);
		}

		/// <summary>
		/// Reads an UTF-8 string from this instance.
		/// </summary>
		/// <param name="reader">Extension method for the BinaryReader class.</param>
		/// <returns>An instance of the Utf8String class decoded from the bytes
		/// read from the underlying stream.</returns>
		public static Utf8String ReadUtf8String(this BinaryReader reader) {
			ushort length = reader.ReadUInt16(true);
			byte[] data = reader.ReadBytes(length);

			return new Utf8String(Encoding.UTF8.GetString(data));
		}
	}
}