Transformalizing NorthWind

#region License
// /*
// See license included in this library folder.
// */
#endregion

using System;
using System.IO;
using System.Runtime.CompilerServices;

namespace Transformalize.Libs.ExcelDataReader.Core.BinaryFormat
{
	/// <summary>
	/// Represents a BIFF stream
	/// </summary>
	internal class XlsBiffStream : XlsStream
	{
		private readonly byte[] bytes;
		private readonly int m_size;
		private int m_offset;

		public XlsBiffStream(XlsHeader hdr, uint streamStart)
			: base(hdr, streamStart)
		{
			bytes = base.ReadStream();
			m_size = bytes.Length;
			m_offset = 0;
		}

		/// <summary>
		/// Returns size of BIFF stream in bytes
		/// </summary>
		public int Size
		{
			get { return m_size; }
		}

		/// <summary>
		/// Returns current position in BIFF stream
		/// </summary>
		public int Position
		{
			get { return m_offset; }
		}

		//TODO:Remove ReadStream
		/// <summary>
		/// Always returns null, use biff-specific methods
		/// </summary>
		/// <returns></returns>
		[Obsolete("Use BIFF-specific methods for this stream")]
		public new byte[] ReadStream()
		{
			return bytes;
		}

		/// <summary>
		/// Sets stream pointer to the specified offset
		/// </summary>
		/// <param name="offset">Offset value</param>
		/// <param name="origin">Offset origin</param>
		[MethodImpl(MethodImplOptions.Synchronized)]
		public void Seek(int offset, SeekOrigin origin)
		{
			switch (origin)
			{
				case SeekOrigin.Begin:
					m_offset = offset;
					break;
				case SeekOrigin.Current:
					m_offset += offset;
					break;
				case SeekOrigin.End:
					m_offset = m_size - offset;
					break;
			}
			if (m_offset < 0)
				throw new ArgumentOutOfRangeException(string.Format("{0} On offset={1}", Errors.ErrorBIFFIlegalBefore, offset));
			if (m_offset > m_size)
				throw new ArgumentOutOfRangeException(string.Format("{0} On offset={1}", Errors.ErrorBIFFIlegalAfter, offset));
		}

		/// <summary>
		/// Reads record under cursor and advances cursor position to next record
		/// </summary>
		/// <returns></returns>
		[MethodImpl(MethodImplOptions.Synchronized)]
		public XlsBiffRecord Read()
		{
			var rec = XlsBiffRecord.GetRecord(bytes, (uint)m_offset);
			m_offset += rec.Size;
			if (m_offset > m_size)
				return null;
			return rec;
		}

		/// <summary>
		/// Reads record at specified offset, does not change cursor position
		/// </summary>
		/// <param name="offset"></param>
		/// <returns></returns>
		public XlsBiffRecord ReadAt(int offset)
		{
			var rec = XlsBiffRecord.GetRecord(bytes, (uint)offset);
			if (m_offset + rec.Size > m_size)
				return null;
			return rec;
		}
	}
}