using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace LarsonDavis.Sdk.SdkCommon
{
	/// <summary>
	/// File download class for 831C
	/// </summary>
	public class Ld831cFileDownloader : IDisposable
	{
		#region Member Variables
		public	uint	FileSize		{ get; private set; }
		public	uint	FileOffset	{ get; private set; }
		public	uint	Progress => FileOffset * 100 / FileSize;

		private	const uint	LD_BIN_HEADER_LENGTH    = 5 * sizeof(uint);
		private	const uint	MAX_BLOCK_SIZE          = 100 * 1024;
		private	const int	VALID_START_BLOCK_SIZE  = 196;
		private	const int	EMPTY_READ_TRIES        = 75;
		private	const uint	CRC_BLOCK_TAG           = 0xABBDCBC3;

		private	readonly Stream	_Stream;
		private	readonly Stream	_Destination;
		private	readonly string	_FileName;
		private	readonly byte[]	_IntBuffer;
		private	readonly byte[]	_Buffer;
		private	BinaryWriter		_BinaryWriter;
		private	DownloadCrcState	_State;

		private	bool	_Continue;
		private  bool  _FirstBlock;
		private	int	_EmptyReads;
		private	int	_ReadSoFar;
		private	int	_CrcBlockSize;

		private enum DownloadCrcState
		{
			None,		// No CRC validation
			Tag,		// Read CRC Tag
			Length,	// Read CRC Block size
			Block,	// Read Block
			Crc,		// Read CRC and validate Block
		}
		#endregion

		/// <summary>
		/// Read from download stream to file
		/// </summary>
		/// <param name="dataStream">Response stream from '831cAddress/download?name={0}&path={1}&offset={2}&addCrc=1'</param>
		/// <param name="destination">Where to store downloaded file</param>
		/// <param name="fileName">Filename of downloaded file</param>
		/// <param name="size">Total download size from file list</param>
		public Ld831cFileDownloader (Stream dataStream, FileStream destination, string fileName, uint size, uint offset = 0)
		{
			_Stream			= dataStream;
			_Destination	= destination;
			_FileName		= fileName;
			FileSize			= size;
			FileOffset		= offset;
			_FirstBlock		= true;
			_Continue		= FileOffset < FileSize;
			_EmptyReads		= 0;
			_ReadSoFar		= 0;
			_CrcBlockSize	= 0;
			_Buffer			= new byte[MAX_BLOCK_SIZE];
			_IntBuffer		= new byte[sizeof(uint)];
			_State			= DownloadCrcState.Tag;

			// Open file if resuming partial download
			if (_Continue && (FileOffset > 0))
			{
				_BinaryWriter = new BinaryWriter(_Destination);
				_BinaryWriter.Seek((int)(FileOffset + LD_BIN_HEADER_LENGTH), SeekOrigin.Begin);
			}
		}

		/// <summary>
		/// Determine download offset from ldbin file
		/// </summary>
		/// <param name="ldBinFile">Download file info</param>
		/// <returns>Offset to use when starting or
		/// resuming a download request</returns>
		public static long CalcOffsetFromFileStream (FileStream ldBinFile)
		{
			long offset = 0;

			if (ldBinFile.CanSeek && ldBinFile.CanWrite && (ldBinFile.Length > LD_BIN_HEADER_LENGTH))
			{
				offset = ldBinFile.Length - LD_BIN_HEADER_LENGTH;
			}

			return offset;
		}

		/// <summary>
		/// Read and validate bytes received from download stream
		/// </summary>
		/// <returns>true while able to continue processing stream, false otherwise</returns>
		public bool ProcessStream ()
		{
			// Calculate how many bytes to read
			(int readLength, bool useIntBuffer) = CalcReadLength(_State);

			// Read from stream into buffer
			int bytesRead = _Stream.Read(useIntBuffer ? _IntBuffer : _Buffer, _ReadSoFar, readLength);

			if (0 == bytesRead)
			{
				System.Threading.Thread.Sleep(200);

				// Restart after many empty reads
				if (++_EmptyReads > EMPTY_READ_TRIES)
				{
					_Continue = false;
				}
			}
			else
			{
				_EmptyReads = 0;

				switch (_State)
				{
					case DownloadCrcState.None:
						_ReadSoFar += bytesRead;

						if ((FileOffset > VALID_START_BLOCK_SIZE)
							|| (_ReadSoFar > VALID_START_BLOCK_SIZE))
						{
							ValidateAndWriteBlock(_ReadSoFar);
						}
						break;

					case DownloadCrcState.Tag:
						_ReadSoFar = 0;

						if (CRC_BLOCK_TAG == BitConverter.ToUInt32(_IntBuffer, 0))
						{
							// Found CRC Tag!
							_State = DownloadCrcState.Length;
							_FirstBlock = false;
						}
						else if (_FirstBlock)
						{
							// Expected CRC tag not found, continuing without CRC.
							_State = DownloadCrcState.None;
							_FirstBlock = false;

							// Copy received bytes to normal buffer and update read length
							_IntBuffer.CopyTo(_Buffer, 0);
							_ReadSoFar = bytesRead;
						}
						else
						{
							_Continue = false;
							// Expected CRC tag not found in new block.
						}
						break;

					case DownloadCrcState.Length:
						// Get CRC block Length
						_CrcBlockSize = BitConverter.ToInt32(_IntBuffer, 0);

						if ((_CrcBlockSize > 0) && (_CrcBlockSize <= MAX_BLOCK_SIZE))
						{
							_State = DownloadCrcState.Block;
						}
						else
						{
							// Bad length! Restart download.
							_Continue = false;
						}
						break;

					case DownloadCrcState.Block:
						_ReadSoFar += bytesRead;

						if (_ReadSoFar == _CrcBlockSize)
						{
							_ReadSoFar = 0;
							_State = DownloadCrcState.Crc;
						}
						break;

					case DownloadCrcState.Crc:
						uint sentCrc = BitConverter.ToUInt32(_IntBuffer, 0);

						// Check block and write out to file
						ValidateAndWriteBlock(_CrcBlockSize, sentCrc);

						_State = DownloadCrcState.Tag;
						break;
				}
			}

			return _Continue;
		}

		/// <summary>
		/// Validate download block before writing to file
		/// </summary>
		/// <param name="blockLength">Length of block to inspect</param>
		/// <param name="sentCrc">CRC Received</param>
		private void ValidateAndWriteBlock (int blockLength, uint sentCrc = 0)
		{
			// Make sure file received is the requested file
			if (FileOffset <= VALID_START_BLOCK_SIZE)
			{
				if (ValidateDataFileHeaderName())
				{
					// Create new file
					_Destination.Seek(0, SeekOrigin.Begin);
					_BinaryWriter = new BinaryWriter(_Destination);
					WriteLDBinHeader(_BinaryWriter, FileSize);
				}
				else
				{
					_Continue = false;
				}
			}

			if (_Continue)
			{
				if ((_State == DownloadCrcState.None)
					|| (sentCrc == LDTranslatorStd.Utilities.Crc.Crc32(0, _Buffer.Take(blockLength))))
				{
					_BinaryWriter.Write(_Buffer, 0, blockLength);
					_BinaryWriter.Flush();

					FileOffset += (uint)blockLength;
					_ReadSoFar = 0;

					if (FileOffset >= FileSize)
					{
						// Download complete
						_Continue = false;
					}
				}
				else
				{
					// Validation failure
					_Continue = false;
				}
			}
		}

		/// <summary>
		/// Verify first block's Data File Header Filename matches requested file
		/// </summary>
		/// <returns>Filename matches</returns>
		private bool ValidateDataFileHeaderName ()
		{
			const int DFH_NAME_OFFSET = 180;
			const int DFH_NAME_LENGTH = 16;

			// Extract file name with mode extension out of Data File Header
			string dfhName = Encoding.ASCII.GetString(_Buffer, DFH_NAME_OFFSET, DFH_NAME_LENGTH);

			// Remove mode extension and any null characters
			int extensionIndex = dfhName.LastIndexOf('.');
			if (extensionIndex > 0)
			{
				dfhName = dfhName.Substring(0, extensionIndex);
			}

			// Verify name from header matches filename
			bool validHeaderName = _FileName.Contains(dfhName);

			return validHeaderName;
		}

		/// <summary>
		/// Determine how much to read and which buffer to use
		/// </summary>
		/// <param name="curState">CRC process state</param>
		/// <returns>Length to read, use single integer buffer</returns>
		private (int, bool) CalcReadLength (DownloadCrcState curState)
		{
			int readLength;
			bool useIntBuffer = false;

			switch (curState)
			{
				default:
				case DownloadCrcState.None:
					{
						int blockSize = (int)MAX_BLOCK_SIZE - _ReadSoFar;

						readLength = Math.Min(blockSize, (int)(FileSize - FileOffset));
					}
					break;

				case DownloadCrcState.Tag:
				case DownloadCrcState.Length:
				case DownloadCrcState.Crc:
					readLength = sizeof(uint);
					useIntBuffer = true;
					break;

				case DownloadCrcState.Block:
					{
						int blockSize = _CrcBlockSize - _ReadSoFar;

						readLength = Math.Min(blockSize, (int)(FileSize - FileOffset));
					}
					break;
			}

			return (readLength, useIntBuffer);
		}

		/// <summary>
		/// Write G4's LD Bin file header
		/// </summary>
		/// <param name="writer"></param>
		/// <param name="fileSize"></param>
		private static void WriteLDBinHeader (BinaryWriter writer, uint fileSize)
		{
			const uint LdBinTag1    = 0x00004C44;
			const uint LdBinTag2    = 0x0042494E;
			const uint LdBinVer     = 1;
			const uint LdBinCount   = 1;

			writer.Write(LdBinTag1);
			writer.Write(LdBinTag2);
			writer.Write(LdBinVer);
			writer.Write(LdBinCount);
			writer.Write(fileSize);
		}

		#region IDisposable Support
		public void Dispose ()
		{
			_Stream?.Dispose();
			_BinaryWriter?.Dispose();
		}
		#endregion
	}

}

#region CRC32 Method definition if no access to LD SDK.
namespace LarsonDavis.Sdk.LDTranslatorStd.Utilities
{
	public static class Crc
	{
		public static uint Crc32 (uint crc, IEnumerable<byte> buffer)
		{
			uint data = 0;

			foreach (byte b in buffer)
			{
				data = b ^ (crc & 0x000000FF);
				crc = s_crc32Table[data] ^ (crc >> 8);
			}

			return crc;
		}

		private readonly static uint[] s_crc32Table =
		{
			0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
			0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
			0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
			0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
			0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
			0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
			0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
			0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
			0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
			0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
			0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
			0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
			0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
			0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
			0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
			0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
			0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
			0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
			0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
			0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
			0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
			0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
			0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
			0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
			0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
			0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
			0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
			0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
			0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
			0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
			0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
			0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
		};
	}
}
#endregion
