using SabreTools.Library.Data;
using SabreTools.Library.Tools;

#if MONO
using System.IO;
#else
using BinaryReader = System.IO.BinaryReader;
using SeekOrigin = System.IO.SeekOrigin;
using Stream = System.IO.Stream;
#endif

namespace SabreTools.Library.FileTypes
{
	/// <summary>
	/// This is code adapted from chd.h and chd.cpp in MAME
	/// Additional archival code from https://github.com/rtissera/libchdr/blob/master/src/chd.h
	/// </summary>
	/// <remarks>
	/// ----------------------------------------------
	/// Common CHD Header:
	/// 0x00-0x07 - CHD signature
	/// 0x08-0x0B - Header size
	/// 0x0C-0x0F - CHD version
	/// ----------------------------------------------
	/// CHD v1 header layout:
	/// 0x10-0x13 - Flags (1: Has parent MD5, 2: Disallow writes)
	/// 0x14-0x17 - Compression
	/// 0x18-0x1B - 512-byte sectors per hunk
	/// 0x1C-0x1F - Hunk count
	/// 0x20-0x23 - Hard disk cylinder count
	/// 0x24-0x27 - Hard disk head count
	/// 0x28-0x2B - Hard disk sector count
	/// 0x2C-0x3B - MD5
	/// 0x3C-0x4B - Parent MD5
	/// ----------------------------------------------
	/// CHD v2 header layout:
	/// 0x10-0x13 - Flags (1: Has parent MD5, 2: Disallow writes)
	/// 0x14-0x17 - Compression
	/// 0x18-0x1B - seclen-byte sectors per hunk
	/// 0x1C-0x1F - Hunk count
	/// 0x20-0x23 - Hard disk cylinder count
	/// 0x24-0x27 - Hard disk head count
	/// 0x28-0x2B - Hard disk sector count
	/// 0x2C-0x3B - MD5
	/// 0x3C-0x4B - Parent MD5
	/// 0x4C-0x4F - Number of bytes per sector (seclen)
	/// ----------------------------------------------
	/// CHD v3 header layout:
	/// 0x10-0x13 - Flags (1: Has parent SHA-1, 2: Disallow writes)
	/// 0x14-0x17 - Compression
	/// 0x18-0x1B - Hunk count
	/// 0x1C-0x23 - Logical Bytes
	/// 0x24-0x2C - Metadata Offset
	/// ...
	/// 0x4C-0x4F - Hunk Bytes
	/// 0x50-0x63 - SHA-1
	/// 0x64-0x77 - Parent SHA-1
	/// 0x78-0x87 - Map
	/// ----------------------------------------------
	/// CHD v4 header layout:
	/// 0x10-0x13 - Flags (1: Has parent SHA-1, 2: Disallow writes)
	/// 0x14-0x17 - Compression
	/// 0x18-0x1B - Hunk count
	/// 0x1C-0x23 - Logical Bytes
	/// 0x24-0x2C - Metadata Offset
	/// ...
	/// 0x2C-0x2F - Hunk Bytes
	/// 0x30-0x43 - SHA-1
	/// 0x44-0x57 - Parent SHA-1
	/// 0x58-0x6b - Raw SHA-1
	/// 0x6c-0x7b - Map
	/// ----------------------------------------------
	/// CHD v5 header layout:
	/// 0x10-0x13 - Compression format 1
	/// 0x14-0x17 - Compression format 2
	/// 0x18-0x1B - Compression format 3
	/// 0x1C-0x1F - Compression format 4
	/// 0x20-0x27 - Logical Bytes
	/// 0x28-0x2F - Map Offset
	/// 0x30-0x37 - Metadata Offset
	/// 0x38-0x3B - Hunk Bytes
	/// 0x3C-0x3F - Unit Bytes
	/// 0x40-0x53 - Raw SHA-1
	/// 0x54-0x67 - SHA-1
	/// 0x68-0x7b - Parent SHA-1
	/// ----------------------------------------------
	/// </remarks>
	public class CHDFile : BaseFile
	{
		#region Private instance variables

		// Core parameters from the header
		private byte[] m_signature;      // signature
		private uint m_headersize;       // size of the header
		private uint m_version;          // version of the header
		private ulong m_logicalbytes;    // logical size of the raw CHD data in bytes
		private ulong m_mapoffset;       // offset of map
		private ulong m_metaoffset;      // offset to first metadata bit
		private uint m_sectorsperhunk;   // number of sectors per hunk
		private uint m_hunkbytes;        // size of each raw hunk in bytes
		private ulong m_hunkcount;       // number of hunks represented
		private uint m_unitbytes;        // size of each unit in bytes
		private ulong m_unitcount;       // number of units represented
		private CHDCodecType[] m_compression = new CHDCodecType[4];   // array of compression types used

		// map information
		private uint m_mapentrybytes;    // length of each entry in a map

		// additional required vars
		private uint? _headerVersion;
		private BinaryReader m_br;       // Binary reader representing the CHD stream

		#endregion

		#region Pubically facing variables

		public uint? Version
		{
			get
			{
				if (_headerVersion == null)
				{
					_headerVersion = ValidateHeaderVersion();
				}

				return _headerVersion;
			}
		}

		#endregion

		#region Constructors

		/// <summary>
		/// Create a new, blank CHDFile
		/// </summary>
		public CHDFile()
		{
			this._fileType = FileType.CHD;
		}

		/// <summary>
		/// Create a new CHDFile from an input file
		/// </summary>
		/// <param name="filename"></param>
		public CHDFile(string filename)
			: this(Utilities.TryOpenRead(filename))
		{
		}

		/// <summary>
		/// Create a new CHDFile from an input stream
		/// </summary>
		/// <param name="chdstream">Stream representing the CHD file</param>
		public CHDFile(Stream chdstream)
		{
			_fileType = FileType.CHD;
			m_br = new BinaryReader(chdstream);

			_headerVersion = ValidateHeaderVersion();

			if (_headerVersion != null)
			{
				byte[] hash = GetHashFromHeader();

				if (hash != null)
				{
					if (hash.Length == Constants.MD5Length)
					{
						_md5 = hash;
					}
					else if (hash.Length == Constants.SHA1Length)
					{
						_sha1 = hash;
					}
				}
			}
		}

		#endregion

		#region Header Parsing

		/// <summary>
		/// Validate the initial signature, version, and header size
		/// </summary>
		/// <returns>Unsigned int containing the version number, null if invalid</returns>
		private uint? ValidateHeaderVersion()
		{
			try
			{
				// Seek to the beginning to make sure we're reading the correct bytes
				m_br.BaseStream.Seek(0, SeekOrigin.Begin);

				// Read and verify the CHD signature
				m_signature = m_br.ReadBytes(8);

				// If no signature could be read, return null
				if (m_signature == null || m_signature.Length == 0)
				{
					return null;
				}

				if (!m_signature.StartsWith(Constants.CHDSignature, exact: true))
				{
					// throw CHDERR_INVALID_FILE;
					return null;
				}

				// Get the header size and version
				m_headersize = m_br.ReadUInt32Reverse();
				m_version = m_br.ReadUInt32Reverse();

				// If we have an invalid combination of size and version
				if ((m_version == 1 && m_headersize != Constants.CHD_V1_HEADER_SIZE)
					|| (m_version == 2 && m_headersize != Constants.CHD_V2_HEADER_SIZE)
					|| (m_version == 3 && m_headersize != Constants.CHD_V3_HEADER_SIZE)
					|| (m_version == 4 && m_headersize != Constants.CHD_V4_HEADER_SIZE)
					|| (m_version == 5 && m_headersize != Constants.CHD_V5_HEADER_SIZE)
					|| (m_version < 1 || m_version > 5))
				{
					// throw CHDERR_UNSUPPORTED_VERSION;
					return null;
				}

				return m_version;
			}
			catch
			{
				return null;
			}
		}

		/// <summary>
		/// Get the internal MD5 (v1, v2) or SHA-1 (v3, v4, v5) from the CHD
		/// </summary>
		/// <returns>MD5 as a byte array, null on error</returns>
		private byte[] GetHashFromHeader()
		{
			// Validate the header by default just in case
			uint? version = ValidateHeaderVersion();

			// Now get the hash, if possible
			byte[] hash;

			// Now parse the rest of the header according to the version
			try
			{
				switch (version)
				{
					case 1:
						hash = ParseCHDv1Header();
						break;
					case 2:
						hash = ParseCHDv2Header();
						break;
					case 3:
						hash = ParseCHDv3Header();
						break;
					case 4:
						hash = ParseCHDv4Header();
						break;
					case 5:
						hash = ParseCHDv5Header();
						break;
					case null:
					default:
						// throw CHDERR_INVALID_FILE;
						return null;
				}
			}
			catch
			{
				// throw CHDERR_INVALID_FILE;
				return null;
			}

			return hash;
		}

		/// <summary>
		/// Parse a CHD v1 header
		/// </summary>
		/// <returns>The extracted MD5 on success, null otherwise</returns>
		private byte[] ParseCHDv1Header()
		{
			// Seek to after the signature to make sure we're reading the correct bytes
			m_br.BaseStream.Seek(16, SeekOrigin.Begin);

			// Set the blank MD5 hash
			byte[] md5 = new byte[16];

			// Set offsets and defaults
			m_mapoffset = 0;
			m_mapentrybytes = 0;

			// Read the CHD flags
			uint flags = m_br.ReadUInt32Reverse();

			// Determine compression
			switch (m_br.ReadUInt32())
			{
				case 0: m_compression[0] = CHDCodecType.CHD_CODEC_NONE; break;
				case 1: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 2: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 3: m_compression[0] = CHDCodecType.CHD_CODEC_AVHUFF; break;
				default: /* throw CHDERR_UNKNOWN_COMPRESSION; */ return null;
			}

			m_compression[1] = m_compression[2] = m_compression[3] = CHDCodecType.CHD_CODEC_NONE;

			m_sectorsperhunk = m_br.ReadUInt32Reverse();
			m_hunkcount = m_br.ReadUInt32Reverse();
			m_br.ReadUInt32Reverse(); // Cylinder count
			m_br.ReadUInt32Reverse(); // Head count
			m_br.ReadUInt32Reverse(); // Sector count

			md5 = m_br.ReadBytes(16);
			m_br.ReadBytes(16); // Parent MD5

			return md5;
		}

		/// <summary>
		/// Parse a CHD v2 header
		/// </summary>
		/// <returns>The extracted MD5 on success, null otherwise</returns>
		private byte[] ParseCHDv2Header()
		{
			// Seek to after the signature to make sure we're reading the correct bytes
			m_br.BaseStream.Seek(16, SeekOrigin.Begin);

			// Set the blank MD5 hash
			byte[] md5 = new byte[16];

			// Set offsets and defaults
			m_mapoffset = 0;
			m_mapentrybytes = 0;

			// Read the CHD flags
			uint flags = m_br.ReadUInt32Reverse();

			// Determine compression
			switch (m_br.ReadUInt32())
			{
				case 0: m_compression[0] = CHDCodecType.CHD_CODEC_NONE; break;
				case 1: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 2: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 3: m_compression[0] = CHDCodecType.CHD_CODEC_AVHUFF; break;
				default: /* throw CHDERR_UNKNOWN_COMPRESSION; */ return null;
			}

			m_compression[1] = m_compression[2] = m_compression[3] = CHDCodecType.CHD_CODEC_NONE;

			m_sectorsperhunk = m_br.ReadUInt32Reverse();
			m_hunkcount = m_br.ReadUInt32Reverse();
			m_br.ReadUInt32Reverse(); // Cylinder count
			m_br.ReadUInt32Reverse(); // Head count
			m_br.ReadUInt32Reverse(); // Sector count

			md5 = m_br.ReadBytes(16);
			m_br.ReadBytes(16); // Parent MD5
			m_br.ReadUInt32Reverse(); // Sector size

			return md5;
		}

		/// <summary>
		/// Parse a CHD v3 header
		/// </summary>
		/// <returns>The extracted SHA-1 on success, null otherwise</returns>
		private byte[] ParseCHDv3Header()
		{
			// Seek to after the signature to make sure we're reading the correct bytes
			m_br.BaseStream.Seek(16, SeekOrigin.Begin);

			// Set the blank SHA-1 hash
			byte[] sha1 = new byte[20];

			// Set offsets and defaults
			m_mapoffset = 120;
			m_mapentrybytes = 16;

			// Read the CHD flags
			uint flags = m_br.ReadUInt32Reverse();

			// Determine compression
			switch (m_br.ReadUInt32())
			{
				case 0: m_compression[0] = CHDCodecType.CHD_CODEC_NONE; break;
				case 1: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 2: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 3: m_compression[0] = CHDCodecType.CHD_CODEC_AVHUFF; break;
				default: /* throw CHDERR_UNKNOWN_COMPRESSION; */ return null;
			}

			m_compression[1] = m_compression[2] = m_compression[3] = CHDCodecType.CHD_CODEC_NONE;

			m_hunkcount = m_br.ReadUInt32Reverse();
			m_logicalbytes = m_br.ReadUInt64Reverse();
			m_metaoffset = m_br.ReadUInt32Reverse();

			m_br.BaseStream.Seek(76, SeekOrigin.Begin);
			m_hunkbytes = m_br.ReadUInt32Reverse();

			m_br.BaseStream.Seek(Constants.CHDv3SHA1Offset, SeekOrigin.Begin);
			sha1 = m_br.ReadBytes(20);

			// guess at the units based on snooping the metadata
			// m_unitbytes = guess_unitbytes();
			m_unitcount = (m_logicalbytes + m_unitbytes - 1) / m_unitbytes;

			return sha1;
		}

		/// <summary>
		/// Parse a CHD v4 header
		/// </summary>
		/// <returns>The extracted SHA-1 on success, null otherwise</returns>
		private byte[] ParseCHDv4Header()
		{
			// Seek to after the signature to make sure we're reading the correct bytes
			m_br.BaseStream.Seek(16, SeekOrigin.Begin);

			// Set the blank SHA-1 hash
			byte[] sha1 = new byte[20];

			// Set offsets and defaults
			m_mapoffset = 108;
			m_mapentrybytes = 16;

			// Read the CHD flags
			uint flags = m_br.ReadUInt32Reverse();

			// Determine compression
			switch (m_br.ReadUInt32())
			{
				case 0: m_compression[0] = CHDCodecType.CHD_CODEC_NONE; break;
				case 1: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 2: m_compression[0] = CHDCodecType.CHD_CODEC_ZLIB; break;
				case 3: m_compression[0] = CHDCodecType.CHD_CODEC_AVHUFF; break;
				default: /* throw CHDERR_UNKNOWN_COMPRESSION; */ return null;
			}

			m_compression[1] = m_compression[2] = m_compression[3] = CHDCodecType.CHD_CODEC_NONE;

			m_hunkcount = m_br.ReadUInt32Reverse();
			m_logicalbytes = m_br.ReadUInt64Reverse();
			m_metaoffset = m_br.ReadUInt32Reverse();

			m_br.BaseStream.Seek(44, SeekOrigin.Begin);
			m_hunkbytes = m_br.ReadUInt32Reverse();

			m_br.BaseStream.Seek(Constants.CHDv4SHA1Offset, SeekOrigin.Begin);
			sha1 = m_br.ReadBytes(20);

			// guess at the units based on snooping the metadata
			// m_unitbytes = guess_unitbytes();
			m_unitcount = (m_logicalbytes + m_unitbytes - 1) / m_unitbytes;
			return sha1;
		}

		/// <summary>
		/// Parse a CHD v5 header
		/// </summary>
		/// <returns>The extracted SHA-1 on success, null otherwise</returns>
		private byte[] ParseCHDv5Header()
		{
			// Seek to after the signature to make sure we're reading the correct bytes
			m_br.BaseStream.Seek(16, SeekOrigin.Begin);

			// Set the blank SHA-1 hash
			byte[] sha1 = new byte[20];

			// Determine compression
			m_compression[0] = (CHDCodecType)m_br.ReadUInt32Reverse();
			m_compression[1] = (CHDCodecType)m_br.ReadUInt32Reverse();
			m_compression[2] = (CHDCodecType)m_br.ReadUInt32Reverse();
			m_compression[3] = (CHDCodecType)m_br.ReadUInt32Reverse();

			m_logicalbytes = m_br.ReadUInt64Reverse();
			m_mapoffset = m_br.ReadUInt64Reverse();
			m_metaoffset = m_br.ReadUInt64Reverse();
			m_hunkbytes = m_br.ReadUInt32Reverse();
			m_hunkcount = (m_logicalbytes + m_hunkbytes - 1) / m_hunkbytes;
			m_unitbytes = m_br.ReadUInt32Reverse();
			m_unitcount = (m_logicalbytes + m_unitbytes - 1) / m_unitbytes;

			// m_allow_writes = !compressed();

			// determine properties of map entries
			// m_mapentrybytes = compressed() ? 12 : 4;

			m_br.BaseStream.Seek(Constants.CHDv5SHA1Offset, SeekOrigin.Begin);
			sha1 = m_br.ReadBytes(20);
			return sha1;
		}

		#endregion
	}
}