// Copyright (c) Dr. Dirk Lellinger. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
using SlobViewer.Common;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;

namespace SlobViewer.Slob
{
  public class SlobReaderWriter
  {
    private readonly string _fileName;
    private System.IO.FileStream _stream;
    private readonly byte[] _buffer = new byte[65536];

    public const long SupposedMagic = 0x212d31534c4f421f;

    public const ulong SupposedVersionHi = 4862287655031097909UL;
    public const ulong SupposedVersionLo = 11718617693102973101UL;


    /// <summary>
    /// Initializes a new instance of the <see cref="SlobReaderWriter"/> class.
    /// </summary>
    /// <param name="fileName">Full file name of the SLOB file (either to read or to write).</param>
    public SlobReaderWriter(string fileName)
    {
      _fileName = fileName;
    }

    /// <summary>
    /// Reads from a SLOB file, and returns the read dictionary.
    /// </summary>
    /// <returns>The read dictionary.</returns>
    public IWordDictionary Read()
    {

      // for format details see
      // https://github.com/itkach/slob

      using (_stream = new FileStream(_fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
      {
        ulong magic = BigEndianBitConverter.ToUInt64(_stream, _buffer);
        if (magic != SupposedMagic)
        {
          throw new InvalidOperationException("Magic number did not match!");
        }

        ulong uuidHi = BigEndianBitConverter.ToUInt64(_stream, _buffer);
        ulong uuidLo = BigEndianBitConverter.ToUInt64(_stream, _buffer);

        /*
        if (uuidHi != SupposedVersionHi || uuidLo != SupposedVersionLo)
        {
          throw new InvalidOperationException("This version is not supported");
        }
        */
        var encoding = System.Text.UTF8Encoding.UTF8;
        string encodingAsString = BigEndianBitConverter.ReadTinyText(_stream, encoding, _buffer);
        switch (encodingAsString.ToLowerInvariant())
        {
          case "utf-7":
            encoding = System.Text.UTF7Encoding.UTF7;
            break;
          case "utf-8":
            encoding = System.Text.UTF8Encoding.UTF8;
            break;
          case "utf-32":
            encoding = System.Text.UTF32Encoding.UTF32;
            break;
          case "ascii":
            encoding = System.Text.ASCIIEncoding.ASCII;
            break;
          default:
            throw new NotImplementedException($"Encoding >>{encodingAsString}<< is not yet implemented!");
        }



        string compression = BigEndianBitConverter.ReadTinyText(_stream, encoding, _buffer);


        // char-sized sequence of tags
        //
        int tagCount = _stream.ReadByte();
        Dictionary<string, string> tagDict = new Dictionary<string, string>();

        for (int i = 0; i < tagCount; ++i)
        {
          string key = BigEndianBitConverter.ReadTinyText(_stream, encoding, _buffer);
          string value = BigEndianBitConverter.ReadTinyText(_stream, encoding, _buffer);
          value = value.TrimEnd('\0');
          tagDict.Add(key, value);
        }

        // char-sized sequence of content types
        //

        int contentTypeCount = _stream.ReadByte();
        string[] contentTypes = new string[contentTypeCount];
        for (int i = 0; i < contentTypeCount; ++i)
        {
          string contentType = BigEndianBitConverter.ReadText(_stream, encoding, _buffer);
          contentTypes[i] = contentType;
        }

        // Blobcount
        uint blobCount = BigEndianBitConverter.ToUInt32(_stream, _buffer);

        // Store offset
        ulong storeOffset = BigEndianBitConverter.ToUInt64(_stream, _buffer);

        // Size
        ulong size = BigEndianBitConverter.ToUInt64(_stream, _buffer);

        // list of long-positioned refs
        uint refCount = BigEndianBitConverter.ToUInt32(_stream, _buffer);
        ulong[] references = new ulong[refCount];
        for (int i = 0; i < refCount; ++i)
        {
          ulong offset = BigEndianBitConverter.ToUInt64(_stream, _buffer);
          references[i] = offset;
        }

        // read-in the keywords
        long refOffset = _stream.Position;
        Reference[] refItems = new Reference[refCount];
        for (int i = 0; i < refCount; ++i)
        {
          _stream.Seek(refOffset + (long)references[i], SeekOrigin.Begin);

          string key = BigEndianBitConverter.ReadText(_stream, encoding, _buffer);
          uint binIndex = BigEndianBitConverter.ToUInt32(_stream, _buffer);
          ushort itemIndex = BigEndianBitConverter.ToUInt16(_stream, _buffer);
          string fragment = BigEndianBitConverter.ReadTinyText(_stream, encoding, _buffer);
          refItems[i] = new Reference(key, binIndex, itemIndex, fragment);
        }


        // list of long-positioned store items
        _stream.Seek((long)storeOffset, SeekOrigin.Begin);
        uint storeCount = BigEndianBitConverter.ToUInt32(_stream, _buffer);
        ulong[] storeOffsets = new ulong[storeCount];
        for (int i = 0; i < storeCount; ++i)
        {
          storeOffsets[i] = BigEndianBitConverter.ToUInt64(_stream, _buffer);
        }

        long storeOffset2 = _stream.Position;

        // Test store offsets
        for (int i = 0; i < storeCount; ++i)
        {
          if (((long)storeOffsets[i] + storeOffset2) >= _stream.Length)
            throw new System.IO.EndOfStreamException("StoreOffset behind end of file");
        }

        if (_stream.Length > 128) // For sizes > 128 MB, we return a file based slob dictionary
        {
          var streamCopy = new FileStream(_fileName, FileMode.Open, FileAccess.Read, FileShare.Read);
          var dictionary = new SlobDictionaryFileBased(streamCopy, encoding, compression, tagDict, contentTypes, refItems, storeOffsets.Select(o => new StoreItemFileBased((long)o + storeOffset2)).ToArray());
          return dictionary;
        }
        else // For sizes that are relatively small we can make an in-memory dictionary
        {
          // Read-in the blobs
          StoreItemInMemory[] storeItems = new StoreItemInMemory[storeCount];

          for (int i = 0; i < storeCount; ++i)
          {
            _stream.Seek(storeOffset2 + (long)storeOffsets[i], SeekOrigin.Begin);
            uint count = BigEndianBitConverter.ToUInt32(_stream, _buffer);
            byte[] contentIds = new byte[count];
            for (int k = 0; k < count; ++k)
            {
              contentIds[k] = (byte)_stream.ReadByte();
            }

            uint contentLen = BigEndianBitConverter.ToUInt32(_stream, _buffer);
            byte[] contentBytes = new byte[contentLen];
            _stream.Read(contentBytes, 0, (int)contentLen);
            storeItems[i] = new StoreItemInMemory(contentIds, contentBytes);
          }

          return new SlobDictionaryInMemory(encoding, compression, tagDict, contentTypes, refItems, storeItems);
        }
      }
    }

    /// <summary>
    /// Writes the specified dictionary as a slob file. Text is encoded as UTF8, and compression is zlib.
    /// </summary>
    /// <param name="dict">The dictionary to write.</param>
    /// <param name="mimeContentType">MIME content type of the values of the dictionary.</param>
    public void Write(Dictionary<string, string> dict, string mimeContentType)
    {
      // for format details see
      // https://github.com/itkach/slob


      KeyValuePair<string, string>[] listDict = dict.ToArray();
      CompareInfo myComp_enUS = new CultureInfo("en-US", false).CompareInfo;
      SortKey[] sortKeys = listDict.Select(x => myComp_enUS.GetSortKey(x.Key)).ToArray();
      Array.Sort(sortKeys, listDict, new UnicodeStringSorter());

      using (_stream = new FileStream(_fileName, FileMode.Create, FileAccess.Write, FileShare.Read))
      {
        System.Text.Encoding encoding = System.Text.UTF8Encoding.UTF8;

        BigEndianBitConverter.WriteUInt64(SupposedMagic, _stream);

        BigEndianBitConverter.WriteUInt64(SupposedVersionHi, _stream);

        BigEndianBitConverter.WriteUInt64(SupposedVersionLo, _stream);

        BigEndianBitConverter.WriteTinyText("utf-8", _stream, encoding);

        BigEndianBitConverter.WriteTinyText("zlib", _stream, encoding);

        // Tag count
        _stream.WriteByte(0);

        // char-sized sequence of content types
        _stream.WriteByte(1); // there is only one content type here
        BigEndianBitConverter.WriteText(mimeContentType, _stream, encoding);



        // Blobcount
        long posBlobCount = _stream.Position;
        BigEndianBitConverter.WriteUInt32(0, _stream); // PlaceHolder for BlobCount

        // Store offset
        long posStoreOffset = _stream.Position;
        BigEndianBitConverter.WriteUInt64(0, _stream);

        // Size
        long posSize = _stream.Position;
        BigEndianBitConverter.WriteUInt64(0, _stream);

        // list of long-positioned refs
        BigEndianBitConverter.WriteUInt32((uint)listDict.Length, _stream);
        long posRefTablePositions = _stream.Position;



        long posRefTableBegin = _stream.Position + 8 * listDict.Length;
        _stream.Seek(posRefTableBegin, SeekOrigin.Begin);

        int i = -1;
        int binIndex = 0;
        int itemIndex = 0;
        int contentLength = 0;
        List<int> listOfEntryCounts = new List<int>(); // for every store item, this list contains the number of elements stored into it

        foreach (KeyValuePair<string, string> entry in listDict)
        {
          ++i;
          // Store current stream position in refTable
          {
            long currentPos = _stream.Position;
            _stream.Seek(posRefTablePositions + i * 8, SeekOrigin.Begin);
            BigEndianBitConverter.WriteUInt64((ulong)(currentPos - posRefTableBegin), _stream);
            _stream.Seek(currentPos, SeekOrigin.Begin);
          }

          BigEndianBitConverter.WriteText(entry.Key, _stream, encoding);

          BigEndianBitConverter.WriteUInt32((uint)binIndex, _stream);
          BigEndianBitConverter.WriteUInt16((ushort)itemIndex, _stream);
          BigEndianBitConverter.WriteTinyText(string.Empty, _stream, encoding);


          ++itemIndex;
          contentLength += entry.Value.Length;
          if (itemIndex >= 32768 || contentLength > 320 * 1024) // limit one store item to 32767 entries or a maximum length of 320 kB
          {
            listOfEntryCounts.Add(itemIndex);
            contentLength = 0;
            itemIndex = 0;
            ++binIndex;
          }
        }
        if (itemIndex != 0)
        {
          listOfEntryCounts.Add(itemIndex);
        }

        // Write the blob count and store offset
        {
          long currentPos = _stream.Position;
          _stream.Seek(posBlobCount, SeekOrigin.Begin);
          BigEndianBitConverter.WriteUInt32((uint)listOfEntryCounts.Count, _stream); // Blob-Count

          // Write the store offset
          BigEndianBitConverter.WriteUInt64((ulong)currentPos, _stream);

          _stream.Seek(currentPos, SeekOrigin.Begin);
        }

        // list of long-positioned store items
        BigEndianBitConverter.WriteUInt32((uint)listOfEntryCounts.Count, _stream); // Store count

        long posStoreOffsetTable = _stream.Position;
        _stream.Seek(posStoreOffsetTable + 8 * listOfEntryCounts.Count, SeekOrigin.Begin);
        long posStoreBegin = _stream.Position;

        int itemIndexOffset = 0;
        for (binIndex = 0; binIndex < listOfEntryCounts.Count; ++binIndex)
        {
          {
            long currentPos = _stream.Position;
            _stream.Seek(posStoreOffsetTable + 8 * binIndex, SeekOrigin.Begin);
            BigEndianBitConverter.WriteUInt64((ulong)(currentPos - posStoreBegin), _stream);
            _stream.Seek(currentPos, SeekOrigin.Begin);
          }

          BigEndianBitConverter.WriteUInt32((uint)listOfEntryCounts[binIndex], _stream);
          for (int j = 0; j < listOfEntryCounts[binIndex]; ++j)
          {
            _stream.WriteByte(0); // Table with content ids
          }

          long posContentLength = _stream.Position;
          BigEndianBitConverter.WriteUInt32(0, _stream); // Placeholder for content length
                                                         // compressStream = new System.IO.Compression.DeflateStream(_stream, System.IO.Compression.CompressionLevel.Optimal, true);
          using (ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream compressStream = new ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream(_stream, new ICSharpCode.SharpZipLib.Zip.Compression.Deflater(), 1024 * 1024) { IsStreamOwner = false })
          {

            // now write the content

            // First list of item offsets (without count)
            int itemPositionOffset = 0;
            for (int k = 0; k < listOfEntryCounts[binIndex]; ++k)
            {
              BigEndianBitConverter.WriteUInt32((uint)itemPositionOffset, compressStream);
              itemPositionOffset += 4 + encoding.GetByteCount(listDict[itemIndexOffset + k].Value);
            }

            // now the content itself
            for (int k = 0; k < listOfEntryCounts[binIndex]; ++k)
            {

              BigEndianBitConverter.WriteBigText(listDict[itemIndexOffset + k].Value, compressStream, encoding);
            }

            itemIndexOffset += listOfEntryCounts[binIndex];

            compressStream.Flush();
            compressStream.Close();
          }

          {
            // Write content length
            long currentPosition = _stream.Position;
            _stream.Seek(posContentLength, SeekOrigin.Begin);
            BigEndianBitConverter.WriteUInt32((uint)(currentPosition - posContentLength - 4), _stream);
            _stream.Seek(currentPosition, SeekOrigin.Begin);
          }



        }

      }
    }
  }


}