using System.Text;
using System.Threading.Channels;
using WarcViewerBlazorWinForm.Backend.IO;
using WarcViewerBlazorWinForm.Backend.IO.Archiving;
using WarcViewerBlazorWinForm.Library.AssemblyInject.Interfaces;
using WarcViewerBlazorWinForm.Library.EventBus;

namespace WarcViewerBlazorWinForm.Backend.Warc;

internal class WarcIndexManager : IAssemblyInjectSingleton, IAssemblyInjectSyncStarStop
{
    private const long Gib = 1024 * 1024 * 1024;

    private static class FolderLayer
    {
        // normal
        //    <input file>.idx/[archive key/]
        //    <input file>.idx/[archive key/]
        // fallback
        //    <app path>/fallback index/<input file>/[archive key/]
        // file name
        //    0.index.xz

        public static string MakeIndexDirOrFallback(FileDescriptor fd)
        {
            var inputFileFullPath = Path.GetFullPath(fd.FilePath);
            var dir = inputFileFullPath + ".idx";
            if (fd.IsReadDirectly == false && fd.ArchiveEntryKey != null) dir = Path.Combine(dir, fd.ArchiveEntryKey.Trim().TrimStart('/', '\\'));

            if (Directory.Exists(dir)) return dir;

            try
            {
                Directory.CreateDirectory(dir);
                return dir;
            }
            catch (IOException)
            {
                var fallbackDir = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "fallback index", Path.GetFileNameWithoutExtension(fd.FilePath), fd.ArchiveEntryKey ?? "");
                Directory.CreateDirectory(fallbackDir);
                return fallbackDir;
            }
        }

        public static string MakeIndexFileName(int gbIndex) => $"{gbIndex:00000}.index.xz";
    }

    private class IndexFormat
    {
        // int32 - NumberOfEntry
        // int32 - LastEntrySize for check index integrity
        // int64* - BLOB entry offset
        // LINES* - LINES: <URL> <TYPE:M, S, R, O>

        public List<long> Offsets { get; }
        public int? LastEntrySize { get; set; }
        public List<(string url, string type)> Urls { get; }

        public IndexFormat()
        {
            Offsets = [];
            Urls = [];
        }

        public IndexFormat(Stream fromStream)
        {
            if (fromStream == null) throw new ArgumentNullException(nameof(fromStream));

            var br = new BinaryReader(fromStream);
            var sr = new StreamReader(fromStream);
            var numberOfEntry = br.ReadInt32();
            LastEntrySize = br.ReadInt32();
            Offsets = new List<long>(numberOfEntry);
            Urls = new List<(string, string)>(numberOfEntry);
            for (var i = 0; i < numberOfEntry; i++) Offsets.Add(br.ReadInt64());

            for (var i = 0; i < numberOfEntry; i++)
            {
                var line = sr.ReadLine();
                var parts = line!.Split(' ', 2);
                Urls.Add((parts[0], parts[1]));
            }
        }

        public void WriteToStream(Stream stream)
        {
            if (LastEntrySize.HasValue == false) throw new InvalidOperationException("LastEntrySize can not be null");
            var count = Offsets.Count;
            if (count != Urls.Count) throw new InvalidOperationException("count not matched between Offsets and Urls");

            var ms = new MemoryStream();

            using var bw = new BinaryWriter(ms, Encoding.ASCII, true);
            using var sw = new StreamWriter(ms, leaveOpen: true);

            bw.Write(count);
            bw.Write(LastEntrySize.Value);
            foreach (var offset in Offsets) bw.Write(offset);
            foreach (var tuple in Urls) sw.WriteLine($"{tuple.type} {tuple.url}");
            sw.Close();
            bw.Close();

            ms.Position = 0;
            ms.CopyTo(stream);
        }
    }

    private readonly CancellationTokenSource _cancellationTokenSource = new();
    private readonly Channel<FileDescriptor> _queue = Channel.CreateBounded<FileDescriptor>(int.MaxValue);
    private readonly IEventBus _eventBus;

    private bool _isWorking = false;
    private FileDescriptor? _currentFileDescriptor;
    private float? _currentProgress;

    public WarcIndexManager(IEventBus eventBus)
    {
        _eventBus = eventBus;
        _eventBus.Subscript<WarcIndexerLoadRequestEvent>(obj => _ = LoadIndexAsync(obj.FileDescriptor));
        _eventBus.Subscript<WarcIndexerStatusRequestEvent>(_ => PublishStatus());
    }

    private void PublishStatus() => _eventBus.Publish(new WarcIndexerStatusEvent(_isWorking, _queue.Reader.Count, _currentFileDescriptor, _currentProgress));

    private async Task LoadIndexAsync(FileDescriptor fd)
    {
        var dir = FolderLayer.MakeIndexDirOrFallback(fd);
        var len = await FileReader.GetLengthAsync(fd);
        var gbIndex = 0;

        do
        {
            var indexFilePath = Path.Combine(dir, FolderLayer.MakeIndexFileName(gbIndex));
            if (File.Exists(indexFilePath) == false)
            {
                await _queue.Writer.WriteAsync(fd);
                return;
            }
            var indexContent = new IndexFormat(XzRwOps.OpenReadXzFile(indexFilePath));

            var batch = new List<WarcIndexEntry>();
            for (var i = 0; i < indexContent.Offsets.Count; i++)
            {
                var (url, type) = indexContent.Urls[i];
                batch.Add(new WarcIndexEntry(fd, indexContent.Offsets[i], type, url));
            }
            _eventBus.Publish(new WarcIndexerLoadedEvent(batch));

            if (indexContent.Offsets.Last() + indexContent.LastEntrySize == len)
            {
                return;
            }

            gbIndex++;
        } while (true);
    }

    public void Start()
    {
        Task.Run(async () =>
        {
            while (_cancellationTokenSource.IsCancellationRequested == false)
            {
                _isWorking = false;
                _currentFileDescriptor = null;
                _currentProgress = null;
                PublishStatus();

                var fileDescriptor = await _queue.Reader.ReadAsync(_cancellationTokenSource.Token);

                _isWorking = true;
                _currentFileDescriptor = fileDescriptor;
                PublishStatus();

                var length = await FileReader.GetLengthAsync(fileDescriptor);

                var indexDir = FolderLayer.MakeIndexDirOrFallback(fileDescriptor);
                var existIndexFile = Directory.GetFiles(indexDir).OrderBy(p => p).ToArray();

                long loadPosition = 0;
                var lastExistIndexFile = existIndexFile.LastOrDefault();
                if (lastExistIndexFile != null)
                {
                    var indexContent = new IndexFormat(XzRwOps.OpenReadXzFile(lastExistIndexFile));
                    loadPosition = indexContent.Offsets.Last() + indexContent.LastEntrySize!.Value;
                    if (loadPosition == length) continue; // skip completely indexed
                }

                // Start(continue) indexing
                await using var stream = await FileReader.OpenReadStreamAsync(fileDescriptor);
                stream.SeekForwardStupid(loadPosition);

                _currentProgress = (float)loadPosition / length;
                PublishStatus();

                IndexFormat? indexingFile = null;
                var indexingGb = (int)(loadPosition / Gib);

                int? lastBlockSize;
                do
                {
                    if (_cancellationTokenSource.IsCancellationRequested) return;

                    if (indexingFile == null) indexingFile = new();

                    //handle index entry
                    indexingFile.Offsets.Add(loadPosition);

                    var block = WarcParser.ReadEntryBlock(stream);
                    lastBlockSize = block.Length;
                    loadPosition += block.Length;
                    _eventBus.Publish(new WarcIndexerStatusEvent(true, _queue.Reader.Count, fileDescriptor, (float)loadPosition / length));
                    var entry = WarcParser.ParseBlockForIndexing(block);
                    indexingFile.Urls.Add((entry.Url, entry.Type));

                    //check per gib split and flip
                    var nowGb = (int)(loadPosition / Gib);
                    if (nowGb != indexingGb)
                    {
                        indexingFile.LastEntrySize = block.Length;

                        await using var xzWriteStream = XzRwOps.OpenWriteXzFile(Path.Combine(indexDir, FolderLayer.MakeIndexFileName(indexingGb)));
                        indexingFile.WriteToStream(xzWriteStream);

                        indexingFile = null;
                        indexingGb = nowGb;
                    }
                } while (loadPosition < length);

                if (indexingFile != null) //write last part of index
                {
                    indexingFile.LastEntrySize = lastBlockSize.Value;

                    await using var xzWriteStream = XzRwOps.OpenWriteXzFile(Path.Combine(indexDir, FolderLayer.MakeIndexFileName(indexingGb)));
                    indexingFile.WriteToStream(xzWriteStream);
                }
            }
        });
    }

    public void Stop() => _cancellationTokenSource.Cancel();

    public enum IndexingState
    {
        NotIndexed,
        PartIndexed,
        CompletelyIndexed
    }
}