using System;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using pkNX.Containers;

namespace pkNX;

/// <summary>
/// More complex container format for large long lived archives.
/// </summary>
public abstract class LargeContainer : IDisposable, IFileContainer
{
    public virtual int Count => Files.Length;

    public Task<byte[][]> GetFiles() => new(() => { CacheAll(); return Files!; });
    public Task<byte[]> GetFile(int file, int subFile = 0) => new(() => GetEntry(file, subFile));
    public Task SetFile(int file, byte[] value, int subFile = 0) => new(() => SetEntry(file, value, subFile));

    public string? Extension => Path.GetExtension(FilePath);
    public string? FileName => Path.GetFileName(FilePath);
    public string? FilePath { get; set; }
    public bool Modified { get; set; }

    protected byte[]?[] Files = Array.Empty<byte[]>();

    /// <summary>
    /// Packs the <see cref="LargeContainer"/> to the specified writing stream.
    /// </summary>
    /// <param name="bw">Stream Writer to write contents to.</param>
    /// <param name="handler">Manager for monitoring progress.</param>
    /// <param name="token">Cancellation object</param>
    /// <returns>Awaitable Task</returns>
    protected abstract Task Pack(BinaryWriter bw, ContainerHandler handler, CancellationToken token);

    #region File Reading

    protected BinaryReader? Reader { get; private set; }
    private Stream? Stream;

    protected void OpenBinary(string path)
    {
        path = FileMitm.GetRedirectedReadPath(path);
        Stream = new FileStream(path, FileMode.Open);
        Reader = new BinaryReader(Stream);
        Initialize();
    }

    protected void OpenRead(BinaryReader br)
    {
        Reader = br;
        Stream = br.BaseStream;
        Initialize();
    }

    protected abstract void Initialize();

    protected abstract int GetFileOffset(int file, int subFile = 0);

    public BinaryReader Seek(int file, long offset = 0, int subFile = 0)
    {
        if (Reader == null)
            throw new NullReferenceException("Reader is not initialized.");
        offset += GetFileOffset(file, subFile);
        Reader.BaseStream.Position = offset;
        return Reader;
    }

    public abstract byte[] GetEntry(int index, int subFile);

    public virtual void SetEntry(int index, byte[]? value, int subFile)
    {
        Files[index] = value;
        Modified |= value != null && !this[index].SequenceEqual(value);
    }

    private byte[] GetCachedValue(int i, int subFile)
    {
        return Files[i] ??= GetEntry(i, subFile);
    }

    #endregion

    public byte[] this[int index]
    {
        get => (byte[]) GetCachedValue(index, 0).Clone();
        set => SetEntry(index, value, 0);
    }

    public void CacheAll()
    {
        for (int i = 0; i < Files.Length; i++)
            Files[i] ??= GetCachedValue(i, 0);

        Reader = null;
        Stream?.Close();
        Stream = null;
    }

    public void CancelEdits()
    {
        if (Reader == null)
            throw new ArgumentNullException(nameof(Reader));

        for (int i = 0; i < Files.Length; i++)
            Files[i] = null;

        Modified = false;
    }

    public abstract void Dump(string path, ContainerHandler handler);

    public async Task SaveAs(string path, ContainerHandler handler, CancellationToken token = new())
    {
        bool sameLocation = path == FilePath && Reader != null;
        var writePath = sameLocation ? Path.GetTempFileName() : path;

        path = FileMitm.GetRedirectedWritePath(path);
        var stream = new FileStream(path, FileMode.CreateNew);
        await using (var bw = new BinaryWriter(stream))
            await Pack(bw, handler, token).ConfigureAwait(false);

        if (token.IsCancellationRequested)
        {
            stream.Close();
            File.Delete(path);
            return;
        }

        if (sameLocation && path != writePath)
        {
            if (File.Exists(path))
                File.Delete(path);
            File.Move(writePath, path);
        }

        Stream?.Dispose();
        Reader?.Dispose();

        Stream = stream;
        Reader = new BinaryReader(Stream);
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        Stream?.Dispose();
        Reader?.Dispose();
    }
}