using LibGit.Extensions;

namespace LibGit;

public class GitPack
{
    public string PackId { get; set; }
    public GitRepo Repo { get; set; }
    
    public int Version { get; set; }
    public int ObjectCount { get; set; }
    public List<GitPackObject> Objects { get; set; } = new List<GitPackObject>();
    
    public GitPack Read(Stream stream)
    {
        stream.Peek(12).HexDump(16);
        
        Console.Write(" Header: "); stream.Peek(04).ToArray()[0..].HexDump(4);
        Console.Write("Version: "); stream.Peek(08).ToArray()[4..].HexDump(4);
        Console.Write(" ObjCnt: "); stream.Peek(12).ToArray()[8..].HexDump(4);
        
        if(!stream.StartsWith("PACK"))
            throw new Exception("Invalid pack file header");

        stream.Skip(4);
        
        Version = stream.ReadInt32BE();
        ObjectCount = stream.ReadInt32BE();
        Console.WriteLine($"Got git v{Version} pack with {ObjectCount} objects");
        for (int i = 0; i < ObjectCount; i++)
        {
            Objects.Add(new GitPackObject().Read(stream));
        }

        return this;
    }
    
    public GitPack(string packId, GitRepo repo)
    {
        PackId = packId;
        Repo = repo;
    }
}

public class GitPackIndex
{
    public int Version { get; set; }
    public int[] fanOutTable = new int[256];
    public GitPackIndex Read(Stream stream)
    {
        if(!stream.StartsWith(new byte[]{0xff,0x74,0x4f,0x63}))
            throw new Exception("Invalid pack index file header or pack is v1");

        stream.Skip(4);
        Version = stream.ReadInt32BE();
        Console.WriteLine($"Got git v{Version} pack index");
        
        //fan-out table
        for (int i = 0; i < 256; i++)
        {
            fanOutTable[i] = stream.ReadInt32BE();
        }
        

        
        
        return this;
    }
}


public class GitPackObject
{
    private const bool _debug = true; 
    public GitPackObject Read(Stream stream)
    {
        stream.Peek(64).HexDump(32);
        var header = stream.ReadBytes(4).ToArray();
        ObjType = (GitObjectType)((header[0] & 0b0111_0000) >> 4);
        if(ObjType == 0 || (int)ObjType == 5 || (int)ObjType > 7)
            throw new Exception($"Invalid object type: {(int)ObjType}");
        Size = header[0] & 0b0000_1111;
        
        Offset = 0;
        for (int i = 1; i < 4; i++)
        {
            Offset <<= 8;
            Offset |= header[i];
        }
        
        if ((Size & 0b0000_1000) != 0)
        {
            Size <<= 4;
            Size |= stream.ReadVLQ();
        }

        // ObjType = Type switch
        // {
        //     1 => GitObjectType.Commit,
        //     2 => GitObjectType.Tree,
        //     3 => GitObjectType.Blob,
        //     4 => GitObjectType.Tag,
        //     5 => GitObjectType.Invalid, 
        //     6 => GitObjectType.OffsDelta,
        //     7 => GitObjectType.RefDelta,
        //     _ => throw new Exception($"Invalid object type {Type}")
        // };

        if(_debug) Console.WriteLine($"pack obj type: {ObjType} ({(int)ObjType}), size: {Size}, offset: {Offset}, sizeBytes: {SizeBytes}");
        Console.WriteLine("Data: ");
        stream.Peek(Size).Take(16).ToArray().HexDump(16);
        stream.ReadBytes(Size).ZlibDecompress().Take(16).HexDump(16);
        
        return this;
    }

    public GitObjectType ObjType { get; set; }

    public int SizeBytes { get; set; }

    public int Size { get; set; }

    public int Offset { get; set; }
}

public enum GitObjectType
{
    Commit = 1,
    Tree,
    Blob,
    Tag,
    Invalid, // Reserved for future expansion, see https://git-scm.com/docs/pack-format#_object_types
    OffsDelta,
    RefDelta
}