// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

#nullable enable

namespace Microsoft.DotNet.Build.Tasks.Installers;

internal sealed class CpioReader(Stream stream, bool leaveOpen) : IDisposable
{
    public CpioEntry? GetNextEntry()
    {
        if (stream.Position == stream.Length)
        {
            return null;
        }

        byte[] magic = new byte[6];
        stream.ReadExactly(magic, 0, 6);
        if (!magic.AsSpan().SequenceEqual("070701"u8))
        {
            throw new InvalidDataException("Invalid header magic");
        }

        byte[] byteBuffer = new byte[8];

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong inode = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        uint mode = uint.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong ownerID = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong groupID = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ushort numberOfLinks = ushort.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong timestamp = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong size = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong devMajor = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong devMinor = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong rdevMajor = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        ulong rdevMinor = ulong.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        stream.ReadExactly(byteBuffer, 0, 8);
        int namesize = int.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        // Ignore checksum
        stream.ReadExactly(byteBuffer, 0, 8);
        _ = int.Parse(Encoding.ASCII.GetString(byteBuffer), NumberStyles.HexNumber);

        byte[] nameBuffer = new byte[namesize];
        stream.ReadExactly(nameBuffer, 0, namesize);
        string name = Encoding.ASCII.GetString(nameBuffer, 0, namesize - 1);

        stream.AlignReadTo(4);

        byte[] data = new byte[size];
        stream.ReadExactly(data, 0, (int)size);            
        MemoryStream dataStream = new(data);

        stream.AlignReadTo(4);

        if (name == "TRAILER!!!")
        {
            // We've reached the end of the archive.
            return null;
        }

        return new CpioEntry(
            inode,
            name,
            timestamp,
            ownerID,
            groupID,
            mode,
            numberOfLinks,
            devMajor,
            devMinor,
            rdevMajor,
            rdevMinor,
            dataStream);
    }

    public void Dispose()
    {
        if (!leaveOpen)
        {
            stream.Dispose();
        }
    }
}