// 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.IO;
using System.IO.Compression;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace Microsoft.DotNet.Build.Tasks.Installers;

public sealed class RpmPackage(RpmLead lead, RpmHeader<RpmSignatureTag> signature, RpmHeader<RpmHeaderTag> header, MemoryStream archiveStream) : IDisposable
{
    public RpmLead Lead { get; set; } = lead;
    public RpmHeader<RpmSignatureTag> Signature { get; set; } = signature;
    public RpmHeader<RpmHeaderTag> Header { get; set; } = header;
    public MemoryStream ArchiveStream { get; set; } = archiveStream;

    public static unsafe RpmPackage Read(Stream stream)
    {
        RpmLead lead = RpmLead.Read(stream);

        RpmHeader<RpmSignatureTag> signature = RpmHeader<RpmSignatureTag>.Read(stream, RpmSignatureTag.HeaderSignatures);
        stream.AlignReadTo(8);
        RpmHeader<RpmHeaderTag> header = RpmHeader<RpmHeaderTag>.Read(stream, RpmHeaderTag.Immutable);

        if (header.Entries.First(e => e.Tag == RpmHeaderTag.PayloadCompressor).Value is not "gzip")
        {
            throw new InvalidDataException("Unsupported payload compressor");
        }

        using GZipStream gzipStream = new(stream, CompressionMode.Decompress, leaveOpen: true);
        MemoryStream archiveStream = new();
        gzipStream.CopyTo(archiveStream);
        archiveStream.Position = 0;
        return new RpmPackage(lead, signature, header, archiveStream);
    }

    public static unsafe MemoryStream GetSignableContent(Stream stream)
    {
        // We don't care about the lead and signature header
        RpmLead.Read(stream);
        RpmHeader<RpmSignatureTag>.Read(stream, RpmSignatureTag.HeaderSignatures);
        stream.AlignReadTo(8);

        // Remaining stream content is the signable content
        // This includes all the magic and alignment bytes in both header and archive sections.
        MemoryStream signableContentStream = new();
        stream.CopyTo(signableContentStream);
        signableContentStream.Position = 0;
        return signableContentStream;
    }

    public void WriteTo(Stream stream)
    {
        Lead.WriteTo(stream);
        Signature.WriteTo(stream, RpmSignatureTag.HeaderSignatures);
        stream.AlignWriteTo(8);
        Header.WriteTo(stream, RpmHeaderTag.Immutable);

        using GZipStream gzipStream = new(stream, CompressionLevel.Optimal, leaveOpen: true);
        ArchiveStream.CopyTo(gzipStream);
    }

    public override string ToString()
    {
        return $"""
            Lead:
            {Lead}
            Signature:
            {Signature}
            Header:
            {Header}
            """;
    }

    public void Dispose() => ArchiveStream.Dispose();
}