// 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.Buffers.Binary;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace Microsoft.DotNet.Build.Tasks.Installers;

[StructLayout(LayoutKind.Sequential)]
public struct RpmLead
{
    public string Name { get; set; }
    public byte Major { get; set; }
    public byte Minor { get; set; }
    public short Type { get; set; }
    public short Architecture { get; set; }
    public short OperatingSystem { get; set; }
    public short SignatureType { get; set; }

    public static RpmLead Read(Stream stream)
    {
        if (!stream.ReadExactly(4).SequenceEqual((ReadOnlySpan<byte>)[0xed, 0xab, 0xee, 0xdb]))
        {
            throw new InvalidDataException("Invalid RPM magic");
        }
        
        RpmLead lead = default;
        lead.Major = (byte)stream.ReadByte();
        lead.Minor = (byte)stream.ReadByte();
        lead.Type = BinaryPrimitives.ReadInt16BigEndian(stream.ReadExactly(2));
        lead.Architecture = BinaryPrimitives.ReadInt16BigEndian(stream.ReadExactly(2));
        byte[] name = new byte[66];
        stream.ReadExactly(name, 0, 66);
        lead.Name = Encoding.UTF8.GetString(name, 0, Array.IndexOf<byte>(name, 0));
        lead.OperatingSystem = BinaryPrimitives.ReadInt16BigEndian(stream.ReadExactly(2));
        lead.SignatureType = BinaryPrimitives.ReadInt16BigEndian(stream.ReadExactly(2));
        stream.ReadExactly(16); // Skip reserved
        return lead;
    }

    public readonly void WriteTo(Stream stream)
    {
        stream.Write([0xed, 0xab, 0xee, 0xdb]);
        stream.WriteByte(Major);
        stream.WriteByte(Minor);
        byte[] beBytes = new byte[2];
        BinaryPrimitives.WriteInt16BigEndian(beBytes, Type);
        stream.Write(beBytes);
        BinaryPrimitives.WriteInt16BigEndian(beBytes, Architecture);
        stream.Write(beBytes);
        byte[] name = new byte[66];
        Encoding.UTF8.GetBytes(Name, 0, Name.Length, name, 0);
        name[65] = 0;
        stream.Write(name);

        BinaryPrimitives.WriteInt16BigEndian(beBytes, OperatingSystem);
        stream.Write(beBytes);
        BinaryPrimitives.WriteInt16BigEndian(beBytes, SignatureType);
        stream.Write(beBytes);
        
        stream.Write(new byte[16]);
    }

    public override string ToString()
    {
        return $"{Name} {Major}.{Minor} {Type} Arch({Architecture}) OS({OperatingSystem}) Sig({SignatureType})";
    }
}