using System.Buffers.Binary;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace Agent.Admin.Client;

public sealed record AdminNetworkEndpoint(string Address, int Port);

public sealed record AdminRequest(
    int Version,
    string Operation,
    Guid TaskId,
    string? ApplicationSid = null,
    string? NetworkAccess = null,
    IReadOnlyList<AdminNetworkEndpoint>? Endpoints = null,
    bool? OriginallyLoopbackExempt = null);

public sealed record AdminResponse(bool Success, string? ErrorCode = null, string? Message = null, bool? LoopbackExempt = null);

public static class AdminProtocol
{
    public const int Version = 1;
    public const int MaxMessageBytes = 64 * 1024;
    private static readonly JsonSerializerOptions Json = new(JsonSerializerDefaults.Web)
    {
        UnmappedMemberHandling = JsonUnmappedMemberHandling.Disallow
    };

    public static async Task WriteAsync<T>(Stream stream, T value, CancellationToken cancellationToken)
    {
        byte[] payload = JsonSerializer.SerializeToUtf8Bytes(value, Json);
        if (payload.Length is <= 0 or > MaxMessageBytes) throw new InvalidDataException("Administrative pipe message exceeds the fixed size limit.");
        byte[] header = new byte[sizeof(int)];
        BinaryPrimitives.WriteInt32LittleEndian(header, payload.Length);
        await stream.WriteAsync(header, cancellationToken).ConfigureAwait(false);
        await stream.WriteAsync(payload, cancellationToken).ConfigureAwait(false);
        await stream.FlushAsync(cancellationToken).ConfigureAwait(false);
    }

    public static async Task<T> ReadAsync<T>(Stream stream, CancellationToken cancellationToken)
    {
        byte[] header = new byte[sizeof(int)];
        await ReadExactlyAsync(stream, header, cancellationToken).ConfigureAwait(false);
        int length = BinaryPrimitives.ReadInt32LittleEndian(header);
        if (length is <= 0 or > MaxMessageBytes) throw new InvalidDataException("Administrative pipe message has an invalid size.");
        byte[] payload = new byte[length];
        await ReadExactlyAsync(stream, payload, cancellationToken).ConfigureAwait(false);
        return JsonSerializer.Deserialize<T>(payload, Json) ?? throw new InvalidDataException("Administrative pipe message is empty.");
    }

    private static async Task ReadExactlyAsync(Stream stream, Memory<byte> buffer, CancellationToken cancellationToken)
    {
        int offset = 0;
        while (offset < buffer.Length)
        {
            int read = await stream.ReadAsync(buffer[offset..], cancellationToken).ConfigureAwait(false);
            if (read == 0) throw new EndOfStreamException("Administrative pipe disconnected.");
            offset += read;
        }
    }
}