using System.IO.Pipes;
using System.Text;
using System.Text.Json;

namespace XFE.SeAgent.Cli;

public sealed class AgentClientException(string code, string message, Exception? inner = null) : Exception(message, inner)
{
    public string Code { get; } = code;
}

public sealed record AgentResponse(JsonElement Envelope)
{
    public bool IsError => Envelope.TryGetProperty("error", out _);
}

public sealed class AgentPipeClient
{
    public const int MaximumRequestBytes = 1048576;
    public const int MaximumResponseBytes = 4194304;

    public async Task<AgentResponse> CallAsync(string pipeName, string method, JsonElement parameters, int timeoutMs = 30000, CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(pipeName) || pipeName.IndexOfAny(['\\', '/', '\0']) >= 0)
            throw new AgentClientException("invalid_pipe", "管道名称必须是本机管道的名称，不能包含路径。");
        if (string.IsNullOrWhiteSpace(method) || method.Length > 128 || parameters.ValueKind != JsonValueKind.Object)
            throw new AgentClientException("invalid_request", "方法名不能为空，params 必须是 JSON 对象。");
        if (timeoutMs is < 1 or > 30000) throw new AgentClientException("invalid_timeout", "请求超时必须在 1 至 30000 毫秒之间。");
        string id = Guid.NewGuid().ToString("N");
        byte[] request = JsonSerializer.SerializeToUtf8Bytes(new { id, method, @params = parameters, timeoutMs });
        if (request.Length + 1 > MaximumRequestBytes) throw new AgentClientException("request_too_large", "请求超过 1 MiB 协议限制。");
        using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(timeoutMs);
        await using var pipe = new NamedPipeClientStream(".", pipeName, PipeDirection.InOut, PipeOptions.Asynchronous);
        try
        {
            await pipe.ConnectAsync(timeout.Token);
            await pipe.WriteAsync(request, timeout.Token);
            await pipe.WriteAsync(new byte[] { (byte)'\n' }, timeout.Token);
            await pipe.FlushAsync(timeout.Token);
            byte[] response = await ReadResponseAsync(pipe, timeout.Token);
            JsonElement envelope;
            try
            {
                using var json = JsonDocument.Parse(response, new JsonDocumentOptions { MaxDepth = 64 });
                envelope = json.RootElement.Clone();
            }
            catch (JsonException ex) { throw new AgentClientException("invalid_response", "Agent 返回的内容不是有效 JSON。", ex); }
            if (envelope.ValueKind != JsonValueKind.Object || !envelope.TryGetProperty("id", out var responseId) || responseId.ValueKind != JsonValueKind.String || responseId.GetString() != id)
                throw new AgentClientException("response_id_mismatch", "Agent 响应 ID 与本次请求不匹配。");
            bool hasResult = envelope.TryGetProperty("result", out _), hasError = envelope.TryGetProperty("error", out var error);
            if (hasResult == hasError || hasError && (error.ValueKind != JsonValueKind.Object || !error.TryGetProperty("code", out _) || !error.TryGetProperty("message", out _)))
                throw new AgentClientException("invalid_response", "Agent 响应必须包含 result 或有效 error。");
            return new(envelope);
        }
        catch (OperationCanceledException ex) when (!cancellationToken.IsCancellationRequested)
        { throw new AgentClientException("timeout", "等待 Agent 响应超时；操作可能已经开始，请读取当前状态后再决定是否重试。", ex); }
        catch (IOException ex) { throw new AgentClientException("pipe_error", "Agent 管道连接中断：" + ex.Message, ex); }
    }

    private static async Task<byte[]> ReadResponseAsync(Stream stream, CancellationToken token)
    {
        using var output = new MemoryStream();
        var buffer = new byte[8192];
        while (true)
        {
            int read = await stream.ReadAsync(buffer, token);
            if (read == 0) throw new AgentClientException("incomplete_response", "Agent 在完整响应结束前关闭了管道。");
            int newline = Array.IndexOf(buffer, (byte)'\n', 0, read);
            int count = newline >= 0 ? newline : read;
            if (output.Length + count + 1 > MaximumResponseBytes)
                throw new AgentClientException("response_too_large", "Agent 响应超过 4 MiB 协议限制。");
            output.Write(buffer, 0, count);
            if (newline < 0) continue;
            for (int index = newline + 1; index < read; index++)
                if (buffer[index] is not ((byte)' ' or (byte)'\r' or (byte)'\n' or (byte)'\t'))
                    throw new AgentClientException("invalid_response", "一个连接只能返回一条 JSON 响应。");
            return output.ToArray();
        }
    }
}