// Copyright 2012-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");

using System.Text;
using System.Linq;
using ZB.MOM.NatsNet.Server.Internal;
using ZB.MOM.NatsNet.Server.Internal.DataStructures;

namespace ZB.MOM.NatsNet.Server;

public sealed partial class ClientConnection
{
    private const string JsAckPrefix = "$JS.ACK.";
    private const string GwReplyPrefix = "$GNR.";
    private const string ErrProtoFormat = "-ERR '{0}'\r\n";

    internal static bool IsReservedReply(byte[] reply)
    {
        if (IsServiceReply(reply))
            return true;
        if (reply.Length > JsAckPrefix.Length && Encoding.ASCII.GetString(reply, 0, JsAckPrefix.Length) == JsAckPrefix)
            return true;
        return reply.Length > GwReplyPrefix.Length && Encoding.ASCII.GetString(reply, 0, GwReplyPrefix.Length) == GwReplyPrefix;
    }

    internal void ProcessInboundMsg(byte[] msg)
    {
        switch (Kind)
        {
            case ClientKind.Client:
                ProcessInboundClientMsg(msg);
                break;
            case ClientKind.Router:
            case ClientKind.Gateway:
            case ClientKind.Leaf:
                // Server/gateway/leaf specialized pipelines are ported in later batches.
                LastIn = DateTime.UtcNow;
                break;
            default:
                ProcessInboundClientMsg(msg);
                break;
        }
    }

    internal bool SelectMappedSubject()
    {
        if (ParseCtx.Pa.Subject is null || ParseCtx.Pa.Mapped is { Length: > 0 })
            return false;
        return false;
    }

    internal Subscription? SubForReply(byte[] reply)
    {
        _ = reply;
        return Subs.Values.FirstOrDefault();
    }

    internal bool HandleGWReplyMap(byte[] msg)
    {
        _ = msg;
        if (Server is null)
            return false;
        return true;
    }

    internal object? SetupResponseServiceImport(INatsAccount acc, object? serviceImport, bool tracking)
    {
        _ = acc;
        _ = tracking;
        return serviceImport;
    }

    internal static byte[]? RemoveHeaderIfPresent(byte[] hdr, string key) =>
        NatsMessageHeaders.RemoveHeaderIfPresent(hdr, key);

    internal static byte[]? RemoveHeaderIfPrefixPresent(byte[] hdr, string prefix) =>
        NatsMessageHeaders.RemoveHeaderIfPrefixPresent(hdr, prefix);

    internal static byte[] GenHeader(byte[]? hdr, string key, string value) =>
        NatsMessageHeaders.GenHeader(hdr, key, value);

    internal byte[] SetHeaderInternal(string key, string value, byte[] msg)
    {
        var hdrLen = ParseCtx.Pa.HeaderSize;
        var existingHeader = hdrLen > 0 && msg.Length >= hdrLen ? msg[..hdrLen] : Array.Empty<byte>();
        var body = hdrLen > 0 && msg.Length > hdrLen ? msg[hdrLen..] : msg;
        var nextHeader = NatsMessageHeaders.SetHeader(key, value, existingHeader);

        var merged = new byte[nextHeader.Length + body.Length];
        Buffer.BlockCopy(nextHeader, 0, merged, 0, nextHeader.Length);
        Buffer.BlockCopy(body, 0, merged, nextHeader.Length, body.Length);

        ParseCtx.Pa.HeaderSize = nextHeader.Length;
        ParseCtx.Pa.Size = merged.Length;
        ParseCtx.Pa.HeaderBytes = Encoding.ASCII.GetBytes(nextHeader.Length.ToString());
        ParseCtx.Pa.SizeBytes = Encoding.ASCII.GetBytes(merged.Length.ToString());
        return merged;
    }

    internal static byte[]? GetHeader(string key, byte[] hdr) =>
        NatsMessageHeaders.GetHeader(key, hdr);

    internal static ReadOnlyMemory<byte>? SliceHeader(string key, byte[] hdr) =>
        NatsMessageHeaders.SliceHeader(key, hdr);

    internal static int GetHeaderKeyIndex(string key, byte[] hdr) =>
        NatsMessageHeaders.GetHeaderKeyIndex(key, hdr);

    internal static byte[] SetHeaderStatic(string key, string value, byte[] hdr) =>
        NatsMessageHeaders.SetHeader(key, value, hdr);

    internal bool ProcessServiceImport(object? serviceImport, INatsAccount? acc, byte[] msg)
    {
        _ = serviceImport;
        _ = acc;
        return msg.Length > 0;
    }

    internal void AddSubToRouteTargets(Subscription sub)
    {
        _in.Rts ??= new List<RouteTarget>(8);
        foreach (var rt in _in.Rts)
        {
            if (ReferenceEquals(rt.Sub?.Client, sub.Client))
            {
                if (sub.Queue is { Length: > 0 })
                {
                    rt.Qs = [.. rt.Qs, .. sub.Queue, (byte)' '];
                }
                return;
            }
        }

        var queueBytes = sub.Queue is { Length: > 0 } q ? [.. q, (byte)' '] : Array.Empty<byte>();
        _in.Rts.Add(new RouteTarget { Sub = sub, Qs = queueBytes });
    }

    internal (bool didDeliver, List<byte[]> queueNames) ProcessMsgResults(
        INatsAccount? acc,
        SubscriptionIndexResult? result,
        byte[] msg,
        byte[]? deliver,
        byte[] subject,
        byte[]? reply,
        PmrFlags flags)
    {
        _ = acc;
        _ = deliver;
        _ = flags;

        if (result is null)
            return (false, []);

        var didDeliver = false;
        var queueNames = new List<byte[]>();
        foreach (var sub in result.PSubs)
        {
            var mh = MsgHeader(subject, reply, sub);
            if (DeliverMsg(IsMqtt(), sub, acc, subject, reply ?? Array.Empty<byte>(), mh, msg, false))
                didDeliver = true;
        }

        foreach (var qgroup in result.QSubs)
        {
            if (qgroup.Count == 0)
                continue;
            var sub = qgroup[0];
            if (sub.Queue is { Length: > 0 } q)
                queueNames.Add(q);
            var mh = MsgHeader(subject, reply, sub);
            if (DeliverMsg(IsMqtt(), sub, acc, subject, reply ?? Array.Empty<byte>(), mh, msg, false))
                didDeliver = true;
        }

        return (didDeliver, queueNames);
    }

    internal bool CheckLeafClientInfoHeader(byte[] msg, out byte[] updated)
    {
        updated = msg;
        if (ParseCtx.Pa.HeaderSize <= 0 || msg.Length < ParseCtx.Pa.HeaderSize)
            return false;

        var hdr = msg[..ParseCtx.Pa.HeaderSize];
        var existing = GetHeader(NatsHeaderConstants.JsResponseType, hdr);
        if (existing is null)
            return false;

        updated = SetHeaderInternal(NatsHeaderConstants.JsResponseType, Encoding.ASCII.GetString(existing), msg);
        return true;
    }

    internal void ProcessPingTimer()
    {
        lock (_mu)
        {
            _pingTimer = null;
            if (IsClosed())
                return;

            var opts = Server?.Options;
            var pingInterval = opts?.PingInterval ?? TimeSpan.FromMinutes(2);
            pingInterval = AdjustPingInterval(Kind, pingInterval);

            var sendPing = Kind is ClientKind.Router or ClientKind.Gateway;
            if (!sendPing)
            {
                var needRtt = Rtt == TimeSpan.Zero || DateTime.UtcNow - RttStart > TimeSpan.FromMinutes(1);
                sendPing = DateTime.UtcNow - LastIn >= pingInterval || needRtt;
            }

            if (sendPing)
            {
                var maxPingsOut = opts?.MaxPingsOut ?? 2;
                if (_pingOut + 1 > maxPingsOut)
                {
                    EnqueueProto(Encoding.ASCII.GetBytes(string.Format(ErrProtoFormat, "Stale Connection")));
                    CloseConnection(ClosedState.StaleConnection);
                    return;
                }
                SendPing();
            }

            SetPingTimer();
        }
    }

    internal static TimeSpan AdjustPingInterval(ClientKind kind, TimeSpan value)
    {
        var routeMax = TimeSpan.FromMinutes(1);
        var gatewayMax = TimeSpan.FromMinutes(2);
        return kind switch
        {
            ClientKind.Router when value > routeMax => routeMax,
            ClientKind.Gateway when value > gatewayMax => gatewayMax,
            _ => value,
        };
    }
}