// Copyright 2012-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Adapted from server/server.go in the NATS server Go source.

using System.Collections.Concurrent;
using System.Threading.Channels;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using ZB.MOM.NatsNet.Server.Auth;
using ZB.MOM.NatsNet.Server.Auth.Ocsp;
using ZB.MOM.NatsNet.Server.Internal;
using ZB.MOM.NatsNet.Server.Internal.DataStructures;
using ZB.MOM.NatsNet.Server.WebSocket;

namespace ZB.MOM.NatsNet.Server;

/// <summary>
/// The core NATS server class.
/// Mirrors Go <c>Server</c> struct in server/server.go.
/// Session 09: initialization, configuration, and account management.
/// Sessions 10-23 add further capabilities as partial class files.
/// </summary>
public sealed partial class NatsServer : INatsServer
{
    // =========================================================================
    // Build-time stamps (mirrors package-level vars in server.go)
    // =========================================================================

    /// <summary>
    /// Binary-stamped trusted operator keys (space-separated NKey public keys).
    /// In Go this is a package-level var that can be overridden at build time.
    /// In .NET it can be set before constructing any server instance.
    /// Mirrors Go package-level <c>trustedKeys</c> var.
    /// </summary>
    public static string StampedTrustedKeys { get; set; } = string.Empty;

    // =========================================================================
    // Atomic counters (mirrors fields accessed with atomic operations)
    // =========================================================================

    private ulong   _gcid;                          // global client id counter
    private long    _pinnedAccFail;                 // pinned-account auth failures
    private int     _activeAccounts;                // number of active accounts

    // =========================================================================
    // Stats (embedded Go structs: stats, scStats, staleStats)
    // =========================================================================

    private readonly ServerStats          _stats        = new();
    private readonly SlowConsumerStats    _scStats      = new();
    private readonly InternalStaleStats   _staleStats   = new();

    // =========================================================================
    // Core identity
    // =========================================================================

    // kp / xkp are NKey keypairs — represented as byte arrays here.
    // Full crypto operations deferred to auth session.
    private byte[]? _kpSeed;                        // server NKey seed
    private string  _pub   = string.Empty;          // server public key (server ID)
    private byte[]? _xkpSeed;                       // x25519 key seed
    private string  _xpub  = string.Empty;          // x25519 public key

    // =========================================================================
    // Server info (wire protocol)
    // =========================================================================

    private readonly ReaderWriterLockSlim _mu       = new(LockRecursionPolicy.SupportsRecursion);
    private readonly ReaderWriterLockSlim _reloadMu = new(LockRecursionPolicy.SupportsRecursion);
    internal         ServerInfo           _info     = new();
    private          string               _configFile = string.Empty;

    // =========================================================================
    // Options (protected by _optsMu)
    // =========================================================================

    private readonly ReaderWriterLockSlim _optsMu = new(LockRecursionPolicy.NoRecursion);
    private          ServerOptions        _opts;

    // =========================================================================
    // Running / shutdown state
    // =========================================================================

    private          int  _running;   // 1 = running, 0 = not (Interlocked)
    private          int  _shutdown;  // 1 = shutting down
    private readonly CancellationTokenSource _quitCts = new();
    private readonly TaskCompletionSource    _startupComplete   = new(TaskCreationOptions.RunContinuationsAsynchronously);
    private readonly TaskCompletionSource    _shutdownComplete  = new(TaskCreationOptions.RunContinuationsAsynchronously);
    private          Task?                   _quitTask;

    // =========================================================================
    // Listeners (forward-declared stubs — fully wired in session 10)
    // =========================================================================

    private System.Net.Sockets.TcpListener? _listener;
    private Exception?                       _listenerErr;

    // HTTP monitoring listener
    private System.Net.Sockets.TcpListener? _http;

    // Route listener
    private System.Net.Sockets.TcpListener? _routeListener;
    private Exception?                       _routeListenerErr;

    // Gateway listener
    private System.Net.Sockets.TcpListener? _gatewayListener;
    private Exception?                       _gatewayListenerErr;

    // Leaf-node listener
    private System.Net.Sockets.TcpListener? _leafNodeListener;
    private Exception?                       _leafNodeListenerErr;

    // Profiling listener
    private System.Net.Sockets.TcpListener? _profiler;

    // Accept-loop done channel — each accept loop sends true when it exits.
    private readonly System.Threading.Channels.Channel<bool> _done =
        System.Threading.Channels.Channel.CreateUnbounded<bool>();

    // Lame-duck channel — created in lameDuckMode, receives one signal per accept loop.
    private System.Threading.Channels.Channel<bool>? _ldmCh;

    // The no-auth user that only the system account can use (auth session).
    private string _sysAccOnlyNoAuthUser = string.Empty;

    // =========================================================================
    // Accounts
    // =========================================================================

    private          Account?                 _gacc;           // global account
    private          Account?                 _sysAccAtomic;   // system account (atomic)
    private readonly ConcurrentDictionary<string, Account> _accounts    = new(StringComparer.Ordinal);
    private readonly ConcurrentDictionary<string, Account> _tmpAccounts = new(StringComparer.Ordinal);
    private          IAccountResolver?        _accResolver;
    private          InternalState?           _sys;            // system messaging state

    // =========================================================================
    // Client/route/leaf tracking
    // =========================================================================

    private readonly Dictionary<ulong, ClientConnection> _clients      = [];
    private readonly Dictionary<ulong, ClientConnection> _leafs        = [];
    private          Dictionary<string, List<ClientConnection>> _routes = [];
    private          int   _routesPoolSize    = 1;
    private          bool  _routesReject;
    private          int   _routesNoPool;
    private          Dictionary<string, Dictionary<string, ClientConnection>>? _accRoutes;
    private readonly ConcurrentDictionary<string, object?> _accRouteByHash = new(StringComparer.Ordinal);
    private          Channel<struct_>?  _accAddedCh;            // stub
    private          string             _accAddedReqId = string.Empty;

    // =========================================================================
    // User / nkey maps
    // =========================================================================

    private Dictionary<string, Auth.User>?     _users;
    private Dictionary<string, Auth.NkeyUser>? _nkeys;

    // =========================================================================
    // Connection tracking
    // =========================================================================

    private ulong            _totalClients;
    private ClosedRingBuffer _closed = new(0);
    private DateTime         _start;
    private DateTime         _configTime;

    // =========================================================================
    // Goroutine / WaitGroup tracking
    // =========================================================================

    private readonly object        _grMu         = new();
    private          bool          _grRunning;
    private readonly Dictionary<ulong, ClientConnection> _grTmpClients = [];
    private readonly WaitGroup _grWg = new();

    // =========================================================================
    // Cluster name (separate lock)
    // =========================================================================

    private readonly ReaderWriterLockSlim _cnMu = new(LockRecursionPolicy.NoRecursion);
    private          string               _cn   = string.Empty;
    private          ServerInfo           _routeInfo = new();
    private          bool                 _leafNoCluster;
    private          bool                 _leafNodeEnabled;
    private          bool                 _leafDisableConnect;
    private          bool                 _ldm;

    // =========================================================================
    // Trusted keys
    // =========================================================================

    private List<string>?            _trustedKeys;
    private HashSet<string>          _strictSigningKeyUsage = [];

    // =========================================================================
    // Monitoring / stats endpoint
    // =========================================================================

    private          string             _httpBasePath = string.Empty;
    private readonly Dictionary<string, ulong> _httpReqStats = [];
    private          object?            _httpHandler;

    // =========================================================================
    // Client connect URLs
    // =========================================================================

    private readonly List<string>        _clientConnectUrls  = [];
    private readonly RefCountedUrlSet    _clientConnectUrlsMap = new();

    // =========================================================================
    // Gateway / Websocket / MQTT / OCSP stubs
    // =========================================================================

    private readonly SrvGateway         _gateway    = new();
    private readonly SrvWebsocket       _websocket  = new();
    private readonly SrvMqtt            _mqtt       = new();
    private          OcspMonitor[]?     _ocsps;
    private          bool               _ocspPeerVerify;
    private          IOcspResponseCache? _ocsprc;

    // =========================================================================
    // Gateway reply map (stub — session 16)
    // =========================================================================

    private readonly SubscriptionIndex _gwLeafSubs;

    // =========================================================================
    // NUID event ID generator
    // =========================================================================

    // Replaced by actual NUID in session 10. Use Guid for now.
    private string NextEventId() => Guid.NewGuid().ToString("N");

    // =========================================================================
    // Various stubs
    // =========================================================================

    private readonly List<string>    _leafRemoteCfgs = [];        // stub — session 15
    private readonly List<object>    _proxiesKeyPairs = [];       // stub — session 09 (proxies)
    private readonly Dictionary<string, Dictionary<ulong, ClientConnection>> _proxiedConns = [];
    private          long            _cproto;                     // count of INFO-capable clients
    private readonly ConcurrentDictionary<string, object?> _nodeToInfo = new(StringComparer.Ordinal);
    private readonly ConcurrentDictionary<string, object?> _raftNodes  = new(StringComparer.Ordinal);
    private          JetStream?            _jetStream;
    private readonly Lock                  _resourceErrorLock = new();
    private          DateTime              _resourceErrorLastUtc;
    private readonly Dictionary<string, string>  _routesToSelf          = [];
    private          string                       _routeTlsName          = string.Empty;
    private          INetResolver?               _routeResolver;
    private readonly ConcurrentDictionary<string, object?> _rateLimitLogging = new();
    private readonly Channel<TimeSpan>           _rateLimitLoggingCh;
    private          RateCounter?                _connRateCounter;

    // GW reply map expiration
    private readonly ConcurrentDictionary<string, object?> _gwrm = new();

    // Catchup bytes
    private readonly ReaderWriterLockSlim _gcbMu = new(LockRecursionPolicy.NoRecursion);
    private          long _gcbOut;
    private          long _gcbOutMax;
    private readonly Channel<struct_>? _gcbKick; // stub

    // Sync-out semaphore
    private readonly SemaphoreSlim _syncOutSem;
    private const int MaxConcurrentSyncRequests = 16;

    // =========================================================================
    // Logging
    // =========================================================================

    private ILogger _logger = NullLogger.Instance;
    private int     _traceEnabled;
    private int     _debugEnabled;
    private int     _traceSysAcc;

    // =========================================================================
    // INatsServer implementation
    // =========================================================================

    /// <inheritdoc/>
    public ulong NextClientId() => Interlocked.Increment(ref _gcid);

    /// <inheritdoc/>
    public ServerOptions Options => GetOpts();

    /// <inheritdoc/>
    public bool TraceEnabled => Interlocked.CompareExchange(ref _traceEnabled, 0, 0) != 0;

    /// <inheritdoc/>
    public bool TraceSysAcc => Interlocked.CompareExchange(ref _traceSysAcc, 0, 0) != 0;

    /// <inheritdoc/>
    public ILogger Logger => _logger;

    /// <inheritdoc/>
    public void DecActiveAccounts() => Interlocked.Decrement(ref _activeAccounts);

    /// <inheritdoc/>
    public void IncActiveAccounts() => Interlocked.Increment(ref _activeAccounts);

    // =========================================================================
    // Logging helpers (mirrors Go s.Debugf / s.Noticef / s.Warnf / s.Errorf)
    // =========================================================================

    internal void Debugf(string fmt, params object?[] args)  => _logger.LogDebug(fmt, args);
    internal void Noticef(string fmt, params object?[] args) => _logger.LogInformation(fmt, args);
    internal void Warnf(string fmt, params object?[] args)   => _logger.LogWarning(fmt, args);
    internal void Errorf(string fmt, params object?[] args)  => _logger.LogError(fmt, args);
    internal void Fatalf(string fmt, params object?[] args)  => _logger.LogCritical(fmt, args);

    // =========================================================================
    // Constructor
    // =========================================================================

    /// <summary>
    /// Direct constructor — do not call directly; use <see cref="NewServer(ServerOptions)"/>.
    /// </summary>
    private NatsServer(ServerOptions opts)
    {
        _opts             = opts;
        _gwLeafSubs       = SubscriptionIndex.NewSublistWithCache();
        _rateLimitLoggingCh = Channel.CreateBounded<TimeSpan>(1);
        _syncOutSem       = new SemaphoreSlim(MaxConcurrentSyncRequests, MaxConcurrentSyncRequests);
    }
}

// Placeholder struct for stub channel types
internal readonly struct struct_ { }