import 'dart:async';
import 'dart:collection';
import 'dart:convert';
import 'dart:io';

import 'package:clide/kernel/src/events/bus.dart';
import 'package:clide/kernel/src/events/types.dart';
import 'package:clide/kernel/src/log.dart';
import 'package:clide/src/cli/argv_dispatch.dart';
import 'package:clide/src/cli/argv_to_request.dart';
import 'package:clide/src/daemon/dispatcher.dart';
import 'package:clide/src/ipc/envelope.dart';
import 'package:clide/src/ipc/paths.dart';
import 'package:clide/src/ipc/schema_v1.dart';

/// Unix-domain IPC server for the running Flutter app.
///
/// First slice of T-99 (D-56 path a). One server per workspace —
/// the socket path is derived from the workspace root per D-70. File
/// perms gate access per D-71 (`0600` socket, `0700` parent). The
/// server's accept loop is multi-connection; dispatch through the
/// supplied [DaemonDispatcher] is serial on the main isolate per
/// D-72. Per-handler isolate offload is the dispatcher / handler's
/// concern, not this layer's.
class IpcServer {
  IpcServer({required this.dispatcher, required this.workspaceRoot, required this.log, this.events, this.replayDepth = 16, this.eventLogDepth = 1024});

  final DaemonDispatcher dispatcher;
  final String workspaceRoot;
  final Logger log;

  /// Bus the server subscribes to for events forwarded to
  /// `clide tail --events` subscribers. Optional — when null, the
  /// tail handler still accepts subscriptions but never gets events
  /// (useful in tests that don't need the full kernel wiring).
  final DaemonBus? events;

  /// Per-subsystem replay-buffer depth (D-6: default 16). New
  /// subscribers receive up to this many recent matching events on
  /// connect so they don't miss effects emitted just before they
  /// subscribed.
  final int replayDepth;

  ServerSocket? _socket;
  String? _socketPath;
  final List<Socket> _clients = [];
  StreamSubscription<Socket>? _accepts;

  // Event streaming (T-129).
  StreamSubscription<DaemonEvent>? _busSub;

  /// Subscribers: client socket → filter (`*` or a subsystem name).
  /// A connection enters this map after it sends `tail --events`.
  final Map<Socket, String> _subscribers = {};

  /// Per-subsystem ring buffer of recent events for replay.
  final Map<String, Queue<IpcEvent>> _replay = {};

  /// Bound on the cursor log that serves `clide events --since` (T-223).
  /// Larger than [replayDepth]: a polling agent reads at its own cadence,
  /// so a deeper window means fewer gaps between polls.
  final int eventLogDepth;

  /// Global, arrival-ordered log of events keyed by a monotonic cursor —
  /// the pull-based read surface (T-223 / D-85). Drop-oldest; never blocks
  /// the producer. [_lastCursor] is the high-water mark handed back as the
  /// next cursor; [_droppedThrough] is the highest evicted cursor, so a pull
  /// whose cursor predates it is told there's a gap rather than silently
  /// missing the dropped events.
  final Queue<_LoggedEvent> _eventLog = Queue<_LoggedEvent>();
  int _lastCursor = 0;
  int _droppedThrough = 0;

  String get socketPath => _socketPath ?? workspaceSocketPath(workspaceRoot);
  bool get isRunning => _socket != null;

  /// Bind the socket and start accepting connections. Idempotent —
  /// a second [start] on the same instance is a no-op.
  ///
  /// Stale sockets left from a crashed previous clide are detected
  /// and unlinked before binding. If a *live* clide is already
  /// listening on the path the bind throws — the caller is the
  /// stale-vs-live arbiter (per D-72 there's one server per
  /// workspace; a colliding live process means a real conflict).
  /// Orphaned sockets from crashed instances of OTHER workspaces are
  /// also swept from the runtime dir on startup (T-247), so the dir
  /// doesn't accumulate dead nodes.
  Future<void> start() async {
    if (isRunning) return;
    final path = workspaceSocketPath(workspaceRoot);
    await _prepareParentDir(path);
    await _sweepStaleSockets(path);
    await _unlinkStale(path);
    final socket = await ServerSocket.bind(InternetAddress(path, type: InternetAddressType.unix), 0);
    try {
      await _chmod(path, 0x180); // 0o600
    } catch (e, st) {
      // chmod failure is fatal — D-71 says perms are the gate.
      await socket.close();
      log.error('ipc', 'chmod 0600 failed on $path', error: e, stackTrace: st);
      rethrow;
    }
    _socket = socket;
    _socketPath = path;
    _accepts = socket.listen(
      _onClient,
      onError: (Object e, StackTrace st) {
        log.error('ipc', 'accept loop error', error: e, stackTrace: st);
      },
    );
    // Subscribe to the bus so we can populate the replay ring AND
    // fan out to live `tail --events` subscribers. Idempotent —
    // we only attach when a bus is supplied.
    final bus = events;
    if (bus != null) {
      _busSub = bus.on<DaemonEvent>().listen(_onBusEvent);
    }
    log.info('ipc', 'IPC server listening at $path');
  }

  /// Close the listening socket, kill any in-flight client
  /// connections, and remove the socket file from disk.
  Future<void> stop() async {
    final s = _socket;
    final path = _socketPath;
    if (s == null) return;
    _socket = null;
    _socketPath = null;
    await _busSub?.cancel();
    _busSub = null;
    _subscribers.clear();
    _replay.clear();
    _eventLog.clear();
    _lastCursor = 0;
    _droppedThrough = 0;
    await _accepts?.cancel();
    _accepts = null;
    for (final c in List<Socket>.from(_clients)) {
      try {
        await c.close();
      } catch (_) {}
    }
    _clients.clear();
    await s.close();
    if (path != null) {
      try {
        final f = File(path);
        if (f.existsSync()) f.deleteSync();
      } catch (e) {
        log.warn('ipc', 'failed to unlink $path: $e');
      }
    }
  }

  void _onClient(Socket client) {
    _clients.add(client);
    unawaited(_serveClient(client));
  }

  /// One read loop per connection: persistent UTF-8 decode, line framing,
  /// and true serial dispatch in a single `await for` (D-72, T-372). The
  /// old async onData handler never paused its subscription — pipelined
  /// requests interleaved mid-handler, the shared StringBuffer could
  /// re-frame while an await was in flight, and per-chunk decode corrupted
  /// runes split across reads.
  Future<void> _serveClient(Socket client) async {
    try {
      await for (final line in client.cast<List<int>>().transform(const Utf8Decoder(allowMalformed: true)).transform(const LineSplitter())) {
        await _handleLine(client, line);
      }
    } catch (e) {
      log.warn('ipc', 'client read error: $e');
    } finally {
      _clients.remove(client);
      _subscribers.remove(client);
    }
  }

  Future<void> _handleLine(Socket client, String line) async {
    final trimmed = line.trim();
    if (trimmed.isEmpty) return;
    IpcResponse response;
    // Tracked across the try so a dispatch failure can be logged against the
    // command that caused it, for log correlation (audit #26 / T-80).
    var reqCmd = '?';
    try {
      final msg = IpcMessage.decode(trimmed);
      if (msg is! IpcRequest) {
        response = IpcResponse.err(
          id: '',
          error: IpcError(code: IpcExitCode.userError, kind: IpcErrorKind.userError, message: 'expected request, got ${msg.runtimeType}'),
        );
      } else {
        // Peel off the `_argv` envelope at the server layer so the
        // streaming check sees the unwrapped command (T-129). Plain
        // typed requests skip this path.
        var req = msg;
        reqCmd = req.cmd;
        if (req.cmd == argvSentinelCmd) {
          final result = unwrapArgvRequest(req);
          if (result is ArgvError) {
            response = result.response;
            // Fall through to write below.
            try {
              client.write('${response.encode()}\n');
              await client.flush();
            } catch (e) {
              log.warn('ipc', 'client write failed: $e');
            }
            return;
          }
          req = (result as ArgvParsed).request;
          reqCmd = req.cmd;
        }
        if (_isTailSubscribe(req)) {
          // Long-lived subscription branch (T-129). Send the streaming
          // ack, replay matching ring buffer entries, register the
          // client. The connection stays open until the client closes.
          await _enterStreamingMode(client, req);
          return;
        }
        response = _isEventsPull(req) ? _eventsSince(req) : await dispatcher.dispatch(req);
      }
    } on FormatException catch (e) {
      response = IpcResponse.err(
        id: '',
        error: IpcError(code: IpcExitCode.userError, kind: IpcErrorKind.userError, message: 'malformed request: ${e.message}'),
      );
    } catch (e, st) {
      log.error('ipc', 'dispatch threw for "$reqCmd"', error: e, stackTrace: st);
      response = IpcResponse.err(
        id: '',
        error: IpcError(code: IpcExitCode.toolError, kind: IpcErrorKind.toolError, message: 'internal error: $e'),
      );
    }
    try {
      client.write('${response.encode()}\n');
      await client.flush();
    } catch (e) {
      log.warn('ipc', 'client write failed: $e');
    }
  }

  Future<void> _prepareParentDir(String socketPath) async {
    final dir = Directory(File(socketPath).parent.path);
    if (!dir.existsSync()) {
      dir.createSync(recursive: true);
    }
    try {
      await _chmod(dir.path, 0x1c0); // 0o700
    } catch (e) {
      log.warn('ipc', 'chmod 0700 on ${dir.path} failed: $e');
    }
  }

  /// Sweep the runtime socket dir for orphaned `*.sock` nodes left by crashed
  /// instances of OTHER workspaces (T-247): probe each, unlink only the dead
  /// ones. A live instance (something answers) or an unresponsive node (could
  /// be a hung instance) is left untouched; the current workspace's own path is
  /// handled by [_unlinkStale]. Best-effort — a sweep failure never blocks our
  /// own startup.
  Future<void> _sweepStaleSockets(String selfPath) async {
    try {
      final dir = Directory(File(selfPath).parent.path);
      if (!dir.existsSync()) return;
      for (final entry in dir.listSync()) {
        if (entry is! File || !entry.path.endsWith('.sock') || entry.path == selfPath) continue;
        try {
          final probe = await Socket.connect(InternetAddress(entry.path, type: InternetAddressType.unix), 0).timeout(const Duration(milliseconds: 200));
          await probe.close(); // live instance — leave it alone
        } on SocketException {
          // No listener — an orphan from a crashed instance. Unlink it.
          try {
            entry.deleteSync();
            log.info('ipc', 'swept orphaned socket ${entry.path}');
          } catch (e) {
            log.warn('ipc', 'failed to sweep ${entry.path}: $e');
          }
        } on TimeoutException {
          // Exists but unresponsive — possibly a hung instance; don't clobber.
        }
      }
    } catch (e) {
      log.warn('ipc', 'socket sweep failed: $e');
    }
  }

  Future<void> _unlinkStale(String path) async {
    final f = File(path);
    if (!f.existsSync()) return;
    // Probe: try connecting. If something answers, refuse to bind.
    try {
      final test = await Socket.connect(InternetAddress(path, type: InternetAddressType.unix), 0).timeout(const Duration(milliseconds: 200));
      await test.close();
      throw StateError('another clide IPC server is already listening on $path');
    } on SocketException {
      // No live listener — safe to unlink the stale node.
      f.deleteSync();
    } on TimeoutException {
      throw StateError('socket $path exists and is unresponsive — refusing to clobber');
    }
  }

  // -- event streaming (T-129) ----------------------------------------------

  /// Recognise the `tail --events [--filter X]` subscription
  /// request that the argv translator (T-125) produces.
  bool _isTailSubscribe(IpcRequest req) {
    if (req.cmd != 'tail') return false;
    final flags = req.args['flags'];
    return flags is Map && flags['events'] == true;
  }

  Future<void> _enterStreamingMode(Socket client, IpcRequest req) async {
    final flags = req.args['flags'] as Map?;
    final filter = (flags?['filter'] as String?) ?? '*';
    // Streaming ack — `data.streaming: true` tells the C client to
    // loop-read instead of exiting after one response.
    final ack = IpcResponse.ok(id: req.id, data: {'streaming': true, 'filter': filter});
    try {
      client.write('${ack.encode()}\n');
      await client.flush();
    } catch (e) {
      log.warn('ipc', 'streaming ack write failed: $e');
      return;
    }
    // Replay matching events from the ring.
    final replay = _replayFor(filter);
    for (final ev in replay) {
      if (!_sendEvent(client, ev)) return;
    }
    _subscribers[client] = filter;
  }

  Iterable<IpcEvent> _replayFor(String filter) {
    if (filter == '*') {
      // Flatten everything in arrival order. Per-subsystem rings
      // preserve order within a subsystem; across subsystems the
      // ordering is best-effort (interleaved-by-subsystem). Good
      // enough for "what just happened".
      return _replay.values.expand((q) => q);
    }
    return _replay[filter] ?? const [];
  }

  // -- event pull (T-223) ---------------------------------------------------

  /// `clide events [--since <cursor>] [--filter X]` — a one-shot, cursor-based
  /// read of the event log, the request/response complement to the
  /// never-returning `tail --events` stream.
  bool _isEventsPull(IpcRequest req) => req.cmd == 'events';

  /// Build the pull response: every logged event with cursor > `since`
  /// (optionally filtered by subsystem), the high-water `cursor` to poll
  /// from next, and `gap: true` when `since` predates the retained window
  /// (events between `since` and the oldest retained entry were dropped).
  IpcResponse _eventsSince(IpcRequest req) {
    final flags = req.args['flags'];
    final flagMap = flags is Map ? flags : const {};
    final filter = (flagMap['filter'] as String?) ?? '*';
    final since = _parseSince(flagMap['since']);
    if (since == null) {
      return IpcResponse.err(
        id: req.id,
        error: IpcError(code: IpcExitCode.userError, kind: IpcErrorKind.userError, message: '--since must be a non-negative integer cursor'),
      );
    }
    final out = <Map<String, Object?>>[];
    for (final logged in _eventLog) {
      if (logged.cursor <= since) continue;
      if (filter != '*' && logged.event.subsystem != filter) continue;
      out.add({...logged.event.toJson(), 'cursor': logged.cursor});
    }
    // A gap only means something when the caller had a prior position
    // (since > 0); a first read (since 0) just gets whatever's retained.
    final gap = since > 0 && since < _droppedThrough;
    return IpcResponse.ok(
      id: req.id,
      data: {'events': out, 'cursor': _lastCursor, 'gap': gap, if (gap) 'oldestCursor': _eventLog.isEmpty ? _lastCursor : _eventLog.first.cursor},
    );
  }

  /// Parse the `--since` flag (a string from argv or an int from a typed
  /// request). Null on an invalid (non-integer / negative) value; absent
  /// means 0 (read from the beginning of the retained window).
  int? _parseSince(Object? raw) {
    if (raw == null) return 0;
    if (raw is int) return raw < 0 ? null : raw;
    final n = int.tryParse('$raw');
    return (n == null || n < 0) ? null : n;
  }

  void _onBusEvent(DaemonEvent e) {
    final ev = IpcEvent(subsystem: e.subsystem, kind: e.kind, data: e.data, timestamp: e.ts);
    // Push to replay ring.
    final ring = _replay.putIfAbsent(e.subsystem, () => Queue<IpcEvent>());
    ring.addLast(ev);
    while (ring.length > replayDepth) {
      ring.removeFirst();
    }
    // Push to the cursor log (T-223). Drop-oldest; record the highest
    // evicted cursor so a later `--since` below it reports a gap.
    final cursor = ++_lastCursor;
    _eventLog.addLast(_LoggedEvent(cursor, ev));
    while (_eventLog.length > eventLogDepth) {
      _droppedThrough = _eventLog.removeFirst().cursor;
    }
    // Fan out to live subscribers whose filter matches.
    final stale = <Socket>[];
    for (final entry in _subscribers.entries) {
      final filter = entry.value;
      if (filter != '*' && filter != e.subsystem) continue;
      if (!_sendEvent(entry.key, ev)) {
        stale.add(entry.key);
      }
    }
    for (final s in stale) {
      _subscribers.remove(s);
    }
  }

  /// Write an event line to [client]. Returns false on failure, which
  /// the caller uses to drop the subscriber. We deliberately don't
  /// await `flush` here — back-pressure handling per D-72: if the
  /// socket's write buffer is full, dart:io's Socket.write enqueues
  /// in-memory, and the kernel pushes through as it can. If the
  /// client is genuinely gone the write throws or onDone fires and
  /// the subscriber gets removed via _onClient's onDone.
  bool _sendEvent(Socket client, IpcEvent ev) {
    try {
      client.write('${ev.encode()}\n');
      return true;
    } catch (e) {
      log.warn('ipc', 'subscriber write failed (dropping): $e');
      return false;
    }
  }

  // -- internals ------------------------------------------------------------

  /// `chmod` via `chmod(1)` because dart:io doesn't expose the
  /// syscall on unix. Cheap; only runs at start/stop. No-op on
  /// Windows: POSIX modes don't exist there, and the socket lives
  /// under `%LOCALAPPDATA%`, whose per-user ACL already provides the
  /// user-only gate D-71 wants.
  Future<void> _chmod(String path, int modeBits) async {
    if (Platform.isWindows) return;
    final octal = modeBits.toRadixString(8).padLeft(3, '0');
    final r = await Process.run('chmod', [octal, path]);
    if (r.exitCode != 0) {
      throw ProcessException('chmod', [octal, path], r.stderr.toString(), r.exitCode);
    }
  }
}

/// One entry in the cursor log (T-223): an [IpcEvent] tagged with the
/// monotonic [cursor] assigned when it was recorded.
class _LoggedEvent {
  _LoggedEvent(this.cursor, this.event);
  final int cursor;
  final IpcEvent event;
}