import 'dart:async';
import 'dart:developer' as developer;

import 'package:flutter/services.dart';
import 'package:iperf3gui/domain/models/iperf3_event.dart';
import 'package:iperf3gui/domain/models/iperf3_result.dart';
import 'package:iperf3gui/domain/models/test_configuration.dart';
import 'package:iperf3gui/domain/services/iperf3_runner.dart';

/// [Iperf3Runner] backed by the native iperf3 library over a MethodChannel.
///
/// On Android, iperf3 is compiled into the app as a shared library (.so).
/// This avoids SELinux restrictions on executing ELF binaries from assets.
///
/// The service talks to the native layer over a MethodChannel. The test runs
/// in `--json-stream` mode, so each native report arrives as one JSON object;
/// they are parsed and published on [events] while the test runs. [run]
/// resolves once the native layer reports completion, carrying the raw JSON
/// lines as the result's output.
class Iperf3Service implements Iperf3Runner {
  Iperf3Service() {
    _channel.setMethodCallHandler(_handleNativeCall);
  }

  /// A channel's handler is keyed by channel name in the binary messenger, so
  /// it is process-global: constructing a second instance would take the
  /// handler away from the first. The app composes exactly one, in main().
  final MethodChannel _channel = const MethodChannel(_channelName);

  static const String _channelName = 'com.novoyuuparosk.iperf3gui/iperf';

  /// Exit code reported when the native layer signalled an error.
  static const int exitCodeNativeError = 1;

  /// Exit code reported when another test is already in flight.
  static const int exitCodeBusy = -2;

  /// Exit code reported when the test could not be started at all.
  static const int exitCodeStartFailed = -1;

  /// Exit code reported when the native layer never signalled completion.
  static const int exitCodeTimeout = -3;

  /// Events parsed from the native layer during the current run.
  final StreamController<Iperf3Event> _eventController =
      StreamController<Iperf3Event>.broadcast();

  /// Live reports, one event per native report. Use this to render progress.
  @override
  Stream<Iperf3Event> get events => _eventController.stream;

  /// Raw JSON lines received during the current (or most recent) run.
  final List<String> _rawLines = [];

  /// Completer that resolves when the native iperf3 test finishes.
  Completer<Iperf3Result>? _runCompleter;

  /// Whether iperf3 is currently running.
  bool _isRunning = false;
  @override
  bool get isRunning => _isRunning;

  /// Whether the native layer reported an error during this run.
  bool _sawError = false;

  /// Whether [stop] was called for the current run.
  bool _stopRequested = false;

  /// Cancel any running test.
  @override
  Future<void> stop() async {
    if (!_isRunning) return;
    _stopRequested = true;
    try {
      await _channel.invokeMethod('stopIperf');
    } catch (e) {
      _log('Iperf3Service: error stopping: $e');
    }
  }

  /// Release the stream controller. Call from the owner's dispose().
  @override
  Future<void> dispose() async {
    _channel.setMethodCallHandler(null);
    await _eventController.close();
  }

  /// Run iperf3 with the given configuration.
  ///
  /// Returns an [Iperf3Result] with the full output and an exit code.
  @override
  Future<Iperf3Result> run(TestConfiguration config) async {
    if (_isRunning) {
      return const Iperf3Result(
        rawOutput: 'Another test is already running.',
        exitCode: exitCodeBusy,
      );
    }

    _isRunning = true;
    _sawError = false;
    _stopRequested = false;
    _rawLines.clear();

    final args = config.toCliArgs();
    _log('Iperf3Service: running: ${args.join(" ")}');

    final completer = Completer<Iperf3Result>();
    _runCompleter = completer;

    try {
      await _channel.invokeMethod('runIperf', {'args': args});
    } catch (e, stackTrace) {
      _log('Iperf3Service exception: $e');
      _log('Iperf3Service stack: $stackTrace');
      _finishRun();
      return Iperf3Result(
        rawOutput: 'Error starting iperf3: $e',
        exitCode: exitCodeStartFailed,
      );
    }

    // Wait for the native layer to signal completion. The grace period covers
    // DNS resolution and the 30s native connect timeout.
    try {
      return await completer.future.timeout(
        config.duration + const Duration(seconds: 45),
        onTimeout: () {
          _log('Iperf3Service: timeout, stopping test');
          // Ask the native layer to wind down, then release local state so a
          // stuck run can never lock the UI out of starting another test.
          _channel.invokeMethod('stopIperf').catchError((Object e) {
            _log('Iperf3Service: error stopping after timeout: $e');
            return null;
          });
          _publish(const Iperf3Error('Timed out waiting for iperf3 to finish.'));
          return Iperf3Result(
            rawOutput: _rawOutput(),
            exitCode: exitCodeTimeout,
          );
        },
      );
    } catch (e) {
      _log('Iperf3Service: error waiting for completion: $e');
      return Iperf3Result(
        rawOutput: 'Test failed: $e',
        exitCode: exitCodeStartFailed,
      );
    } finally {
      _finishRun();
    }
  }

  /// Handle a callback pushed up from the Kotlin/JNI layer.
  Future<void> _handleNativeCall(MethodCall call) async {
    switch (call.method) {
      case 'onOutput':
        final output = call.arguments['output'] as String?;
        if (output != null) {
          _rawLines.add(output);
          final event = Iperf3Event.parse(output);
          // iperf3 reports a failed test as an `error` event rather than a
          // non-zero return, so this is where most failures surface.
          if (event is Iperf3Error) _sawError = true;
          _publish(event);
        }
      case 'onError':
        final error = call.arguments['error'] as String?;
        if (error != null) {
          // Not terminal on its own — iperf3 reports the failure reason and
          // then completes, so wait for onComplete before resolving.
          _sawError = true;
          _publish(Iperf3Error(error));
        }
      case 'onComplete':
        _log('Iperf3Service: test completed');
        final completer = _runCompleter;
        if (completer != null && !completer.isCompleted) {
          completer.complete(
            Iperf3Result(
              rawOutput: _rawOutput(),
              // A user-requested stop is a normal outcome, not a failure.
              exitCode:
                  (_sawError && !_stopRequested) ? exitCodeNativeError : 0,
              stopped: _stopRequested,
            ),
          );
        }
      default:
        _log('Iperf3Service: unhandled native call ${call.method}');
    }
  }

  void _publish(Iperf3Event event) {
    if (!_eventController.isClosed) {
      _eventController.add(event);
    }
  }

  /// The raw JSON stream as received, one event per line.
  String _rawOutput() => _rawLines
      .map((line) => line.endsWith('\n') ? line : '$line\n')
      .join();

  void _finishRun() {
    _isRunning = false;
    _runCompleter = null;
  }
}

void _log(String message) =>
    developer.log(message, name: 'Iperf3Service');