// Enforces the layering. A convention nobody checks is a convention that
// decays, so these read the real import statements in lib/ and fail on a
// violation rather than trusting review to catch it.
//
// The rule, in one line: dependencies point inward. ui → domain ← data, and
// never the reverse.

import 'dart:io';

import 'package:flutter_test/flutter_test.dart';

void main() {
  group('layering', () {
    test('domain imports no Flutter at all', () {
      final offenders = _importsMatching(
        'lib/domain',
        (import) => import.startsWith('package:flutter/'),
      );
      expect(
        offenders,
        isEmpty,
        reason: 'The domain layer must stay pure Dart so it can be reused '
            'without a Flutter runtime. Offending imports:\n'
            '${_render(offenders)}',
      );
    });

    test('domain does not depend on data or ui', () {
      final offenders = _importsMatching(
        'lib/domain',
        (import) =>
            import.contains('/data/') ||
            import.contains('/ui/') ||
            import.contains('main.dart'),
      );
      expect(offenders, isEmpty,
          reason: 'The domain layer is the innermost layer; it may depend on '
              'nothing else in this package.\n${_render(offenders)}');
    });

    test('data does not depend on ui', () {
      final offenders = _importsMatching(
        'lib/data',
        (import) => import.contains('/ui/') || import.contains('main.dart'),
      );
      expect(offenders, isEmpty,
          reason: 'The data layer must not know about presentation.\n'
              '${_render(offenders)}');
    });

    test('data imports no Flutter widget libraries', () {
      // flutter/services is allowed: MethodChannel lives there, and that is
      // the whole reason this layer is Flutter-aware at all.
      const allowed = {'package:flutter/services.dart'};
      final offenders = _importsMatching(
        'lib/data',
        (import) =>
            import.startsWith('package:flutter/') && !allowed.contains(import),
      );
      expect(
        offenders,
        isEmpty,
        reason: 'The data layer may import package:flutter/services.dart only. '
            'Anything else drags presentation into the transport.\n'
            '${_render(offenders)}',
      );
    });

    test('ui does not depend on a concrete data implementation', () {
      // The UI talks to Iperf3Runner. main.dart is the composition root and is
      // the one file allowed to name an implementation.
      final offenders = _importsMatching(
        'lib/ui',
        (import) => import.contains('/data/'),
      );
      expect(
        offenders,
        isEmpty,
        reason: 'Presentation must depend on domain/services/iperf3_runner.dart '
            'rather than on a transport. Only main.dart may pick an '
            'implementation.\n${_render(offenders)}',
      );
    });

    test('every layer directory is actually covered by these rules', () {
      // Guards against a new top-level layer appearing and silently escaping
      // every rule above.
      final layers = Directory('lib')
          .listSync()
          .whereType<Directory>()
          .map((d) => d.path.split(Platform.pathSeparator).last)
          .toSet();
      expect(
        layers,
        equals({'domain', 'data', 'ui'}),
        reason: 'A new layer appeared under lib/. Add rules for it here.',
      );
    });
  });
}

/// Every `(file, import)` pair under [directory] whose import satisfies [test].
List<({String file, String import})> _importsMatching(
  String directory,
  bool Function(String import) test,
) {
  final results = <({String file, String import})>[];
  final dir = Directory(directory);
  if (!dir.existsSync()) return results;

  final pattern = RegExp(r'''^\s*import\s+['"]([^'"]+)['"]''', multiLine: true);
  for (final entity in dir.listSync(recursive: true)) {
    if (entity is! File || !entity.path.endsWith('.dart')) continue;
    final source = entity.readAsStringSync();
    for (final match in pattern.allMatches(source)) {
      final import = match.group(1)!;
      if (test(import)) {
        results.add((file: entity.path, import: import));
      }
    }
  }
  return results;
}

String _render(List<({String file, String import})> offenders) =>
    offenders.map((o) => '  ${o.file} → ${o.import}').join('\n');