import 'dart:async';

import 'package:build/build.dart';

Builder appInfoBuilder(BuilderOptions options) => _AppInfoBuilder();

class _AppInfoBuilder implements Builder {
  @override
  Map<String, List<String>> get buildExtensions => const {
        r'$package$': ['lib/app_info.g.dart'],
      };

  @override
  Future<void> build(BuildStep buildStep) async {
    final pkg = buildStep.inputId.package;
    final raw = await buildStep.readAsString(AssetId(pkg, 'pubspec.yaml'));
    final match =
        RegExp(r'^version:\s*([^\s#]+)', multiLine: true).firstMatch(raw);
    final combined = match?.group(1) ?? '0.0.0+0';
    final plus = combined.indexOf('+');
    final version = plus < 0 ? combined : combined.substring(0, plus);
    final buildNumber =
        plus < 0 ? 0 : int.tryParse(combined.substring(plus + 1)) ?? 0;

    final enableFfmpeg = _readUxFlag(raw, 'enable_ffmpeg');

    await buildStep.writeAsString(
      AssetId(pkg, 'lib/app_info.g.dart'),
      '''
// GENERATED by build_runner from pubspec.yaml — do not edit.
import 'package:ux/ux.dart';

const kAppInfo = AppInfo(version: '$version', buildNumber: $buildNumber);

/// Mirrors the app's `ux: enable_ffmpeg` pubspec setting as a compile-time
/// constant. Gate FFmpeg-dependent code (e.g. registerFfmpegLicense()) on
/// this — pubspec stays the single source of truth.
const kUxEnableFfmpeg = $enableFfmpeg;
''',
    );
  }

  /// Reads a boolean under the top-level `ux:` mapping, e.g. `ux: { $key: ... }`.
  /// Scans manually (no YAML dep) and ignores the indented `ux:` dependency
  /// entry by only entering the block on a non-indented `ux:` line.
  static bool _readUxFlag(String pubspec, String key) {
    var inUxBlock = false;
    var enabled = false;
    for (final rawLine in pubspec.split('\n')) {
      final hash = rawLine.indexOf('#');
      final line = hash >= 0 ? rawLine.substring(0, hash) : rawLine;
      if (line.trim().isEmpty) continue;
      final indented = line.startsWith(' ') || line.startsWith('\t');
      if (!indented) {
        inUxBlock = line.trimRight() == 'ux:' || line.startsWith('ux:');
      } else if (inUxBlock) {
        final t = line.trim();
        if (t.startsWith('$key:')) {
          enabled = t.substring(key.length + 1).trim().toLowerCase() == 'true';
        }
      }
    }
    return enabled;
  }
}