import 'package:flutter/foundation.dart';
import 'package:package_info_plus/package_info_plus.dart';

/// Single source of truth for the app's identity shown inside the running app.
///
/// **Source of truth** for the version numbers is the `version:` field in
/// `pubspec.yaml` (e.g. `1.0.0+1`). At runtime we read that value via
/// `package_info_plus`, which Flutter populates from `pubspec.yaml` *unless*
/// overridden at build time with `--build-name` / `--build-number`.
///
/// If `package_info_plus` cannot resolve the values (e.g. running in a unit
/// test that hasn't initialised the plugin platform), we fall back to the
/// [fallbackVersion] constant. Keep that constant in sync with `pubspec.yaml`
/// when you bump versions; the release process described in
/// `docs/RELEASING.md` owns that update.
class AppInfo {
  AppInfo._();

  /// Hard-coded fallback. Must mirror the `version:` field in `pubspec.yaml`.
  /// Format: `MAJOR.MINOR.PATCH+BUILD`.
  static const String fallbackVersion = '1.0.0+1';

  /// Cached result so we only hit the platform once.
  static PackageInfo? _cached;

  /// Asynchronously loads the package info, caching the result.
  static Future<PackageInfo> _load() async {
    return _cached ??= await PackageInfo.fromPlatform();
  }

  /// Resolves the build version in the form `MAJOR.MINOR.PATCH+BUILD`
  /// (e.g. `1.0.0+1`). Falls back to [fallbackVersion] on error.
  static Future<String> versionString() async {
    try {
      final info = await _load();
      final name = info.version.isEmpty ? '0.0.0' : info.version;
      final build = info.buildNumber.isEmpty ? '0' : info.buildNumber;
      return '$name+$build';
    } catch (e, st) {
      debugPrint('AppInfo.versionString() fell back to constant: $e\n$st');
      return fallbackVersion;
    }
  }

  /// The user-facing `MAJOR.MINOR.PATCH` portion (e.g. `1.0.0`).
  static Future<String> versionName() async {
    try {
      final info = await _load();
      return info.version.isEmpty ? '0.0.0' : info.version;
    } catch (_) {
      // Extract the part before the '+' from the fallback.
      return fallbackVersion.split('+').first;
    }
  }

  /// The monotonically increasing `+BUILD` portion (e.g. `1`).
  static Future<String> buildNumber() async {
    try {
      final info = await _load();
      return info.buildNumber.isEmpty ? '0' : info.buildNumber;
    } catch (_) {
      return fallbackVersion.split('+').last;
    }
  }
}