import 'dart:typed_data';

import 'native_ocr_backend.dart';
import 'ocr_backend.dart';
import 'onnx_recognition_backend.dart';

/// Selects and caches the active local OCR backend.
///
/// Preference order: the embedded ONNX recognition backend if its model is
/// bundled and loads, otherwise the native platform backend, otherwise none.
class OcrBackends {
  OcrBackends._();

  static OcrBackend? _active;
  static bool _resolved = false;

  /// Resolve (once) and return the preferred available backend, or null when
  /// no backend is available on this device/build.
  static Future<OcrBackend?> active() async {
    if (_resolved) return _active;

    final candidates = <OcrBackend>[
      OnnxRecognitionBackend(),
      NativeOcrBackend(),
    ];

    for (final backend in candidates) {
      if (await backend.isAvailable()) {
        _active = backend;
        break;
      }
    }

    _resolved = true;
    return _active;
  }

  /// Recognize text using the active backend. Returns null when no backend is
  /// available or nothing was recognized.
  static Future<String?> recognize(Uint8List png) async {
    final backend = await active();
    if (backend == null) return null;
    return backend.recognize(png);
  }
}