import 'dart:async';

import 'package:flutter/material.dart';
import 'package:mobile_scanner/mobile_scanner.dart';
import 'package:mobile_scanner_example/picklist/classes/barcode_at_center.dart';

import 'package:mobile_scanner_example/picklist/widgets/crosshair.dart';
import 'package:mobile_scanner_example/scanner_error_widget.dart';

class BarcodeScannerPicklist extends StatefulWidget {
  const BarcodeScannerPicklist({super.key});

  @override
  State<BarcodeScannerPicklist> createState() => _BarcodeScannerPicklistState();
}

class _BarcodeScannerPicklistState extends State<BarcodeScannerPicklist>
    with WidgetsBindingObserver {
  final _mobileScannerController = MobileScannerController(
    autoStart: false,
  );
  StreamSubscription<Object?>? _barcodesSubscription;

  final _scannerEnabled = ValueNotifier(true);

  bool barcodeDetected = false;

  @override
  void initState() {
    WidgetsBinding.instance.addObserver(this);
    _barcodesSubscription = _mobileScannerController.barcodes.listen(
      _handleBarcodes,
    );
    super.initState();
    unawaited(_mobileScannerController.start());
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (!_mobileScannerController.value.isInitialized) {
      return;
    }

    switch (state) {
      case AppLifecycleState.detached:
      case AppLifecycleState.hidden:
      case AppLifecycleState.paused:
        return;
      case AppLifecycleState.resumed:
        _barcodesSubscription =
            _mobileScannerController.barcodes.listen(_handleBarcodes);

        unawaited(_mobileScannerController.start());
      case AppLifecycleState.inactive:
        unawaited(_barcodesSubscription?.cancel());
        _barcodesSubscription = null;
        unawaited(_mobileScannerController.stop());
    }
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    unawaited(_barcodesSubscription?.cancel());
    _barcodesSubscription = null;
    super.dispose();
    _mobileScannerController.dispose();
  }

  void _handleBarcodes(BarcodeCapture capture) {
    if (!_scannerEnabled.value) {
      return;
    }

    for (final barcode in capture.barcodes) {
      if (isBarcodeAtCenterOfImage(
        cameraOutputSize: _mobileScannerController.value.size,
        barcode: barcode,
      )) {
        if (!barcodeDetected) {
          barcodeDetected = true;
          Navigator.of(context).pop(barcode);
        }
        return;
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Picklist scanner')),
      backgroundColor: Colors.black,
      body: StreamBuilder(
        stream: _mobileScannerController.barcodes,
        builder: (context, snapshot) {
          return Listener(
            behavior: HitTestBehavior.opaque,
            onPointerDown: (_) => _scannerEnabled.value = false,
            onPointerUp: (_) => _scannerEnabled.value = true,
            onPointerCancel: (_) => _scannerEnabled.value = true,
            child: Stack(
              fit: StackFit.expand,
              children: [
                MobileScanner(
                  controller: _mobileScannerController,
                  errorBuilder: (context, error, child) =>
                      ScannerErrorWidget(error: error),
                  fit: BoxFit.contain,
                ),
                ValueListenableBuilder(
                  valueListenable: _scannerEnabled,
                  builder: (context, value, child) {
                    return Crosshair(
                      scannerEnabled: value,
                    );
                  },
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}