Barcode refactor (#363)

* Move barcode.dart

* Fix

* Refactoring barcode scanner code:

- Abstract the "controller" class (for future development)
- Break barcode scanning code out into multiple files
- Add CameraBarcodeController class (qr_code_scanner)

* Add await

* Make barcode scan delay configurable

* remove unused import

* Handle camera exceptions

* Improve sequencing for camera scanner

- Show loading overlay
- Prevent reload if view is no longer mounted

* Update docstring

* Update release notes

lib/barcode/camera_controller.dart

@@ -0,0 +1,154 @@
+import "dart:io";
+import "package:flutter/material.dart";
+
+import "package:qr_code_scanner/qr_code_scanner.dart";
+
+import "package:inventree/l10.dart";
+
+import "package:inventree/barcode/handler.dart";
+import "package:inventree/barcode/controller.dart";
+
+/*
+ * Barcode controller which uses the device's camera to scan barcodes.
+ * Under the hood it uses the qr_code_scanner package.
+ */
+class CameraBarcodeController extends InvenTreeBarcodeController {
+
+  const CameraBarcodeController(BarcodeHandler handler, {Key? key}) : super(handler, key: key);
+
+  @override
+  State<StatefulWidget> createState() => _CameraBarcodeControllerState();
+
+}
+
+
+class _CameraBarcodeControllerState extends InvenTreeBarcodeControllerState {
+
+  _CameraBarcodeControllerState() : super();
+
+  QRViewController? _controller;
+
+  bool flash_status = false;
+
+  /* Callback function when the Barcode scanner view is initially created */
+  void _onViewCreated(BuildContext context, QRViewController controller) {
+    _controller = controller;
+
+    controller.scannedDataStream.listen((barcode) {
+      handleBarcodeData(barcode.code);
+    });
+  }
+
+  // In order to get hot reload to work we need to pause the camera if the platform
+  // is android, or resume the camera if the platform is iOS.
+  @override
+  void reassemble() {
+    super.reassemble();
+
+    if (mounted) {
+      if (Platform.isAndroid) {
+        _controller!.pauseCamera();
+      }
+
+      _controller!.resumeCamera();
+    }
+  }
+
+  @override
+  void dispose() {
+    _controller?.dispose();
+    super.dispose();
+  }
+
+  @override
+  Future<void> pauseScan() async {
+    try {
+      await _controller?.pauseCamera();
+    } on CameraException {
+      // do nothing
+    }
+  }
+
+  @override
+  Future<void> resumeScan() async {
+    try {
+      await _controller?.resumeCamera();
+    } on CameraException {
+      // do nothing
+    }
+  }
+
+  // Toggle the status of the camera flash
+  Future<void> updateFlashStatus() async {
+    final bool? status = await _controller?.getFlashStatus();
+
+    if (mounted) {
+      setState(() {
+        flash_status = status != null && status;
+      });
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+
+    return Scaffold(
+        appBar: AppBar(
+          title: Text(L10().scanBarcode),
+          actions: [
+            IconButton(
+              icon: Icon(Icons.flip_camera_android),
+              onPressed: () {
+                _controller?.flipCamera();
+              }
+            ),
+            IconButton(
+              icon: flash_status ? Icon(Icons.flash_off) : Icon(Icons.flash_on),
+              onPressed: () {
+                _controller?.toggleFlash();
+                updateFlashStatus();
+              },
+            )
+          ],
+        ),
+        body: Stack(
+          children: <Widget>[
+            Column(
+              children: [
+                Expanded(
+                  child: QRView(
+                    key: barcodeControllerKey,
+                    onQRViewCreated: (QRViewController controller) {
+                      _onViewCreated(context, controller);
+                    },
+                    overlay: QrScannerOverlayShape(
+                      borderColor: Colors.red,
+                      borderRadius: 10,
+                      borderLength: 30,
+                      borderWidth: 10,
+                      cutOutSize: 300,
+                    ),
+                  )
+                )
+              ]
+            ),
+            Center(
+                child: Column(
+                    children: [
+                      Spacer(),
+                      Padding(
+                        child: Text(widget.handler.getOverlayText(context),
+                          style: TextStyle(
+                              fontWeight: FontWeight.bold,
+                              color: Colors.white),
+                        ),
+                        padding: EdgeInsets.all(20),
+                      ),
+                    ]
+                )
+            )
+          ],
+        )
+    );
+  }
+}