Adds "barcode" field handler for API forms

lib/api_form.dart

@@ -7,6 +7,7 @@ import "package:date_field/date_field.dart";
 
 import "package:inventree/api.dart";
 import "package:inventree/app_colors.dart";
+import 'package:inventree/barcode.dart';
 import "package:inventree/helpers.dart";
 import "package:inventree/inventree/part.dart";
 import "package:inventree/inventree/sentry.dart";
@@ -269,7 +270,7 @@ class APIFormField {
   }
 
   // Construct a widget for this input
-  Widget constructField() {
+  Widget constructField(BuildContext context) {
     switch (type) {
       case "string":
       case "url":
@@ -288,6 +289,8 @@ class APIFormField {
         return _constructFileField();
       case "date":
         return _constructDateField();
+      case "barcode":
+        return _constructBarcodeField(context);
       default:
         return ListTile(
           title: Text(
@@ -300,6 +303,52 @@ class APIFormField {
     }
   }
 
+  // Field for capturing a barcode
+  Widget _constructBarcodeField(BuildContext context) {
+
+    TextEditingController controller = TextEditingController();
+
+    String barcode = (value ?? "").toString();
+
+    if (barcode.isEmpty) {
+      barcode = L10().barcodeNotAssigned;
+    }
+
+    controller.text = barcode;
+
+    return InputDecorator(
+      decoration: InputDecoration(
+        labelText: required ? label + "*" : label,
+        labelStyle: _labelStyle(),
+        helperText: helpText,
+        helperStyle: _helperStyle(),
+        hintText: placeholderText,
+      ),
+      child: ListTile(
+        title: TextField(
+          readOnly: true,
+          controller: controller,
+        ),
+        trailing: IconButton(
+          icon: FaIcon(FontAwesomeIcons.qrcode),
+          onPressed: () async {
+
+            var handler = UniqueBarcodeHandler((String hash) {
+              print("Scanned barcode: " + hash);
+            });
+
+            Navigator.push(
+              context,
+              MaterialPageRoute(builder: (context) => InvenTreeQRView(handler)
+              )
+            );
+          },
+        ),
+      )
+    );
+
+  }
+
   // Field for displaying and selecting dates
   Widget _constructDateField() {
 
@@ -937,7 +986,7 @@ class _APIFormWidgetState extends State<APIFormWidget> {
         }
       }
 
-      widgets.add(field.constructField());
+      widgets.add(field.constructField(context));
 
       if (field.hasErrors()) {
         for (String error in field.errorMessages()) {

lib/barcode.dart

@@ -305,7 +305,7 @@ class StockItemBarcodeAssignmentHandler extends BarcodeHandler {
           }
         ).then((result) {
           if (result) {
-            failureTone();
+            successTone();
 
             Navigator.of(context).pop();
 
@@ -315,7 +315,7 @@ class StockItemBarcodeAssignmentHandler extends BarcodeHandler {
                 icon: FontAwesomeIcons.qrcode
             );
           } else {
-            successTone();
+            failureTone();
 
             showSnackIcon(
                 L10().barcodeNotAssigned,
@@ -464,6 +464,63 @@ class StockLocationScanInItemsHandler extends BarcodeHandler {
 }
 
 
+class UniqueBarcodeHandler extends BarcodeHandler {
+  /*
+   * Barcode handler for finding a "unique" barcode (one that does not match an item in the database)
+   */
+
+  UniqueBarcodeHandler(this.callback);
+
+  // Callback function when a "unique" barcode hash is found
+  final Function(String) callback;
+
+  @override
+  String getOverlayText(BuildContext context) => L10().barcodeScanAssign;
+
+  @override
+  Future<void> onBarcodeMatched(BuildContext context, Map<String, dynamic> data) async {
+
+    failureTone();
+
+    // If the barcode is known, we can"t assign it to the stock item!
+    showSnackIcon(
+        L10().barcodeInUse,
+        icon: FontAwesomeIcons.qrcode,
+        success: false
+    );
+  }
+
+  @override
+  Future<void> onBarcodeUnknown(BuildContext context, Map<String, dynamic> data) async {
+    // If the barcode is unknown, we *can* assign it to the stock item!
+
+    if (!data.containsKey("hash")) {
+      showServerError(
+        L10().missingData,
+        L10().barcodeMissingHash,
+      );
+    } else {
+      String hash = (data["hash"] ?? "") as String;
+
+      if (hash.isEmpty) {
+        failureTone();
+
+        showSnackIcon(
+          L10().barcodeError,
+          success: false,
+        );
+      } else {
+
+        // Close the barcode scanner
+        Navigator.of(context).pop();
+
+        callback(hash);
+      }
+    }
+  }
+}
+
+
 class InvenTreeQRView extends StatefulWidget {
 
   const InvenTreeQRView(this._handler, {Key? key}) : super(key: key);

lib/widget/purchase_order_detail.dart

@@ -195,6 +195,13 @@ class _PurchaseOrderDetailState extends RefreshableState<PurchaseOrderDetailWidg
         "nested": true,
       },
       "location": {
+      },
+      "barcode": {
+        "parent": "items",
+        "nested": true,
+        "type": "barcode",
+        "label": L10().barcodeAssign,
+        "required": false,
       }
     };