fix: PDF471 codes on desktop Mac (#466)

The native BarcodeDetector implementation on desktop Mac seems to
support PDF417 codes but when scanning (always?) returns an empty
string. Thus, now falling back to polyfill under these conditions.

Closes: #459

src/misc/scanner.ts

@@ -1,6 +1,7 @@
 import { type DetectedBarcode, type BarcodeFormat, BarcodeDetector, type BarcodeDetectorOptions } from 'barcode-detector/pure'
 import { eventOn } from './callforth'
 import { DropImageFetchError } from './errors'
+import { isMac } from './util'
 
 declare global {
   interface Window { 
@@ -48,6 +49,12 @@ async function createBarcodeDetector(formats: BarcodeFormat[]): Promise<BarcodeD
     return new BarcodeDetector({ formats })
   }
 
+  if (isMac() && formats.includes('pdf417')) {
+    // See: #459
+    console.debug(`[vue-qrcode-reader] Native BarcodeDetector is buggy for PDF417 codes on MacOS. Will use polyfill.`)
+    return new BarcodeDetector({ formats })
+  }
+
   console.debug('[vue-qrcode-reader] Will use native BarcodeDetector.')
   return new window.BarcodeDetector({ formats })
 }

src/misc/util.ts

@@ -49,3 +49,10 @@ export function assert(condition: boolean, failureMessage?: string): asserts con
 export function assertNever(_witness: never): never {
   throw new Error('this code should be unreachable')
 }
+
+/**
+ * Returns true iff the users operating system is desktop MacOS.
+ */
+export function isMac(): boolean {
+  return navigator.platform.toUpperCase().includes('MAC')
+}