add new error code constants

+package dev.steenbakker.mobile_scanner.objects
+
+class MobileScannerErrorCodes {
+    companion object {
+        const val ALREADY_STARTED_ERROR = "MOBILE_SCANNER_ALREADY_STARTED_ERROR"
+        const val ALREADY_STARTED_ERROR_MESSAGE = "The scanner was already started."
+        // The error code 'BARCODE_ERROR' does not have an error message,
+        // because it uses the error message from the underlying error.
+        const val BARCODE_ERROR = "MOBILE_SCANNER_BARCODE_ERROR"
+        // The error code 'CAMERA_ACCESS_DENIED' does not have an error message,
+        // because it is used for a boolean result.
+        const val CAMERA_ACCESS_DENIED = "MOBILE_SCANNER_CAMERA_PERMISSION_DENIED"
+        const val CAMERA_ERROR = "MOBILE_SCANNER_CAMERA_ERROR"
+        const val CAMERA_ERROR_MESSAGE = "An error occurred when opening the camera."
+        const val CAMERA_PERMISSIONS_REQUEST_ONGOING = "MOBILE_SCANNER_CAMERA_PERMISSION_REQUEST_PENDING"
+        const val CAMERA_PERMISSIONS_REQUEST_ONGOING_MESSAGE = "Another request is ongoing and multiple requests cannot be handled at once."
+        const val GENERIC_ERROR = "MOBILE_SCANNER_GENERIC_ERROR"
+        const val GENERIC_ERROR_MESSAGE = "An unknown error occurred."
+        const val INVALID_ZOOM_SCALE_ERROR_MESSAGE = "The zoom scale should be between 0 and 1 (both inclusive)"
+        const val NO_CAMERA_ERROR = "MOBILE_SCANNER_NO_CAMERA_ERROR"
+        const val NO_CAMERA_ERROR_MESSAGE = "No cameras available."
+        const val SET_SCALE_WHEN_STOPPED_ERROR = "MOBILE_SCANNER_SET_SCALE_WHEN_STOPPED_ERROR"
+        const val SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE = "The zoom scale cannot be changed when the camera is stopped."
+    }
+}
\ No newline at end of file

+//
+//  MobileScannerErrorCodes.swift
+//  mobile_scanner
+//
+//  Created by Navaron Bracke on 28/05/2024.
+//
+
+import Foundation
+
+/// This struct defines the error codes and error messages for MobileScanner errors.
+///
+/// These are used by `FlutterError` as error code and error message.
+/// 
+/// This struct should not be confused with `MobileScannerError`,
+/// which is an implementation detail for the iOS implementation.
+struct MobileScannerErrorCodes {
+    static let ALREADY_STARTED_ERROR = "MOBILE_SCANNER_ALREADY_STARTED_ERROR"
+    static let ALREADY_STARTED_ERROR_MESSAGE = "The scanner was already started."
+    // The error code 'BARCODE_ERROR' does not have an error message,
+    // because it uses the error message from the undelying error.
+    static let BARCODE_ERROR = "MOBILE_SCANNER_BARCODE_ERROR"
+    // The error code 'CAMERA_ERROR' does not have an error message,
+    // because it uses the error message from the underlying error.    
+    static let CAMERA_ERROR = "MOBILE_SCANNER_CAMERA_ERROR"
+    static let GENERIC_ERROR = "MOBILE_SCANNER_GENERIC_ERROR"
+    static let GENERIC_ERROR_MESSAGE = "An unknown error occurred."
+    // This message is used with the 'GENERIC_ERROR' error code.
+    static let INVALID_ZOOM_SCALE_ERROR_MESSAGE = "The zoom scale should be between 0 and 1 (both inclusive)"
+    static let NO_CAMERA_ERROR = "MOBILE_SCANNER_NO_CAMERA_ERROR"
+    static let NO_CAMERA_ERROR_MESSAGE = "No cameras available."
+    static let SET_SCALE_WHEN_STOPPED_ERROR = "MOBILE_SCANNER_SET_SCALE_WHEN_STOPPED_ERROR"
+    static let SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE = "The zoom scale cannot be changed when the camera is stopped."
+}

+import 'package:flutter/services.dart';
 import 'package:mobile_scanner/src/mobile_scanner_controller.dart';
 
 /// This enum defines the different error codes for the mobile scanner.
@@ -24,5 +25,25 @@ enum MobileScannerErrorCode {
   permissionDenied,
 
   /// Scanning is unsupported on the current device.
-  unsupported,
+  unsupported;
+
+  /// Convert the given [PlatformException.code] to a [MobileScannerErrorCode].
+  factory MobileScannerErrorCode.fromPlatformException(
+    PlatformException exception,
+  ) {
+    // The following error code mapping should be kept in sync with their native counterparts.
+    // These are located in `MobileScannerErrorCodes.kt` and `MobileScannerErrorCodes.swift`.
+    return switch (exception.code) {
+      // In case the scanner was already started, report the right error code.
+      // If the scanner is already starting,
+      // this error code is a signal to the controller to just ignore the attempt.
+      'MOBILE_SCANNER_ALREADY_STARTED_ERROR' =>
+        MobileScannerErrorCode.controllerAlreadyInitialized,
+      // In case no cameras are available, using the scanner is not supported.
+      'MOBILE_SCANNER_NO_CAMERA_ERROR' => MobileScannerErrorCode.unsupported,
+      'MOBILE_SCANNER_CAMERA_PERMISSION_DENIED' =>
+        MobileScannerErrorCode.permissionDenied,
+      _ => MobileScannerErrorCode.genericError,
+    };
+  }
 }

+//
+//  MobileScannerErrorCodes.swift
+//  mobile_scanner
+//
+//  Created by Navaron Bracke on 27/05/2024.
+//
+
+import Foundation
+
+struct MobileScannerErrorCodes {
+    static let ALREADY_STARTED_ERROR = "MOBILE_SCANNER_ALREADY_STARTED_ERROR"
+    static let ALREADY_STARTED_ERROR_MESSAGE = "The scanner was already started."
+    // The error code 'BARCODE_ERROR' does not have an error message,
+    // because it uses the error message from the undelying error.
+    static let BARCODE_ERROR = "MOBILE_SCANNER_BARCODE_ERROR"
+    // The error code 'CAMERA_ERROR' does not have an error message,
+    // because it uses the error message from the underlying error.       
+    static let CAMERA_ERROR = "MOBILE_SCANNER_CAMERA_ERROR"
+    static let NO_CAMERA_ERROR = "MOBILE_SCANNER_NO_CAMERA_ERROR"
+    static let NO_CAMERA_ERROR_MESSAGE = "No cameras available."
+}