take into account the auto mode on iOS/MacOS

@@ -74,6 +74,7 @@ class MobileScannerHandler(
     private var mobileScanner: MobileScanner? = null
 
     private val torchStateCallback: TorchStateCallback = {state: Int ->
+        // Off = 0, On = 1
         barcodeHandler.publishEvent(mapOf("name" to "torchState", "data" to state))
     }
 

@@ -138,6 +138,17 @@ class ToggleFlashlightButton extends StatelessWidget {
         }
 
         switch (state.torchState) {
+          case TorchState.auto:
+            return IconButton(
+              color: Colors.white,
+              iconSize: 32.0,
+              icon: const Icon(Icons.flash_auto),
+              onPressed: () async {
+                // This button only turns off the auto mode.
+                // Perhaps we can switch between on / off / auto?
+                await controller.toggleTorch();
+              },
+            );
           case TorchState.off:
             return IconButton(
               color: Colors.white,

@@ -347,7 +347,7 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
     public override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
         switch keyPath {
         case "torchMode":
-            // off = 0; on = 1; auto = 2
+            // Off = 0, On = 1, Auto = 2
             let state = change?[.newKey] as? Int
             torchModeChangeCallback(state)
         case "videoZoomFactor":

 /// The state of the flashlight.
 enum TorchState {
+  /// The flashlight turns on automatically in low light conditions.
+  ///
+  /// This is currently only supported on iOS.
+  auto(2),
+
   /// The flashlight is off.
   off(0),
 
@@ -7,18 +12,20 @@ enum TorchState {
   on(1),
 
   /// The flashlight is unavailable.
-  unavailable(2);
+  unavailable(-1);
 
   const TorchState(this.rawValue);
 
   factory TorchState.fromRawValue(int value) {
     switch (value) {
+      case -1:
+        return TorchState.unavailable;
       case 0:
         return TorchState.off;
       case 1:
         return TorchState.on;
       case 2:
-        return TorchState.unavailable;
+        return TorchState.auto;
       default:
         throw ArgumentError.value(value, 'value', 'Invalid raw value.');
     }

@@ -410,7 +410,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
     public override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
         switch keyPath {
         case "torchMode":
-            // off = 0 on = 1 auto = 2
+            // Off = 0, On = 1, Auto = 2
             let state = change?[.newKey] as? Int
             let event: [String: Any?] = ["name": "torchState", "data": state]
             sink?(event)

@@ -7,7 +7,8 @@ void main() {
       const values = <int, TorchState>{
         0: TorchState.off,
         1: TorchState.on,
-        2: TorchState.unavailable,
+        2: TorchState.auto,
+        -1: TorchState.unavailable,
       };
 
       for (final MapEntry<int, TorchState> entry in values.entries) {
@@ -18,7 +19,7 @@ void main() {
     });
 
     test('invalid raw value throws argument error', () {
-      const int negative = -1;
+      const int negative = -2;
       const int outOfRange = 3;
 
       expect(() => TorchState.fromRawValue(negative), throwsArgumentError);
@@ -27,9 +28,10 @@ void main() {
 
     test('can be converted to raw value', () {
       const values = <TorchState, int>{
+        TorchState.unavailable: -1,
         TorchState.off: 0,
         TorchState.on: 1,
-        TorchState.unavailable: 2,
+        TorchState.auto: 2,
       };
 
       for (final MapEntry<TorchState, int> entry in values.entries) {