add unavailable torch state

@@ -4,7 +4,10 @@ enum TorchState {
   off(0),
 
   /// The flashlight is on.
-  on(1);
+  on(1),
+
+  /// The flashlight is unavailable.
+  unavailable(2);
 
   const TorchState(this.rawValue);
 
@@ -14,6 +17,8 @@ enum TorchState {
         return TorchState.off;
       case 1:
         return TorchState.on;
+      case 2:
+        return TorchState.unavailable;
       default:
         throw ArgumentError.value(value, 'value', 'Invalid raw value.');
     }

@@ -7,6 +7,7 @@ void main() {
       const values = <int, TorchState>{
         0: TorchState.off,
         1: TorchState.on,
+        2: 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 outOfRange = 2;
+      const int outOfRange = 3;
 
       expect(() => TorchState.fromRawValue(negative), throwsArgumentError);
       expect(() => TorchState.fromRawValue(outOfRange), throwsArgumentError);
@@ -28,6 +29,7 @@ void main() {
       const values = <TorchState, int>{
         TorchState.off: 0,
         TorchState.on: 1,
+        TorchState.unavailable: 2,
       };
 
       for (final MapEntry<TorchState, int> entry in values.entries) {