add check for user location on alarm click

screens/UsingScreen.js

@@ -18,19 +18,37 @@ const MAXIMUM_DISTANCE = 1000000000 // meters
 
 const UsingScreen = (props) => {
 
-  const { time, userId, token } = props;
+  const { location, time, userId, token } = props;
   const { timeRemaining } = time
 
   const startAlarm = () => {
-    const distance = computeDistance(fredVictorCoordinates, props.location.coords)
-    if( distance > MAXIMUM_DISTANCE ) Alert.alert("Cannot start alarm", "There are no responders within your area", [
-      { text: 'OK' }
-    ], { cancelable: false })
-    else {
-      Actions.alarm();
+    // Check if location has been set
+    console.log({location})
+    if( location === null
+        || location.coords === null
+        || (location.coords.lat !== 0 && location.coords.lng !== 0)
+      ) {
+      Alert.alert("Cannot start alarm", "Your location is not set. Please set your location in the 'locations' page' and enable location services on your device.", [
+        { text: 'Set my location now', onPress: () => {
+          Actions.location()
+        } },
+        { text: 'Cancel', onPress: () => {} }
+        ], { cancelable: false })
+      return null
+    }
 
-      props.makeAlarmLog(userId, timeRemaining, token);
+    // Check for responders in the area (for beta-testing, compare to the coordinates of the Fred Victor Building)
+    const distance = computeDistance(fredVictorCoordinates, location.coords)
+    if( distance > MAXIMUM_DISTANCE ) {
+      Alert.alert("Cannot start alarm", "There are no responders within your area", [
+      { text: 'OK' }
+      ], { cancelable: false })
+      return null
     }
+
+    Actions.alarm();
+
+    props.makeAlarmLog(userId, timeRemaining, token);
   }
 
   return (