Add documentation.

app/src/main/java/com/github/swent/echo/connectivity/GPSService.kt

@@ -3,11 +3,15 @@ package com.github.swent.echo.connectivity
 import com.mapbox.mapboxsdk.geometry.LatLng
 import kotlinx.coroutines.flow.StateFlow
 
-/** A GPS service. Allows the location to be accessed either as */
+/** A service that provides the user's current location if it's accessible. */
 interface GPSService {
+
+    /** The user location as a state flow. */
     val userLocation: StateFlow<LatLng?>
 
+    /** The current user location. */
     fun currentUserLocation(): LatLng?
 
+    /** Force the service to refresh the user location */
     fun refreshUserLocation()
 }

app/src/main/java/com/github/swent/echo/connectivity/GPSServiceImpl.kt

@@ -12,12 +12,22 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
 
+/**
+ * A simple implementation of a [GPSService]
+ *
+ * @param context The context of the application that's using this service.
+ */
 class GPSServiceImpl(val context: Context) : GPSService {
     private val locationProviderClient = LocationServices.getFusedLocationProviderClient(context)
+
+    // This manager allows to check whether the location is disabled in settings.
     private val locationManager: LocationManager? =
         getSystemService(context, LocationManager::class.java)
+
+    // User's last known location
     private var _location = MutableStateFlow<LatLng?>(null)
 
+    /** Updates the last known location. */
     private fun getLocation() {
         if (
             LOCATION_PERMISSIONS.any {
@@ -32,7 +42,9 @@ class GPSServiceImpl(val context: Context) : GPSService {
                         this.let { location -> LatLng(location.latitude, location.longitude) }
                     )
                 }
-                // Request again if null, unless location is turned off in settings
+                // Request again if null, unless location is turned off in settings.
+                // Even if this process has permissions to access the location, as
+                // long as it's disabled in settings, the listener will return null.
                 locationManager?.apply {
                     // TODO maybe also check for NETWORK_PROVIDER
                     if (isProviderEnabled(LocationManager.GPS_PROVIDER)) {