ios: Implement getBaseDirectory in the platform-channel

This is one of the many platform-channels that needs to be implemented
for ios. We may as well get started.

ios/Runner/AppDelegate.m

@@ -1,12 +1,46 @@
 #include "AppDelegate.h"
 #include "GeneratedPluginRegistrant.h"
 
+NSString* GetDirectoryOfType(NSSearchPathDirectory dir) {
+    NSArray* paths = NSSearchPathForDirectoriesInDomains(dir, NSUserDomainMask, YES);
+    return paths.firstObject;
+}
+
 @implementation AppDelegate
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
+    FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;
+
+    FlutterMethodChannel* gitChannel = [FlutterMethodChannel
+        methodChannelWithName:@"gitjournal.io/git" binaryMessenger:controller];
+
+    [gitChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
+        NSString* filesDir = [self getApplicationDocumentsDirectory];
+        if ([@"getBaseDirectory" isEqualToString:call.method]) {
+            /*
+             int batteryLevel = [weakSelf getBatteryLevel];
+
+             if (batteryLevel == -1) {
+             result([FlutterError errorWithCode:@"UNAVAILABLE"
+             message:@"Battery info unavailable"
+             details:nil]);
+             } else {
+             result(@(batteryLevel));
+             }
+             */
+            result(filesDir);
+        } else {
+            result(FlutterMethodNotImplemented);
+        }
+    }];
+
     [GeneratedPluginRegistrant registerWithRegistry:self];
     // Override point for customization after application launch.
     return [super application:application didFinishLaunchingWithOptions:launchOptions];
 }
 
+- (NSString*)getApplicationDocumentsDirectory {
+    return GetDirectoryOfType(NSDocumentDirectory);
+}
+
 @end