feat: add alias api with previousId support (#554)

* chore: update podfile.lock

* fix: set previousId as anonmousId in alias API if userId is not present

* Revert "chore: update podfile.lock"

This reverts commit e96188c.

* feat: add alias api with previousId support

* feat: add new alias api in header file

* refactor: address comment

* fix: update Alias API by having previousId filed in the middle

* chore: fix alias api in RSClient.h

Sources/Classes/Headers/Public/RSClient.h

@@ -51,6 +51,7 @@ typedef void (^Callback)(NSObject *_Nullable);
 - (void) group:(NSString *)groupId traits:(NSDictionary<NSString*, id>*)traits;
 - (void) group:(NSString *)groupId;
 
+- (void) alias:(NSString *)newId previousId:(NSString * _Nullable)previousId options:(RSOption * _Nullable) options;
 - (void) alias:(NSString *)newId options:(RSOption * _Nullable) options;
 - (void) alias:(NSString *)newId;
 

Sources/Classes/RSClient.m

@@ -225,18 +225,22 @@ - (void)alias:(NSString *)newId {
         [self reportDiscardedEvent];
         return;
     }
-    [self alias:newId options:nil];
+    [self alias:newId previousId:nil options:nil];
 }
 
 - (void) alias:(NSString *)newId options:(RSOption *) options {
+    [self alias:newId previousId:nil options:options];
+}
+
+- (void) alias:(NSString *)newId previousId:(NSString *)previousId options:(RSOption *) options {
     if ([RSClient getOptStatus]) {
         [self reportDiscardedEvent];
         return;
     }
     RSContext *rc = [RSElementCache getContext];
     NSMutableDictionary<NSString*,NSObject*>* traits = [rc.traits mutableCopy];
 
-    NSObject *prevId = [traits objectForKey:@"userId"] ?: [traits objectForKey:@"id"] ?: self.anonymousId;
+    NSObject *prevId = previousId ?: [traits objectForKey:@"userId"] ?: [traits objectForKey:@"id"] ?: self.anonymousId;
 
     traits[@"id"] = newId;
     traits[@"userId"] = newId;