Promise: add flatMapErrorThen

1 files changed, 12 insertions, 0 deletions

diff --git a/ios/MullvadVPN/Promise/Promise+Result.swift b/ios/MullvadVPN/Promise/Promise+Result.swift
index 4dc7509a61..575a196d51 100644
--- a/ios/MullvadVPN/Promise/Promise+Result.swift
+++ b/ios/MullvadVPN/Promise/Promise+Result.swift
@@ -99,6 +99,18 @@ extension Promise where Value: AnyResult {
             return result.asConcreteType().flatMapError(transform)
         }
     }
+
+    /// Map failure to Result producing Promise. Passes successful result downstream.
+    func flatMapErrorThen<NewFailure>(_ transform: @escaping (Failure) -> Result<Success, NewFailure>.Promise) -> Result<Success, NewFailure>.Promise {
+        return then { result in
+            switch result.asConcreteType() {
+            case .success(let value):
+                return .success(value)
+            case .failure(let error):
+                return transform(error)
+            }
+        }
+    }
 }
 
 extension Promise where Value: AnyResult {