From e7c5c1d652679b905b4922619b9b70e142f89c0f Mon Sep 17 00:00:00 2001
From: Eric Rabil <ericjrabil@gmail.com>
Date: Mon, 25 Jul 2022 16:34:02 -0400
Subject: [PATCH] Add utility function for waiting for a promise to complete

---
 Sources/Pwomise/Extensions/Promise+Wait.swift | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 Sources/Pwomise/Extensions/Promise+Wait.swift

diff --git a/Sources/Pwomise/Extensions/Promise+Wait.swift b/Sources/Pwomise/Extensions/Promise+Wait.swift
new file mode 100644
index 0000000..54f0166
--- /dev/null
+++ b/Sources/Pwomise/Extensions/Promise+Wait.swift
@@ -0,0 +1,38 @@
+//
+//  File.swift
+//  
+//
+//  Created by Eric Rabil on 7/25/22.
+//
+
+import Foundation
+
+public extension Promise {
+    enum TimeoutError: Error { case timedOut }
+    
+    func wait(upTo time: DispatchTime) throws -> Output {
+        var completion: Completion!
+        let semaphore = DispatchSemaphore(value: 0)
+        var semaphoreLocked: Bool {
+            if semaphore.wait(timeout: .now()) == .success {
+                semaphore.signal()
+                return false
+            }
+            return true
+        }
+        always {
+            completion = $0
+            if semaphoreLocked {
+                semaphore.signal()
+            }
+        }.resolving(on: DispatchQueue.global())
+        if semaphore.wait(timeout: time) == .success {
+            // finished in time, signal and return
+            semaphore.signal()
+        } else {
+            // did not finish in time, throw
+            throw TimeoutError.timedOut
+        }
+        return try completion.get()
+    }
+}