From 87a1e22dca80dee87f1b70806757f17696627875 Mon Sep 17 00:00:00 2001
From: Eric Rabil <ericjrabil@gmail.com>
Date: Fri, 17 Sep 2021 14:26:06 -0400
Subject: [PATCH] Add support for Promise races

---
 Sources/Pwomise/Pwomise.swift         | 24 ++++++++++++++++++++++++
 Tests/PwomiseTests/PwomiseTests.swift | 17 ++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/Sources/Pwomise/Pwomise.swift b/Sources/Pwomise/Pwomise.swift
index 45d1a2c..4900c95 100644
--- a/Sources/Pwomise/Pwomise.swift
+++ b/Sources/Pwomise/Pwomise.swift
@@ -7,12 +7,36 @@ public protocol PromiseConvertible {
     var asPromise: Promise<Output> { get }
 }
 
+public enum PromiseInconsistencyError: Error {
+    case emptyArray
+}
+
 public class Promise<Output>: CustomDebugStringConvertible {
     internal typealias Pending = PendingPromise<Output, Error>
     public typealias Completion = Result<Output, Error>
     public typealias Resolve = (Output) -> ()
     public typealias Reject = (Error) -> ()
     
+    public static func any(_ promises: [Promise<Output>]) -> Promise<Output> {
+        guard promises.count > 0 else {
+            return .failure(PromiseInconsistencyError.emptyArray)
+        }
+        
+        let superPromise = Promise()
+        
+        for promise in promises {
+            promise.always { completion in
+                guard superPromise.pending else {
+                    return
+                }
+                
+                superPromise.result = .resolved(completion)
+            }
+        }
+        
+        return superPromise
+    }
+    
     public static func all(_ promises: [Promise<Output>]) -> Promise<[Output]> {
         guard promises.count > 0 else {
             return .success([])
diff --git a/Tests/PwomiseTests/PwomiseTests.swift b/Tests/PwomiseTests/PwomiseTests.swift
index d1b76d3..2450b26 100644
--- a/Tests/PwomiseTests/PwomiseTests.swift
+++ b/Tests/PwomiseTests/PwomiseTests.swift
@@ -2,5 +2,20 @@
     @testable import Pwomise
 
     final class PwomiseTests: XCTestCase {
-        
+        func testRace() {
+            var fulfilled = false
+            
+            Promise<Void>.any([
+                Promise { resolve, reject in
+                    resolve(())
+                },
+                Promise { resolve, reject in
+                    resolve(())
+                }
+            ]).then { _ in
+                XCTAssert(!fulfilled, "resolved multiple times")
+                
+                fulfilled = true
+            }
+        }
     }