Add MessengerRegisterReceiveFileCallback function

Sources/XXMessengerClient/Messenger/Functions/MessengerRegisterReceiveFileCallback.swift

+import XCTestDynamicOverlay
+import XXClient
+
+public struct MessengerRegisterReceiveFileCallback {
+  public var run: (ReceiveFileCallback) -> Cancellable
+
+  public func callAsFunction(_ callback: ReceiveFileCallback) -> Cancellable {
+    run(callback)
+  }
+}
+
+extension MessengerRegisterReceiveFileCallback {
+  public static func live(_ env: MessengerEnvironment) -> MessengerRegisterReceiveFileCallback {
+    MessengerRegisterReceiveFileCallback { callback in
+      env.receiveFileCallbacksRegistry.register(callback)
+    }
+  }
+}
+
+extension MessengerRegisterReceiveFileCallback {
+  public static let unimplemented = MessengerRegisterReceiveFileCallback(
+    run: XCTUnimplemented("\(Self.self)", placeholder: Cancellable {})
+  )
+}

Sources/XXMessengerClient/Messenger/Messenger.swift

@@ -40,6 +40,7 @@ public struct Messenger {
   public var stopBackup: MessengerStopBackup
   public var setLogLevel: MessengerSetLogLevel
   public var startLogging: MessengerStartLogging
+  public var registerReceiveFileCallback: MessengerRegisterReceiveFileCallback
   public var startFileTransfer: MessengerStartFileTransfer
   public var sendFile: MessengerSendFile
   public var receiveFile: MessengerReceiveFile
@@ -87,6 +88,7 @@ extension Messenger {
       stopBackup: .live(env),
       setLogLevel: .live(env),
       startLogging: .live(env),
+      registerReceiveFileCallback: .live(env),
       startFileTransfer: .live(env),
       sendFile: .live(env),
       receiveFile: .live(env)
@@ -135,6 +137,7 @@ extension Messenger {
     stopBackup: .unimplemented,
     setLogLevel: .unimplemented,
     startLogging: .unimplemented,
+    registerReceiveFileCallback: .unimplemented,
     startFileTransfer: .unimplemented,
     sendFile: .unimplemented,
     receiveFile: .unimplemented

Tests/XXMessengerClientTests/Messenger/Functions/MessengerRegisterReceiveFileCallbackTests.swift

+import CustomDump
+import XCTest
+import XXClient
+@testable import XXMessengerClient
+
+final class MessengerRegisterReceiveFileCallbackTests: XCTestCase {
+  func testRegisterCallback() {
+    var registeredCallbacks: [ReceiveFileCallback] = []
+    var didHandleResult: [ReceiveFileCallback.Result] = []
+    var didCancelRegisteredCallback = 0
+
+    var env: MessengerEnvironment = .unimplemented
+    env.receiveFileCallbacksRegistry.register = { callback in
+      registeredCallbacks.append(callback)
+      return Cancellable { didCancelRegisteredCallback += 1 }
+    }
+    let registerCallback: MessengerRegisterReceiveFileCallback = .live(env)
+    let cancellable = registerCallback(ReceiveFileCallback { result in
+      didHandleResult.append(result)
+    })
+
+    XCTAssertEqual(registeredCallbacks.count, 1)
+
+    registeredCallbacks.forEach { callback in
+      callback.handle(.success(.stub(1)))
+    }
+
+    XCTAssertNoDifference(didHandleResult, [.success(.stub(1))])
+
+    cancellable.cancel()
+
+    XCTAssertEqual(didCancelRegisteredCallback, 1)
+  }
+}