Handling "is already presenting" error

Nivelir.xcodeproj/project.pbxproj

@@ -99,6 +99,8 @@
 		C027115E25F60A5100ECC57C /* AnyStackScreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = C0270EE925F4A61F00ECC57C /* AnyStackScreen.swift */; };
 		C027116325F60A5600ECC57C /* AnyTabsScreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = C0270EF025F4A63400ECC57C /* AnyTabsScreen.swift */; };
 		C027116825F60A5600ECC57C /* AnyTabsScreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = C0270EF025F4A63400ECC57C /* AnyTabsScreen.swift */; };
+		C04C26E22B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift in Sources */ = {isa = PBXBuildFile; fileRef = C04C26E12B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift */; };
+		C04C26E32B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift in Sources */ = {isa = PBXBuildFile; fileRef = C04C26E12B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift */; };
 		C052C7B52822D9E100132875 /* ScreenObservation.swift in Sources */ = {isa = PBXBuildFile; fileRef = C052C7B42822D9E100132875 /* ScreenObservation.swift */; };
 		C052C7B62822D9E100132875 /* ScreenObservation.swift in Sources */ = {isa = PBXBuildFile; fileRef = C052C7B42822D9E100132875 /* ScreenObservation.swift */; };
 		C052C7CD2823A90F00132875 /* ScreenObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = C052C7CC2823A90F00132875 /* ScreenObserver.swift */; };
@@ -729,6 +731,7 @@
 		C027107A25F50FE300ECC57C /* DefaultScreenIterator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DefaultScreenIterator.swift; sourceTree = "<group>"; };
 		C027108A25F5120300ECC57C /* ScreenIterationPredicate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenIterationPredicate.swift; sourceTree = "<group>"; };
 		C027109E25F51C7F00ECC57C /* ScreenIterationResult.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenIterationResult.swift; sourceTree = "<group>"; };
+		C04C26E12B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenContainerAlreadyPresentingError.swift; sourceTree = "<group>"; };
 		C052C7B42822D9E100132875 /* ScreenObservation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenObservation.swift; sourceTree = "<group>"; };
 		C052C7CC2823A90F00132875 /* ScreenObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenObserver.swift; sourceTree = "<group>"; };
 		C052C7CF2823A94500132875 /* ScreenObserverPredicate.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ScreenObserverPredicate.swift; sourceTree = "<group>"; };
@@ -2243,6 +2246,7 @@
 				C0238F2C27A9477000148E91 /* ScreenCanceledError.swift */,
 				C0F9A47425FD61EB00DAE060 /* ScreenContainerNotFoundError.swift */,
 				C088605B26B9737C00CA0A77 /* ScreenContainerNotSupportedError.swift */,
+				C04C26E12B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift */,
 				C0F9A47325FD61EB00DAE060 /* ScreenContainerTypeMismatchError.swift */,
 				C0AADA2F25EED85C0087439E /* ScreenError.swift */,
 			);
@@ -2633,6 +2637,7 @@
 				C052C7CD2823A90F00132875 /* ScreenObserver.swift in Sources */,
 				C0885F9826B6BA0100CA0A77 /* ScreenPresentingAction.swift in Sources */,
 				C0885F7626B6BA0100CA0A77 /* ScreenTryResolution.swift in Sources */,
+				C04C26E22B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift in Sources */,
 				C0885FB026B6C0A500CA0A77 /* ScreenStackPopPredicate.swift in Sources */,
 				C0885F7026B6BA0100CA0A77 /* ScreenRefreshableContainer.swift in Sources */,
 				C0270E5F25F3EC7200ECC57C /* DefaultScreenLogger.swift in Sources */,
@@ -3152,6 +3157,7 @@
 				C0F9A47625FD61EB00DAE060 /* ScreenContainerTypeMismatchError.swift in Sources */,
 				C089D8E92A0B18C800B6400C /* KeyboardHandler.swift in Sources */,
 				C078FD482861A1DA0008FC6E /* ProgressSuccessIndicatorView.swift in Sources */,
+				C04C26E32B970FB90086F4E4 /* ScreenContainerAlreadyPresentingError.swift in Sources */,
 				C0270E9125F4245800ECC57C /* ScreenDecorator.swift in Sources */,
 				C078FD722861A1DA0008FC6E /* ProgressEmptyHeader.swift in Sources */,
 				C0238ED127A40F6C00148E91 /* DictionaryNonConformingFloatDecodingStrategy.swift in Sources */,

Sources/Addons/ActionSheet/ScreenShowActionSheetAction.swift

@@ -94,6 +94,10 @@ public struct ScreenShowActionSheetAction<Container: UIViewController>: ScreenAc
     ) {
         navigator.logInfo("Presenting \(actionSheet) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         let alertContainer = makeAlertContainer()
 
         switch UIDevice.current.userInterfaceIdiom {

Sources/Addons/Alert/ScreenShowAlertAction.swift

@@ -87,6 +87,10 @@ public struct ScreenShowAlertAction<Container: UIViewController>: ScreenAction {
     ) {
         navigator.logInfo("Presenting \(alert) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         let alertContainer = makeAlertContainer()
 
         container.present(alertContainer, animated: animated) {

Sources/Addons/MediaPicker/ScreenShowMediaPickerAction.swift

@@ -144,6 +144,10 @@ public struct ScreenShowMediaPickerAction<Container: UIViewController>: ScreenAc
     ) {
         navigator.logInfo("Presenting \(mediaPicker) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         requestAccessIfNeeded { authorized in
             guard authorized else {
                 return completion(.mediaPickerSourceAccessDenied(for: self))

Sources/Addons/Safari/ScreenShowSafariAction.swift

@@ -25,6 +25,10 @@ public struct ScreenShowSafariAction<Container: UIViewController>: ScreenAction
     ) {
         navigator.logInfo("Presenting \(safari) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         guard safari.url.scheme.map({ ["http", "https"].contains($0) }) ?? false else {
             return completion(.invalidSafariURL(for: self))
         }

Sources/Addons/Sharing/ScreenShareAction.swift

@@ -106,6 +106,10 @@ public struct ScreenShareAction<Container: UIViewController>: ScreenAction {
     ) {
         navigator.logInfo("Sharing \(sharing.items) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         let activitiesContainer = makeActivitiesContainer(navigator: navigator)
 
         switch UIDevice.current.userInterfaceIdiom {

Sources/Addons/StoreProduct/ScreenShowStoreProductAction.swift

@@ -25,6 +25,10 @@ public struct ScreenShowStoreProductAction<Container: UIViewController>: ScreenA
     ) {
         navigator.logInfo("Presenting \(storeProduct) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         guard let storeProductID = Int(storeProduct.itemID).map(NSNumber.init(value:)) else {
             return completion(.invalidStoreProductID(for: self))
         }

Sources/Screen/Actions/Modal/ScreenPresentAction.swift

@@ -36,6 +36,10 @@ public struct ScreenPresentAction<
     ) {
         navigator.logInfo("Presenting \(screen) on \(type(of: container))")
 
+        guard container.presented == nil else {
+            return completion(.containerAlreadyPresenting(container, for: self))
+        }
+
         let presented = screen.build(navigator: navigator)
 
         container.present(presented, animated: animated) {

Sources/Screen/Errors/ScreenContainerAlreadyPresentingError.swift

@@ -0,0 +1,46 @@
+import Foundation
+
+/// The container is already presenting another container.
+///
+/// This error occurs whenever an action fails to present a modal container on a container
+/// which is already presenting another container.
+public struct ScreenContainerAlreadyPresentingError: ScreenError {
+
+    public var description: String {
+        """
+        The container \(container) is already presenting another container for:
+          \(trigger)
+        """
+    }
+
+    /// Container that is already presenting another screen.
+    public let container: ScreenContainer
+
+    /// The action that caused the error.
+    public let trigger: Any
+
+    /// Creates an error.
+    ///
+    /// - Parameters:
+    ///   - container: Container that is already presenting another screen.
+    ///   - trigger: The action that caused the error.
+    public init(container: ScreenContainer, for trigger: Any) {
+        self.container = container
+        self.trigger = trigger
+    }
+}
+
+extension Result where Failure == Error {
+
+    internal static func containerAlreadyPresenting(
+        _ container: ScreenContainer,
+        for trigger: Any
+    ) -> Self {
+        .failure(
+            ScreenContainerAlreadyPresentingError(
+                container: container,
+                for: trigger
+            )
+        )
+    }
+}