Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/MessagesUI/Sources/MFMailComposeViewController+Promise.swift

@@ -0,0 +1,81 @@
+import MessageUI.MFMailComposeViewController
+import UIKit.UIViewController
+#if !PMKCocoaPods
+import PromiseKit
+#endif
+
+/**
+ To import this `UIViewController` category:
+
+    use_frameworks!
+    pod "PromiseKit/MessageUI"
+
+ And then in your sources:
+
+    import PromiseKit
+*/
+extension UIViewController {
+    /// Presents the message view controller and resolves with the user action.
+    public func promise(_ vc: MFMailComposeViewController, animated: Bool = true, completion:(() -> Void)? = nil) -> Promise<MFMailComposeResult> {
+        let proxy = PMKMailComposeViewControllerDelegate()
+        proxy.retainCycle = proxy
+        vc.mailComposeDelegate = proxy
+        present(vc, animated: animated, completion: completion)
+        _ = proxy.promise.ensure {
+            self.dismiss(animated: animated, completion: nil)
+        }
+        return proxy.promise
+    }
+}
+
+extension MFMailComposeViewController {
+    /// Errors representing PromiseKit MFMailComposeViewController failures
+    public enum PMKError: CancellableError, CustomStringConvertible {
+        /// The user cancelled sending mail
+        case cancelled
+        case failed
+
+        /// - Returns: true
+        public var isCancelled: Bool {
+            switch self {
+            case .cancelled:
+                return true
+            case .failed:
+                return false
+            }
+        }
+        
+        public var description: String {
+            switch self {
+            case .failed:
+                return "The attempt to save or send the message was unsuccessful."
+            case .cancelled:
+                return "The mail was cancelled"
+            }
+                
+        }
+    }
+}
+
+private class PMKMailComposeViewControllerDelegate: NSObject, MFMailComposeViewControllerDelegate, UINavigationControllerDelegate {
+
+    let (promise, seal) = Promise<MFMailComposeResult>.pending()
+    var retainCycle: NSObject?
+
+    @objc func mailComposeController(_ controller: MFMailComposeViewController, didFinishWith result: MFMailComposeResult, error: Error?) {
+        defer { retainCycle = nil }
+
+        if let error = error {
+            seal.reject(error)
+        } else {
+            switch result {
+            case .failed:
+                seal.reject(MFMailComposeViewController.PMKError.failed)
+            case .cancelled:
+                seal.reject(MFMailComposeViewController.PMKError.cancelled)
+            default:
+                seal.fulfill(result)
+            }
+        }
+    }
+}

Carthage/Checkouts/PromiseKit/Extensions/MessagesUI/Sources/MFMessageComposeViewController+Promise.swift

@@ -0,0 +1,78 @@
+import Foundation
+import MessageUI.MFMessageComposeViewController
+import UIKit.UIViewController
+#if !PMKCocoaPods
+import PromiseKit
+#endif
+
+/**
+ To import this `UIViewController` category:
+
+    use_frameworks!
+    pod "PromiseKit/MessageUI"
+
+ And then in your sources:
+
+    import PromiseKit
+*/
+extension UIViewController {
+    /// Presents the message view controller and resolves with the user action.
+    public func promise(_ vc: MFMessageComposeViewController, animated: Bool = true, completion:(() -> Void)? = nil) -> Promise<Void> {
+        let proxy = PMKMessageComposeViewControllerDelegate()
+        proxy.retainCycle = proxy
+        vc.messageComposeDelegate = proxy
+        present(vc, animated: animated, completion: completion)
+        _ = proxy.promise.ensure {
+            vc.dismiss(animated: animated, completion: nil)
+        }
+        return proxy.promise
+    }
+}
+
+extension MFMessageComposeViewController {
+    /// Errors representing PromiseKit MFMailComposeViewController failures
+    public enum PMKError: CancellableError, CustomStringConvertible {
+        /// The user cancelled sending the message
+        case cancelled
+        case failed
+
+        /// - Returns: true
+        public var isCancelled: Bool {
+            switch self {
+            case .cancelled:
+                return true
+            case .failed:
+                return false
+            }
+        }
+        
+        public var description: String {
+            switch self {
+            case .failed:
+                return "The attempt to save or send the message was unsuccessful."
+            case .cancelled:
+                return "The message was cancelled"
+            }
+                
+        }
+    }
+}
+
+private class PMKMessageComposeViewControllerDelegate: NSObject, MFMessageComposeViewControllerDelegate, UINavigationControllerDelegate {
+
+    let (promise, seal) = Promise<Void>.pending()
+    var retainCycle: NSObject?
+
+    @objc func messageComposeViewController(_ controller: MFMessageComposeViewController, didFinishWith result: MessageComposeResult) {
+        defer { retainCycle = nil }
+
+        switch result {
+        case .sent:
+            seal.fulfill(())
+        case .failed:
+            seal.reject(MFMessageComposeViewController.PMKError.failed)
+        case .cancelled:
+            seal.reject(MFMessageComposeViewController.PMKError.cancelled)
+        }
+    }
+}