Support pasting images to create attachments

Closes #91

Tusker/Screens/Compose/Attachments/ComposeAttachmentsViewController.swift

@@ -57,6 +57,8 @@ class ComposeAttachmentsViewController: UITableViewController {
         
         heightConstraint = tableView.heightAnchor.constraint(equalToConstant: tableView.contentSize.height)
         heightConstraint.isActive = true
+        
+        pasteConfiguration = UIPasteConfiguration(forAccepting: UIImage.self)
     }
     
     override func viewWillAppear(_ animated: Bool) {
@@ -65,8 +67,11 @@ class ComposeAttachmentsViewController: UITableViewController {
     }
     
     func setAttachments(_ attachments: [CompositionAttachment]) {
-        self.attachments = attachments
+        tableView.performBatchUpdates({
-        tableView.reloadData()
+            tableView.deleteRows(at: self.attachments.indices.map { IndexPath(row: $0, section: 0) }, with: .automatic)
+            self.attachments = attachments
+            tableView.insertRows(at: self.attachments.indices.map { IndexPath(row: $0, section: 0) }, with: .automatic)
+        })
         updateHeightConstraint()
         delegate?.composeRequiresAttachmentDescriptionsDidChange()
     }
@@ -88,6 +93,35 @@ class ComposeAttachmentsViewController: UITableViewController {
         let cell = tableView.cellForRow(at: IndexPath(row: 0, section: 1)) as! AddAttachmentTableViewCell
         cell.setEnabled(isAddAttachmentsButtonEnabled())
     }
+
+    override func canPaste(_ itemProviders: [NSItemProvider]) -> Bool {
+        switch mastodonController.instance.instanceType {
+        case .pleroma:
+            return true
+        case .mastodon:
+            return itemProviders.count + attachments.count <= 4
+        }
+    }
+    
+    override func paste(itemProviders: [NSItemProvider]) {
+        for provider in itemProviders {
+            provider.loadObject(ofClass: UIImage.self) { (object, error) in
+                if let error = error {
+                    fatalError("Couldn't load image from NSItemProvider: \(error)")
+                }
+                guard let image = object as? UIImage else {
+                    fatalError("Couldn't convert object from NSItemProvider to UIImage")
+                }
+                
+                DispatchQueue.main.async {
+                    let attachment = CompositionAttachment(data: .image(image))
+                    self.attachments.append(attachment)
+                    self.tableView.insertRows(at: [IndexPath(row: self.attachments.count - 1, section: 0)], with: .automatic)
+                    self.updateHeightConstraint()
+                }
+            }
+        }
+    }
     
     func uploadAll(stepProgress: @escaping () -> Void, completion: @escaping (_ success: Bool, _ uploadedAttachments: [Attachment]) -> Void) {
         let group = DispatchGroup()

Tusker/Screens/Compose/ComposeViewController.swift

@@ -146,6 +146,8 @@ class ComposeViewController: UIViewController {
         composeAttachmentsViewController.tableView.isScrollEnabled = false
         composeAttachmentsViewController.tableView.translatesAutoresizingMaskIntoConstraints = false
         embedChild(composeAttachmentsViewController, in: composeAttachmentsContainerView)
+        
+        pasteConfiguration = composeAttachmentsViewController.pasteConfiguration
 
         NotificationCenter.default.addObserver(self, selector: #selector(contentWarningTextFieldDidChange), name: UITextField.textDidChangeNotification, object: contentWarningTextField)
     }
@@ -329,6 +331,14 @@ class ComposeViewController: UIViewController {
         xcbSession?.complete(with: .cancel)
     }
     
+    override func canPaste(_ itemProviders: [NSItemProvider]) -> Bool {
+        return composeAttachmentsViewController.canPaste(itemProviders)
+    }
+    
+    override func paste(itemProviders: [NSItemProvider]) {
+        composeAttachmentsViewController.paste(itemProviders: itemProviders)
+    }
+    
     // MARK: - Interaction
     
     @objc func showSaveAndClosePrompt() {