Support dragging and dropping attachments in the compose view controller

Allos dragging in attachments from other apps and drag/dropping with the
compose VC to reorder attachments

Tusker/Info.plist

@@ -2,6 +2,17 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
+	<key>UTExportedTypeDeclarations</key>
+	<array>
+		<dict>
+			<key>UTTypeConformsTo</key>
+			<array/>
+			<key>UTTypeIdentifier</key>
+			<string>space.vaccor.Tusker.composition-attachment</string>
+			<key>UTTypeTagSpecification</key>
+			<dict/>
+		</dict>
+	</array>
 	<key>CFBundleDevelopmentRegion</key>
 	<string>$(DEVELOPMENT_LANGUAGE)</string>
 	<key>CFBundleExecutable</key>
@@ -49,7 +60,7 @@
 	<key>NSMicrophoneUsageDescription</key>
 	<string>Post videos from the camera.</string>
 	<key>NSPhotoLibraryAddUsageDescription</key>
-	<string>Save photos directly from other people's posts.</string>
+	<string>Save photos directly from other people&apos;s posts.</string>
 	<key>NSPhotoLibraryUsageDescription</key>
 	<string>Post photos from the photo library.</string>
 	<key>NSUserActivityTypes</key>

Tusker/Screens/Compose/Attachments/ComposeAttachmentTableViewCell.swift

@@ -23,6 +23,7 @@ class ComposeAttachmentTableViewCell: UITableViewCell {
     @IBOutlet weak var assetImageView: UIImageView!
     @IBOutlet weak var descriptionTextView: UITextView!
     @IBOutlet weak var descriptionPlaceholderLabel: UILabel!
+    @IBOutlet weak var removeButton: UIButton!
     
     var attachment: CompositionAttachment!
     
@@ -38,7 +39,7 @@ class ComposeAttachmentTableViewCell: UITableViewCell {
     func updateUI(for attachment: CompositionAttachment) {
         self.attachment = attachment
         
-        descriptionTextView.text = attachment.description
+        descriptionTextView.text = attachment.attachmentDescription
         updateDescriptionPlaceholderLabel()
 
         switch attachment.data {
@@ -63,6 +64,16 @@ class ComposeAttachmentTableViewCell: UITableViewCell {
         descriptionPlaceholderLabel.isHidden = !descriptionTextView.text.isEmpty
     }
     
+    func setEnabled(_ enabled: Bool) {
+        descriptionTextView.isEditable = enabled
+        removeButton.isEnabled = enabled
+    }
+    
+    override func prepareForReuse() {
+        super.prepareForReuse()
+        assetImageView.image = nil
+    }
+
     @IBAction func removeButtonPressed(_ sender: Any) {
         delegate?.removeAttachment(self)
     }
@@ -72,7 +83,7 @@ class ComposeAttachmentTableViewCell: UITableViewCell {
 extension ComposeAttachmentTableViewCell: UITextViewDelegate {
     func textViewDidChange(_ textView: UITextView) {
         delegate?.attachmentDescriptionChanged(self)
-        attachment.description = textView.text
+        attachment.attachmentDescription = textView.text
         updateDescriptionPlaceholderLabel()
     }
 }

Tusker/Screens/Compose/Attachments/ComposeAttachmentTableViewCell.xib

@@ -27,6 +27,7 @@
                         <subviews>
                             <imageView clipsSubviews="YES" userInteractionEnabled="NO" contentMode="scaleAspectFill" horizontalHuggingPriority="251" verticalHuggingPriority="251" translatesAutoresizingMaskIntoConstraints="NO" id="GLY-o8-47z">
                                 <rect key="frame" x="0.0" y="0.0" width="80" height="80"/>
+                                <color key="backgroundColor" systemColor="secondarySystemBackgroundColor" red="0.94901960780000005" green="0.94901960780000005" blue="0.96862745100000003" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                                 <constraints>
                                     <constraint firstAttribute="width" constant="80" id="X6q-g9-dPN"/>
                                     <constraint firstAttribute="height" constant="80" id="xgQ-E3-0QI"/>
@@ -72,6 +73,7 @@
                 <outlet property="assetImageView" destination="GLY-o8-47z" id="hZH-ur-m4z"/>
                 <outlet property="descriptionPlaceholderLabel" destination="h6T-x4-yzl" id="jBe-R0-Sfn"/>
                 <outlet property="descriptionTextView" destination="cwP-Eh-5dJ" id="pxJ-zF-GKC"/>
+                <outlet property="removeButton" destination="Lvf-I9-aV3" id="3qk-Zr-je1"/>
             </connections>
             <point key="canvasLocation" x="107" y="181"/>
         </tableViewCell>

Tusker/Screens/Compose/Attachments/ComposeAttachmentsViewController.swift

@@ -8,6 +8,7 @@
 
 import UIKit
 import Pachyderm
+import MobileCoreServices
 
 protocol ComposeAttachmentsViewControllerDelegate: class {
     func composeSelectedAttachmentsDidChange()
@@ -55,10 +56,20 @@ class ComposeAttachmentsViewController: UITableViewController {
         tableView.register(UINib(nibName: "AddAttachmentTableViewCell", bundle: .main), forCellReuseIdentifier: "addAttachment")
         tableView.register(UINib(nibName: "ComposeAttachmentTableViewCell", bundle: .main), forCellReuseIdentifier: "composeAttachment")
         
-        heightConstraint = tableView.heightAnchor.constraint(equalToConstant: tableView.contentSize.height)
+        // you would think the table view could handle this itself, but no, using a constraint on the table view's contentLayoutGuide doesn't work
+        // add extra space, so when dropping items, the add attachment cell doesn't disappear
+        heightConstraint = tableView.heightAnchor.constraint(equalToConstant: tableView.contentSize.height + 80)
         heightConstraint.isActive = true
 
-        pasteConfiguration = UIPasteConfiguration(forAccepting: UIImage.self)
+        // prevents extra separator lines from appearing when the height of the table view is greater than the height of the content
+        tableView.tableFooterView = UIView()
+        
+        pasteConfiguration = UIPasteConfiguration(forAccepting: CompositionAttachment.self)
+        
+        // enable dragging on iPhone to allow reordering
+        tableView.dragInteractionEnabled = true
+        tableView.dragDelegate = self
+        tableView.dropDelegate = self
     }
     
     override func viewWillAppear(_ animated: Bool) {
@@ -77,7 +88,8 @@ class ComposeAttachmentsViewController: UITableViewController {
     }
     
     private func updateHeightConstraint() {
-        heightConstraint.constant = tableView.contentSize.height
+        // add extra space, so when dropping items, the add attachment cell doesn't disappear
+        heightConstraint.constant = tableView.contentSize.height + 80
     }
     
     private func isAddAttachmentsButtonEnabled() -> Bool {
@@ -90,7 +102,7 @@ class ComposeAttachmentsViewController: UITableViewController {
     }
     
     private func updateAddAttachmentsButtonEnabled() {
-        let cell = tableView.cellForRow(at: IndexPath(row: 0, section: 1)) as! AddAttachmentTableViewCell
+        guard let cell = tableView.cellForRow(at: IndexPath(row: 0, section: 1)) as? AddAttachmentTableViewCell else { return }
         cell.setEnabled(isAddAttachmentsButtonEnabled())
     }
 
@@ -105,16 +117,15 @@ class ComposeAttachmentsViewController: UITableViewController {
     
     override func paste(itemProviders: [NSItemProvider]) {
         for provider in itemProviders {
-            provider.loadObject(ofClass: UIImage.self) { (object, error) in
+            provider.loadObject(ofClass: CompositionAttachment.self) { (object, error) in
                 if let error = error {
                     fatalError("Couldn't load image from NSItemProvider: \(error)")
                 }
-                guard let image = object as? UIImage else {
+                guard let attachment = object as? CompositionAttachment else {
-                    fatalError("Couldn't convert object from NSItemProvider to UIImage")
+                    fatalError("Couldn't convert object from NSItemProvider to CompositionAttachment")
                 }
                 
                 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()
@@ -219,6 +230,7 @@ class ComposeAttachmentsViewController: UITableViewController {
             let cell = tableView.dequeueReusableCell(withIdentifier: "composeAttachment", for: indexPath) as! ComposeAttachmentTableViewCell
             cell.delegate = self
             cell.updateUI(for: attachment)
+            cell.setEnabled(true)
             return cell
         case 1:
             let cell = tableView.dequeueReusableCell(withIdentifier: "addAttachment", for: indexPath) as! AddAttachmentTableViewCell
@@ -229,6 +241,12 @@ class ComposeAttachmentsViewController: UITableViewController {
         }
     }
     
+    override func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
+        guard sourceIndexPath != destinationIndexPath, sourceIndexPath.section == 0, destinationIndexPath.section == 0 else { return }
+        
+        attachments.insert(attachments.remove(at: sourceIndexPath.row), at: destinationIndexPath.row)
+    }
+    
     // MARK: Table view delegate
     
     override func tableView(_ tableView: UITableView, willSelectRowAt indexPath: IndexPath) -> IndexPath? {
@@ -254,6 +272,88 @@ class ComposeAttachmentsViewController: UITableViewController {
 
 }
 
+extension ComposeAttachmentsViewController: UITableViewDragDelegate {
+    func tableView(_ tableView: UITableView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
+        let attachment = attachments[indexPath.row]
+        let provider = NSItemProvider(object: attachment)
+        let dragItem = UIDragItem(itemProvider: provider)
+        dragItem.localObject = attachment
+        return [dragItem]
+    }
+    
+    func tableView(_ tableView: UITableView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
+        let attachment = attachments[indexPath.row]
+        let provider = NSItemProvider(object: attachment)
+        let dragItem = UIDragItem(itemProvider: provider)
+        dragItem.localObject = attachment
+        return [dragItem]
+    }
+    
+    func tableView(_ tableView: UITableView, dragPreviewParametersForRowAt indexPath: IndexPath) -> UIDragPreviewParameters? {
+        let cell = tableView.cellForRow(at: indexPath) as! ComposeAttachmentTableViewCell
+        let rect = cell.convert(cell.assetImageView.bounds, from: cell.assetImageView)
+        let path = UIBezierPath(roundedRect: rect, cornerRadius: cell.assetImageView.layer.cornerRadius)
+        let params = UIDragPreviewParameters()
+        params.visiblePath = path
+        return params
+    }
+}
+
+extension ComposeAttachmentsViewController: UITableViewDropDelegate {
+    func tableView(_ tableView: UITableView, canHandle session: UIDropSession) -> Bool {
+        return session.canLoadObjects(ofClass: CompositionAttachment.self)
+    }
+    
+    func tableView(_ tableView: UITableView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UITableViewDropProposal {
+        // if items were dragged out of ourself, then the items are only being moved
+        if tableView.hasActiveDrag {
+            // todo: should moving multiple items actually be prohibited?
+            if session.items.count > 1 {
+                return UITableViewDropProposal(operation: .cancel)
+            } else {
+                return UITableViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
+            }
+        } else {
+            return UITableViewDropProposal(operation: .copy, intent: .insertAtDestinationIndexPath)
+        }
+    }
+    
+    func tableView(_ tableView: UITableView, performDropWith coordinator: UITableViewDropCoordinator) {
+        let destinationIndexPath = coordinator.destinationIndexPath ?? IndexPath(row: attachments.count, section: 0)
+        
+        // we don't need to handle local items here, when the .move operation is used returned from the tableView(_:dropSessionDidUpdate:withDestinationIndexPath:) method,
+        // the table view will handle animating and call the normal data source tableView(_:moveRowAt:to:)
+        
+        for (index, item) in coordinator.items.enumerated() {
+            let provider = item.dragItem.itemProvider
+            
+            if provider.canLoadObject(ofClass: CompositionAttachment.self) {
+                let indexPath = IndexPath(row: destinationIndexPath.row + index, section: 0)
+                let placeholder = UITableViewDropPlaceholder(insertionIndexPath: indexPath, reuseIdentifier: "composeAttachment", rowHeight: 96)
+                placeholder.cellUpdateHandler = { (cell) in
+                    let cell = cell as! ComposeAttachmentTableViewCell
+                    cell.setEnabled(false)
+                }
+                let placeholderContext = coordinator.drop(item.dragItem, to: placeholder)
+                
+                provider.loadObject(ofClass: CompositionAttachment.self) { (object, error) in
+                    DispatchQueue.main.async {
+                        if let attachment = object as? CompositionAttachment {
+                            placeholderContext.commitInsertion { (insertionIndexPath) in
+                                self.attachments.insert(attachment, at: insertionIndexPath.row)
+                            }
+                        } else {
+                            placeholderContext.deletePlaceholder()
+                        }
+                    }
+                }
+            }
+        }
+        
+        updateHeightConstraint()
+    }
+}
+
 extension ComposeAttachmentsViewController: AssetPickerViewControllerDelegate {
     func assetPicker(_ assetPicker: AssetPickerViewController, shouldAllowAssetOfType type: CompositionAttachmentData.AttachmentType) -> Bool {
         switch mastodonController.instance.instanceType {

Tusker/Screens/Compose/Attachments/CompositionAttachment.swift

@@ -7,19 +7,72 @@
 //
 
 import Foundation
+import UIKit
+import MobileCoreServices
+
+final class CompositionAttachment: NSObject, Codable {
+    static let typeIdentifier = "space.vaccor.Tusker.composition-attachment"
     
-class CompositionAttachment: Codable {
     let data: CompositionAttachmentData
-    var description: String
+    var attachmentDescription: String
     
     init(data: CompositionAttachmentData, description: String = "") {
         self.data = data
-        self.description = description
+        self.attachmentDescription = description
     }
-}
     
-extension CompositionAttachment: Equatable {
     static func ==(lhs: CompositionAttachment, rhs: CompositionAttachment) -> Bool {
         return lhs.data == rhs.data
     }
 }
+
+private let imageType = kUTTypeImage as String
+private let dataType = kUTTypeData as String
+
+extension CompositionAttachment: NSItemProviderWriting {
+    static var writableTypeIdentifiersForItemProvider: [String] {
+        [typeIdentifier]
+    }
+    
+    func loadData(withTypeIdentifier typeIdentifier: String, forItemProviderCompletionHandler completionHandler: @escaping (Data?, Error?) -> Void) -> Progress? {
+        if typeIdentifier == CompositionAttachment.typeIdentifier {
+            do {
+                completionHandler(try PropertyListEncoder().encode(self), nil)
+            } catch {
+                completionHandler(nil, error)
+            }
+        }
+        
+        completionHandler(nil, ItemProviderError.incompatibleTypeIdentifier)
+        return nil
+    }
+    
+    enum ItemProviderError: Error {
+        case incompatibleTypeIdentifier
+
+        var localizedDescription: String {
+            switch self {
+            case .incompatibleTypeIdentifier:
+                return "Cannot provide data for given type"
+            }
+        }
+    }
+}
+
+extension CompositionAttachment: NSItemProviderReading {
+    static var readableTypeIdentifiersForItemProvider: [String] {
+        [typeIdentifier] + UIImage.readableTypeIdentifiersForItemProvider + NSURL.readableTypeIdentifiersForItemProvider
+    }
+    
+    static func object(withItemProviderData data: Data, typeIdentifier: String) throws -> Self {
+        if typeIdentifier == CompositionAttachment.typeIdentifier {
+            return try PropertyListDecoder().decode(Self.self, from: data)
+        } else if UIImage.readableTypeIdentifiersForItemProvider.contains(typeIdentifier), let image = try? UIImage.object(withItemProviderData: data, typeIdentifier: typeIdentifier) {
+            return CompositionAttachment(data: .image(image)) as! Self
+        } else if NSURL.readableTypeIdentifiersForItemProvider.contains(typeIdentifier), let url = try? NSURL.object(withItemProviderData: data, typeIdentifier: typeIdentifier) as URL {
+            return CompositionAttachment(data: .video(url)) as! Self
+        } else {
+            throw ItemProviderError.incompatibleTypeIdentifier
+        }
+    }
+}