Add support for link previews on iOS

Sources/Share/Link.swift

@@ -0,0 +1,82 @@
+#if canImport(UIKit)
+
+@_exported import LinkPresentation
+
+extension Share {
+
+    @available(iOS 13.0, *)
+    public class Link: NSObject, UIActivityItemSource {
+        public let url: URL
+        public let placeholder: Any
+
+        public var title: String? = nil
+        public var icon: URL? = nil
+        public var image: URL? = nil
+        public var video: URL? = nil
+
+        public typealias ShareValue = (_ link: Link, _ activityType: UIActivity.ActivityType?) -> Any
+        private let shareValue: ShareValue?
+
+        public func activityViewControllerLinkMetadata(_ activityViewController: UIActivityViewController) -> LPLinkMetadata? {
+            let metadata = LPLinkMetadata()
+
+            metadata.title = title
+            metadata.originalURL = url
+
+            if let url = icon {
+                metadata.iconProvider = NSItemProvider(contentsOf: url)
+            }
+
+            if let url = image {
+                metadata.imageProvider = NSItemProvider(contentsOf: url)
+            }
+
+            if let url = video, let scheme = url.scheme {
+                if scheme.hasPrefix("http") {
+                    metadata.remoteVideoURL = url
+                } else {
+                    metadata.videoProvider = NSItemProvider(contentsOf: url)
+                }
+            }
+
+            return metadata
+        }
+
+        public func activityViewControllerPlaceholderItem(_ activityViewController: UIActivityViewController) -> Any {
+            return placeholder
+        }
+
+        public func activityViewController(_ activityViewController: UIActivityViewController, itemForActivityType activityType: UIActivity.ActivityType?) -> Any? {
+
+            return shareValue?(self, activityType) ?? url
+        }
+
+        public init(url: URL, placeholder: Any = "", shareValue: ShareValue? = nil) {
+            self.url = url
+            self.placeholder = placeholder
+            self.shareValue = shareValue
+        }
+
+        public func title(_ title: String) -> Link {
+            self.title = title
+            return self
+        }
+
+        public func icon(_ url: URL) -> Link {
+            icon = url
+            return self
+        }
+
+        public func image(_ url: URL) -> Link {
+            self.image = url
+            return self
+        }
+
+        public func video(_ url: URL) -> Link {
+            self.video = url
+            return self
+        }
+    }
+}
+
+#endif