Implement link previews for group conversations

Signal/src/Loki/LokiGroupChatPoller.swift

@@ -93,6 +93,15 @@ public final class LokiGroupChatPoller : NSObject {
                 guard let messageID = message.uniqueId else { return print("[Loki] Failed to save group message.") }
                 storage.setIDForMessageWithServerID(UInt(messageServerID), to: messageID, in: transaction)
             }
+            if let url = OWSLinkPreview.previewUrl(forMessageBodyText: message.body, selectedRange: nil) {
+                let _ = OWSLinkPreview.tryToBuildPreviewInfo(previewUrl: url).done { linkPreviewDraft in
+                    OWSPrimaryStorage.shared().dbReadWriteConnection.readWrite { transaction in
+                        guard let linkPreview = try? OWSLinkPreview.buildValidatedLinkPreview(fromInfo: linkPreviewDraft, transaction: transaction) else { return }
+                        message.linkPreview = linkPreview
+                        message.save(with: transaction)
+                    }
+                }
+            }
         }
         // Poll
         let _ = LokiGroupChatAPI.getMessages(for: group.serverID, on: group.server).done { messages in

SignalServiceKit/src/Messages/Interactions/OWSLinkPreview.swift

@@ -435,6 +435,11 @@ public class OWSLinkPreview: MTLModel {
         return previewUrl(forMessageBodyText: body, selectedRange: selectedRange)
     }
 
+    @objc
+    public class func previewURL(forRawBodyText body: String?) -> String? {
+        return previewUrl(forMessageBodyText: body, selectedRange: nil)
+    }
+
     public class func previewUrl(forMessageBodyText body: String?, selectedRange: NSRange?) -> String? {
         AssertIsOnMainThread()
 

SignalServiceKit/src/Messages/OWSMessageManager.m

@@ -1407,19 +1407,18 @@ NS_ASSUME_NONNULL_BEGIN
                     [self.primaryStorage setIDForMessageWithServerID:dataMessage.publicChatInfo.serverID to:incomingMessage.uniqueId in:transaction];
                 }
 
-                if (linkPreview != nil) {
-                    [OWSLinkPreview tryToBuildPreviewInfoObjcWithPreviewUrl:linkPreview.urlString]
+                NSString *url = [OWSLinkPreview previewURLForRawBodyText:incomingMessage.body];
+                if (url != nil) {
+                    [OWSLinkPreview tryToBuildPreviewInfoObjcWithPreviewUrl:url]
                     .thenOn(dispatch_get_main_queue(), ^(OWSLinkPreviewDraft *linkPreviewDraft) {
-                        if (linkPreviewDraft.jpegImageData == nil) { return; }
                         [OWSPrimaryStorage.sharedManager.dbReadWriteConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
-                            NSString *attachmentID = [OWSLinkPreview buildValidatedLinkPreviewFromInfo:linkPreviewDraft transaction:transaction error:nil].imageAttachmentId;
-                            linkPreview.imageAttachmentId = attachmentID;
+                            OWSLinkPreview *linkPreview = [OWSLinkPreview buildValidatedLinkPreviewFromInfo:linkPreviewDraft transaction:transaction error:nil];
                             incomingMessage.linkPreview = linkPreview;
                             [incomingMessage saveWithTransaction:transaction];
                         }];
                     });
-                };
-                
+                }
+
                 return incomingMessage;
             }
             default: {