altered DcMsg model to retrieve prev and next media

deltachat-ios/DC/Wrapper.swift

@@ -880,6 +880,32 @@ class DcMsg: MessageType {
     func sendInChat(id: Int) {
         dc_send_msg(mailboxPointer, UInt32(id), messagePointer)
     }
+
+    func previousMediaURLs() -> [URL] {
+        var urls: [URL] = []
+        var prev: Int = Int(dc_get_next_media(mailboxPointer, UInt32(id), -1, Int32(type), 0, 0))
+        while prev != 0 {
+            let prevMessage = DcMsg(id: prev)
+            if let url = prevMessage.fileURL {
+                urls.insert(url, at: 0)
+            }
+            prev = Int(dc_get_next_media(mailboxPointer, UInt32(prevMessage.id), -1, Int32(prevMessage.type), 0, 0))
+        }
+        return urls
+    }
+
+    func nextMediaURLs() -> [URL] {
+        let urls: [URL] = []
+        var next: Int = Int(dc_get_next_media(mailboxPointer, UInt32(message.id), 1, Int32(message.type), 0, 0))
+        while next != 0 {
+            let nextMessage = DcMsg(id: next)
+            if let url = nextMessage.fileURL {
+                urls.append(url)
+            }
+            next = Int(dc_get_next_media(mailboxPointer, UInt32(nextMessage.id), 1, Int32(nextMessage.type), 0, 0))
+        }
+        return urls
+    }
 }
 
 class DcContact {