Try to avoid generating link previews while user is actively editing the URL

Signal/src/ViewControllers/ConversationView/ConversationInputTextView.h

@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import <SignalMessaging/OWSTextView.h>
@@ -23,6 +23,7 @@ NS_ASSUME_NONNULL_BEGIN
 @protocol ConversationTextViewToolbarDelegate <NSObject>
 
 - (void)textViewDidChange:(UITextView *)textView;
+- (void)textViewDidChangeSelection:(UITextView *)textView;
 
 @end
 

Signal/src/ViewControllers/ConversationView/ConversationInputTextView.m

@@ -189,6 +189,11 @@ NS_ASSUME_NONNULL_BEGIN
     [self.textViewToolbarDelegate textViewDidChange:self];
 }
 
+- (void)textViewDidChangeSelection:(UITextView *)textView
+{
+    [self.textViewToolbarDelegate textViewDidChangeSelection:self];
+}
+
 #pragma mark - Key Commands
 
 - (nullable NSArray<UIKeyCommand *> *)keyCommands

Signal/src/ViewControllers/ConversationView/ConversationInputToolbar.m

@@ -869,6 +869,11 @@ const CGFloat kMaxTextViewHeight = 98;
     [self updateInputLinkPreview];
 }
 
+- (void)textViewDidChangeSelection:(UITextView *)textView
+{
+    [self updateInputLinkPreview];
+}
+
 - (void)updateHeightWithTextView:(UITextView *)textView
 {
     // compute new height assuming width is unchanged
@@ -922,7 +927,10 @@ const CGFloat kMaxTextViewHeight = 98;
         return;
     }
 
-    NSString *_Nullable previewUrl = [OWSLinkPreview previewUrlForMessageBodyText:body];
+    // It's key that we use the *raw/unstripped* text, so we can reconcile cursor position with the
+    // selectedRange.
+    NSString *_Nullable previewUrl = [OWSLinkPreview previewUrlForRawBodyText:self.inputTextView.text
+                                                                selectedRange:self.inputTextView.selectedRange];
     if (previewUrl.length < 1) {
         [self clearLinkPreviewStateAndView];
         return;

SignalServiceKit/src/Messages/Interactions/OWSLinkPreview.swift

@@ -432,7 +432,11 @@ public class OWSLinkPreview: MTLModel {
     private static var previewUrlCache: NSCache<AnyObject, AnyObject> = NSCache()
 
     @objc
-    public class func previewUrl(forMessageBodyText body: String?) -> String? {
+    public class func previewUrl(forRawBodyText body: String?, selectedRange: NSRange) -> String? {
+        return previewUrl(forMessageBodyText: body, selectedRange: selectedRange)
+    }
+
+    public class func previewUrl(forMessageBodyText body: String?, selectedRange: NSRange?) -> String? {
         AssertIsOnMainThread()
 
         // Exit early if link previews are not enabled in order to avoid
@@ -440,10 +444,15 @@ public class OWSLinkPreview: MTLModel {
         guard OWSLinkPreview.featureEnabled else {
             return nil
         }
+
         guard SSKPreferences.areLinkPreviewsEnabled() else {
             return nil
         }
 
+        guard let body = body else {
+            return nil
+        }
+
         if let cachedUrl = previewUrlCache.object(forKey: body as AnyObject) as? String {
             Logger.verbose("URL parsing cache hit.")
             guard cachedUrl.count > 0 else {
@@ -451,27 +460,45 @@ public class OWSLinkPreview: MTLModel {
             }
             return cachedUrl
         }
-        let previewUrls = allPreviewUrls(forMessageBodyText: body)
-        guard let previewUrl = previewUrls.first else {
+        let previewUrlMatches = allPreviewUrlMatches(forMessageBodyText: body)
+        guard let urlMatch = previewUrlMatches.first else {
             // Use empty string to indicate "no preview URL" in the cache.
             previewUrlCache.setObject("" as AnyObject, forKey: body as AnyObject)
             return nil
         }
 
-        previewUrlCache.setObject(previewUrl as AnyObject, forKey: body as AnyObject)
-        return previewUrl
+        if let selectedRange = selectedRange {
+            Logger.verbose("match: urlString: \(urlMatch.urlString) range: \(urlMatch.matchRange) selectedRange: \(selectedRange)")
+            if selectedRange.location != body.count,
+                urlMatch.matchRange.intersection(selectedRange) != nil {
+                Logger.debug("ignoring URL, since the user is currently editing it.")
+                // we don't want to cache the result here, as we want to fetch the link preview
+                // if the user moves the cursor.
+                return nil
+            }
+            Logger.debug("considering URL, since the user is not currently editing it.")
+        }
+
+        previewUrlCache.setObject(urlMatch.urlString as AnyObject, forKey: body as AnyObject)
+        return urlMatch.urlString
     }
 
-    class func allPreviewUrls(forMessageBodyText body: String?) -> [String] {
+    struct URLMatchResult {
+        let urlString: String
+        let matchRange: NSRange
+    }
+
+    class func allPreviewUrls(forMessageBodyText body: String) -> [String] {
+        return allPreviewUrlMatches(forMessageBodyText: body).map { $0.urlString }
+    }
+
+    class func allPreviewUrlMatches(forMessageBodyText body: String) -> [URLMatchResult] {
         guard OWSLinkPreview.featureEnabled else {
             return []
         }
         guard SSKPreferences.areLinkPreviewsEnabled() else {
             return []
         }
-        guard let body = body else {
-            return []
-        }
 
         let detector: NSDataDetector
         do {
@@ -481,7 +508,7 @@ public class OWSLinkPreview: MTLModel {
             return []
         }
 
-        var previewUrls = [String]()
+        var urlMatches: [URLMatchResult] = []
         let matches = detector.matches(in: body, options: [], range: NSRange(location: 0, length: body.count))
         for match in matches {
             guard let matchURL = match.url else {
@@ -490,10 +517,11 @@ public class OWSLinkPreview: MTLModel {
             }
             let urlString = matchURL.absoluteString
             if isValidLinkUrl(urlString) {
-                previewUrls.append(urlString)
+                let matchResult = URLMatchResult(urlString: urlString, matchRange: match.range)
+                urlMatches.append(matchResult)
             }
         }
-        return previewUrls
+        return urlMatches
     }
 
     // MARK: - Preview Construction