feat: added markdown links

frontend/app_flowy/packages/appflowy_editor/lib/src/service/internal_key_event_handlers/markdown_syntax_to_styled_text.dart

@@ -124,3 +124,58 @@ ShortcutEventHandler backquoteToCodeHandler = (editorState, event) {
 
   return KeyEventResult.handled;
 };
+
+/// To create a link, enclose the link text in brackets (e.g., [link text]).
+/// Then, immediately follow it with the URL in parentheses (e.g., (https://example.com)).
+ShortcutEventHandler markdownLinkToLinkHandler = (editorState, event) {
+  final selectionService = editorState.service.selectionService;
+  final selection = selectionService.currentSelection.value;
+  final textNodes = selectionService.currentSelectedNodes.whereType<TextNode>();
+  if (selection == null || !selection.isSingle || textNodes.length != 1) {
+    return KeyEventResult.ignored;
+  }
+
+  // find all of the indexs for important characters
+  final textNode = textNodes.first;
+  final text = textNode.toRawString();
+  final firstOpeningBracket = text.indexOf('[');
+  final firstClosingBracket = text.indexOf(']');
+
+  // use regex to validate the format of the link
+  // note: this enforces that the link has http or https
+  final regexp = RegExp(r'\[([\w\s\d]+)\]\(((?:\/|https?:\/\/)[\w\d./?=#]+)$');
+  final match = regexp.firstMatch(text);
+  if (match == null) {
+    return KeyEventResult.ignored;
+  }
+
+  // extract the text and the url of the link
+  final linkText = match.group(1);
+  final linkUrl = match.group(2);
+
+  // Delete the initial opening bracket,
+  // update the href attribute of the text surrounded by [ ] to the url,
+  // delete everything after the text,
+  // and update the cursor position.
+  TransactionBuilder(editorState)
+    ..deleteText(textNode, firstOpeningBracket, 1)
+    ..formatText(
+      textNode,
+      firstOpeningBracket,
+      firstClosingBracket - firstOpeningBracket - 1,
+      {
+        BuiltInAttributeKey.href: linkUrl,
+      },
+    )
+    ..deleteText(textNode, firstClosingBracket - 1,
+        selection.end.offset - firstClosingBracket)
+    ..afterSelection = Selection.collapsed(
+      Position(
+        path: textNode.path,
+        offset: firstOpeningBracket + linkText!.length,
+      ),
+    )
+    ..commit();
+
+  return KeyEventResult.handled;
+};

frontend/app_flowy/packages/appflowy_editor/lib/src/service/shortcut_event/built_in_shortcut_events.dart

@@ -257,6 +257,11 @@ List<ShortcutEvent> builtInShortcutEvents = [
     command: 'backquote',
     handler: backquoteToCodeHandler,
   ),
+  ShortcutEvent(
+    key: 'Markdown link to link',
+    command: 'shift+parenthesis right',
+    handler: markdownLinkToLinkHandler,
+  ),
   // https://github.com/flutter/flutter/issues/104944
   // Workaround: Using space editing on the web platform often results in errors,
   //  so adding a shortcut event to handle the space input instead of using the