Add ensureTrailingNewLine to OrgContent, OrgHeadline, OrgSection

Author: amake

lib/src/org/model/org_content.dart

@@ -30,4 +30,18 @@ class OrgContent extends OrgParentNode {
 
   OrgContent copyWith({List<OrgNode>? children, String? id}) =>
       OrgContent(children ?? this.children, id ?? this.id);
+
+  OrgContent ensureTrailingNewLine() {
+    if (children.isNotEmpty) {
+      final [...rest, last] = children;
+      if (last is OrgElement) {
+        return copyWith(
+          children: [...rest, last.ensureTrailingNewLine()],
+        );
+      }
+    }
+    return copyWith(
+      children: [...children, OrgParagraph('', OrgContent([]), '\n')],
+    );
+  }
 }

lib/src/org/model/org_headline.dart

@@ -166,4 +166,7 @@ class OrgHeadline extends OrgParentNode {
             ?.isEndState(keyword!.value) ==
         true;
   }
+
+  OrgHeadline ensureTrailingNewLine() =>
+      trailing.contains('\n') ? this : copyWith(trailing: '$trailing\n');
 }

lib/src/org/model/org_section.dart

@@ -210,11 +210,8 @@ class OrgSection extends OrgTree {
       );
 
   @override
-  OrgSection _ensureContent({required OrgContent content}) => copyWith(
-      headline: headline.trailing?.contains('\n') == true
-          ? headline
-          : headline.copyWith(trailing: '\n'),
-      content: content);
+  OrgSection _ensureContent({required OrgContent content}) =>
+      copyWith(headline: headline.ensureTrailingNewLine(), content: content);
 
   @override
   bool contains(Pattern pattern, {bool includeChildren = true}) =>
@@ -223,4 +220,10 @@ class OrgSection extends OrgTree {
 
   @override
   String toString() => 'OrgSection';
+
+  OrgSection ensureTrailingNewLine() {
+    return content == null
+        ? copyWith(headline: headline.ensureTrailingNewLine())
+        : copyWith(content: content!.ensureTrailingNewLine());
+  }
 }