Refactor: extract helpers to satisfy detekt (throws, returns, loops)

web/src/main/kotlin/ru/ysu/lms/web/learn/LearnController.kt

@@ -32,6 +32,21 @@ class LearnController(
 
     private fun isAdmin(session: HttpSession): Boolean = (session.getAttribute(SessionKeys.USER) as? SessionUser)?.isAdmin == true
 
+    private fun treeContainsArticle(
+        tree: ContentTreeNodeDto,
+        chapter: String,
+        section: String,
+        article: String,
+    ): Boolean {
+        val sec =
+            tree.chapters
+                .firstOrNull { it.slug == chapter }
+                ?.sections
+                ?.firstOrNull { it.slug == section }
+                ?: return false
+        return sec.articles.any { it.slug == article }
+    }
+
     private fun sectionChoices(tree: ContentTreeNodeDto): List<Map<String, String>> =
         tree.chapters.flatMap { chapter ->
             chapter.sections.map { section ->
@@ -103,9 +118,7 @@ class LearnController(
     ): String {
         val admin = isAdmin(session)
         val tree: ContentTreeNodeDto = api.contentTree(token(session), all = admin)
-        val ch = tree.chapters.firstOrNull { it.slug == chapter } ?: return "redirect:/learn"
-        val sec = ch.sections.firstOrNull { it.slug == section } ?: return "redirect:/learn"
-        if (sec.articles.none { it.slug == article }) return "redirect:/learn"
+        if (!treeContainsArticle(tree, chapter, section, article)) return "redirect:/learn"
 
         val a: ContentArticleDto =
             try {