Transform a list of html headings and return a TOC tree

heading-tree.cljc

;; I had to create a Table of Contents component for my personal site, and in
;; order to do that I had to scan all headings in the document (using .querySelectorAll)
;; and transform them into a list of maps that I could use to nest them properly.
;; The idea is to get a plain vector of nodes created using `make-node` and return
;; a tree in which nodes are nested according to their level.

(defn make-node
  "Creates the representation of an HTML heading. You can search for all headings 
   in your document and convert them to this structure."
  [tag-name tag-level value]
  {:tag (keyword tag-name)
   :level tag-level
   :value value})

(defn parse-nodes
  "Given a vector of nodes created with `make-node`, transforms the vector into a
   tree composed of nested vectors."
  [elements current-level]
  (loop [elements-left elements
         parsed-elements []]
    (if-not (empty? elements-left)
      (let [next-element (first elements-left)
            element-level (:level next-element)]
        (cond
          (> element-level current-level) (let [[r-parsed r-left] (parse-nodes elements-left (inc current-level))]
                                                     (recur r-left (conj parsed-elements r-parsed)))
          (< element-level current-level) [parsed-elements elements-left]
          :else (recur (drop 1 elements-left) (conj parsed-elements next-element))))
      [parsed-elements elements-left])))