Text decoration à la Bluesky

bsky.clj

(defn size-table [{:keys [text urls tags mentions]}]
  {:text {:content text
          :size (count (.getBytes text StandardCharsets/UTF_8))}
   :urls (map (fn [url] {:content url
                        :size (count (.getBytes url StandardCharsets/UTF_8))}) urls)
   :tags (map (fn [tag] {:content tag
                        :size (count (.getBytes tag StandardCharsets/UTF_8))}) tags)
   :mentions (map (fn [mention] {:content mention
                                :size (count (.getBytes mention StandardCharsets/UTF_8))}) mentions)})


(defmulti create-facet (fn [m] (key (first m))))
(defmethod create-facet :uri [m]
  {:$type "app.bsky.richtext.facet#link"
   :uri (val (first m))})
(defmethod create-facet :tag [m]
  {:$type "app.bsky.richtext.facet#tag"
   :tag (val (first m))})
(defmethod create-facet :mention [m]
  {:$type "app.bsky.richtext.facet#mention"
   :did (val (first m))})

(defn create-index [start end]
  {:index {:byteStart start
           :byteEnd end}})

(defn create-feature [facet]
  {:features [facet]})

(defn facets [start-bytes k v]
  (loop [els v
         result []
         start start-bytes]
    (if els
      (let [{content :content size :size} (first els)
            end (inc (+ start size))]
        (recur (next els)
               (conj result (merge (create-index start end)
                                   (create-feature (create-facet {k content}))))
               (inc (+ start size))))
      result)))

;; And now we can use it like this, for example

(defn decoration-payload [info]
  (let [xs (size-table info)
        start-bytes-url (inc (:size (:text xs)))
        facets-url (facets start-bytes-url :uri (:urls xs))
        start-bytes-tags (+ start-bytes-url (reduce (fn [prev url] (+ prev (:size url))) 0 (:urls xs)))
        facets-tags (facets start-bytes-tags :tag (:tags xs))]
    (into facets-url facets-tags)))

(comment
  (let [post {:text "Hello, World!" :urls ["https://example.org"] :tags ["#yay" "#lol"]}]
    (decoration-payload post)))