(ns adventofcode2019.day06
    [:require [adventofcode2019.lib :refer :all]
              [clojure.string :as str]])

(defn a-orbits-b [orbits-map [b a]]
  (if (contains? orbits-map b)
    (-> (assoc orbits-map a {:parent b, :children (get-in orbits-map [a :children] [])})
        (update-in [b :children] conj a))
    (-> (assoc orbits-map b {:parent nil, :children []})
        (a-orbits-b [b a]))))

(defn distances-from [tree node]
  (letfn [(path-rc [dist tree node]
            (let [seen? #(some? (get-in tree [% :dist]))
                  neighbors (remove (some-fn nil? seen?) 
                                    (cons (get-in tree [node :parent]) 
                                          (get-in tree [node :children])))]
              (as-> tree it 
                    (assoc-in it [node :dist] dist)
                    (reduce #(path-rc (inc dist) %1 %2) it neighbors))))]
    (path-rc 0 tree node)))

(defn assign-depth [tree]
  (let [is-root? #(nil? (get-in tree [% :parent]))
        root (first (filter is-root? (keys tree)))]
    (letfn [(depth-rc [depth tree root]
              (as-> tree it 
                    (assoc-in it [root :depth] depth)
                    (reduce #(depth-rc (inc depth) %1 %2) 
                            it (get-in tree [root :children]))))]
      (depth-rc 0 tree root))))

(defn day06 []
  (let [input (map #(str/split % #"\)") (get-list-from-file (input-file)))
        orbits-map (reduce a-orbits-b {} input)
        with-depths (assign-depth orbits-map)] 
    (part1 (reduce + (map :depth (vals with-depths))))
    (part2 (- (get-in (distances-from orbits-map "YOU") ["SAN" :dist]) 2))))