(ns adventofcode2019.day12
  [:require [adventofcode2019.lib :refer :all]
   [adventofcode2019.intcode :as i]
   [clojure.string :as str]
   [clojure.core.match :refer [match]]
   [clojure.math.combinatorics :as combo]
   [clojure.pprint :refer [pprint]]])

; <x=1, y=2, z=3> -> [[1 2 3] [0 0 0]]
(defn parse-coords [coords]
  [(mapv parse-int (str/split (str/replace coords #"[<>xyz=,]" "") #" "))
   [0 0 0]])

(defn gravity [[pos1 vel1] [pos2 vel2]]
  (let [adjust-velocity (fn [a b]
                          (cond
                            (< a b) [inc dec]
                            (= a b) [identity identity]
                            (> a b) [dec inc]))
        velocity-diffs (map adjust-velocity pos1 pos2)
        apply-diffs (fn [acc vel] (mapv #(%1 %2) (map acc velocity-diffs) vel))]
    [(apply-diffs first vel1)
     (apply-diffs second vel2)]))

(defn velocity [[pos vel]]
  [(mapv + pos vel) vel])

(defn total-energy [[pos vel]]
  (let [abs+ (fn [& args] (apply + (map #(Math/abs %) args)))
        potential (apply abs+ pos)
        kinetic (apply abs+ vel)]
    (* potential kinetic)))

(defn step-simulation [bodies]
  (let [indices (range (count bodies))
        all-pairs (combo/combinations indices 2)
        apply-gravity (fn [bodies [i j]]
                        (let [[nv1 nv2] (gravity (bodies i) (bodies j))]
                          (-> bodies
                              (assoc-in [i 1] nv1)
                              (assoc-in [j 1] nv2))))]
    (mapv velocity (reduce apply-gravity bodies all-pairs))))

(defn find-cycle [states]
  (let [detect-dup (fn [[ct prev] state]
                     (if (= (flatten prev)
                            (map - (flatten state)))
                       (reduced (inc ct))
                       [(inc ct) state]))]
    (* 2 (reduce detect-dup [0 []] states))))

(defn day12 []
  (let [input (mapv parse-coords (get-list-from-file (input-file)))
        simulate (iterate step-simulation input)]
    (part1 (reduce + (map total-energy (nth simulate 1000))))
    (part2 (find-cycle simulate))))