(ns day2
  (:require [clojure.string :as s]))

(defn line->vec [steps]
  (->>
   (re-seq #"\d+" steps)
   (mapv parse-long)))

(def input
  (->> "inputs/day2"
       slurp
       s/split-lines
       (map line->vec)))

(defn diff [steps]
  (->>
   (partition 2 1 steps)
   (map (partial apply -))))

(defn safe? [steps]
  (let [diffs (diff steps)
        sign (pos? (first diffs))]
    (loop [diffs diffs]
      (if (empty? diffs)
        true
        (if (zero? (first diffs))
          false
          (if-not (= sign (pos? (first diffs)))
            false
            (if (> (abs (first diffs)) 3)
              false
              (recur (rest diffs)))))))))

(defn cut-nth [steps n]
  (concat (subvec steps 0 n)
          (subvec steps (inc n))))

(defn safe?-2 [steps]
  (if (safe? steps)
    true
    (not-empty
     (for [i (range (count steps))
           :let [safe (safe? (cut-nth steps i))]
           :when (true? safe)]
       safe))))

(println "Number of safe reports:"
         (->> (map safe? input)
              (filter true?)
              count))

(println "Number of safe reports (part 2):"
         (->> (map safe?-2 input)
              (remove nil?)
              count))