aoc

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(ns aoc.day12
  (:require [clojure.java.io :as io]))

(def example "F10
N3
F7
R90
F11")

(def start-pos {:facing :east
                :north 0
                :east 0})

(def start-pos-2 {:wp {:north 1
                       :east 10}
                  :ship {:north 0
                         :east 0}})

(defn translate [direction [x y]]
  (case direction
      :right [y (- x)]
      :left [(- y) x]))

(defn translate-wp [pos direction]
  (update-in pos [:wp] (fn [{:keys [north east]}]
                         (let [[x y] (translate direction [east north])]
                           {:north y :east x}))))

(defn parse-inst [[h & body]]
  {:direction (case h
                \N :north
                \E :east
                \S :south
                \W :west
                \F :forward
                \L :left
                \R :right)
   :value (read-string (clojure.string/join body))})

(defn read-input []
  (->> 
       (io/resource "input12.txt")
       slurp
       ;; example
       clojure.string/split-lines
       (map parse-inst)
       ))

(defn move [direction value]
  (fn [old]
    (let [op (case direction
               :north +
               :south -
               :east +
               :west -)]
      (if (nil? op)
        old
        (op old value)))))

(def right-turns (cycle [:east :south :west :north]))
(def left-turns (cycle [:east :north :west :south]))

(defn turn-count [n]
  (case n
    90 1
    180 2
    270 3
    0 0))

(defn turn [pos {:keys [value direction]}]
  (let [current-direction (:facing pos)
        tc (turn-count value)
        turns (case direction
                :left left-turns
                :right right-turns
                [])
        next-turns (drop-while #(not= current-direction %) turns)]
    (nth next-turns tc)))

(defn move-forward [pos {:keys [value direction]}]
  (let [facing (:facing pos)
        op (case facing
             :north +
             :east +
             :south -
             :west -)]
    (if (contains? #{:north :south} facing)
      (assoc pos :north (op (:north pos) value))
      (assoc pos :east (op (:east pos) value)))))

(defn navigate [pos {:keys [value direction]}]
  (case direction
    :north   (update pos :north (move direction value))
    :south   (update pos :north (move direction value))
    :east    (update pos :north (move direction value))
    :west    (update pos :north (move direction value))
    :left    (assoc  pos :facing (turn pos {:direction direction :value value}))
    :right   (assoc  pos :facing (turn pos {:direction direction :value value}))
    :forward (move-forward pos {:direction direction :value value})
    pos))

(defn should-move-wp? [direction]
  (not= direction :forward))

(defn should-move-ship? [direction]
  (= direction :forward))

(defn move-ship [pos {:keys [value]}]
  (let [wx (get-in pos [:wp :east])
        wy (get-in pos [:wp :north])
        pos (update-in pos [:ship :east] #(+ % (* wx value)))
        pos (update-in pos [:ship :north] #(+ % (* wy value)))]
    pos))

;; (move-ship {:wp {:east -1 :north -2} :ship {:east 1 :north 1}}
;;            {:value 0})

(defn rotate-wp [pos {:keys [value direction]}]
  (let [tc (turn-count value)]
    (reduce (fn [acc _]
              (translate-wp acc direction))
            pos
            (range tc))))

(defn move-wp [pos {:keys [value direction] :as i}]
  (case direction
    :north (update-in pos [:wp :north] #(+ % value))
    :south (update-in pos [:wp :north] #(- % value))
    :east  (update-in pos [:wp :east ] #(+ % value))
    :west  (update-in pos [:wp :east ] #(- % value))
    :right (rotate-wp pos i)
    :left  (rotate-wp pos i)))

(defn navigate-2 [pos {:keys [value direction] :as i}]
  (cond
    (should-move-wp? direction) (move-wp pos i)
    (should-move-ship? direction) (move-ship pos i)
    :else pos))

(defn compute-1 [input]
  (let [final (reduce navigate start-pos input)]
    (+ (Math/abs (:north final))
       (Math/abs (:east final)))))

(defn compute-2 [input]
  (let [final (reduce navigate-2 start-pos-2 input)]
    (+ (Math/abs (get-in final [:ship :north]))
       (Math/abs (get-in final [:ship :east])))))

(defn main []
  (let [input (read-input)]
    (println (compute-1 input))
    (println (compute-2 input))))

(main)