(ns adventofcode2019.day14
    [:require [adventofcode2019.lib :refer :all]
              [adventofcode2019.intcode :as i]
              [clojure.string :as str]
              [clojure.set :as set]
              [clojure.core.match :refer [match]]
              [clojure.math.combinatorics :as combo]])

(defn parse-reaction [reaction-text]
  (let [parse-chemical (fn [text]
                         (let [[ct chem] (str/split (str/trim text) #" ")]
                           {chem (parse-int ct)}))
        [inputs output] (str/split reaction-text #"=>")
        [[out-chem out-ct]] (seq (parse-chemical output))]
    {out-chem {(reduce merge {} (map parse-chemical (str/split inputs #","))) out-ct}}))

(defn normalize-reaction [reaction]
  (let [[output] (keys reaction)
        arrows (reaction output)
        inputs (keys arrows)
        normalize-arrow (fn [[akey aval]]
                          {(reduce-kv (fn [m k v]
                                        (assoc m k (rationalize (/ v aval)))) 
                                      {} akey) 1})]
    {output (reduce merge {} (map normalize-arrow arrows))}))

(defn make-graph [input]
  (reduce (partial merge-with merge)
          (map (comp normalize-reaction parse-reaction) input)))

(defn find-lowest-exchange-rate [graph start end]
  (let [reactions (graph start)
        input-lists (keys reactions)
        input-chems (mapv keys input-lists)
        trade (fn [recv exch]
                (let [rx (if (ratio? exch) (numerator exch) exch)
                      xc (if (ratio? exch) (denominator exch) 1)
                      units (int (Math/ceil (/ recv xc)))]
                  (* units rx)))
        find-terminal #(match [%]
                              [({end v} :only [end])] v
                              :else nil)
        calculate-er (fn [[chem ct]] 
                       (trade ct (find-lowest-exchange-rate graph chem end)))
        reaction-er #(reduce + (map calculate-er %))]
    (if (some #{[end]} input-chems)
      (->> input-lists
           (map find-terminal)
           (remove nil?)
           (reduce min))
      (->> input-lists
           (map reaction-er)
           (reduce min)))))

(defn day14 []
  (let [graphed (make-graph (get-list-from-file (input-file)))]
    (part1 (find-lowest-exchange-rate graphed "FUEL" "ORE"))
    #_(part2)))