#!/usr/bin/env -S emacs --script

;; -*- lexical-binding: t; -*-

;; Copyright (C) 2022 

;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <https://www.gnu.org/licenses/>.

(add-to-list 'load-path "../")

(require 'ert)
(require 'advent-of-code)

(defvar solution-input
  "../../input/day-3.txt")

(defvar solution-example-input
  "../../input/day-3-example.txt")

(defun solution-letter-priority (char)
  (if (char-uppercase-p char)
      (+ (- char ?A) 26 1)
    (+ (- char ?a) 1)))

(defun solution-3-way-intersection (a b c)
  (seq-intersection (seq-intersection a b) c))

(defun solution-part-1 (input)
  (let* ((char-lists (seq-map 'string-to-list input))
         (split-into-halves (seq-map (lambda (char-list)
                                       (seq-split char-list (/ (length char-list) 2)))
                                     char-lists))
         (common-items (seq-map (lambda (halves)
                                  (if-let ((intersection (seq-intersection (car halves) (cadr halves))))
                                      (car intersection)
                                    nil))
                                split-into-halves))
         (filter-nils (seq-filter (lambda (item)
                                    (not (null item)))
                                  common-items))
         (item-priorities (seq-map 'solution-letter-priority common-items)))
    (apply '+ item-priorities)))

(defun solution-part-2 (input)
  (let* ((char-lists (seq-map 'string-to-list input))
         (groups (seq-split char-lists 3))
         (common-items (seq-map (lambda (group)
                                  (car (seq-intersection (seq-intersection (car group)
                                                                           (cadr group))
                                                         (caddr group))))
                                groups))
         (item-priorites (seq-map 'solution-letter-priority common-items)))
    (apply '+ item-priorites)))

(ert-deftest solution-part-1-example ()
  (should (equal (solution-part-1 (aoc-read-file-lines solution-example-input)) 157)))

(ert-deftest solution-part-1 ()
  (should (equal (solution-part-1 (aoc-read-file-lines solution-input)) 7878)))

(ert-deftest solution-part-2-example ()
  (should (equal (solution-part-2 (aoc-read-file-lines solution-example-input)) 70)))

(ert-deftest solution-part-2 ()
  (should (equal (solution-part-2 (aoc-read-file-lines solution-input)) 2760)))

(when noninteractive
  (ert-run-tests-batch))

;; Local Variables:
;; read-symbol-shorthands: (("solution-" . "advent-of-code-day-3-") ("aoc-" . "advent-of-code-"))
;; End: