;;; solver.el --- Day 03 -*- lexical-binding: t; -*-
;;
;; Copyright (C) 2022 Óscar Nájera
;;
;; Author: Óscar Nájera <hi@oscarnajera.com>
;; Maintainer: Óscar Nájera <hi@oscarnajera.com>
;; Created: December 04, 2022
;; Modified: December 04, 2022
;;
;; This file is not part of GNU Emacs.
;;
;;; Commentary:
;;
;;  Day 03
;;
;;; Code:
(require 'subr-x)
(require 'ert)
(defsubst solver-recover-value (cross)
  (let ((result 0))
    (while (= 0 (logand cross 1))
      (setq cross (ash cross -1))
      (cl-incf result))
    result))

(ert-deftest test-recover ()
  (should (eq ?t (+ 64 (solver-recover-value (ash 1 (- ?t 64))))))
  (should (eq ?s (+ 64 (solver-recover-value (ash 1 (- ?s 64))))))
  (should (eq ?C (+ 64 (solver-recover-value (ash 1 (- ?C 64))))))) ;; small cap starts at a=97, but already took 64

(defsubst solver-to-priority (value)
  (if (< value 31) ;; It is a capital letter in range [1;26]
      (+ value 26)
    (- value 32)))

(defun solver-line-priority (str)
  (cl-assert (length> str 0))
  (let ((mid (/ (length str) 2)))
    (thread-first
      (cl-intersection (string-to-list (substring str 0 mid))
                       (string-to-list (substring str mid)))
      (car) (- 64)
      (solver-to-priority))))

(ert-deftest test-line-priority ()
  (should (= 16 (solver-line-priority  "vJrwpWtwJgWrhcsFMMfFFhFp")))
  (should (= 19 (solver-line-priority  "hMHLcmGLMLhHmsRMsSvsQSqrsrlJTTdV" )))
  (should (= 20 (solver-line-priority  "ttgJtRGJQctTZtZT"))))

(defun solver-badge-priority (group-packs)
  (thread-last  group-packs
                (mapcar #'string-to-list)
                (cl-reduce #'cl-intersection)
                (car) (+ -64)
                (solver-to-priority)))

(defun solver (task lines)
  (with-temp-buffer
    (insert-file-contents "input")
    (let ((packs (split-string (buffer-string))))
      (apply #'+
             (mapcar task (if (= lines 1)
                              packs (seq-partition packs 3)))))))

(ert-deftest test-problems ()
  (should (= 8072 (solver #'solver-line-priority 1)))
  (should (= 2567 (solver #'solver-badge-priority 3))))