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

;; 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/>.

(require 'asdf)
(require 'uiop)
(require 'str)
(require 'iterate)

(defpackage :advent-of-code-day-10
  (:use :cl :iterate)
  (:import-from :uiop :read-file-lines))

(in-package :advent-of-code-day-10)

(defun signal-strength-at-cycle (instructions cycle)
  (iter (for instruction in instructions)
        (for noop? = (not (consp instruction)))
        (for counter initially 1 then (+ counter (if noop? 1 2)))
        (for register initially 1 then (if noop? register (+ register (cdr instruction))))
        (for previous-counter previous counter)
        (for previous-register previous register)                
        (when (> counter cycle)
          (return (* cycle previous-register)))))

(defun parse-input (lines)
  (iter (for line in lines)
        (collect (if (string= line "noop")
                     :noop
                     (cons :addx (parse-integer (cadr (str:split " " line))))))))

(let ((input (parse-input (read-file-lines "example.txt"))))
  (assert (= 420 (signal-strength-at-cycle input 20)))
  (assert (= 1140 (signal-strength-at-cycle input 60)))
  (assert (= 1800 (signal-strength-at-cycle input 100)))
  (assert (= 2940 (signal-strength-at-cycle input 140)))
  (assert (= 2880 (signal-strength-at-cycle input 180)))
  (assert (= 3960 (signal-strength-at-cycle input 220)))
  (assert (= 13140 (iter (for cycle from 20 to 220 by 40)
                         (sum (signal-strength-at-cycle input cycle))))))

(let ((input (parse-input (read-file-lines "input.txt"))))
  (assert (= 14320 (iter (for cycle from 20 to 240 by 40)
                         (sum (signal-strength-at-cycle input cycle))))))

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;; mode: lisp
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