;; // https://adventofcode.com/2022/day/21
(defpackage :day-21
  (:use :cl))
(in-package :day-21)

(ql:quickload 'cl-ppcre)

(defun parse-integer-or-symbol (str)
  (let ((maybe-int (parse-integer str :junk-allowed t)))
    (if maybe-int
        maybe-int
        (intern (string-upcase str)))))


(defun line-to-quoted-operation (line)
  (let* ((words (ppcre:split " " (ppcre:regex-replace ":" line "")))
         (symbols (mapcar #'parse-integer-or-symbol words)))
    (cond
      ((= 4 (length symbols))
       ;; with operation
       (destructuring-bind (name operand1 op operand2)
           symbols
         `(defparameter ,name '(,op (eval ,operand1) (eval ,operand2)))))

      ((= 2 (length symbols))
       ;; just number
       (destructuring-bind (name value)
           symbols
         `(defparameter ,name ,value))))))

(defun load-file-defs (filename)
  (loop
  for line in (uiop:read-file-lines filename)
  for definition = (line-to-quoted-operation line)
  do (eval definition)))

(defun reverse-operation (op)
  (case op
    ('*  '/)
    ('/  '*)
    ('+ '-)
    ('- '+)))

(defun back-symbol (symb)
  (intern (format nil "BACK-~a" symb)))

;; adding BACK-symbol computations.
(defun line-to-quoted-operation-2 (line)
  (let* ((words (ppcre:split " " (ppcre:regex-replace ":" line "")))
         (symbols (mapcar #'parse-integer-or-symbol words)))
    (cond
      ((= 4 (length symbols))
       ;; with operation
       (destructuring-bind (name operand1 op operand2)
           symbols
         (if (eq name 'ROOT)
             `(progn (defparameter ,(back-symbol operand1) '(eval ,operand2))
                      (defparameter ,(back-symbol operand2) '(eval ,operand1)))
             (let ((forward-calc
                     `(defparameter ,name '(,op (eval ,operand1) (eval ,operand2))))
                   (backward-calc
                     (case op
                       ('+ `((defparameter
                                 ,(back-symbol operand1)
                               '(- (eval ,(back-symbol name)) (eval ,operand2)))
                             (defparameter
                                 ,(back-symbol operand2)
                               '(- (eval ,(back-symbol name)) (eval ,operand1)))))
                       ('- `((defparameter
                                 ,(back-symbol operand1)
                               '(+ (eval ,(back-symbol name)) (eval ,operand2)))
                             (defparameter
                                 ,(back-symbol operand2)
                               '(- (eval ,operand1) (eval ,(back-symbol name))))))
                       (t `((defparameter
                                ,(back-symbol operand1)
                              '(,(reverse-operation op) (eval ,(back-symbol name)) (eval ,operand2)))
                            (defparameter
                                ,(back-symbol operand2)
                              '(,(reverse-operation op) (eval ,(back-symbol name)) (eval ,operand1)))))
                       )))
               `(progn
                  ,forward-calc
                  ,@backward-calc
                  ;; (defparameter ,(innern (format t "BACK~a" name) ))
                  )))))

      ((= 2 (length symbols))
       ;; just number
       (destructuring-bind (name value)
           symbols
         `(defparameter ,name ,value))))))

(defun load-file-defs-2 (filename)
  (loop
  for line in (uiop:read-file-lines filename)
  for definitions = (line-to-quoted-operation-2 line)
  do (eval definitions)))