(ql:quickload '(fiveam cl-ppcre))

(defparameter eg-input "467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..")


(defun inbounds (row-max col-max)
  (lambda (cell)
    (destructuring-bind (row . col) cell
      (and (<= 0 row row-max)
           (<= 0 col col-max)))))

(defun in-line-numbers (line symbol-pos)
  (loop for (num-start num-end) on (cl-ppcre:all-matches "\\d+" line) by #'cddr
        when (<= (1- num-start) symbol-pos num-end)
          collect (parse-integer (subseq line num-start num-end))))

(defun adjacent-numbers (rows row limits symbol-pos)
  (loop for y in (list (1- row) row (1+ row))
        when (funcall limits (cons y symbol-pos))
          nconc (in-line-numbers (aref rows y) symbol-pos)))

(defun solver (lines symbol-regex reducer)
  (let* ((rows (make-array (length lines) :initial-contents lines
                                          :adjustable t))
         (limits (inbounds (1- (length lines))
                           (1- (length (car lines))))))
    (loop for row below (length lines)
          sum (loop for (start _end) on (cl-ppcre:all-matches symbol-regex (aref rows row)) by #'cddr
                    sum (funcall reducer (adjacent-numbers rows row limits start))))))

(defun solver1 (lines)
  (solver lines "[^.\\d]" (lambda (numbers) (apply #'+ numbers))))


(defun solver2 (lines)
  (solver lines "\\*"
          (lambda (ratios)
            (if (= 2 (length ratios))
                (* (car ratios) (cadr ratios))
                0))))

(fiveam:test solutions
  (fiveam:is (= 4361 (solver1 (uiop:split-string eg-input :separator '(#\Newline)))))
  (fiveam:is (= 467835  (solver2 (uiop:split-string eg-input :separator '(#\Newline)))))
  (fiveam:is (= 531561 (solver1 (uiop:read-file-lines "input"))))
  (fiveam:is (= 83279367(solver2 (uiop:read-file-lines "input")))))