(defpackage #:advent.2024.09
  (:use #:cl #:advent.2024.00)
  (:import-from #:serapeum
                #:take-while)
  (:import-from #:alexandria
                #:compose))
(in-package #:advent.2024.09)

(defparameter *input* "09.example")

;;; Day 1.
;; 1. Decode / expand compact disc map representation
;; 2. Move blocks left to fill empty space
;; 3. Checksum

(defun decode (&optional (str (uiop:read-file-line *input*)))
  (loop with id = 0
        with res = (make-array '(1000) :adjustable t
                                       :fill-pointer 0)
        for c across str
        for n = (parse-integer (string c))
        while n
        for filep = t then (not filep)
        if filep do
          (progn
            (loop for i from 1 to n do
              (vector-push-extend id res))
            (incf id))
        else do
          (loop for i from 1 to n do
            (vector-push-extend nil res))
        finally (return res)))

(defun shift (&optional (str (uiop:read-file-line *input*)))
  (let* ((mem (decode str))
         (rev (nreverse (remove-if #'null (vector->list mem)))))
    (loop for i from 0 below (length rev)
          collect (or (aref mem i)
                      (pop rev)))))

(defun checksum (&optional (str (uiop:read-file-line *input*))) ; also solve1
  (loop for i from 0
        for n in (shift str)
        sum (* i n)))

;;; 24551621791131 is too high
;; ... change `until (eq beg end)` to `until (> beg end)` ...
;; 2096 is too low
;;; ... change to (>= beg end) ...
;; 6415449222092 is too high
;; 6414919955263 is wrong
;; 6415184586041 IS RIGHT THANK GOD :)

;;; Part 2.
;; Move whole files instead of just blocks.....
;; ex.
;; 00...111...2...333.44.5555.6666.777.888899
;; 0099.111...2...333.44.5555.6666.777.8888..
;; 0099.1117772...333.44.5555.6666.....8888..
;; 0099.111777244.333....5555.6666.....8888..
;; 00992111777.44.333....5555.6666.....8888..

;; Do i want to redefine the input format to be a list of files with size and
;; id?

(defun length-encode (v)
  (do ((i 0 (1+ i))
       tmp res
       (start 0))
      ((>= i (length v))
       (nreverse (cons (list (car tmp) start (length tmp)) res)))
    (if (eq (aref v i)
            (car tmp))
        (push (aref v i) tmp)
        (progn
          (push (list (car tmp) start (length tmp)) res)
          (setf tmp (list (aref v i)))
          (setf start i)))))

(defun shift2 (&optional (str (uiop:read-file-line *input*)))
  (let* ((mem (length-encode (decode str)))
         (frees (remove-if-not (compose #'null #'car) mem))
         (files (nreverse (remove-if (compose #'null #'car) mem))))
    (loop for (id . len) in files
          if (find len frees :key #'third)
            )))