(defvar %cave-hash% (hash))

(defstruct cave ()
  name
  neighbors

  (:postinit (cv)
    (assert cv.name)
    (set [%cave-hash% cv.name] cv)))

(defstruct small-cave cave
  (:method visit (cv path fn)
    (unless (member cv path)
      (push cv path)
      (each ((n cv.neighbors))
        n.(visit path fn)))))

(defstruct big-cave cave
  (:method visit (cv path fn)
    (push cv path)
    (each ((n cv.neighbors))
      n.(visit path fn))))

(defstruct end-cave cave
  (:method visit (cv path fn)
    (push cv path)
    [fn path]))

(defun ensure-cave (name)
  (or [%cave-hash% name]
      (set [%cave-hash% name]
           (match-case name
             ("end" (new end-cave name name))
             (@[all @str chr-islower] (new small-cave name name))
             (@else (new big-cave name name))))))

(defun read-caves (: (name "input"))
  (with-stream (s (open-file name))
    (whilet ((line (get-line s)))
      (match `@a-@b` line
        (let ((ca (ensure-cave a))
              (cb (ensure-cave b)))
          (pushnew cb ca.neighbors)
          (pushnew ca cb.neighbors))))))

(defun find-paths (fn)
  (let ((start [%cave-hash% "start"]))
    (assert start)
    start.(visit nil fn)))