;;; ll-list --- ll list -*- lexical-binding: t -*-
;;
;;; Commentary:
;;
;;; Code:

(require 'cl-lib)
(cl-pushnew "." load-path :test #'string=)

(require 'll      nil t)
(require 'll-type nil t)

(defun --- (s) (if (sequ s) (length s) 0))

(defun ll-drop-center (lst)
  (cl-assert (su lst))
  (when-let* ((len (--- lst))
              (hlf (/ len 2)))
    `(,@(take hlf lst) ,@(last lst (if (evenp len) (1- hlf) hlf)))))

;; (ll-drop-center '( ) )              ; ( )
;; (ll-drop-center '( 1 ))             ; ( _ )
;; (ll-drop-center '( 1 2 ))           ; ( 1 _ )
;; (ll-drop-center '( 1 2 3 ))         ; ( 1 _ 3 )
;; (ll-drop-center '( 1 2 3 4 ))       ; ( 1 2 _ 4 )
;; (ll-drop-center '( 1 2 3 4 5 ))     ; ( 1 2 _ 4 5 )
;; (ll-drop-center '( 1 2 3 4 5 6 ))   ; ( 1 2 3 _ 5 6 )
;; (ll-drop-center '( 1 2 3 4 5 6 7 )) ; ( 1 2 3 _ 5 6 7 )

(defun l= (l1 l2)
  (cl-assert (su l1))
  (cl-assert (su l2))
  (equal l1 l2))

(defun !l= (l1 l2)
  (cl-assert (lu l1))
  (cl-assert (lu l2))
  (! (l= l1 l2)))

(defun 1st (l) (or (& (lu l) (car l))    (& (vu l) (aref l 0))))
(defun 2nd (l) (or (& (lu l) (cadr l))   (& (vu l) (aref l 1))))
(defun 3rd (l) (or (& (lu l) (caddr l))  (& (vu l) (aref l 2))))
(defun 4th (l) (or (& (lu l) (cadddr l)) (& (vu l) (aref l 3))))
;; used to be up to          (caddddr l)
;; used to be up to          (cadddddr l)
;; used to be up to          (caddddddr l)
;; used to be up to          (cadddddddr l)

(defmacro ll-pushlast (e lst)
  (declare (debug (form gv-place)))
  (macroexp-let2 macroexp-copyable-p x e
    (gv-letplace (get set) lst
      (funcall set `(append ,get (cons ,e nil))))))

(defun seq-butlast (l &optional n)
  (cl-assert (lu l))
  (cl-assert (ni n))
  (seq-take l (- (--- l) n)))

(defun seq-last (l &optional n)
  (cl-assert (lu l))
  (cl-assert (ni n))
  (seq-subseq l (- (--- l) n)))

(defun ll-shift (l &optional n)
  (cl-assert (lu l))
  (or (& (ni n) n) (& (nf n) (r n)) (setf n 1))
  (let ((len (--- l)))
    (if (or (--- len) (z n))
        l
      (setf n (m n len))
      (append (last l n) (butlast l n)))))

(provide 'll-list)
;;; ll-list.el ends here