;;; Gash -- Guile As SHell
;;; Copyright 2018 Timothy Sample <samplet@ngyro.com>
;;;
;;; This file is part of Gash.
;;;
;;; Gash is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; Gash is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with Gash.  If not, see <http://www.gnu.org/licenses/>.

(define-module (gash built-ins shift)
  #:use-module (gash environment)
  #:use-module (ice-9 match)
  #:use-module (srfi srfi-1))

;;; Commentary:
;;;
;;; The 'shift' utility.
;;;
;;; Code:

(define (main . args)
  (match args
    (() (main "1"))
    ((n-string)
     (let ((n (string->number n-string)))
       (cond
        ((and n (exact? n) (>= n 0)
              (<= n (length (cdr (program-arguments)))))
         (set-program-arguments
          (cons (car (program-arguments))
                (drop (cdr (program-arguments)) n)))
         EXIT_SUCCESS)
        (else
         (format (current-error-port)
                 "~a: shift: Invalid option ~s.~%"
                 (car (program-arguments)) n-string)
         EXIT_FAILURE))))
    (_ (format (current-error-port)
               "~a: shift: Invalid options ~s.~%"
               (car (program-arguments)) args)
       EXIT_FAILURE)))