verify ISSN (issn-verify.el)

[Emanuel Berg via "Emacs development discussions." <emacs-devel@gnu.org>]

;;; issn-verify.el --- verify ISSN -*- lexical-binding: t
;;
;;; Commentary:
;;
;; This Elisp package provides functions to verify
;; ISSN by computing their check digits.
;;
;; Author: Emanuel Berg (incal) <moasenwood@zoho.eu>
;; Created: 2020-09-06
;; Keywords: bib, tex
;; License: GPL3+
;; Package-Requires: ((cl-lib "1.0"))
;; URL: https://dataswamp.org/~incal/emacs-init/issn-verify.el
;; Version: 1.0.0
;;
;; Also see:
;;
;;   https://dataswamp.org/~incal/emacs-init/isbn-verify.el
;;
;; To install this package, with this file in
;; a buffer, do:
;;
;;   M-x load-file RET RET
;;
;; International Standard Serial Number:
;;
;;   ISO 3297, 1975
;;
;; format:
;;
;;   The Ring Magazine: ISSN 0035-5410
;;   d_1d_2d_3d_4-d_5d_6d_7c
;;   d_i for i \in [1, 7] is an integer
;;   c, the check digit, is 0..9 or X for 10
;;
;; compute check digit c:
;;
;;     c' = 8d_1*7d_2*6d_3*5d_4*4d_5*3d_6*2d_7 mod 11
;;
;;         { 0        c' = 0
;;     c = {
;;         { 11 - c'    else
;;
;;; Code:

(require 'cl-lib)

(defun issn--get-digits (issn)
  (when (string-match "[[:digit:]]\\{4\\}-[[:digit:]]\\{3\\}[X[:digit:]]" issn)
    (let*((hyphen-pos 4)
          (issn-lst   (string-to-list issn)) )
      (mapcar (lambda (c) (if (eq ?X c) "X" (- c ?0)))
              (append (cl-subseq issn-lst 0 hyphen-pos)
                      (cl-subseq issn-lst (1+ hyphen-pos)) )))))

(defun issn-verify-issn (issn)
  (let*((issn-lst (issn--get-digits issn))
        (c-prop  (car (last issn-lst)))
        (c-w 0) )
    (cl-loop for d in issn-lst
             for w downfrom 8 to 2
             do (cl-incf c-w (* w d)) )
    (let*((c-prime (mod c-w 11))
          (c       (cond ((= c-prime  0) 0)
                         (t (- 11 c-prime) )))
          (c-x     (if (= 10 c) "X" c)) )
      (if (equal c-prop c-x)
          (message "%s (OK)" c-x)
        (message "NOT OK! is %s, should be %s" c-prop c-x) ))))

;; Bicycle Quarterly   (issn-verify-issn "1941-8809")
;; Bicycling           (issn-verify-issn "1651-9744")
;; Black Belt          (issn-verify-issn "0277-3066")
;; Filter              (issn-verify-issn "1654-9813")
;; Linux Pro           (issn-verify-issn "1471-5678")
;; National Geographic (issn-verify-issn "2535-4124")
;; Outside             (issn-verify-issn "0278-1433")
;; The Ring            (issn-verify-issn "0035-5410")

;; The Economist       (issn-verify-issn "0013-0614") ; NOT OK! is 4, should be 3

(provide 'issn-verify)
;;; issn-verify.el ends here

-- 
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