isbn.scm

(define-module isbn
  (use simply)
  (export get-isbn-type isbn10->isbn13 isbn13->isbn10)
  )
(select-module isbn)

#|             *-- PUBLIC --*
 |#

; =get-isbn-type
; --------------------------------------------------
(define (get-isbn-type isbn-str)
  (let* ((isbn (isbn-encode isbn-str))
         (len (string-length isbn))
         )
    (cond
      [(= len 10)
       (if (and (#/^[0123457][0-9]{8}[0-9Xx]$/ isbn) (check-isbn10 isbn))
         'isbn10 '()
         )
       ]
      [(= len 13)
       (if (and (#/^(978|979)[0-9]{10}$/ isbn) (check-isbn13 isbn))
         'isbn13 '()
         )
       ]
      [else '()]
      )
    )
  )

; =isbn10->isbn13
; --------------------------------------------------
(define (isbn10->isbn13 isbn-str)
  (let1 isbn (isbn-encode isbn-str)
    (cond
      [(eq? 'isbn10 (get-isbn-type isbn))
       (let* ((tmp (string-append "978" (substring isbn 0 9)))
              (check-digit (get-check-digit-for-isbn13 tmp))
              )
         (string-append tmp (number->string check-digit))
         )
       ]
      [else isbn]
      )
    )
  )

; =isbn13->isbn10
; --------------------------------------------------
(define (isbn13->isbn10 isbn-str)
  (let1 isbn (isbn-encode isbn-str)
    (cond
      [(eq? 'isbn13 (get-isbn-type isbn))
       (let* ((tmp (substring isbn 3 12))
              (check-digit (get-check-digit-for-isbn10 tmp))
              )
         (string-append tmp (case check-digit
                              [(10) "X"]
                              [(11) 0]
                              [else (number->string check-digit)]
                              )
                        )
         )
       ]
      [else isbn]
      )
    )
  )


#|             *-- PRIVATE --*
 |#

; =isbn-encode
; --------------------------------------------------
(define (isbn-encode isbn)
  (regexp-replace-all* isbn #/[\s\-]/ "")
  )

; =get-check-digit-for-isbn10
; --------------------------------------------------
(define (get-check-digit-for-isbn10 isbn)
  (let loop((ls (string->list (substring isbn 0 9)))
            (index 0)
            (total 0)
            )
    (cond
      [(null? ls) (- 11 (modulo total 11))]
      [else
        (loop (cdr ls) (++ index) (+ total (* (- 10 index) (digit->integer (car ls)))))
        ]
      )
    )
  )


; =get-check-digit-for-isbn13
; --------------------------------------------------
(define (get-check-digit-for-isbn13 isbn)
  (let loop((ls (string->list (substring isbn 0 12)))
            (index 0)
            (total 0)
            )
    (cond
      [(null? ls)
       (let* ((res (- 10 (modulo total 10)))
              (res-str (number->string res))
              )
         (if (char=? #\0 (string-ref res-str (- (string-length res-str) 1))) 0 res)
         )
       ]
      [else
        (loop (cdr ls) (++ index) (+ total (* (digit->integer (car ls)) (if (= 0 (modulo index 2)) 1 3))))
        ]
      )
    )
  )

; =check=isbn10
; --------------------------------------------------
(define (check-isbn10 isbn)
  (let* ((c (char-downcase (string-ref isbn 9)))
         (check-digit (if (char=? #\x c) 10 (digit->integer c)))
         )
    (values
      (= check-digit (get-check-digit-for-isbn10 isbn))
      check-digit
      )
    )
  )


; =check-isbn13
; --------------------------------------------------
(define (check-isbn13 isbn)
  (let1 check-digit (digit->integer (string-ref isbn 12))
    (values
      (= check-digit (get-check-digit-for-isbn13 isbn))
      check-digit
      )
    )
  )

(provide "isbn")