#lang scheme/base


#|

PBM  Portable BitMap   B/W
PGM  Portable GreyMap  Grey   P5
PPM  Portable PixMap   RGB    P6

PNM  Portable aNyMap



|#

(define (pgm-type->reader type)
  (case type
    ((P5) (lambda (w h) (read-bytes (* w h))))
    ((P6) (lambda (w h) (read-bytes (/ (* w h) 8))))
    (else
     (error 'not-a-pgm-file "~s" type))))

(define (read-pgm [p (current-input-port)])
  (parameterize ((current-input-port p))
    (let* ((header (read))
           (read-body (pgm-type->reader header))
           (_ (read-line)) ;; newline
           (_ (read-line)) ;; comment line
           (width  (read))
           (height (read))
           (levels (read))
           (_ (read-line))) ;; newline
      (printf "pgm: ~a ~a ~a\n" width height levels)
      ;; The rest is binary data
      (values width
              height
              ;(read-body width height)
              ))))


; pdftoppm -f 22 -l 22 ~/library/link/AITR-595.pdf >/tmp/page.ppm
(define (test)
  (read-pgm (open-input-file "/tmp/page.ppm")))