;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
;;;
;;; This file is part of R7RS-PNM.
;;;
;;; R7RS-PNM is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as published
;;; by the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; R7RS-PNM 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 Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public License
;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.

(define-library (image-format pnm pbm)
  (export make-pbm-image
          %make-pbm-image)
  (import (scheme base)
          (scheme case-lambda)
          (image-format pnm image)
          (image-format pnm private checker)
          (image-format pnm private bitwise))
  (begin
    (define make-pbm-image
      (case-lambda
        ((width height)
         (make-pbm-image width height #f))
        ((width height unsafe?)
         (let* ((byte-width (ceiling (/ width 8)))
                (byte-count (* byte-width height))
                (data (make-bytevector byte-count 0)))
           (%make-pbm-image width height data unsafe?)))))

    (define (%make-pbm-image width height data unsafe?)
      (let* ((byte-width (ceiling (/ width 8)))
             (byte-count (* byte-width height)))
        (define (xy->byte-idx+bit-idx x y)
          (let-values (((byte-x bit-x) (floor/ x 8)))
            (values (+ (* y byte-width)
                       byte-x)
                    bit-x)))
        (define (pixel-getter x y)
          (let-values (((byte-idx bit-idx) (xy->byte-idx+bit-idx x y)))
            (let ((byte (bytevector-u8-ref data byte-idx)))
              (bit-set? (- 7 bit-idx) byte))))
        (define (pixel-setter x y b)
          (let-values (((byte-idx bit-idx) (xy->byte-idx+bit-idx x y)))
            (let ((byte (bytevector-u8-ref data byte-idx)))
              (bytevector-u8-set! data byte-idx
                                  (copy-bit (- 7 bit-idx) byte b)))))
        (unless (= byte-count (bytevector-length data))
          (error (string-append "(image-format pnm pbm) make-pbm-image: Invalid bytevector length" byte-count)))
        (let ((check-xy (make-xy-checker width height))
              (check-boolean-value (make-boolean-value-checker)))
          (make-pnm-image 'pbm width height #t data
                          (if unsafe?
                              pixel-getter
                              (lambda (x y)
                                (check-xy x y)
                                (pixel-getter x y)))
                          (if unsafe?
                              pixel-setter
                              (lambda (x y v)
                                (check-xy x y)
                                (check-boolean-value v)
                                (pixel-setter x y v)))))))))