;;; 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 ppm)
  (export make-ppm-image
          %make-ppm-image)
  (import (scheme base)
          (scheme case-lambda)
          (image-format pnm image)
          (image-format pnm private checker)
          (image-format pnm private double-byte))
  (begin
    (define make-ppm-image
      (case-lambda
        ((width height)
         (make-ppm-image width height 255))
        ((width height maxval)
         (make-ppm-image width height maxval #f))
        ((width height maxval unsafe?)
         (when (or (< maxval 0)
                   (< 65536 maxval))
           (error "(image-format pnm ppm) make-ppm-image: Maxval is out of range"))
         (let ((data (make-bytevector (* width
                                         height
                                         (if (< maxval 256)
                                             3
                                             6))
                                      0)))
           (%make-ppm-image width height maxval data unsafe?)))))

    (define (%make-ppm-image width height maxval data unsafe?)
      (define (make-safe-pixel-getter pixel-getter)
        (let ((check-xy (make-xy-checker width height)))
          (lambda (x y)
            (check-xy x y)
            (pixel-getter x y))))
      (define (make-safe-pixel-setter pixel-setter)
        (let ((check-xy (make-xy-checker width height))
              (check-value-r (make-value-checker maxval 'r))
              (check-value-g (make-value-checker maxval 'g))
              (check-value-b (make-value-checker maxval 'b)))
          (lambda (x y r g b)
            (check-xy x y)
            (check-value-r r)
            (check-value-g g)
            (check-value-b b)
            (pixel-setter x y r g b))))
      (when (or (< maxval 0)
                (< 65536 maxval))
        (error "(image-format pnm ppm) make-ppm-image: Maxval is out of range"))
      (if (< maxval 256)
          (let* ((w*3 (* width 3))
                 (byte-count (* w*3 height)))
            (define (xy->idx x y) (+ (* 3 x) (* y w*3)))
            (define (pixel-getter x y)
              (let ((idx (xy->idx x y)))
                (values (bytevector-u8-ref data idx)
                        (bytevector-u8-ref data (+ idx 1))
                        (bytevector-u8-ref data (+ idx 2)))))
            (define (pixel-setter x y r g b)
              (let ((idx (xy->idx x y)))
                (bytevector-u8-set! data idx r)
                (bytevector-u8-set! data (+ idx 1) g)
                (bytevector-u8-set! data (+ idx 2) b)))
            (unless (= byte-count (bytevector-length data))
              (error (string-append "(image-format pnm pbm) make-pbm-image: Invalid bytevector length" byte-count)))
            (make-pnm-image 'ppm width height maxval data
                            (if unsafe? pixel-getter (make-safe-pixel-getter pixel-getter))
                            (if unsafe? pixel-setter (make-safe-pixel-setter pixel-setter))))
          (let* ((w*6 (* width 6))
                 (byte-count (* w*6 height)))
            (define (xy->idx x y) (+ (* 6 x) (* y w*6)))
            (define (pixel-getter x y)
              (let ((idx (xy->idx x y)))
                (values (combine-bytes (bytevector-u8-ref data idx)
                                       (bytevector-u8-ref data (+ idx 1)))
                        (combine-bytes (bytevector-u8-ref data (+ idx 2))
                                       (bytevector-u8-ref data (+ idx 3)))
                        (combine-bytes (bytevector-u8-ref data (+ idx 4))
                                       (bytevector-u8-ref data (+ idx 5))))))
            (define (pixel-setter x y r g b)
              (let ((idx (xy->idx x y)))
                (let-values (((r1 r2) (split-double-byte r))
                             ((g1 g2) (split-double-byte g))
                             ((b1 b2) (split-double-byte b)))
                  (bytevector-u8-set! data idx r1)
                  (bytevector-u8-set! data (+ idx 1) r2)
                  (bytevector-u8-set! data (+ idx 2) g1)
                  (bytevector-u8-set! data (+ idx 3) g2)
                  (bytevector-u8-set! data (+ idx 4) b1)
                  (bytevector-u8-set! data (+ idx 5) b2))))
            (unless (= byte-count (bytevector-length data))
              (error (string-append "(image-format pnm pbm) make-pbm-image: Invalid bytevector length" byte-count)))
            (make-pnm-image 'ppm width height maxval data
                            (if unsafe? pixel-getter (make-safe-pixel-getter pixel-getter))
                            (if unsafe? pixel-setter (make-safe-pixel-setter pixel-setter))))))))