;;
;; chicken-web-colors:
;; Parse and write HTML/CSS color strings in CHICKEN Scheme.
;;
;; Copyright © 2019  John Croisant.
;; All rights reserved.
;;
;; Redistribution and use in source and binary forms, with or without
;; modification, are permitted provided that the following conditions
;; are met:
;;
;; - Redistributions of source code must retain the above copyright
;;   notice, this list of conditions and the following disclaimer.
;;
;; - Redistributions in binary form must reproduce the above copyright
;;   notice, this list of conditions and the following disclaimer in
;;   the documentation and/or other materials provided with the
;;   distribution.
;;
;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
;; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
;; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
;; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
;; COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
;; INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
;; (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
;; SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
;; HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
;; STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
;; ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
;; OF THE POSSIBILITY OF SUCH DAMAGE.


(export +web-color-types+
        color-list?
        normalize-web-color
        rgb-color->bytes)


(define +web-color-types+ '(rgb rgb% hsl))

(: color-list? (any #!optional (list-of symbol) --> boolean))
(define (color-list? x #!optional (types +web-color-types+))
  (and (list? x)
       (= 5 (length x))
       (memq (car x) types)
       (real? (list-ref x 1))
       (real? (list-ref x 2))
       (real? (list-ref x 3))
       (real? (list-ref x 4))))


(: normalize-web-color (color-list --> color-list))
(define (normalize-web-color color)
  (assert (color-list? color)
          "Invalid color list" color)
  (case (car color)
    ((rgb)
     (list 'rgb
           (%byte (list-ref color 1))
           (%byte (list-ref color 2))
           (%byte (list-ref color 3))
           (%clamp (list-ref color 4) 0 1)))
    ((rgb%)
     (list 'rgb%
           (%clamp (list-ref color 1) 0 1)
           (%clamp (list-ref color 2) 0 1)
           (%clamp (list-ref color 3) 0 1)
           (%clamp (list-ref color 4) 0 1)))
    ((hsl)
     (list 'hsl
           (%wrap (inexact->exact (round (list-ref color 1))) 360)
           (%clamp (list-ref color 2) 0 1)
           (%clamp (list-ref color 3) 0 1)
           (%clamp (list-ref color 4) 0 1)))))


(: rgb-color->bytes (color-list --> (list fixnum fixnum fixnum fixnum)))
(define (rgb-color->bytes color)
  (assert (color-list? color '(rgb rgb%))
          "Invalid rgb color list" color)
  (let ((scale (if (eq? 'rgb% (car color)) 255 1)))
    (list (%byte (* scale (list-ref color 1)))
          (%byte (* scale (list-ref color 2)))
          (%byte (* scale (list-ref color 3)))
          (%byte (* 255 (list-ref color 4))))))


(: %byte (number --> number))
(define (%byte n)
  (%clamp (inexact->exact (round n)) 0 255))

(: %clamp (number number number --> number))
(define (%clamp n lower upper)
  (cond ((<= n lower) lower)
        ((<= upper n) upper)
        (else n)))

(: %wrap (number number --> number))
(define (%wrap n upper)
  (let loop ((n n))
    (cond ((and (<= 0 n) (< n upper)) n)
          ((< n 0) (loop (+ n upper)))
          ((<= upper n) (loop (- n upper))))))