gbacklight.scm

#!/usr/bin/guile \
-e main -s
!#
(use-modules ((ice-9 rdelim)
              #:prefix dlm:))
(use-modules ((ice-9 getopt-long)
              #:prefix gl:))

(define (current-max)
  (call-with-input-file "/sys/class/backlight/intel_backlight/max_brightness"
    (lambda (x)
      (string->number (dlm:read-line x)))))

(define (current-brightness)
  (call-with-input-file "/sys/class/backlight/intel_backlight/brightness"
    (lambda (x)
      (string->number (dlm:read-line x)))))

(define (step-increment pct max-brightness)
  (round (/ (current-max) pct)))

(define (compute-change change-pct)
  (let* ((max (current-max))
         (brightness (current-brightness))
         (maybe-increase-amount (+ brightness (step-increment change-pct max))))

    (cond
     ((>= brightness max)
      0)
     ((>= maybe-increase-amount max)
      max)
     ((<= maybe-increase-amount 50)
      50)
     (else maybe-increase-amount))))

(define (apply-brightness-change change-value)
  (call-with-output-file "/sys/class/backlight/intel_backlight/brightness"
    (lambda (out)
      (write change-value out))))

(define options-spec
  '((help (single-char #\h) (value #f))
    (get (single-char #\g) (value #f))
    (dec (single-char #\d) (value #t))
    (inc (single-char #\i) (value #t))))

(define (print-help)
  (display "\
gbacklight [options]
  -h, --help              Display this help
  -g, --get               Display the current brightness
  -i, --inc <percentage>  Increment by percentage
  -d, --dec <percentage>  Decrement by percentage
"))

(define (print-current)
  (display
   (string-append
    (number->string
     (round (* 100 (/ (current-brightness) (current-max)))))
    "\n")))

(define (main args)
  (let* ((options (gl:getopt-long (command-line) options-spec))
         (help? (gl:option-ref options 'help #f))
         (get? (gl:option-ref options 'get #f))
         (inc-pct (gl:option-ref options 'inc #f))
         (dec-pct (gl:option-ref options 'dec #f)))
    (cond
     (help?
      (print-help))
     (get?
      (print-current))
     (inc-pct
      (apply-brightness-change (compute-change (string->number inc-pct)))
      (print-current))
     (dec-pct
      (apply-brightness-change (compute-change (- (string->number dec-pct))))
      (print-current)))))