(require 'stdlib)

(define sampling-frequency 1000)        ; Hz
(define bits 8)
(define range (ash 1 (1- bits)))
(define min (- (ash 1 (1- bits))))
(define max (1- (ash 1 (1- bits))))

(printf "(bits %s min %s max %s)\n" bits min max)

(define (clip value)
  (cond ((< value min) min)
        ((> value max) max)
        (t (inexact->exact (round value)))))

(define (a-d value)
  "[-1.0 .. 1.0] -> [-128 .. 127]"
  (clip (* value range)))

(define (d-a value)
  (exact->inexact (/ value range)))
  
(dolist (v '(-1.0 0 1.0))
  (printf "%s -> %s\n" v (a-d v)))
(dolist (v (list min 0 max))
  (printf "%s -> %s\n" v (d-a v)))

;; effects
(define (volume sample value)
  (clip (* sample value)))

(define (limiter sample max)
  (if (> sample max)
      max
    sample))

(define (process fx sound)
  (let (result)
    (printf "original: %s\n" sound)
    ;;(setq result (mapcar convert-a-d sound))
    (setq result (mapcar (lambda (x) (volume x 12/10)) sound))
    ;;(setq result (mapcar (lambda (x) (limiter x 95/100)) result))
    ;;(setq result (mapcar d-a result))
    ;;(setq result (mapcar clip result))
    (printf "result  : %s\n" result)))

(define silence (make-list 10 0))
(process nil silence)
(define noise '(-100 -60 2 50 127 127 3 -4 -53 -128 100))
(process nil noise)

;; generate a wave using sine function composite
;; start with a-d conversion
(define (generate fn duration)
  (let* ((samples (* duration sampling-frequency))
         (i 0)
         (wave (make-vector samples 0)))
    (while (< i samples)
      (aset wave i (fn i))
      (setq i (1+ i)))
    (vector->list wave)))

(define (wave-440hz x)
  (sin (* 440 x)))

(define w (mapcar a-d (generate wave-440hz 1)))
;;(process nil w)