#!/bin/bash
# (C) 2018-2020 Felix Hauri - felix@f-hauri.ch
# Licensed under terms of GPL v3. www.gnu.org
# There are 2 functions:
#    hsv <red> <green> <blue> <varname>
#             to compute Hue, Saturation and Value from Red, Green and Blue,
#             then store result in Varname array
#    rgb <hue> <saturation> <value> <varname>
#             to compute Red, Green and Blue from Hue, Saturation and Value,
#             then store result in Varname array
# Values: Red, Green, Blue and Value are positive integer <256: [0..255]
# value Hue is a positive integer < 360 and
# value Saturation is a (pseudo) floating between 0.0 and 1.0.

hsv() {
    local -n _result=$4
    local -i _hsv_min _hsv_t
    local _hsv_s
    local -i _hsv_max=" $1 > $2 ?
		(_hsv_min=($2 > $3 ? $3:$2 ), ( $1 > $3 ? $1 : $3 )) :
		(_hsv_min=($1 > $3 ? $3:$1 ), $2) > $3 ? $2 : $3 "
    case $_hsv_max in 
        $_hsv_min) _hsv_t=0 ;;
        $1) _hsv_t=" ( 60 * ( $2 - $3 ) / ( _hsv_max-_hsv_min )+ 360 )%360";;
        $2) _hsv_t=" 60 * ( $3 - $1 ) / ( _hsv_max-_hsv_min )+ 120 " ;;
        $3) _hsv_t=" 60 * ( $1 - $2 ) / ( _hsv_max-_hsv_min )+ 240 " ;;
    esac
    _hsv_s=0000000$(( _hsv_max==0?0 : 100000000-100000000*_hsv_min / _hsv_max ))
    printf -v _hsv_s %.7f ${_hsv_s::-8}.${_hsv_s: -8}
    _result=($_hsv_t $_hsv_s $_hsv_max)
}
rgb() {
    local -n _result=$4
    local -i _rgb_i=" (($1%360)/60)%6 "
    local -i _rgb_f=" 100000000*($1%360)/60-_rgb_i*100000000 "
    local _rgb_s
    printf -v _rgb_s %.8f "$2"
    _rgb_s=$((10#${_rgb_s/.}))
    local -i _rgb_l=" $3*(100000000-_rgb_s)/100000000 "
    case $_rgb_i in
	0 )
	    local -i _rgb_n="$3*(100000000-(100000000-_rgb_f)*_rgb_s/100000000)/
				100000000 "
	    _result=("$3" "$_rgb_n" "$_rgb_l") ;;
	1 )
	    local -i _rgb_m=" $3*(100000000-_rgb_f*_rgb_s/100000000)/100000000 "
	    _result=("$_rgb_m" "$3" "$_rgb_l") ;;
	2 )
	    local -i _rgb_n="$3*(100000000-(100000000-_rgb_f)*_rgb_s/100000000)/
				100000000 "
	    _result=("$_rgb_l" "$3" "$_rgb_n") ;;
	3 )
	    local -i _rgb_m=" $3*(100000000-_rgb_f*_rgb_s/100000000)/100000000 "
	    _result=("$_rgb_l" "$_rgb_m" "$3") ;;
	4 )
	    local -i _rgb_n="$3*(100000000-(100000000-_rgb_f)*_rgb_s/100000000)/
				100000000 "
	    _result=("$_rgb_n" "$_rgb_l" "$3") ;;
	* )
	    local -i _rgb_m=" $3*(100000000-_rgb_f*_rgb_s/100000000)/100000000 "
	    _result=("$3" "$_rgb_l" "$_rgb_m") ;;
    esac
}