#!/bin/bash

# should also work with compositor=compton, untested
compositor=picom

function usage {

    bin=$(basename $0)

    echo
    echo "Toggle monitors between color and grayscale mode."
    echo 
    echo "$bin [$compositor|nvidia|ddc|auto]"
    echo "$bin $compositor [$compositor args]"
    echo "$bin nvidia [nv mon]"
    echo "$bin ddc [ddc mon]"
    echo
    echo "$compositor:   use a GLX shader to set grayscale"
    echo "nvidia:  use NVIDIA proprietary driver Digital Vibrance setting to set grayscale"
    echo "ddc:     use DDC/CI monitor protocol to set the monitor saturation to 0 (grayscale) if supported by monitor"
    echo "auto:    use $compositor if running, otherwise nvidia if available, otherwise ddc if available"
    echo
    echo "$compositor args: in $compositor mode, optional $compositor parameters"
    echo
    echo "nv mon:     in nvidia mode, an optional monitor name as enumerated by xrandr."
    echo "            if unspecified, apply to all monitors managed by the NVIDIA driver"
    echo "ddc mon:    in ddc mode, optional ddcutil options to identify the monitor. See 'man ddcutil'"
    echo "            if unspecified, apply to the first monitor detected by ddcutil"
    echo "if invoked with no argument, auto is used."
    echo

    exit 0
}

function toggle_nvidia {

    dpy=$1
    
    value=$(nvidia-settings -t -q DigitalVibrance)

    # set a value in ]-1024..0[ range to desaturate colors instead of full grayscale
    # -1024 => full grayscale
    desaturate_value=-1024
    
    if (( value == $desaturate_value )); then
	value=0
	toggle_mode="color"
    else
	value=$desaturate_value
	toggle_mode="grayscale"
    fi

    if [ -n "$dpy" ]; then
	param="[DPY:$dpy]/DigitalVibrance"
    else
	param="DigitalVibrance"
    fi

    nvidia-settings -a ${param}=${value} > /dev/null
}

function toggle_compositor {


    if $compositor --help | grep legacy-backends > /dev/null; then
	use_experimental_backends=1;
	grep_string="window-shader-fg"
    else
	use_experimental_backends=0;
	grep_string="glx-fshader-win"
    fi
    
    if pgrep -a -x $compositor | grep $grep_string  > /dev/null; then
	pkill -x $compositor
	sleep 1
	$compositor $* -b
	toggle_mode="color"
    else
	pkill -x $compositor
	sleep 1

	if (( $use_experimental_backends == 1 )); then

	    tmpfile=$(mktemp)
	    trap 'rm -f "${tmpfile}"' EXIT

	    cat > ${tmpfile} <<EOF
#version 330
in vec2 texcoord;

uniform sampler2D tex;
uniform float opacity;

vec4 default_post_processing(vec4 c);

vec4 window_shader() {
    vec4 c = default_post_processing(texelFetch(tex, ivec2(texcoord), 0));
    float y = dot(c.rgb, vec3(0.2126, 0.7152, 0.0722));
    c = opacity*vec4(y, y, y, c.a);
    return c;
}
EOF
	    
	    $compositor $* -b --backend glx --window-shader-fg ${tmpfile} 2> /dev/null

	else

	    shader='uniform sampler2D tex; uniform float opacity; void main() { vec4 c = texture2D(tex, gl_TexCoord[0].xy); float y = dot(c.rgb, vec3(0.2126, 0.7152, 0.0722)); gl_FragColor = opacity*vec4(y, y, y, c.a); }'
	    $compositor $* -b --backend glx --glx-fshader-win "${shader}" 2> /dev/null

	fi
	    
	    
	toggle_mode="grayscale"
    fi
}

function toggle_ddc {
    
    out=($(ddcutil $* getvcp 8a -t))
    
    if (( $? != 0 )); then
	echo "ddc: this monitor does not support saturation control"
	exit 1
    fi

    # out array:
    #
    # VCP 8A C 100 200
    #           |   |
    #          cur max
   
    if (( ${#out[@]} != 5 )); then
	echo "ddc: unexpected output getting current saturation state"
	exit 1
    fi

    cur_saturation=${out[3]}
    max_saturation=${out[4]}

    # set a value in ]0..max/2[ range to desaturate colors instead of full grayscale
    # 0 => full grayscale
    desaturate_value=0

    if (( cur_saturation == desaturate_value  )); then
	new_saturation=$(( max_saturation / 2 )) # nominal saturation 
	toggle_mode="color"
    else
        new_saturation=$desaturate_value
	toggle_mode="grayscale"
    fi

    ddcutil $* setvcp 8a $new_saturation
}

mode=$1

case $mode in

    --help|-h)
	usage
	;;

    $compositor)
	if ! pgrep -x $compositor > /dev/null; then
            echo "$compositor is not running"
            exit 1
	fi
	;;

    nvidia)
	if ! which nvidia-settings &> /dev/null; then
	    echo "nvidia-settings is not installed"
	    exit 1
	fi
	;;	   	
    ddc)
	if ! which ddcutil &> /dev/null; then 
	    echo "ddcutil is not installed"
	    exit 1
	fi
        ;;
    
    *)
	[ -z "$mode" ] && mode=auto
	
	if [ "$mode" = "auto" ]; then

	    if pgrep -x $compositor > /dev/null; then
		mode=$compositor
	    elif which nvidia-settings &> /dev/null; then
		mode=nvidia
	    elif which ddcutil &> /dev/null; then
		mode=ddc
	    else
		echo "neither $compositor is running, nor nvidia-settings installed, nor ddcutil installed"
		exit 1
	    fi
	else
	    usage
	fi
	
esac

# pass eventual remaining arguments to toggle_* function
if (( $# > 0 )); then
   shift
fi

if [ "$mode" = "nvidia" ]; then
    toggle_nvidia $*
elif [ "$mode" = "$compositor" ]; then
    toggle_compositor $*
else
    toggle_ddc $*
fi

if (( $? == 0 )); then
    echo "$mode: set to $toggle_mode"
else
    echo "$mode: toggle failed"
fi