Auto-HDMI on a per-screen basis

etc--udev--rules.d--95-hdmi-plug.rules

ACTION=="change", SUBSYSTEM=="drm", RUN+="/usr/bin/systemctl --no-block start hdmi-config.service"

home--<USER>--.hdmi-auto--script.sh

#!/bin/bash

# first let's check that the screen isn't locked so we don't pop arandr unnecessarily
if ps aux | grep i3lock | grep -vE "(xautolock|grep)" > /dev/null;
then
   echo "The screen is locked, external monitors may just have been put to sleep, not changing anything."
   exit
fi

until xrandr > /dev/null
do
    echo "Waiting for X11"
    sleep 1
done

# get a unique ID depending on the screen combination that's plugged in
hash_dp1_edid=$(md5sum -b /sys/class/drm/card0-DP-1/edid | awk '{print $1;}')
hash_dp2_edid=$(md5sum -b /sys/class/drm/card0-DP-2/edid | awk '{print $1;}')
hash_edp1_edid=$(md5sum -b /sys/class/drm/card0-eDP-1/edid | awk '{print $1;}')
hash_hdmia1_edid=$(md5sum -b /sys/class/drm/card0-HDMI-A-1/edid | awk '{print $1;}')

hash_edid=$(echo "$hash_dp1_edid $hash_dp2_edid $hash_edp1_edid $hash_hdmia1_edid" | md5sum - | awk '{print $1;}')

if test -f "$hash_edid";
then
    if [[ "$(md5sum $hash_edid | awk '{print $1;}')" = "$(unxrandr | md5sum | awk '{print $1;}')" ]];
    then :
    else
       echo "This screen has already been configured in $hash_edid, using that config."
       sh $hash_edid
    fi
else
   echo "The configuration for screen if $hash_edid does not exist, creating it with arandr and saving it."
   arandr
   unxrandr > $hash_edid
   echo "Configuration for $hash_edid has been written."
fi

usr--lib--systemd--system--hdmi-config.service

[Unit]
Description=Automatic HDMI screen configuration

[Service]
Environment="DISPLAY=:0"
Environment="XAUTHORITY=/home/<USER>/.Xauthority"
WorkingDirectory=/home/<USER>/.hdmi-auto
User=<USER>
ExecStart=/bin/bash /home/<USER>/.hdmi-auto/script.sh

[Install]
WantedBy=graphical.target

Update: check all the screens available on my card0