Waybar hamster module (custom/hamster) https://github.com/projecthamster/hamster

hamster.sh

#!/bin/bash

activity=`hamster current`
if [[ $activity == "No activity" ]]; then
    text=""
    class=""
else
    start_date=`echo $activity | cut -d' ' -f1`
    start_time=`echo $activity | cut -d' ' -f2`
    name=`echo $activity | sed 's/[0-9\-]\+\s[0-9\:]\+[[:space:]]\([[:alnum:] \.,@-]\+\)[[:space:]][0-9\:]\+/\1/'`
    duration=`echo $activity | sed 's/.*\([0-9\:]\{2\}:[0-9\:]\{2\}\)/\1/g'`
    text="${duration} ${name}"
    class="has-activity"
fi

tooltip=`hamster list day`
tooltip="${tooltip//$'\n'/\\n}"

output="{ \"text\": \"$text\", \"tooltip\": \"<tt>$(echo "$tooltip")</tt>\", \"class\": \"$class\" }"

echo  "$output"

style.css

#custom-hamster.has-activity {
    color: #839e00;
}

waybar-config

{
  "custom/hamster": {
    "exec": "~/.config/waybar/scripts/hamster.sh",
    "on-click": "hamster add",
    "on-click-right": "hamster",
    "on-click-middle": "hamster stop",
    "interval": 1,
    "return-type": "json"
  }
}