#!/bin/bash

# variables
time_start="08:30"
time_end="18:00"

# check for arguments
if [ $# -eq 0 ]; then
	printf "Decimal overtime calculator\\nUsage: %s HH:MM (HH:MM)\\n" "${0##*/}"
	exit 1
fi

# main logic
# no second variable, calculate singularly
if [ -z ${2+x} ]; then
	start="$(date -d "Yesterday $1" "+%s")"
	if [ "${time_start:0:2}" -gt "${1:0:2}" ]; then
		end="$(date -d "Yesterday $time_start" "+%s")"
		printf "Early start: %s hours\\n" "$(date -d\@$((end - start)) -u +'scale=2; %H + %M/60' | bc)"
	else
		end="$(date -d "Yesterday $time_end" "+%s")"
		printf "Late finish: %s hours\\n" "$(date -d\@$((start - end)) -u +'scale=2; %H + %M/60' | bc)"
	fi
# second variable, calculate both and combine
else
	start_am="$(date -d "Yesterday $1" "+%s")"
	start_pm="$(date -d "Yesterday $2" "+%s")"
	end_am="$(date -d "Yesterday $time_start" "+%s")"
	end_pm="$(date -d "Yesterday $time_end" "+%s")"
	printf "Combined overtimes: %s hours\\n" "$(echo "$(date -d\@$((end_am - start_am)) -u +'scale=2; %H + %M/60' | bc)" + "$(date -d\@$((start_pm - end_pm)) -u +'scale=2; %H + %M/60' | bc)" | bc)"

fi