timedelta

#!/usr/bin/env bash

###########################################################################
# Made by    : Ewoud Dronkert
# Licence    : GNU GPL v3
# Platform   : macOS, Raspbian
# Requires   : bash
# Location   : ~/bin or /usr/local/bin
# Name       : timedelta
# Version    : 1.1.0
# Date       : 2017-05-29
# Purpose    : Calculate time value plus or minus "x" minutes
# Parameters : 1. <time> = 24h time as HMM or H:MM or H.MM (or HH etc.)
#            : 2. +|-<delta> = time difference in minutes as +M or -M
# Output     : New 24h time value as HMM
# Exit     0 : No errors
#          1 : Wrong parameter count
#          2 : Invalid time format
#          3 : Time hours >= 24
#          4 : Time minutes >= 60
#          5 : Delta not signed
#          6 : Delta not a number
###########################################################################

[ $# -ne "2" ] && echo "Usage: $(basename $0) <time> +|-<delta>" 1>&2 && exit 1

# First argument
TIME=${1//:}
TIME=${TIME//.}
L=${#TIME}
N=$(expr "$TIME" : '[0-9]*')
(( L < 3 || L > 4 || L != N )) && echo "First argument must be a time value, e.g. 1432 or 14:32." 1>&2 && exit 2
if (( L == 3 )); then
	H=${TIME:0:1}
	M=${TIME:1:2}
	M=${M#0}
else
	H=${TIME:0:2}
	M=${TIME:2:2}
	H=${H#0}
	M=${M#0}
fi
(( H >= 24 )) && echo "Hours out of range (0-23)." 1>&2 && exit 3
(( M >= 60 )) && echo "Minutes out of range (0-59)." 1>&2 && exit 4

# Second argument
SIGN=${2:0:1}
[ "$SIGN" != "+" -a "$SIGN" != "-" ] && echo "Second argument must start with + or -." 1>&2 && exit 5
DELTA=${2:1}
N=$(expr "$DELTA" : '^0*')
DELTA=${DELTA:$N}
[ -z "$DELTA" ] && DELTA=0
L=${#DELTA}
N=$(expr "$DELTA" : '[0-9]*')
(( L != N )) && echo "Second argument must be a signed number." 1>&2 && exit 6

# Calculation
(( T = 60 * H + M ))
if [ "$SIGN" = "-" ]; then
	(( T -= DELTA ))
	while (( T < 0 )); do
		(( T += 1440 ))
	done
else
	(( T += DELTA ))
	while (( T >= 1440 )); do
		(( T -= 1440 ))
	done
fi
(( H = T / 60 ))
(( M = T - 60 * H ))
(( M < 10 )) && M="0$M"

echo "$H$M"
exit 0