#!/bin/bash
# Desc: Template to report seconds until beginning of next day

#==BEGIN Define script parameters==
#===BEGIN Declare local script functions===
yell() { echo "$0: $*" >&2; } # Yell, Die, Try Three-Fingered Claw technique; # Ref/Attrib: https://stackoverflow.com/a/25515370
die() { yell "$*"; exit 111; }
try() { "$@" || die "cannot $*"; }
timeUntilNextDay(){
    # Desc: Report seconds until next day.
    # Version: 1.0.3
    # Output: stdout: integer seconds until next day
    # Output: exit code 0 if stdout > 0; 1 if stdout = 0; 2 if stdout < 0
    # Usage: timeUntilNextDay
    # Usage: if ! myTTL="$(timeUntilNextDay)"; then yell "ERROR in if statement"; exit 1; fi
    # Depends: date 8, echo 8, yell, try
    
    local returnState timeCurrent timeNextDay secondsUntilNextDay
    timeCurrent="$(date --iso-8601=seconds)" ; # Produce `date`-parsable current timestamp with resolution of 1 second.
    timeNextDay="$(date -d "$timeCurrent next day" --iso-8601=date)"; # Produce timestamp of beginning of tomorrow with resolution of 1 second.
    secondsUntilNextDay="$(( $(date +%s -d "$timeNextDay") - $(date +%s -d "$timeCurrent") ))" ; # Calculate seconds until closest future midnight (res. 1 second).
    if [[ "$secondsUntilNextDay" -gt 0 ]]; then
	returnState="true";
    elif [[ "$secondsUntilNextDay" -eq 0 ]]; then
	returnState="warning_zero";
	yell "WARNING:Reported time until next day exactly zero.";
    elif [[ "$secondsUntilNextDay" -lt 0 ]]; then
	returnState="warning_negative";
	yell "WARNING:Reported time until next day is negative.";
    fi

    try echo "$secondsUntilNextDay"; # Report
    
    # Determine function return code
    if [[ "$returnState" = "true" ]]; then
	return 0;
    elif [[ "$returnState" = "warning_zero" ]]; then
	return 1;
    elif [[ "$returnState" = "warning_negative" ]]; then
	return 2;
    fi
} # Report seconds until next day
#===END Declare local script functions===
#==END Define script parameters==


#==BEGIN sample code==
try echo "Time until next day (seconds):$(timeUntilNextDay)" # simple report

if ! myTTL="$(timeUntilNextDay)"; then yell "ERROR in if statement for myTTL:$myTTL"; exit 1; fi # Use of exit code to exit early if time <= 0.
#==END sample code==

# Author: Steven Baltaktei Sandoval
# License: GPLv3+