#!/bin/bash
# Desc: Template to report seconds until beginning of next day
# Author: Steven Baltaktei Sandoval; License: GPLv3+

#==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 $*"; }
timeUntilNextDay(){
    # Desc: Report seconds until next day.
    # Output: stdout: integer seconds until next day
    # Output: exit code 0 if stdout > 0; 1 if stdout = 0; 2 if stdout < 0
    # Usage: timeUntilNextDay
    # Usage: if ! myTTL="$(timeUntilNextDay)"; then yell "ERROR in if statement"; exit 1; fi
    local returnState
    TIME_CURRENT="$(date --iso-8601=seconds)" ; # Produce `date`-parsable current timestamp with resolution of 1 second.
    TIME_CURRENT_SHORT="$(date -d "$TIME_CURRENT" +%Y%m%dT%H%M%S%z)" # Produce separator-less current timestamp with resolution 1 second.
    DATE_CURRENT="$(date -d "$TIME_CURRENT" --iso-8601=date)" ; # Produce `date`-parsable current timestamp with resolution of 1 day.
    DATE_CURRENT_SHORT="$(date -d "$TIME_CURRENT" +%Y%m%d)" ; # Produce separator-less current timestamp with resolution 1 day.
    DATE_TOMORROW="$(date -d "$TIME_CURRENT next day" --iso-8601=date)" ; # Produce timestamp of tomorrow's date (res. 1 day).
    TIME_NEXT_DAY="$(date -d "$DATE_TOMORROW" --iso-8601=seconds)" ; # Produce `date`-parsable timestamp of closest next day (res. 1 second).
    SECONDS_UNTIL_NEXT_DAY="$(( $(date +%s -d "$TIME_NEXT_DAY") - $(date +%s -d "$TIME_CURRENT") ))" ; # Calculate seconds until closest future midnight (res. 1 second).
    if [[ "$SECONDS_UNTIL_NEXT_DAY" -gt 0 ]]; then
	returnState="true";
    elif [[ "$SECONDS_UNTIL_NEXT_DAY" -eq 0 ]]; then
	returnState="WARNING_ZERO";
	yell "WARNING:Reported time until next day exactly zero.";
    elif [[ "$SECONDS_UNTIL_NEXT_DAY" -lt 0 ]]; then
	returnState="WARNING_NEGATIVE";
	yell "WARNING:Reported time until next day is negative.";
    fi

    try echo "$SECONDS_UNTIL_NEXT_DAY"; # 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 midnight
#===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==