#!/bin/bash

# Desc: Template to indicate time duration in ISO-8601 format

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 $*"; }
timeDuration(){
    # Desc: Output approximate time duration string before given time (default:current date)
    # Ref/Attrib: ISO-8601:2004(E), §4.4.4.2 Representations of time intervals by duration and context information
    # Note: "1 month" ("P1M") is assumed to be "30 days" (see ISO-8601:2004(E), §2.2.1.2)
    # Usage: timeDuration [arg1] ([arg2])
    # Input: arg1: seconds as base 10 integer >= 0  (ex: 3601)
    #        arg2: precision level (optional; default=2)
    # Output: stdout: ISO-8601 duration string (ex: "P1H1S", "P2Y10M15DT10H30M20S")
    # Example: 'timeDuration 111111 3' yields 'P1DT6H51M'
    # Depends: date 8 (gnucoreutils)
    local returnState fullHours fullMinutes fullSeconds;
    ARG1="$1";
    ARG2="$2";
    precision=2; # set default precision
    returnState="true"; # set default return state

    # Check that between one and two arguments is supplied
    if ! { [[ $# -ge 1 ]] && [[ $# -le 2 ]]; }; then
	yell "ERROR:Invalid number of arguments:$# . Exiting.";
	returnState="ERROR_INPUT"; fi

    # Check that arg1 provided
    if [[ $# -ge 1 ]]; then
	# Check that arg1 is a positive integer
	if [[ "$ARG1" =~ ^[[:digit:]]+$ ]]; then
   	    arg1Valid="true";
	else
	    yell "ERROR:ARG1 not a digit.";
	    returnState="ERROR_INPUT";
	    arg1Valid="false";
	fi
    else
	yell "ERROR:No argument provided. Exiting.";
	exit 1;
    fi

    # Consider whether arg2 was provided
    if  [[ $# -eq 2 ]]; then
	# Check that the second arg is a positive integer
	if [[ "$ARG2" =~ ^[[:digit:]]+$ ]] && [[ "ARG2" -gt 0 ]]; then
	arg2Valid="true";
	precision="$ARG2";
	else
	    yell "ERROR:ARG2 not a positive integer. (is $ARG2 ). Leaving early.";
	    returnState="ERROR_INPUT";
	    arg2Valid="false";
	fi;
    else
	arg2Valid="false";
    fi;
    
    remainder="$ARG1" ; # seconds
    ## Calculate full years Y, update remainder
    fullYears=$(( remainder / (365*24*60*60) ));
    remainder=$(( remainder - (fullYears*365*24*60*60) ));
    ## Calculate full months M, update remainder
    fullMonths=$(( remainder / (30*24*60*60) ));
    remainder=$(( remainder - (fullMonths*30*24*60*60) ));
    ## Calculate full days D, update remainder
    fullDays=$(( remainder / (24*60*60) ));
    remainder=$(( remainder - (fullDays*24*60*60) ));
    ## Calculate full hours H, update remainder
    fullHours=$(( remainder / (60*60) ));
    remainder=$(( remainder - (fullHours*60*60) ));
    ## Calculate full minutes M, update remainder
    fullMinutes=$(( remainder / (60) ));
    remainder=$(( remainder - (fullMinutes*60) ));
    ## Calculate full seconds S, update remainder
    fullSeconds=$(( remainder / (1) ));
    remainder=$(( remainder - (remainder*1) ));
    ## Check which fields filled
    if [[ $fullYears -gt 0 ]]; then hasYears="true"; else hasYears="false"; fi
    if [[ $fullMonths -gt 0 ]]; then hasMonths="true"; else hasMonths="false"; fi
    if [[ $fullDays -gt 0 ]]; then hasDays="true"; else hasDays="false"; fi
    if [[ $fullHours -gt 0 ]]; then hasHours="true"; else hasHours="false"; fi
    if [[ $fullMinutes -gt 0 ]]; then hasMinutes="true"; else hasMinutes="false"; fi
    if [[ $fullSeconds -gt 0 ]]; then hasSeconds="true"; else hasSeconds="false"; fi
    
    ## Determine which fields to display (see ISO-8601:2004 §4.4.3.2)
    witherPrecision="false"
    
    ### Years
    if $hasYears && [[ $precision -gt 0 ]]; then
	displayYears="true";
	witherPrecision="true";
    else
	displayYears="false";
    fi;
    if $witherPrecision; then ((precision--)); fi;
    
    ### Months
    if $hasMonths && [[ $precision -gt 0 ]]; then
	displayMonths="true";
	witherPrecision="true";
    else
	displayMonths="false";
    fi;
    if $witherPrecision && [[ $precision -gt 0 ]]; then
	displayMonths="true";
    fi;
    if $witherPrecision; then ((precision--)); fi;

    ### Days
    if $hasDays && [[ $precision -gt 0 ]]; then
	displayDays="true";
	witherPrecision="true";
    else
	displayDays="false";
    fi;
    if $witherPrecision && [[ $precision -gt 0 ]]; then
	displayDays="true";
    fi;
    if $witherPrecision; then ((precision--)); fi;

    ### Hours
    if $hasHours && [[ $precision -gt 0 ]]; then
	displayHours="true";
	witherPrecision="true";
    else
	displayHours="false";
    fi;
    if $witherPrecision && [[ $precision -gt 0 ]]; then
	displayHours="true";
    fi;
    if $witherPrecision; then ((precision--)); fi;

    ### Minutes
    if $hasMinutes && [[ $precision -gt 0 ]]; then
	displayMinutes="true";
	witherPrecision="true";
    else
	displayMinutes="false";
    fi;
    if $witherPrecision && [[ $precision -gt 0 ]]; then
	displayMinutes="true";
    fi;
    if $witherPrecision; then ((precision--)); fi;

    ### Seconds

    if $hasSeconds && [[ $precision -gt 0 ]]; then
	displaySeconds="true";
	witherPrecision="true";
    else
	displaySeconds="false";
    fi;
    if $witherPrecision && [[ $precision -gt 0 ]]; then
	displaySeconds="true";
    fi;
    if $witherPrecision; then ((precision--)); fi;



    ## Determine whether or not the "T" separator is needed to separate date and time elements
    if ( $displayHours || $displayMinutes || $displaySeconds); then
	displayDateTime="true"; else displayDateTime="false"; fi
    
    ## Construct duration output string
    OUTPUT="P"
    if $displayYears; then
	OUTPUT=$OUTPUT$fullYears"Y"; fi
    if $displayMonths; then
	OUTPUT=$OUTPUT$fullMonths"M"; fi
    if $displayDays; then
	OUTPUT=$OUTPUT$fullDays"D"; fi
    if $displayDateTime; then
	OUTPUT=$OUTPUT"T"; fi
    if $displayHours; then
	OUTPUT=$OUTPUT$fullHours"H"; fi
    if $displayMinutes; then
	OUTPUT=$OUTPUT$fullMinutes"M"; fi
    if $displaySeconds; then
	OUTPUT=$OUTPUT$fullSeconds"S"; fi

    ## Output duration string to stdout
    if [[ "$returnState" = "true" ]]; then echo "$OUTPUT"; fi

    #===Determine function return code===
    if [ "$returnState" = "true" ]; then
	return 0;
    else
	echo "$returnState" 1>&2;
	return 1;
    fi

} # Get duration (ex: PT10M4S )

#==BEGIN sample code==
echo "Precision 6 duration:$(timeDuration "$(date +%s)" 6)"
echo "Precision 5 duration:$(timeDuration "$(date +%s)" 5)"
echo "Precision 4 duration:$(timeDuration "$(date +%s)" 4)"
echo "Precision 3 duration:$(timeDuration "$(date +%s)" 3)"
echo "Precision 2 duration:$(timeDuration "$(date +%s)" 2)"
echo "Precision 1 duration:$(timeDuration "$(date +%s)" 1)"
echo "Precision 6 duration:$(timeDuration $((60+60*60+60*60*24+60*60*24*30+60*60*24*365 - (60+60*60+60*60*24+60*60*24*30) )) 6)"
timeDuration "$@"
#==END sample code==

# Author: Steven Baltakatei Sandoval
# License: GPLv3+