from.php

<?php 

/*
CREDITS & LICENCE
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Made by Julien Dubedout / judbd.com
Released under Do What the Fuck You Want to Public License. https://en.wikipedia.org/wiki/WTFPL

PURPOSE
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This script is for simple date interval calculation in year/month/days in kirby text for my portfolio
eg display "I'm 30 years old and I have 10 years of experience" without update it each year
in kirbytext : "I'm (from:1982-06-28) years old and I have (from:2005) years of experience"

It does not calculate intervals in hours, minutes or seconds

if you want something more complete, try https://github.com/distantnative/relative-date

WARNING : THOUGHTS ON DATE FORMATS
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Sometimes strtotime does weird shit, and if you can write your date nearly as you want, sometimes it misinterprets
dates end leads to false calculations.

The bulletproof method is to write it in the the good ol' 'murican way, eg yyyy-mm-dd.

you can also try those syntaxes :
Forward slash (/) signifies American M/D/Y
a dash (-) signifies European D-M-Y
a period (.) signifies ISO Y.M.D


ACCEPTED CUSTOM FORMATS
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	http://php.net/manual/en/dateinterval.format.php
%Y	Years, numeric, at least 2 digits with leading 0	01, 03
%y	Years, numeric	1, 3
%M	Months, numeric, at least 2 digits with leading 0	01, 03, 12
%m	Months, numeric	1, 3, 12
%D	Days, numeric, at least 2 digits with leading 0	01, 03, 31
%d	Days, numeric	1, 3, 31
%a	Total number of days as a result of a DateTime::diff() or (unknown) otherwise	4, 18, 8123
%H	Hours, numeric, at least 2 digits with leading 0	01, 03, 23
%h	Hours, numeric	1, 3, 23
%I	Minutes, numeric, at least 2 digits with leading 0	01, 03, 59
%i	Minutes, numeric	1, 3, 59
%S	Seconds, numeric, at least 2 digits with leading 0	01, 03, 57
%s	Seconds, numeric	1, 3, 57
%R	Sign "-" when negative, "+" when positive	-, +
%r	Sign "-" when negative, empty when positive	-,

You can do custom stuff like (from:2005-03-06 format:It was %y years and %m months ago)
It still a little buggy with parenthesis in the (format) espression

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*/

kirbytext::$tags['from'] = array(
	'attr' => array(
		'to',
		'format'
		),
	'html' => function( $tag ) {
		# define the default date to now
		$now = date('Y-m-d');
		# grab the "from" argument
		$from = $tag->attr( 'from' );
		# grab the "to" argument, set to "now" if not defined
		$to = $tag->attr( 'to', $now );
		# grab the output format or set it to year if not defined
		$format = $tag->attr( 'format', 'y' );

        # find the $to and $from length
		$fromLen = strlen( $from );
		$toLen = strlen( $to );

        # if from is just 4 chars yyyy add additionnal characters to avoid bad interpretation (hours instead of years) by strtotime
		if ( $fromLen == 4 ) $from .= '-01-01';
        # same if date is yyyy-mm
		elseif ( $fromLen == 7 ) $from .= '-01';
        # if it's another format, display error message
		elseif ( $fromLen != 10 ) throw new Exception( 'invalid date format (try yyyy or yyyy-mm or yyyy-mm-dd).' );

        # same check for the $to variable
		if ( $toLen == 4 ) $to .= '-01-01';
		elseif ( $toLen == 7 ) $to .= '-01';
        # if the format is wrong, use the current date
		elseif ( $toLen != 10 ) $to = 'now';
		$dtFrom = new DateTime( $from );
		$dtTo = new DateTime( $to );

		# if the output format is set on "d" ou "j" for days, replace it by "a" the correct syntax for day count.
		if ( $format == 'j'||$format == 'd' ) $format = 'a';
		# if the output format is set on "m" calculate the number in month additionning years ×12 + number of months.
		if ( $format == 'm' ) return $dtFrom->diff( $dtTo )->m + ($dtFrom->diff( $dtTo )->y * 12);
		# if the output format is set on "y" or "a" just display it.
		elseif ( $format == 'y'||$format == 'a') return $dtFrom->diff( $dtTo )->format( '%'.$format );
		# if the output format is a custom combination (including % in kirby), display it as is
		elseif ( strpos($format, '%') !== false ) return $dtFrom->diff( $dtTo )->format( $format );
		# else just display in years
		else return $dtFrom->diff( $dtTo )->format( 'y' );
	}
	);