use strict;
use warnings;

sub ical_parse {
    my $fh = shift;
    my %ical_hash;
    my ( $lastelement, $lastdata );
    my %event;

    while (<$fh>) {
	chomp;       
	if (/^\s+(.+)/) {  }
        if (/^(METHOD|PRODID|VERSION):(.+)/) { 
		$ical_hash{$1} = $2; 
	}
        if ( /^BEGIN:VEVENT/ .. /^END:VEVENT/ ) { 
            if (/^BEGIN:/) {
                %event = ();
                next;
            }
	    if (/^END:/) {
                $ical_hash{_events_}{$event{SUMMARY}} = { %event };
                %event = ();
                next;
            }
            if (/^(\w[^:]+):(.+)/) { 
                $event{$1} = $2;
                next;
            }
            
        }

    }
    return %ical_hash;
}

sub ical_add_event {
	my ($to_hash) = shift;
	my (%event) = @_;
	
	# entweder die Daten werden hier drin umgewandelt oder richtig übergeben
	
	# und weiterer Code ;)
	#... 
	# 
	
	die "iCal entry $event{SUMMARY} exists!" 
		if exists $to_hash->{_events_}{$event{SUMMARY}};
	
	$to_hash->{_events_}{$event{SUMMARY}} = \%event;	
}


sub ISO_datetime {
	my ($time) = shift // time;
	#  0    1    2     3     4    5     6     7     8
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime($time);
	
	return 
		sprintf '%4d%02d%02dT%02d%02d%02dZ',$year+1900,$mon+1,$mday,$hour,$min,$sec;
	
}


my %hash = ical_parse(*DATA);
use Data::Dumper;
say Dumper( \%hash );

ical_add_event( 
	\%hash, 
	CREATED => ISO_datetime(),
	'LAST-MODIFIED' =>  ISO_datetime(),
	'DTSTART;VALUE=DATE' => '20140101',
	'DTEND;VALUE=DATE' => '20140101',
	SUMMARY => 'Sylvesterferien',
	DESCRIPTION => 'Sonderferien in Bayern',
	URL => 'http://mydomain.tld/',
	# einzigartige Zeichenfolge! + @ + domain
	UID => 'Sonderferien_in_Bayern1235473253483773463535353@mydomain.tld',
	TRANSP => 'TRANSPARENT',
	DTSTAMP => ISO_datetime(),
);
say Dumper( \%hash );


__DATA__
BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Winterferien Bayern
DTSTART;VALUE=DATE:20140303
DTEND;VALUE=DATE:20140308
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Winterferien-Bayern-201403081093325744@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Osterferien Bayern
DTSTART;VALUE=DATE:20140414
DTEND;VALUE=DATE:20140427
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Osterferien-Bayern-201404271062227588@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Pfingstferien Bayern
DTSTART;VALUE=DATE:20140610
DTEND;VALUE=DATE:20140622
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Pfingstferien-Bayern-201406221052186503@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Sommerferien Bayern
DTSTART;VALUE=DATE:20140730
DTEND;VALUE=DATE:20140916
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Sommerferien-Bayern-201409161222283686@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Herbstferien Bayern
DTSTART;VALUE=DATE:20141027
DTEND;VALUE=DATE:20141101
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Herbstferien-Bayern-201411011005635868@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Weihnachtsferien Bayern
DTSTART;VALUE=DATE:20140101
DTEND;VALUE=DATE:20140105
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Weihnachtsferien-Bayern-201401051129637466@schulferien.org
END:VEVENT
BEGIN:VEVENT
CREATED:20130104T150430Z
LAST-MODIFIED:20130104T150430Z
DTSTAMP:20130104T150430Z
SUMMARY:Weihnachtsferien Bayern
DTSTART;VALUE=DATE:20141224
DTEND;VALUE=DATE:20150101
URL:http://www.schulferien.org
DESCRIPTION:Alle Termine auf www.schulferien.org
TRANSP:TRANSPARENT
UID:Weihnachtsferien-Bayern-201501011322846554@schulferien.org
END:VEVENT
END:VCALENDAR