#!/usr/bin/perl -w
#
# What's Going On.  Given one or more .ics files on the command line,
# produces a text report showing what's happening in the next six weeks.
#
# This was my main reason for working on this -- I've been producing things
# like this by hand for a mailing list of friends on and off for the past
# six years, and was too lazy to automate the damn thing.
#
# To see it in action, try fetching the london.pm calendar from
# http://london.pm.org/ical.ics, then run "perl wgo ical.ics"
#
# Nik Clayton, <nik@FreeBSD.org>

use strict;

use lib '../lib';
use Text::vFile::asData;

use DateTime;
use DateTime::Span;
use DateTime::Format::ICal;

use IO::File;

# Could use Lingua::*::Inflect, but it's overkill for a quick demo
#                1  2  3  4  5  6  7  8  9  10
my @inflect = qw(st nd rd th th th th th th th
		 th th th th th th th th th th
		 st nd rd th th th th th th th
		 st);

# Get the current time, and the time six weeks from now.  Then build a
# DateTime::Span.  We'll test every event we find to see if it, or any of
# it's recurrences, are inside this span.  If they are, we need to include
# them in the output.
#
# Yes, start time and end time should be parameters to the script.
my $start_dt = DateTime->now();
my $end_dt = $start_dt + DateTime::Duration->new(weeks => 6);

my $span = DateTime::Span->from_datetimes(start => $start_dt,
                                          end   => $end_dt);

my @cals = ();                  # List of refs returned by parse()

my %events = ();                # Events we're interested in.  Key is
                                # date/time formatted as an ICal string,
                                # value is a list of events happening at
                                # that time.

foreach(@ARGV) {
  push @cals, Text::vFile::asData->new->parse(IO::File->new($_));
}

foreach my $cal (@cals) {
  foreach my $obj (@{ $cal->{objects}->[0]->{objects} }) {
    next if $obj->{type} ne 'VEVENT';   # Not interested in non events

    my %e = ();                         # Info about this event
    my $p = $obj->{properties};         # The event's properties

    next if ! defined $p->{SUMMARY}->[0]->{value};

    $e{start} =
      DateTime::Format::ICal->parse_datetime($p->{DTSTART}->[0]->{value});

    if(defined $p->{DTEND}->[0]->{value}) {
      $e{end} =
        DateTime::Format::ICal->parse_datetime($p->{DTEND}->[0]->{value});
      # iCal represents all-day events by using ;VALUE=DATE and setting
      # DTEND=end_date + 1
      $e{end}->subtract( days => 1 )
        if $p->{DTEND}[0]{param}{VALUE} && $p->{DTEND}[0]{param}{VALUE} eq 'DATE'

    } else {
      $e{duration} =
        DateTime::Format::ICal->parse_duration($p->{DURATION}[0]{value} || "PT1S" );
      $e{end} = $e{start} + $e{duration};
    }

    $e{span} = DateTime::Span->from_datetimes(start => $e{start},
                                              end   => $e{end});

    $e{summary} = $p->{SUMMARY}->[0]->{value};
    $e{desc}    = $p->{DESCRIPTION}->[0]->{value};

    $e{desc} ||= '';

    $e{summary} =~ s/\\(.)/$1/g;        # Backslash escape removal
    $e{desc}    =~ s/\\(.)/$1/g;

    # Handle event recurrences.  If there's a recurrence rule (RRULE), then
    # use that.
    if(exists $p->{RRULE}) {            # $e{recur} = DateTime::Set
      $e{recur} =
        DateTime::Format::ICal->parse_recurrence(recurrence => $p->{RRULE}->[0]->{value},
                                                 dtstart => $e{start});
    } else {
      # If the event is a multi-day event then synthesise copies of the
      # event for every day on which it occurs.
      #
      # Why?  Suppose you're looking at a 5 day span, and you have an
      # event that starts on day 2 and finishes on day 4 (3 days in total).
      # The ->iterator() considers that this is one occurence of the event,
      # rather than 3.  So create recurrences so the iterator behaves in a
      # more useful fashion.
      $e{recur} =
        DateTime::Set->from_recurrence(
                                       recurrence => sub {
                                         $_[0]->truncate(to => 'day')->add(days => 1);
                                       },
                                       span => $e{span});
      $e{recur} = 
	$e{recur}->union(DateTime::Set->from_datetimes(dates => [$e{start}]));
    }

    # Synthesise a flag that indicates that this is an all-day event.  Not
    # sure if this is the correct way of detecting this, but it works so
    # far...
    $e{allday} =
      exists $p->{DTSTART}->[0]->{param}->{VALUE} and
        $p->{DTSTART}->[0]->{param}->{VALUE} eq 'DATE' ? 1 : 0;

    # Check to see if it's in the time span we're interested in
    if($e{recur}->intersects($span)) {
      my $int_set = $e{recur}->intersection($span);

      # Change the event's recurrence details so that only the events
      # inside the time span we're interested in are listed.
      $e{recur} = $int_set;
      my $iter = $int_set->iterator();

      while(my $dt = $iter->next()) {
        $e{dt} = $dt;

        # Save a copy of the event (es = event saved), and store it in
        # the list of event refs keyed off the ICal date
        my %es = %e;
        push @{$events{ $dt->ymd() }}, \%es;
      }
    }
  }
}

my $e;                          # Hash ref of event info
my $last_ed = '';		# Last event date we processed

foreach my $ed (sort keys %events) { # $ed = event date ('yyyy-mm-dd')
  foreach $e (sort by_type_time @{$events{$ed}}) {
    # Build the first part of the output line.  For the first event of the
    # day include the date, month, and day abbreviation.  For subsequent
    # events on the same day this is the empty string.  This makes for
    # nicer output, as it's more obvious which events share a day.
    if($ed ne $last_ed) {	# First event of the day
      $e->{startstring} = sprintf("%2d %s (%s)",
				  $e->{dt}->day(),
				  $e->{dt}->month_abbr(),
				  $e->{dt}->day_abbr());
    } else {			# Second and subsequent events
      $e->{startstring} = '';
    }

    $last_ed = $ed;

    # If it's not an all day event then the first part of the summary is
    # the time the event occurs
    $e->{summary} = sprintf("%02d:%02d - %02d:%02d, %s",
                            $e->{span}->start()->hour(),
                            $e->{span}->start()->minute(),
                            $e->{span}->end()->hour(),
                            $e->{span}->end()->minute(),
                            $e->{summary})
      unless $e->{allday};

    # If this is the second or subsequent appearance of a multi-day event,
    # replace the description (if it exists) with a pointer to the first
    # occurence of the description
    if($e->{recur}->min()->ymd() ne $ed and $e->{desc} ne '') {
      $e->{desc} = sprintf("See %d%s %s entry for details.",
			   $e->{recur}->min()->day(),
			   $inflect[$e->{recur}->min()->day() - 1],
			   $e->{recur}->min()->month_abbr());
    }

    $e->{summary}  = punctuate($e->{summary}) . '  ' .
      punctuate($e->{desc}) if $e->{desc} ne '';

    write;
  }
}

exit;

sub by_type_time {		# For sorting lists of events
  # Two events on the same day?  All day events come first
  return -1 if $a->{allday} and ! $b->{allday};
  return  1 if $b->{allday} and ! $a->{allday};

  # If they're both all day events, sort by summary text
  return $a->{summary} cmp $b->{summary} if $a->{allday} and $b->{allday};

  # Otherwise, sort by start time
  return $a->{dt} <=> $b->{dt};
}

# Try and make sure a string ends with sensible punctuation
sub punctuate {
  my $str = shift;
  return '' if ! defined $str;
  $str =~ s/\s*$//g;
  $str .= '.' unless $str =~ /[\.\?!]$/;
  return $str;
}

format STDOUT =
@<<<<<<<<<<<  |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$e->{startstring}, $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
~             |  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                $e->{summary}
              |
.