#!/usr/bin/perl -w

# $Id: Cron.pm,v 1.3 2000/06/12 07:25:41 roland Exp $

=head1 NAME

Cron - cron-like scheduler for Perl subroutines

=head1 SYNOPSIS

  use Schedule::Cron;

  # Subroutines to be called
  sub dispatcher { 
    print "ID:   ",shift,"\n"; 
    print "Args: ","@_","\n";
  }

  sub check_links { 
    # do something... 
  }

  # Create new object with default dispatcher
  my $cron = new Schedule::Cron(\&dispatcher);

  # Load a crontab file
  $cron->load_crontab("/var/spool/cron/perl");

  # Add dynamically  crontab entries
  $cron->add_entry("3 4  * * *",ROTATE => "apache","sendmail");
  $cron->add_entry("0 11 * * Mon-Fri",\&check_links);

  # Run scheduler 
  $cron->run(detach=>1);
		   

=head1 DESCRIPTION

This  module provides  a simple  but complete  cron like
scheduler.    I.e   this  modules   can   be  used   for
periodically executing Perl  subroutines.  The dates and
parameters  for   the  subroutines  to   be  called  are
specified   with  a  format   known  as   crontab  entry
(L<"METHODS">, C<add_entry()> and L<crontab(5)>)

The  philosophy  behind  C<Schedule::Cron>  is  to  call
subroutines  periodically from  within  one single  Perl
program  instead  of  letting  C<cron>  trigger  several
(possibly different) perl  scripts. Everything under one
roof.  Furthermore  C<Schedule::Cron> provides mechanism
to create crontab  entries dynamically, which isn't that
easy with C<cron>.

C<Schedule::Cron> knows  about all extensions  (well, at
least all extensions  I'm aware of, i.e those  of the so
called  "Vixie" cron)  for crontab  entries  like ranges
including  'steps', specification of  month and  days of
the week by  name or coexistence of lists  and ranges in
the same  field.  And  even a bit  more (like  lists and
ranges with symbolic names).

=head1 METHODS

=over 4

=cut

#'

package Schedule::Cron;

use Time::ParseDate;
use Data::Dumper;

use strict;
use vars qw($VERSION  $DEBUG);
use subs qw(dbg);

$VERSION = q$Revision: 1.3 $ =~ /(\d+)\.(\d+)/ && sprintf("%d.%02d",$1-1,$2 );

my $DEBUG = 0;

my @WDAYS = qw(
		 Sunday
		 Monday
		 Tuesday
		 Wednesday
		 Thursday
		 Friday
		 Saturday
		 Sunday
		);

my @ALPHACONV = (
		 { },
		 { },
		 { },
		 { qw(jan 1 feb 2 mar 3 apr 4 may 5 jun 6 jul 7 aug 8
		      sep 9 oct 10 nov 11 dec 12) },
		 { qw(sun 0 mon 1 tue 2 wed 3 thu 4 fri 5 sat 6)}
		);
my @RANGES = ( 
	      [ 0,59 ],
	      [ 0,23 ],
	      [ 0,31 ],
	      [ 0,12 ],
	      [ 0,7  ]
	     );

my @LOWMAP = ( 
	      {},
	      {},
	      { 0 => 1},
	      { 0 => 1},
	      { 7 => 0}
	     );

sub REAPER {
  my $waitedpid = 0;
  while($waitedpid != -1) {
    $waitedpid = wait;
  }
  $SIG{CHLD} = \&REAPER;
}
$SIG{CHLD} = \&REAPER;

=item $cron = new Schedule::Cron($dispatcher,[extra args])

Creates  a new  C<Cron> object.   C<$dispatcher> is  a reference  to a
subroutine, which  will be called by default.   C<$dispatcher> will be
invoked with the arguments parameter  provided in the crontab entry if
no other subroutine is specified. This can be either a single argument
containing  the  argument  parameter  literally  has  string  (default
behavior)  or a  list  of  arguments when  using  the C<eval>  option
described below.

The date  specifications must  be either provided  via a  crontab like
file or added explicitly with C<add_entry()> (L<"add_entry">).

I<extra_args>  can  be  a   hash  or  hash  reference  for  additional
arguments.  The following parameters are recognized:

 file => <crontab>  Load the crontab entries from <crontab>

 eval =>  1         Eval  the argument  parameter in  a crontab
                    entry   before   calling   the   subroutine
                    (instead    of   literally    calling   the
                    dispatcher  with the argument  parameter as
                    string

=cut

sub new { 
  my $class = shift;
  my $dispatcher = shift || die "No dispatching sub provided";
  die "Dispatcher not a ref to a subroutine" unless ref($dispatcher) eq "CODE";
  my $cfg = ref($_[0]) eq "HASH" ? $_[0] : {  @_ };
  my $self = { 
	      cfg => $cfg,
	      dispatcher => $dispatcher,
	      queue => [ ],
	      map => { }
	     };
  bless $self,(ref($class) || $class);

  $self->load_crontab if $cfg->{file};
  $self;
}

=item $cron->load_crontab($file)

=item $cron->load_crontab(file=>$file,[eval=>1])

Loads and parses the crontab  file C<$file>. The entries found in this
file   will   be   B<added>   to   the   current   time   table   with
C<$cron-E<gt>add_entry>.

The format of  the file consists of cron  commands containing of lines
with at least 5 columns, whereas the first 5 columns specify the date.
The rest of the line (i.e columns 6 and greater) contains the argument
with which the dispatcher subroutine  will be called.  By default, the
dispatcher will  be called with one single  string argument containing
the  rest of  the line  literally.   Alternatively, if  you call  this
method with  the optional argument  C<eval=E<gt>1> (you must  then use
the second  format shown above), the  rest of the line  will be evaled
before used as argument for the dispatcher.

For the format of the first 5 columns, please see L<"add_entry">.

Blank lines and lines starting with a C<#> will be ignored. 

There's  no  way to  specify  another  subroutine  within the  crontab
file.  All  calls   will  be  made  to  the   dispatcher  provided  at
construction time.

If    you   want    to    start   up    fresh,    you   should    call
C<$cron-E<gt>clean_timetable()> before.

Example of a crontab fiqw(le:)

   # The following line runs on every Monday at 2:34 am
   34 2 * * Mon  "make_stats"
   # The next line should be best read in with an eval=>1 argument
   *  * 1 1 *    { NEW_YEAR => '1',HEADACHE => 'on' }

=cut

#'

sub load_crontab {
  my $self = shift;
  my $cfg = shift;

  if ($cfg) {
    if (@_) {
      $cfg = ref($cfg) eq "HASH" ? $cfg : { $cfg,@_ };
    } elsif (!ref($cfg)) {
      my $new_cfg = { };
      $new_cfg->{file} = $cfg;
      $cfg = $new_cfg;
    }
  }

  my $file = $cfg->{file} || $self->{cfg}->{file} || die "No filename provided";
  my $eval = $cfg->{eval} || $self->{cfg}->{eval};

  open(F,$file) || die "Cannot open schedule $file : $!";
  my $line = 0;
  while (<F>) {
    $line++;
    next if /^$/;
    next if /^\s*#/;
    chomp;
    s/\s*(.*)\s*$/$1/;
    my ($min,$hour,$dmon,$month,$dweek,$args) = split (/\s+/,$_,6);
    my $time = [ $min,$hour,$dmon,$month,$dweek ];
    $self->add_entry($time,{ 'args' => $args, 'eval' => $eval});
  }
  close F;
}

=item $cron->add_entry($timespec,[arguments])

Adds a new entry to the list of scheduled cron jobs.

B<Time and Date specification>

C<$timespec> is the  specification of the scheduled time
in  crontab format  (L<crontab(5)>) which  contains five
time and date fields. C<$timespec> can be either a plain
string, which  contains a whitespace  separated time and
date specification.   Alternatively, C<$timespec> can be
a reference to an array containing the five elements for
the date fields.

The time and date  fields are (cited from L<crontab(5)>,
"Vixie" cron):

   field          values
   =====          ======
   minute         0-59
   hour           0-23
   day of month   1-31 
   month          1-12 (or as names)
   day of week    0-7 (0 or 7 is Sunday, or as names )

 A field may be an asterisk (*), which always stands for
 ``first-last''.

 Ranges of numbers are  allowed.  Ranges are two numbers
 separated  with  a  hyphen.   The  specified  range  is
 inclusive.   For example, 8-11  for an  ``hours'' entry
 specifies execution at hours 8, 9, 10 and 11.

 Lists  are allowed.   A list  is a  set of  numbers (or
 ranges)  separated by  commas.   Examples: ``1,2,5,9'',
 ``0-4,8-12''.

 Step  values can  be used  in conjunction  with ranges.
 Following a range with ``/<number>'' specifies skips of
 the  numbers value  through the  range.   For example,
 ``0-23/2'' can  be used in  the hours field  to specify
 command execution every  other hour (the alternative in
 the V7 standard is ``0,2,4,6,8,10,12,14,16,18,20,22'').
 Steps are  also permitted after an asterisk,  so if you
 want to say ``every two hours'', just use ``*/2''.

 Names can also  be used for the ``month''  and ``day of
 week''  fields.  Use  the  first three  letters of  the
 particular day or month (case doesn't matter).

 Note: The day of a command's execution can be specified
       by two fields  -- day of month, and  day of week.
       If both fields are restricted (ie, aren't *), the
       command will be run when either field matches the
       current  time.  For  example, ``30  4 1,15  * 5''
       would cause a command to be run at 4:30 am on the
       1st and 15th of each month, plus every Friday

In addition, ranges or lists of names are allowed.

Examples:

 "8  0 * * *"       ==> 8 minutes after midnight, every day
 "5 11 * * Sat,Sun" ==> at 11:05 on each Saturday and Sunday
 "0-59/5 * * * *"   ==> every five minutes
 "42 12 3 Feb Sat"  ==> at 12:42 on 3rd of February and on 
                        each Saturday in February

B<Command specification>

The subroutine to be  executed when the the C<$timespec>
matches can be specified in several ways.

First,  if the  optional C<arguments>  are  lacking, the
default dispatching  subroutine provided at construction
time will be called without arguments.

If the second parameter to this method is a reference to
a subroutine,  this subroutine  will be used  instead of
the dispatcher.

Any additional parameters will  be given as arguments to
the subroutine  to be executed.  You can also  specify a
reference to an array instead of a list of parameters.

You can also  use a named parameter list  provided as an
hashref.  The named parameters recognized are:

   subroutine      reference to subroutine to be executed
   sub

   arguments       reference to array containing arguments
   args            to be use when calling the subroutine

   eval            if  set, provide the  subroutine with
                   the  evaled string provided  with the
                   'arguments'      parameter.       The
                   evaluation     will     take    place
                   immediately (not  when the subroutine
                   is to be called)

Examples:

   $cron->add_entry("* * * * *");
   $cron->add_entry("* * * * *","doit");
   $cron->add_entry("* * * * *",\&dispatch,"first",2,"third");
   $cron->add_entry("* * * * *",{'subroutine' => \&dispatch,
				 'arguments'  => [ "first",2,"third" ]});
   $cron->add_entry("* * * * *",{'subroutine' => \&dispatch,
				 'arguments'  => '[ "first",2,"third" ]',
				 'eval'       => 1});

=cut 

sub add_entry { 
  my $self = shift;
  my $time = shift;
  my $args = shift; 
  my $dispatch;

#  dbg "Args: ",Dumper($time,$args);

  if (ref($args) eq "HASH") {
    my $cfg = $args;
    $args = undef;
    $dispatch = $cfg->{subroutine} || $cfg->{sub};
    $args = $cfg->{arguments} || $cfg->{args};
    if ($cfg->{eval} && $cfg) {
      die "You have to provide a simple scalar if using eval" if (ref($args));
      $args = [ eval $args ];
#      dbg "Evaled args ",Dumper($args);
      die "Cannot evaluate args ($args)"
	if $@;
    }
  } elsif (ref($args) eq "CODE") {
    $dispatch = $args;
    $args = shift;
  }


  if (ref($args) ne "ARRAY") {
    $args = [ $args,@_ ];
  }

  $dispatch ||= $self->{dispatcher};

#  dbg "Adding ",Dumper($time);
  push @{$self->{time_table}},$time;
  push @{$self->{args}},[$dispatch,$args];

#  dbg "Added Args ",Dumper($self->{args});

  my $index = $#{$self->{time_table}};
  my $id = $args->[0];
  $self->{map}->{$id} = $index if $id;

  return $#{$self->{time_table}};
}

=item $cron->run([options])

This method starts the scheduler.

When  called  without options,  this  method will  never
return  and executes the  scheduled subroutine  calls as
needed.

Alternatively,  you can detach  the main  scheduler loop
from the  current process  (daemon mode). In  this case,
the  pid  of  the   forked  scheduler  process  will  be
returned.

The C<options>  parameter specifies the  running mode of
C<Schedule::Cron>.  It can be  either a plain list which
will be interpreted  as a hash or it  can be a reference
to  hash. The  following named  parameters (keys  of the
provided hash) are recognized:

   detach    if set to one, detach the scheduler process
             from the current process

   pid_file  if  running   in  daemon  mode,   name  the
             optional file,  in which the  process id of
             the scheduler process should be written. By
             default, no PID File will be created.

Examples:

   # Start  scheduler, detach  from current  process and
   # write  the  PID  of  the forked  scheduler  to  the
   # specified file
   $cron->run(detach=>1,pid_file=>"/var/run/scheduler.pid");

   # Start scheduler and wait forever.
   $cron->run();

=cut

sub run { 
  my $self = shift;
  my $cfg = ref($_[0]) eq "HASH" ? $_[0] : {  @_ };
  
  $self->build_initial_queue;
  die "Nothing in schedule queue" unless @{$self->{queue}};

  my $mainloop = sub {
    while (42) {
      my ($index,$time) = @{shift @{$self->{queue}}};
      $0 = "Schedule::Cron MainLoop - next: ".scalar(localtime($time));
      die "No time found" unless $time;
      my $now = time;
      dbg "R: ",scalar(localtime($time))," (",scalar(localtime($now)),")";
      while ($time > $now) {
	sleep($time-$now);
	$now = time;
      }
      $self->execute($index);
      $self->update_queue($index);
    } 
  };

  if ($cfg->{detach}) {
    defined(my $pid = fork) or die "Can't fork: $!";
    if ($pid) {
      # Parent:
      if ($cfg->{pid_file}) {
	if (open(P,">".$cfg->{pid_file})) {
	  print P $pid,"\n";
	  close P;
	} else {
	  warn "Warning: Cannot open ",$cfg->{pid_file}," : $!";
	}

      }
      return $pid;
    } else {
      # Child:
      # Try to detach from terminal:
      chdir '/';
      open STDIN, '/dev/null' or die "Can't read /dev/null: $!";
      open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!";

      eval { require POSIX; };
      if ($@) {
#      if (1) {
	if (open(T,"/dev/tty")) {
	  dbg "No setsid found, trying ioctl() (Error: $@)";
	  eval { require 'ioctl.ph'; };
	  if ($@) {
	    eval { require 'sys/ioctl.ph'; };
	    if ($@) {
	      die "No 'ioctl.ph'. Probably you have to run h2ph (Error: $@)";
	    }
	  }
	  my $notty = &TIOCNOTTY;
	  die "No TIOCNOTTY !" if $@ || !$notty;
	  ioctl(T,$notty,0) || die "Cannot issue ioctl(..,TIOCNOTTY) : $!";
	  close(T);
	};
      } else {
	&POSIX::setsid() || die "Can't start a new session: $!";
      }
      open STDERR, '>&STDOUT' or die "Can't dup stdout: $!";
      
      $0 = "Schedule::Cron MainLoop";
      &$mainloop();
    }
  } else {
    &$mainloop(); 
  }
}


=item $cron->clean_timetable()

Remove all scheduled entries

=cut

sub clean_timetable { 
  my $self = shift;
  $self->{time_table} = [];
  $self->{args} = [];
}


=item $cron->check_entry($id)

Check, whether the given ID is already registered in the timetable. 
A ID is the first argument in the argument parameter of the 
a crontab entry.

Returns (one of) the index in the  timetable (can be 0, too) if the ID
could be found or C<undef> otherwise.

Example:

   $cron->add_entry("* * * * *","ROTATE");
   .
   .
   defined($cron->check_entry("ROTATE")) || die "No ROTATE entry !"

=cut 

sub check_entry { 
  my $self = shift;
  my $id = shift;
  return $self->{map}->{$id};
}


=item $cron->get_next_execution_time($cron_entry,[$ref_time])

Well, this is mostly an internal method, but it might be useful on 
its own. 

The purpose of this method is to calculate the next execution time
from a specified crontab entry

Parameters:

  $cron_entry  The crontab entry as specified in L<"add_entry">
  $ref_time    the reference time for which the next time should be
               searched which matches $cron_entry. By default, take
               the current time

This method returns the number of epoch-seconds of the next matched 
date for C<$cron_entry>.

Since I suspect, that this calculation of the next execution time might
fail in some circumstances (bugs are lurking everywhere ;-) an
additional interactive method C<bug()> is provided for checking
crontab entries against your expected output. Refer to the
top-level README for additional usage information for this method.

=cut

sub get_next_execution_time { 
  my $self = shift;
  my $cron_entry = shift;
  my $time = shift;
  
  $cron_entry = [ split /\s+/,$cron_entry ] unless ref($cron_entry);


  # Expand and check entry:
  # =======================
  die "Exactly 5 columns has to be specified for a crontab entry ! (not ",
  scalar(@$cron_entry),")"
    unless $#$cron_entry == 4;
  
  my @expanded;
  my $w;

  for my $i (0..4) {
    my @e = split /,/,$cron_entry->[$i];
    my @res;
    my $t;
    while (defined($t = shift @e)) {
      if ($t =~ m|^([^-]+)-([^-/]+)(/(.*))?$|) {
	my ($low,$high,$step) = ($1,$2,$4);
	$step = 1 unless $step;
	if ($low !~ /^(\d+)/) {
	  $low = $ALPHACONV[$i]{lc $low};
	}
	if ($high !~ /^(\d+)/) {
	  $high = $ALPHACONV[$i]{lc $high};
	}
	if (! defined($low) || !defined($high) ||  $low > $high || $step !~ /^\d+$/) {
	  die "Invalid cronentry '",$cron_entry->[$i],"'";
	}
	my $j;
	for ($j = $low; $j <= $high; $j += $step) {
	  push @e,$j;
	}
      } else {
	$t = $ALPHACONV[$i]{lc $t} if $t !~ /^(\d+|\*)$/;
	$t = $LOWMAP[$i]{$t} if exists($LOWMAP[$i]{$t});
	
	die "Invalid cronentry '",$cron_entry->[$i],"'" 
	  if (!defined($t) || ($t ne '*' && ($t < $RANGES[$i][0] || $t > $RANGES[$i][1])));
	push @res,$t;
      }
    }
    push @expanded, [ sort { $a <=> $b} @res];
  }

  # Calculating time:
  # =================
  my $now = $time || time;

  if ($expanded[2]->[0] ne '*' && $expanded[4]->[0] ne '*') {
    # Special check for which time is lower (Month-day or Week-day spec):
    my @bak = @{$expanded[4]};
    $expanded[4] = [ '*' ];
    my $t1 = $self->calc_time($now,\@expanded);
    $expanded[4] = \@bak;
    $expanded[2] = [ '*' ];
    my $t2 = $self->calc_time($now,\@expanded);
    dbg "MDay : ",scalar(localtime($t1))," -- WDay : ",scalar(localtime($t2));
    return $t1 < $t2 ? $t1 : $t2;
  } else {
    # No conflicts possible:
    return $self->calc_time($now,\@expanded);
  }
}

# ==================================================
# PRIVATE METHODS:
# ==================================================

# Build up executing queue and delete any
# existing entries
sub build_initial_queue { 
  my $self = shift;
  $self->{queue} = [ ];
#  dbg "TT: ",$#{$self->{time_table}};
  for my $id (0..$#{$self->{time_table}}) {
    $self->update_queue($id);
  }
}


# Execute a subroutine whose time has come
sub execute { 
  my $self = shift;
  
  my $index = shift;
  my $args = $self->{args}->[$index];
  my $pid;

  if ($pid = fork) {
    # Parent
    return;
  } else {
    # Child
    my $dispatch = $self->{dispatcher};

    $dispatch = $args->[0];
    die "No subroutine provided with $dispatch" 
      unless ref($dispatch) eq "CODE";
    $args = $args->[1];
    
    my @args;
    if (defined($args)) {
      push @args,@$args;
    }
    dbg "Calling dispatch with ","@args";
    $0 = "Schedule::Cron Dispatch (".join(",",@$args).")";
    
    &$dispatch(@args);
    dbg "Exiting";
    exit;
  }
}

# Udate the scheduler queue with a new entry
sub update_queue { 
  my $self = shift;

  my $index = shift;
  
  my $entry = $self->{time_table}->[$index];
  
  $entry = [ split(/\s+/,$entry) ] unless ref($entry);
  my $new_time = $self->get_next_execution_time($entry);
  dbg "Updating Queue: ",scalar(localtime($new_time));
  $self->{queue} = [ sort { $a->[1] <=> $b->[1] } @{$self->{queue}},[$index,$new_time] ];
#  dbg "Queue now: ",Dumper($self->{queue});
}


# The heart of the module.
# calulate the next concrete date
# for execution from a cronta entry
sub calc_time { 
  my $self = shift;
  my $now = shift;
  my $expanded = shift;
  
  my ($now_min,$now_hour,$now_mday,$now_mon,$now_wday,$now_year) = 
    (localtime($now+60))[1,2,3,4,6,5];
  $now_mon++; 
  $now_year += 1900;

  # Notes on variables set:
  # $now_... : the current date, fixed at call time
  # $dest_...: date used for backtracking. At the end, it contains
  #            the desired lowest matching date

  my ($dest_mon,$dest_mday,$dest_wday,$dest_hour,$dest_min,$dest_year) = 
    ($now_mon,$now_mday,$now_wday,$now_hour,$now_min,$now_year);

  while ($dest_year <= $now_year + 1) { # Airbag...
    dbg "Parsing $dest_hour:$dest_min $dest_year/$dest_mon/$dest_mday";
    

    # Check month:
    if ($expanded->[3]->[0] ne '*') {
      unless (defined ($dest_mon = $self->get_nearest($dest_mon,$expanded->[3]))) {
	$dest_mon = $expanded->[3]->[0];
	$dest_year++;
      } 
    } 
  
    # Check for day of month:
    if ($expanded->[2]->[0] ne '*') {		
      if ($dest_mon != $now_mon) {	
 	$dest_mday = $expanded->[2]->[0];
      } else {
	unless (defined ($dest_mday = $self->get_nearest($dest_mday,$expanded->[2]))) {
	  # Next day matched is within the next month. ==> redo it
	  $dest_mday = $expanded->[2]->[0];
	  $dest_mon++;
	  if ($dest_mon > 12) {
	    $dest_mon = 1;
	    $dest_year++;
	  }
	  dbg "Backtrack mday: $dest_mday/$dest_mon/$dest_year";
	  next;
	}
      }
    } else {
      $dest_mday = ($dest_mon == $now_mon ? $dest_mday : 1);
    }
  
    # Check for day of week:
    if ($expanded->[4]->[0] ne '*') {
      $dest_wday = $self->get_nearest($dest_wday,$expanded->[4]);
      $dest_wday = $expanded->[4]->[0] unless $dest_wday;
    
      my ($mon,$mday,$year);
#      dbg "M: $dest_mon MD: $dest_mday WD: $dest_wday Y:$dest_year";
      $dest_mday = 1 if $dest_mon != $now_mon;
      my $t = parsedate("$dest_year/$dest_mon/$dest_mday");
      ($mon,$mday,$year) = 
	(localtime(parsedate("$WDAYS[$dest_wday]",PREFER_FUTURE=>1,NOW=>$t-1)))[4,3,5];
      $mon++;
      $year += 1900;

      dbg "$mday/$mon/$year";
      if ($mon != $dest_mon || $year != $dest_year) {
	dbg "backtracking";
	$dest_mon = $mon;
	$dest_year = $year;
	$dest_mday = 1;
	$dest_wday = (localtime(parsedate("$dest_year/$dest_mon/$dest_mday")))[6];
	next;
      }
      
      $dest_mday = $mday;
    } else {
      unless ($dest_mday) {
	$dest_mday = ($dest_mon == $now_mon ? $dest_mday : 1);
      }
    }
  
    # Check for hour
    if ($expanded->[1]->[0] ne '*') {
      if ($dest_mday != $now_mday) {
	$dest_hour = $expanded->[1]->[0];
      } else {
#	dbg "Checking for next hour $dest_hour";
	unless (defined ($dest_hour = $self->get_nearest($dest_hour,$expanded->[1]))) {
	  # Hour to match is at the next day ==> redo it
	  $dest_hour = $expanded->[1]->[0];
	  my $t = parsedate("$dest_hour:$dest_min $dest_year/$dest_mon/$dest_mday");
	  ($dest_mday,$dest_mon,$dest_year,$dest_wday) = 
	    (localtime(parsedate("+ 1 day",NOW=>$t)))[3,4,5,6];
	  $dest_mon++;
	  $dest_year += 1900;
	  next;
	}
      }
    } else {
      $dest_hour = ($dest_mday == $now_mday ? $dest_hour : 0);
    }
    
    # Check for minute
    if ($expanded->[0]->[0] ne '*') {
      if ($dest_hour != $now_hour) {
	$dest_min = $expanded->[0]->[0];
      } else {
	unless (defined ($dest_min = $self->get_nearest($dest_min,$expanded->[0]))) {
	  # Minute to match is at the next hour ==> redo it
	  $dest_min = $expanded->[0]->[0];
	  my $t = parsedate("$dest_hour:$dest_min $dest_year/$dest_mon/$dest_mday");
	  ($dest_hour,$dest_mday,$dest_mon,$dest_year,$dest_wday) = 
	    (localtime(parsedate(" + 1 hour",NOW=>$t)))  [2,3,4,5,6];
	  $dest_mon++;
	  $dest_year += 1900;
	  next;
	}
      }
    } else {
      $dest_min = ($dest_hour == $now_hour ? $dest_min : 0);
    }
    
    # We did it !!
    dbg "Next execution time: $dest_hour:$dest_min $dest_mday/$dest_mon/$dest_year ",
    $WDAYS[$dest_wday];
    return parsedate(sprintf("%2.2d:%2.2d %4.4d/%2.2d/%2.2d",
			     $dest_hour,$dest_min,$dest_year,$dest_mon,$dest_mday));
  }
}

# get next entry in list or 
# undef if is the highest entry found
sub get_nearest { 
  my $self = shift;
  my $x = shift;
  my $to_check = shift;
  foreach my $i (0 .. $#$to_check) {
    if ($$to_check[$i] >= $x) {
      return $$to_check[$i] ;
    }
  }
  return undef;
}

# our very own debugging routine
# ('guess everybody has its own style ;-)
sub dbg  {
  if ($DEBUG) {
    my $args = join('',@_) || "";
    my $caller = (caller(1))[0];
    my $line = (caller(0))[2];
    $caller ||= $0;
    if (length $caller > 22) {
      $caller = substr($caller,0,10)."..".substr($caller,-10,10);
    }
    print STDERR sprintf ("%02d:%02d:%02d [%22.22s %4.4s]  %s\n",
			  (localtime)[2,1,0],$caller,$line,$args);
  }
}

# Helper method for reporting bugs concerning calculation
# of execution bug:
*bug = \&report_exectime_bug;	# Shortcut
sub report_exectime_bug {
  my $self = shift;
  my $endless = shift;
  my $time = time;
  my $inp;
  my $now = $self->time_as_string($time);
  my $email;

  do {
    while (1) {
      $inp = $self->get_input("Reference time\n(default: $now)  : ");
      if ($inp) {
	parsedate($inp) || (print "Couldn't parse \"$inp\"\n",next);
	$now = $inp;
      }
      last;
    }
    my $now_time = parsedate($now);
    
    my ($next_time,$next);
    my @entries;
    while (1) {
      $inp = $self->get_input("Crontab time (5 columns)            : ");
      @entries = split (/\s+/,$inp);
      if (@entries != 5) {
	print "Invalid crontab entry \"$inp\"\n";
	next;
      }
      eval { 
	local $SIG{ALRM} = sub {  die "TIMEOUT" };
	alarm(60);
	$next_time = Schedule::Cron->get_next_execution_time(\@entries,$now_time);
	alarm(0);
      };
      if ($@) {
	alarm(0);
	if ($@ eq "TIMEOUT") {
	  $next_time = -1;
	} else {
	  print "Invalid crontab entry \"$inp\" ($@)\n";
	  next;
	}
      }
      
      if ($next_time > 0) {
	$next = $self->time_as_string($next_time);
      } else {
	$next = "Run into infinite loop !!";
      }
      last;
    }
    
    my ($expected,$expected_time);
    while (1) {
      $inp = $self->get_input("Expected time                       : ");
      unless ($expected_time = parsedate($inp)) {
	print "Couldn't parse \"$inp\"\n";
	next;
      } 
      $expected = $self->time_as_string($expected_time);
      last;
    }
    
    # Print out bug report:
    if ($expected eq $next) {
      print "\nHmm, seems that everything's ok, or ?\n\n";
      print "Calculated time: ",$next,"\n";
      print "Expected time  : ",$expected,"\n";
    } else {
      print <<EOT;
Congratulation, you hit a bug. 

EOT
      $email = $self->get_input("Your E-Mail Address (if available)  : ") 
	unless defined($email);
      $email = "" unless defined($email);
      
      print "\n","=" x 80,"\n";
      print <<EOT;
Please report the following lines
to roland\@consol.de

EOT
      print "# ","-" x 78,"\n";
      print "Reftime: ",$now,"\n";
      print "# Reported by : ",$email,"\n" if $email;
      printf "%8s %8s %8s %8s %8s         %s\n",@entries,$expected;
      print "# Calculated  : \n";
      printf "# %8s %8s %8s %8s %8s         %s\n",@entries,$next;
      unless ($endless) {
	require Config;
	my $vers = `uname -r 2>/dev/null` || $Config::Config{'osvers'} ;
	chomp $vers;
	my $osname = `uname -s 2>/dev/null` || $Config::Config{'osname'};
	chomp $osname;
	print "# OS: $osname ($vers)\n";
	print "# Perl-Version: $]\n";
	print "# Time::ParseDate-Version: ",$Time::ParseDate::VERSION,"\n";
      }
      print "# ","-" x 78,"\n";
    }
    
    print "\n","=" x 80,"\n";
  } while ($endless);
}

my ($input_initialized,$term);
sub get_input { 
  my $self = shift;
  my $prompt = shift;
  use vars qw($term);

  unless (defined($input_initialized)) {
    eval { require Term::ReadLine; };
    
    $input_initialized = $@ ? 0 : 1;
    if ($input_initialized) {
      $term = new Term::ReadLine;
      $term->ornaments(0);
    }
  }
  
  unless ($input_initialized) {
    print $prompt;
    my $inp = <STDIN>;
    chomp $inp;
    return $inp;
  } else {
    chomp $prompt;
    my @prompt = split /\n/s,$prompt;
    if ($#prompt > 0) {
      print join "\n",@prompt[0..$#prompt-1],"\n";
    }
    my $inp = $term->readline($prompt[$#prompt]);
    return $inp;
  }
}

sub time_as_string { 
  my $self = shift;
  my $time = shift; 

  my ($min,$hour,$mday,$month,$year,$wday) = (localtime($time))[1..6];
  $month++;
  $year += 1900;
  $wday = $WDAYS[$wday];
  return sprintf("%2.2d:%2.2d %2.2d/%2.2d/%4.4d %s",
		 $hour,$min,$mday,$month,$year,$wday);
}
=back

=head1 TODO

=over 

=item *

Provide a C<reload()> method for reexaming the crontab file 

=item * 

Clean up C<get_next_execution_time()> and give it at least some 
rational grounding ;-)

=item * 

Provide support for systems without C<fork()> via C<OS::Process>

=item * 

Add logging

=back


=head1 COPYRIGHT

Copyright 1999,2000 Roland Huss.

This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

=head1 AUTHOR

                                                    ...roland

=cut

1;