[[!tag wishlist]]I would quite like the ability to write a page (blog post in
practice) but for the page to not be displayed until a date and time after it
is added to the wiki. I've thought this through a bit, but would appreciate
feedback from people before I go any further. Would anyone else find this
useful?

Thinking about how to implement this in ikiwiki, perhaps a conditional
pagespec would be best (which could be tidied up into a template)

    \[[!if test="current_date_before(<TMPL_VAR date>)"
    then="""[[!tag draft]]"""
    else="""[[!meta date="<TMPL_VAR date>"]]"""
    ]]

…pre-supposing a scheme whereby tagging 'draft' hides the page from an
aggregation somewhere.  With a template, this could collapse to

    \[[!template id=publishafter date="Thu Aug 30 14:13:06 BST 2012"]]

This would require implementing the `current_date_before` pagespec.

You would also need a regularly scheduled wiki refresh and a way of marking the
unpublished pages as 'dirty' so they were always scanned on refresh until their
publish date has occurred. That could perhaps be implemented via a small plugin
which defined a pagespec which ensured the page was 'dirty':

    \[[!meta date="<TMPL_VAR date>"]]
    \[[!if test="!current_date_before(<TMPL_VAR date>)"
    then="""[[!tag draft]][[!dirty]]"""
    ]]

The following is an attempt at the dirty part:

    #!/usr/bin/perl
    package IkiWiki::Plugin::dirty;
    # provides a pagespec 'dirty' which ensures the page will always be
    # re-scanned for content on wiki refresh.
    
    use warnings;
    use strict;
    use IkiWiki 3.00;
    
    hook(type => "preprocess", id => "dirty", call => \&preprocess);
    hook(type => "needsbuild", id => "dirty", call => \&needsbuild);
    
    sub preprocess (@) {
      my %params = @_;
      $pagestate{$params{page}}{dirty}{dirty} = 1;
      return '';
    }
    
    sub needsbuild (@) {
      my $pages= shift;
      my %p2 = map { $_ => 1 } @$pages;
      my %d2 = map { $_ => 1 } @$deleted;
    
      foreach my $page (keys %pagestate) {
        if(exists $pagestate{$page}{dirty}{dirty}) {
          push @$pages, $pagesources{$page} unless
            (exists $p2{$pagesources{$page}} or exists $d2{$pagesources{$page}});
          delete $pagestate{$page}{dirty}{dirty};
        }
      }
    
      return $pages;
    }
    
    1

Although it doesn't fit, the `current_date_before` pagespec could be implemented
in the same plugin. I tried the following (before the trailing `1`):

    package IkiWiki::PageSpec;
    use Date::Parse;
    
    sub match_current_date_before ($$;@) {
      shift;
      my $date = shift;
      my $out = str2time($date);
      if(defined $out) {
        return IkiWiki::SuccessReason->new("time before now") if $out < time();
        return IkiWiki::FailReason->new("time not before now");
      } else { return IkiWiki::ErrorReason->new("couldn't parse time $date")};
    }

I always hit the `ErrorReason` branch when I try to use it, even with strings
which work fine in test scripts.  If anyone can help me debug that I'd be very
grateful.
If anyone has any clues as to why this doesn't work 

Thoughts on the whole idea? — [[Jon]]

> There is an old todo about it: [[tagging_with_a_publication_date]].
> I feel my idea there about making a pagespec that is limited to
> items in the present/past, combined with setting the meta data, is a good
> way.. --[[Joey]]  

>> Thanks for your response Joey. Should I merge these two TODOs, then?
>> So if I understand you correctly, you would prefer some new pagespecs
>> to match future/past dates, and a plugin which kept track of pages with
>> a future date and kept them 'dirty' (similar to the above), which means
>> avoiding the need for a `dirty` pagespec in the page itself. Is that
>> about right?
>> 
>> I came up with the following, but I haven't adapted `dirty.pm` inline
>> with my understanding above, yet.

    sub match_infuture ($$;@) {
      my $page = shift;
      return IkiWiki::SuccessReason->new("page time is in the future")
        if $IkiWiki::pagectime{$page} > time;
      return IkiWiki::FailReason->new("page time is not in the future");
    }

>> I've managed to get my original suggestion working. The problem was
>> I was using quotes when invoking the pagespec, which stopped `str2time`
>> working. 
>> 
>> Let me know if I've understood your POV correctly and I'll see about
>> tidying this up and putting it in a branch.
>> 
>> Finally, a way of scheduling future runs of ikiwiki *within ikiwiki
>> itself* might be useful for other things too, and would avoid the 
>> need for a cron job in this case. (I'm thinking of a plugin that
>> implemented itself in terms of cron, or at, or both, or possibly
>> other things depending on what people want to support). But that would
>> be substantially more work, more than I can afford atm at least. — [[Jon]]
