18 Jun 2012

Schedule posts in Jekyll

In my previous posts about Jekyll I explained what is Jekyll, how I installed it and that I wanted to be able to schedule a post to be published later.

So I decided to write a plugin for that. There is two elements in it, first the plugin itself and a bash script. The plugin write a file with the publication date of next post. The bash script is executed by a cron on a regular basis, read the file with the next post date and rebuild the site if necessary.

Here is the plugin, called schedule_build.rb:

module Jekyll
  class Post
    alias_method :pre_initialize, :initialize
    
    def initialize(site, source, dir, name)
      pre_initialize(site, source, dir, name)
      if site.config['no_schedule']
        site.config['next_build'] = nil
        return
      end
      if self.data.has_key?('no_schedule') && self.data['no_schedule'] == true
        return
      end
      if (Time.new <=> self.date) < 0
        if self.published
          next_build = site.config['next_build']
          if next_build == nil or (next_build <=> self.date) > 0
            site.config['next_build'] = self.date
          end
          site.config['next_build']
        end
        self.published = false
      end
    end
  end

  class ScheduleBuildGenerator < Generator
    def generate(site)
      next_build = site.config['next_build']
      date_file = File.join(site.dest, 'next_build.txt')
      if !(next_build == nil)
        f = File.new(date_file, 'w')
        f.write(next_build.strftime("%s"))
        f.close
        site.static_files << Jekyll::StaticFile.new(site, site.dest, '', 'next_build.txt')
      end
    end
  end
end

As you can see, each post update a next_build variable if their publication date is in the future and more recent than current next_build value.

Then the generator write a file called next_build.txt in _site directory with this date in it.

When writing your post you can put no_schedule: true in your _config.yml if you want to have all your future posts to be generated. Likewise, put no_schedule: true in your post to have it generated even if it's in the future.

Now we just need a script schedule_build.sh (with execution right) to rebuild the website if necessary:

#!/bin/bash

next_build_date=`cat /srv/blog.example.com/_site/next_build.txt`
current_date=`date +%s`

if (( $current_date > $next_build_date )) ; then
  ~/blog.example.com.git/hooks/post-receive
fi