module Jekyll
 
   class Pagination < Generator
     # This generator is safe from arbitrary code execution.
     safe true
 
     # Generate paginated pages if necessary.
     #
     # site - The Site.
     #
     # Returns nothing.
     def generate(site)
       site.pages.dup.each do |page|
         paginate(site, page) if Pager.pagination_enabled?(site.config, page)
       end
     end
 
     # Paginates the blog's posts. Renders the index.html file into paginated
     # directories, e.g.: page2/index.html, page3/index.html, etc and adds more
     # site-wide data.
     #
     # site - The Site.
     # page - The index.html Page that requires pagination.
     #
     # {"paginator" => { "page" => <Number>,
     #                   "per_page" => <Number>,
     #                   "posts" => [<Post>],
     #                   "total_posts" => <Number>,
     #                   "total_pages" => <Number>,
     #                   "previous_page" => <Number>,
     #                   "next_page" => <Number> }}
     def paginate(site, page)
       all_posts = site.site_payload['site']['posts']
       pages = Pager.calculate_pages(all_posts, site.config['paginate'].to_i)
       page_dir = page.destination('').sub(/\/[^\/]+$/, '')
       page_dir_config = site.config['pagination_dir']
       dir = ((page_dir_config || page_dir) + '/').sub(/^\/+/, '')
 
       (1..pages).each do |num_page|

         pager = Pager.new(site.config, num_page, all_posts, page_dir+'/', '/'+dir, pages)

         if num_page > 1
           newpage = Page.new(site, site.source, page_dir, page.name)
           newpage.pager = pager
           newpage.dir = File.join(page.dir, "#{dir}page/#{num_page}")
           site.pages << newpage
         else
           page.pager = pager
         end
       end
     end
   end
 
   class Pager
     attr_reader :page, :per_page, :posts, :total_posts, :total_pages, :previous_page, :next_page
 
     # Calculate the number of pages.
     #
     # all_posts - The Array of all Posts.
     # per_page  - The Integer of entries per page.
     #
     # Returns the Integer number of pages.
     def self.calculate_pages(all_posts, per_page)
       (all_posts.size.to_f / per_page.to_i).ceil
     end
 
     # Determine if pagination is enabled for a given file.
     #
     # config - The configuration Hash.
     # file   - The String filename of the file.
     #
     # Returns true if pagination is enabled, false otherwise.
     def self.pagination_enabled?(config, file)
       file.name == 'index.html' && !config['paginate'].nil? && file.content =~ /paginator\./
     end
 
     # Initialize a new Pager.
     #
     # config    - The Hash configuration of the site.
     # page      - The Integer page number.
     # all_posts - The Array of all the site's Posts.
     # num_pages - The Integer number of pages or nil if you'd like the number
     #             of pages calculated.

     def initialize(config, page, all_posts, index_dir, pagination_dir, num_pages = nil)

       @page = page
       @per_page = config['paginate'].to_i
       @page_dir = pagination_dir + 'page/'
       @total_pages = num_pages || Pager.calculate_pages(all_posts, @per_page)
       @previous_page = nil
 
       if @page > @total_pages
         raise RuntimeError, "page number can't be greater than total pages: #{@page} > #{@total_pages}"
       end
 
       init = (@page - 1) * @per_page
       offset = (init + @per_page - 1) >= all_posts.size ? all_posts.size : (init + @per_page - 1)
 
       @total_posts = all_posts.size
       @posts = all_posts[init..offset]
       @previous_page = @page != 1 ? @page_dir + (@page - 1).to_s + '/' : nil
       @previous_page = index_dir if @page - 1 == 1
       @next_page = @page != @total_pages ? @page_dir + (@page + 1).to_s + '/' : nil
     end
 
     # Convert this Pager's data to a Hash suitable for use by Liquid.
     #
     # Returns the Hash representation of this Pager.
     def to_liquid
       {
         'page' => page,
         'per_page' => per_page,
         'posts' => posts,
         'total_posts' => total_posts,
         'total_pages' => total_pages,
         'previous_page' => previous_page,
         'next_page' => next_page
       }
     end
   end
 
 end