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