module Octopress
  module Ink
    module Filters

      # Returns the site's config root or '/' if the config isn't set
      #
      def root
        root_url = Ink.site.config['root']
        root_url.nil? ? '/' : File.join('/', root_url)
      end

      # Prepends input with a url fragment
      #
      # input - An absolute url, e.g. /images/awesome.gif
      # url   - The fragment to prepend the input, e.g. /blog
      #
      # Returns the modified url, e.g /blog
      #
      def expand_url(input, url=nil)
        url ||= root
        if input =~ /^#{url}/
          input
        else
          File.join(url, input)
        end
      end

      # Prevent orphans in text by inserting a non-breaking space between the two last words of a string.
      def unorphan(input)
        input.sub(/\s+(\S+)\s*$/, ' \1')
      end

      # Prepend all absolute urls with a url fragment
      #
      # input - The content of a page or post
      # url   - The fragment to prepend absolute urls
      #
      # Returns input with modified urls
      #
      def expand_urls(input, url=nil)
        url ||= root
        input.gsub /(\s+(href|src)\s*=\s*["|']{1})(\/[^\/>]{1}[^\"'>]*)/ do
          $1 + expand_url($3, url)
        end
      end

      # Prepend all urls with the full site url
      #
      # input - The content of a page or post
      #
      # Returns input with all urls expanded to include the full site url
      # e.g. /images/awesome.gif => http://example.com/images/awesome.gif
      #
      def full_urls(input)
        url = Ink.site.config['url']
        if url.nil?
          raise IOError.new "Could not expand urls: Please add your published url to your _config.yml, eg url: http://example.com/"
        else
          expand_urls(input, url)
        end
      end
      
      # Prepend a url with the full site url
      #
      # input - a url
      #
      # Returns input with all urls expanded to include the full site url
      # e.g. /images/awesome.gif => http://example.com/images/awesome.gif
      #
      def full_url(input)
        url = Ink.site.config['url']
        if url.nil?
          raise IOError.new "Could not expand url in #{input}: Please add your site's published url to your _config.yml, eg url: http://example.com/"
        else
          expand_url(input, url)
        end
      end

      # Escapes HTML content for XML
      def cdata_escape(input)
        input.gsub(/<!\[CDATA\[/, '&lt;![CDATA[').gsub(/\]\]>/, ']]&gt;')
      end

      # Returns a title cased string based on John Gruber's title case http://daringfireball.net/2008/08/title_case_update
      def titlecase(input)
        Octopress::Utils.titlecase!(input)
      end

      # Formats a string for use as a css classname, removing illegal characters
      def classify(input)
        input.gsub(/ /,'-').gsub(/[^\w-]/,'').downcase
      end

      alias_method :sluggify, :classify

      # Remove empty lines
      def compact_newlines(input)
        input.gsub(/\n{2,}/, "\n").gsub(/^ +\n/,"")
      end

      # Join newlines 
      def join_lines(input, separator='')
        compact_newlines(input).strip.gsub(/\s*\n\s*/, separator)
      end

      module_function :root, :expand_url, :expand_urls, :full_url, :full_urls, :cdata_escape, :titlecase, :classify, :sluggify, :join_lines, :compact_newlines, :unorphan
      public :expand_url, :expand_urls, :full_url, :full_urls, :cdata_escape, :titlecase, :classify, :sluggify, :join_lines, :compact_newlines, :unorphan
    end
  end
end