begin
  require 'pygments'
rescue LoadError
  # Pygments is not supported so we try instead with CodeRay
  begin
    require 'coderay'
  rescue LoadError
    # No code syntax highlighting
  end
end

module Orgmode

  class HtmlOutputBuffer < OutputBuffer

    HtmlBlockTag = {
      :paragraph => "p",
      :ordered_list => "ol",
      :unordered_list => "ul",
      :list_item => "li",
      :definition_list => "dl",
      :definition_term => "dt",
      :definition_descr => "dd",
      :table => "table",
      :table_row => "tr",
      :quote => "blockquote",
      :example => "pre",
      :src => "pre",
      :inline_example => "pre",
      :center => "div",
      :heading1 => "h1",
      :heading2 => "h2",
      :heading3 => "h3",
      :heading4 => "h4",
      :heading5 => "h5",
      :heading6 => "h6"
    }

    attr_reader :options

    def initialize(output, opts = {})
      super(output)
      if opts[:decorate_title] then
        @title_decoration = " class=\"title\""
      else
        @title_decoration = ""
      end
      @buffer_tag = "HTML"
      @options = opts
      @new_paragraph = :start
      @footnotes = {}
      @unclosed_tags = []
      @logger.debug "HTML export options: #{@options.inspect}"
    end

    # Output buffer is entering a new mode. Use this opportunity to
    # write out one of the block tags in the HtmlBlockTag constant to
    # put this information in the HTML stream.
    def push_mode(mode, indent)
      super(mode, indent)

      if HtmlBlockTag[mode]
        unless ((mode_is_table?(mode) and skip_tables?) or
                (mode == :src and defined? Pygments))
          css_class = case
                      when (mode == :src and @block_lang.empty?)
                        " class=\"src\""
                      when (mode == :src and not @block_lang.empty?)
                        " class=\"src\" lang=\"#{@block_lang}\""
                      when (mode == :example || mode == :inline_example)
                        " class=\"example\""
                      when mode == :center
                        " style=\"text-align: center\""
                      else
                        @title_decoration
                      end

          add_paragraph unless @new_paragraph == :start
          @new_paragraph = true

          @logger.debug "#{mode}: <#{HtmlBlockTag[mode]}#{css_class}>"
          @output << "<#{HtmlBlockTag[mode]}#{css_class}>"
          # Entering a new mode obliterates the title decoration
          @title_decoration = ""
        end
      end
    end

    # We are leaving a mode. Close any tags that were opened when
    # entering this mode.
    def pop_mode(mode = nil)
      m = super(mode)
      if HtmlBlockTag[m]
        unless ((mode_is_table?(m) and skip_tables?) or
                (m == :src and defined? Pygments))
          add_paragraph if @new_paragraph
          @new_paragraph = true
          @logger.debug "</#{HtmlBlockTag[m]}>"
          @output << "</#{HtmlBlockTag[m]}>"
        end
      end
      @list_indent_stack.pop
    end

    def flush!
      return false if @buffer.empty?
      case
      when preserve_whitespace?
        strip_code_block! if mode_is_code? current_mode

        # NOTE: CodeRay and Pygments already escape the html once, so
        # no need to escapeHTML
        case
        when (current_mode == :src and defined? Pygments)
          lang = normalize_lang @block_lang
          @output << "\n" unless @new_paragraph == :start
          @new_paragraph = true

          begin
            @buffer = Pygments.highlight(@buffer, :lexer => lang)
          rescue
            # Not supported lexer from Pygments, we fallback on using the text lexer
            @buffer = Pygments.highlight(@buffer, :lexer => 'text')
          end
        when (current_mode == :src and defined? CodeRay)
          lang = normalize_lang @block_lang

          # CodeRay might throw a warning when unsupported lang is set,
          # then fallback to using the text lexer
          silence_warnings do
            begin
              @buffer = CodeRay.scan(@buffer, lang).html(:wrap => nil, :css => :style)
            rescue ArgumentError
              @buffer = CodeRay.scan(@buffer, 'text').html(:wrap => nil, :css => :style)
            end
          end
        when (current_mode == :html or current_mode == :raw_text)
          @buffer.gsub!(/\A\n/, "") if @new_paragraph == :start
          @new_paragraph = true
        else
          # *NOTE* Don't use escape_buffer! through its sensitivity to @<text> forms
          @buffer = escapeHTML @buffer
        end

        # Whitespace is significant in :code mode. Always output the
        # buffer and do not do any additional translation.
        @logger.debug "FLUSH CODE ==========> #{@buffer.inspect}"
        @output << @buffer

      when (mode_is_table? current_mode and skip_tables?)
        @logger.debug "SKIP       ==========> #{current_mode}"

      else
        @buffer.lstrip!
        @new_paragraph = nil
        @logger.debug "FLUSH      ==========> #{current_mode}"

        case current_mode
        when :definition_term
          d = @buffer.split(/\A(.*[ \t]+|)::(|[ \t]+.*?)$/, 4)
          d[1] = d[1].strip
          unless d[1].empty?
            @output << inline_formatting(d[1])
          else
            @output << "???"
          end
          indent = @list_indent_stack.last
          pop_mode

          @new_paragraph = :start
          push_mode(:definition_descr, indent)
          @output << inline_formatting(d[2].strip + d[3])
          @new_paragraph = nil
          # FIXME: Need to restore tags once again (this should be done in escape_buffer!)
          @output.gsub!(/@(<[^<>\n]*>)/, "\\1")

        when :horizontal_rule
          add_paragraph unless @new_paragraph == :start
          @new_paragraph = true
          @output << "<hr />"

        else
          @output << inline_formatting(@buffer)
        end
      end
      @buffer = ""
    end

    def add_line_attributes headline
      if @options[:export_heading_number] then
        level = headline.level
        heading_number = get_next_headline_number(level)
        @output << "<span class=\"heading-number heading-number-#{level}\">#{heading_number}</span> "
      end
      if @options[:export_todo] and headline.keyword then
        keyword = headline.keyword
        @output << "<span class=\"todo-keyword #{keyword}\">#{keyword}</span> "
      end
    end

    def output_footnotes!
      return false unless @options[:export_footnotes] and not @footnotes.empty?

      @output << "\n<div id=\"footnotes\">\n<h2 class=\"footnotes\">Footnotes:</h2>\n<div id=\"text-footnotes\">\n"

      @footnotes.each do |name, defi|
        @buffer = defi
        @output << "<p class=\"footnote\"><sup><a class=\"footnum\" name=\"fn.#{name}\" href=\"#fnr.#{name}\">#{name}</a></sup>" \
                << inline_formatting(@buffer) \
                << "</p>\n"
      end

      @output << "</div>\n</div>"

      return true
    end

    # Test if we're in an output mode in which whitespace is significant.
    def preserve_whitespace?
      super or current_mode == :html
    end

    ######################################################################
    private

    def skip_tables?
      @options[:skip_tables]
    end

    def mode_is_table?(mode)
      (mode == :table or mode == :table_row or
       mode == :table_separator or mode == :table_header)
    end

    # Escapes any HTML content in the output accumulation buffer @buffer.
    def escape_buffer!
      @buffer.gsub!(/&/, "&amp;")
      # Escapes the left and right angular brackets but construction
      # @<text> which is formatted to <text>
      @buffer.gsub! /<([^<>\n]*)/ do |match|
        if $`[-1..-1] == "@" and $'[0..0] == ">" then $&
        else "&lt;#{$1}"
        end
      end
      @buffer.gsub! /([^<>\n]*)>/ do |match|
        if $`[-2..-1] == "@<" then $&
        else "#{$1}&gt;"
        end
      end
      @buffer.gsub!(/@(<[^<>\n]*>)/, "\\1")
    end

    def buffer_indentation
      indent = "  " * @list_indent_stack.length
      @buffer << indent
    end

    def add_paragraph
      indent = "  " * (@list_indent_stack.length - 1)
      @output << "\n" << indent
    end

    Tags = {
      "*" => { :open => "b", :close => "b" },
      "/" => { :open => "i", :close => "i" },
      "_" => { :open => "span style=\"text-decoration:underline;\"",
        :close => "span" },
      "=" => { :open => "code", :close => "code" },
      "~" => { :open => "code", :close => "code" },
      "+" => { :open => "del", :close => "del" }
    }

    # Applies inline formatting rules to a string.
    def inline_formatting(str)
      @re_help.rewrite_emphasis str do |marker, s|
        if marker == "=" or marker == "~"
          s = escapeHTML s
          "<#{Tags[marker][:open]}>#{s}</#{Tags[marker][:close]}>"
        else
          "@<#{Tags[marker][:open]}>#{s}@</#{Tags[marker][:close]}>"
        end
      end
      if @options[:use_sub_superscripts] then
        @re_help.rewrite_subp str do |type, text|
          if type == "_" then
            "@<sub>#{text}@</sub>"
          elsif type == "^" then
            "@<sup>#{text}@</sup>"
          end
        end
      end
      @re_help.rewrite_links str do |link, defi|
        [link, defi].compact.each do |text|
          # We don't support search links right now. Get rid of it.
          text.sub!(/\A(file:[^\s]+)::[^\s]*?\Z/, "\\1")
          text.sub!(/\A(file:[^\s]+)\.org\Z/i, "\\1.html")
          text.sub!(/\Afile:(?=[^\s]+\Z)/, "")
        end

        # We don't add a description for images in links, because its
        # empty value forces the image to be inlined.
        defi ||= link unless link =~ @re_help.org_image_file_regexp

        if defi =~ @re_help.org_image_file_regexp
          defi = "@<img src=\"#{defi}\" alt=\"#{defi}\" />"
        end

        if defi
          link = @options[:link_abbrevs][link] if @options[:link_abbrevs].has_key? link
          "@<a href=\"#{link}\">#{defi}@</a>"
        else
          "@<img src=\"#{link}\" alt=\"#{link}\" />"
        end
      end
      if @output_type == :table_row
        str.gsub!(/^\|\s*/, "@<td>")
        str.gsub!(/\s*\|$/, "@</td>")
        str.gsub!(/\s*\|\s*/, "@</td>@<td>")
      end
      if @output_type == :table_header
        str.gsub!(/^\|\s*/, "@<th>")
        str.gsub!(/\s*\|$/, "@</th>")
        str.gsub!(/\s*\|\s*/, "@</th>@<th>")
      end
      if @options[:export_footnotes] then
        @re_help.rewrite_footnote str do |name, defi|
          # TODO escape name for url?
          @footnotes[name] = defi if defi
          "@<sup>@<a class=\"footref\" name=\"fnr.#{name}\" href=\"#fn.#{name}\">#{name}@</a>@</sup>"
        end
      end
      # Two backslashes \\ at the end of the line make a line break without breaking paragraph.
      if @output_type != :table_row and @output_type != :table_header then
        str.sub!(/\\\\$/, "@<br />")
      end
      escape_buffer!
      Orgmode.special_symbols_to_html str
      str = @re_help.restore_code_snippets str
    end

    def normalize_lang(lang)
      case lang
      when 'emacs-lisp', 'common-lisp', 'lisp'
        'scheme'
      when ''
        'text'
      else
        lang
      end
    end

    # Helper method taken from Rails
    # https://github.com/rails/rails/blob/c2c8ef57d6f00d1c22743dc43746f95704d67a95/activesupport/lib/active_support/core_ext/kernel/reporting.rb#L10
    def silence_warnings
      warn_level = $VERBOSE
      $VERBOSE = nil
      yield
    ensure
      $VERBOSE = warn_level
    end

    def strip_code_block!
      @code_block_indent ||= 0
      strip_regexp = Regexp.new("^" + " " * @code_block_indent)
      @buffer.gsub!(strip_regexp, "")
      @code_block_indent = nil

      # Strip proctective commas generated by Org mode (C-c ')
      @buffer.gsub! /^\s*(,)(\s*)([*]|#\+)/ do |match|
        "#{$2}#{$3}"
      end
    end

    # The CGI::escapeHTML function backported from the Ruby standard library
    # as of commit fd2fc885b43283aa3d76820b2dfa9de19a77012f
    #
    # Implementation of the cgi module can change among Ruby versions
    # so stabilizing on a single one here to avoid surprises.
    #
    # https://github.com/ruby/ruby/blob/trunk/lib/cgi/util.rb
    #
    # The set of special characters and their escaped values
    TABLE_FOR_ESCAPE_HTML__ = {
      "'" => '&#39;',
      '&' => '&amp;',
      '"' => '&quot;',
      '<' => '&lt;',
      '>' => '&gt;',
    }
    # Escape special characters in HTML, namely &\"<>
    #   escapeHTML('Usage: foo "bar" <baz>')
    #      # => "Usage: foo &quot;bar&quot; &lt;baz&gt;"
    private
    def escapeHTML(string)
      string.gsub(/['&\"<>]/, TABLE_FOR_ESCAPE_HTML__)
    end
  end                           # class HtmlOutputBuffer
end                             # module Orgmode
