# class Kramdown::Converter::Base

## Base class for converters¶ ↑

This class serves as base class for all converters. It provides methods that can/should be used by all converters (like generate_id) as well as common functionality that is automatically applied to the result (for example, embedding the output into a template).

A converter object is used as a throw-away object, i.e. it is only used for storing the needed state information during conversion. Therefore one can't instantiate a converter object directly but only use the ::convert method.

## Implementing a converter¶ ↑

Implementing a new converter is rather easy: just derive a new class from this class and put it in the Kramdown::Converter module (the latter is only needed if auto-detection should work properly). Then you need to implement the convert method which has to contain the conversion code for converting an element and has to return the conversion result.

The actual transformation of the document tree can be done in any way. However, writing one method per element type is a straight forward way to do it - this is how the Html and Latex converters do the transformation.

Have a look at the ::convert method for additional information!

### Attributes

data[R]

Can be used by a converter for storing arbitrary information during the conversion process.

options[R]

The hash with the conversion options.

root[R]

The root element that is converted.

warnings[R]

The warnings array.

### Public Class Methods

convert(tree, options = {}) click to toggle source

Convert the element tree `tree` and return the resulting conversion object (normally a string) and an array with warning messages. The parameter `options` specifies the conversion options that should be used.

Initializes a new instance of the calling class and then calls the convert method with `tree` as parameter.

If the `template` option is specified and non-empty, the template is evaluate with ERB before and/or after the tree conversion depending on the result of apply_template_before? and apply_template_after?. If the template is evaluated before, an empty string is used for the body; if evaluated after, the result is used as body. See ::apply_template.

The template resolution is done in the following way (for the converter ConverterName):

1. Look in the current working directory for the template.

2. Append `.converter_name` (e.g. `.html`) to the template name and look for the resulting file in the current working directory (the form `.convertername` is deprecated).

3. Append `.converter_name` to the template name and look for it in the kramdown data directory (the form `.convertername` is deprecated).

4. Check if the template name starts with 'string://' and if so, strip this prefix away and use the rest as template.

    # File lib/kramdown/converter/base.rb, line 100
    def self.convert(tree, options = {})
      converter = new(tree, ::Kramdown::Options.merge(options.merge(tree.options[:options] || {})))

      apply_template(converter, '') if !converter.options[:template].empty? && converter.apply_template_before?
      result = converter.convert(tree)
      result.encode!(tree.options[:encoding]) if result.respond_to?(:encode!) && result.encoding != Encoding::BINARY
      result = apply_template(converter, result) if !converter.options[:template].empty? && converter.apply_template_after?

      [result, converter.warnings]
    end

get_template(template) click to toggle source

Return the template specified by `template`.

    # File lib/kramdown/converter/base.rb, line 131
    def self.get_template(template)
      #DEPRECATED: use content of #get_template_new in 2.0
      format_ext = '.' + self.name.split(/::/).last.downcase
      shipped = File.join(::Kramdown.data_dir, template + format_ext)
      if File.exist?(template)
        File.read(template)
      elsif File.exist?(template + format_ext)
        File.read(template + format_ext)
      elsif File.exist?(shipped)
        File.read(shipped)
      elsif template.start_with?('string://')
        template.sub(/\Astring:\/\//, '')
      else
        get_template_new(template)
      end
    end

### Private Class Methods

new(root, options) click to toggle source

Initialize the converter with the given `root` element and `options` hash.

    # File lib/kramdown/converter/base.rb, line 54
    def initialize(root, options)
      @options = options
      @root = root
      @data = {}
      @warnings = []
    end

### Public Instance Methods

apply_template_after?() click to toggle source

Returns whether the template should be applied after the conversion of the tree.

Defaults to true.

    # File lib/kramdown/converter/base.rb, line 72
    def apply_template_after?
      true
    end

apply_template_before?() click to toggle source

Returns whether the template should be applied before the conversion of the tree.

Defaults to false.

    # File lib/kramdown/converter/base.rb, line 65
    def apply_template_before?
      false
    end

basic_generate_id(str) click to toggle source

The basic version of the ID generator, without any special provisions for empty or unique IDs.

    # File lib/kramdown/converter/base.rb, line 246
    def basic_generate_id(str)
      gen_id = str.gsub(/^[^a-zA-Z]+/, '')
      gen_id.tr!('^a-zA-Z0-9 -', '')
      gen_id.tr!(' ', '-')
      gen_id.downcase!
      gen_id
    end

convert(el) click to toggle source

Convert the element `el` and return the resulting object.

This is the only method that has to be implemented by sub-classes!

    # File lib/kramdown/converter/base.rb, line 114
    def convert(el)
      raise NotImplementedError
    end

extract_code_language(attr) click to toggle source

Extract the code block/span language from the attributes.

    # File lib/kramdown/converter/base.rb, line 183
    def extract_code_language(attr)
      if attr['class'] && attr['class'] =~ /\blanguage-\S+/
        attr['class'].scan(/\blanguage-(\S+)/).first.first
      end
    end

extract_code_language!(attr) click to toggle source

See extract_code_language

Warning: This version will modify the given attributes if a language is present.

    # File lib/kramdown/converter/base.rb, line 192
    def extract_code_language!(attr)
      lang = extract_code_language(attr)
      attr['class'] = attr['class'].sub(/\blanguage-\S+/, '').strip if lang
      attr.delete('class') if lang && attr['class'].empty?
      lang
    end

format_math(el, opts = {}) click to toggle source

Format the given math element with the math engine configured through the option 'math_engine'.

    # File lib/kramdown/converter/base.rb, line 215
    def format_math(el, opts = {})
      return nil unless @options[:math_engine]

      engine = ::Kramdown::Converter.math_engine(@options[:math_engine])
      if engine
        engine.call(self, el, opts)
      else
        warning("The configured math engine #{@options[:math_engine]} is not available.")
        nil
      end
    end

generate_id(str) click to toggle source

Generate an unique alpha-numeric ID from the the string `str` for use as a header ID.

Uses the option `auto_id_prefix`: the value of this option is prepended to every generated ID.

    # File lib/kramdown/converter/base.rb, line 231
    def generate_id(str)
      str = ::Kramdown::Utils::Unidecoder.decode(str) if @options[:transliterated_header_ids]
      gen_id = basic_generate_id(str)
      gen_id = 'section' if gen_id.length == 0
      @used_ids ||= {}
      if @used_ids.has_key?(gen_id)
        gen_id += '-' << (@used_ids[gen_id] += 1).to_s
      else
        @used_ids[gen_id] = 0
      end
      @options[:auto_id_prefix] + gen_id
    end

highlight_code(text, lang, type, opts = {}) click to toggle source

Highlight the given `text` in the language `lang` with the syntax highlighter configured through the option 'syntax_highlighter'.

    # File lib/kramdown/converter/base.rb, line 201
    def highlight_code(text, lang, type, opts = {})
      return nil unless @options[:syntax_highlighter]

      highlighter = ::Kramdown::Converter.syntax_highlighter(@options[:syntax_highlighter])
      if highlighter
        highlighter.call(self, text, lang, type, opts)
      else
        warning("The configured syntax highlighter #{@options[:syntax_highlighter]} is not available.")
        nil
      end
    end

output_header_level(level) click to toggle source

Return the output header level given a level.

Uses the `header_offset` option for adjusting the header level.

    # File lib/kramdown/converter/base.rb, line 178
    def output_header_level(level)
      [[level + @options[:header_offset], 6].min, 1].max
    end

smart_quote_entity(el) click to toggle source

Return the entity that represents the given smart_quote element.

    # File lib/kramdown/converter/base.rb, line 257
    def smart_quote_entity(el)
      res = @options[:smart_quotes][SMART_QUOTE_INDICES[el.value]]
      ::Kramdown::Utils::Entities.entity(res)
    end

warning(text) click to toggle source

Add the given warning `text` to the warning array.

    # File lib/kramdown/converter/base.rb, line 165
    def warning(text)
      @warnings << text
    end