# frozen_string_literal: true

module Bridgetown
  module Tags
    class HighlightBlock < Liquid::Block
      include Liquid::StandardFilters

      # The regular expression syntax checker. Start with the language specifier.
      # Follow that by zero or more space separated options that take one of three
      # forms: name, name=value, or name="<quoted list>"
      #
      # <quoted list> is a space-separated list of numbers
      SYNTAX = %r!^([a-zA-Z0-9.+#_-]+)((\s+\w+(=(\w+|"([0-9]+\s)*[0-9]+"))?)*)$!.freeze

      def initialize(tag_name, markup, tokens)
        super
        unless markup.strip =~ SYNTAX
          raise SyntaxError, <<~MSG
            Syntax Error in tag 'highlight' while parsing the following markup:

            #{markup}

            Valid syntax: highlight <lang> [linenos]
          MSG
        end

        @lang = Regexp.last_match(1).downcase
        @highlight_options = parse_options(Regexp.last_match(2))
      end

      LEADING_OR_TRAILING_LINE_TERMINATORS = %r!\A(\n|\r)+|(\n|\r)+\z!.freeze

      def render(context)
        prefix = context["highlighter_prefix"] || ""
        suffix = context["highlighter_suffix"] || ""
        code = super.to_s.gsub(LEADING_OR_TRAILING_LINE_TERMINATORS, "")

        output =
          case context.registers[:site].config.highlighter
          when "rouge"
            render_rouge(code)
          else
            h(code).strip
          end

        rendered_output = add_code_tag(output)
        prefix + rendered_output + suffix
      end

      private

      OPTIONS_REGEX = %r!(?:\w="[^"]*"|\w=\w|\w)+!.freeze

      def parse_options(input)
        options = {}
        return options if input.empty?

        # Split along 3 possible forms -- key="<quoted list>", key=value, or key
        input.scan(OPTIONS_REGEX) do |opt|
          key, value = opt.split("=")
          # If a quoted list, convert to array
          if value&.include?('"')
            value.delete!('"')
            value = value.split
          end
          options[key.to_sym] = value || true
        end

        options[:linenos] = "inline" if options[:linenos] == true
        options
      end

      def render_rouge(code)
        require "rouge"
        formatter = ::Rouge::Formatters::HTMLLegacy.new(
          line_numbers: @highlight_options[:linenos],
          wrap: false,
          css_class: "highlight",
          gutter_class: "gutter",
          code_class: "code"
        )
        lexer = ::Rouge::Lexer.find_fancy(@lang, code) || Rouge::Lexers::PlainText
        formatter.format(lexer.lex(code))
      end

      def add_code_tag(code)
        code_attributes = [
          "class=\"language-#{@lang.to_s.tr("+", "-")}\"",
          "data-lang=\"#{@lang}\"",
        ].join(" ")
        "<figure class=\"highlight\"><pre><code #{code_attributes}>" \
          "#{code.chomp}</code></pre></figure>"
      end
    end
  end
end

Liquid::Template.register_tag("highlight", Bridgetown::Tags::HighlightBlock)