Add advanced text formatting back into glitch-soc

1 files changed, 131 insertions, 0 deletions

diff --git a/app/lib/advanced_text_formatter.rb b/app/lib/advanced_text_formatter.rb
new file mode 100644
index 000000000..5ce87d306
--- /dev/null
+++ b/app/lib/advanced_text_formatter.rb
@@ -0,0 +1,131 @@
+# frozen_string_literal: true
+
+class AdvancedTextFormatter < TextFormatter
+  class HTMLRenderer < Redcarpet::Render::HTML
+    def initialize(options, &block)
+      super(options)
+      @format_link = block
+    end
+
+    def block_code(code, _language)
+      <<~HTML.squish
+        <pre><code>#{h(code).gsub("\n", '<br/>')}</code></pre>
+      HTML
+    end
+
+    def autolink(link, link_type)
+      return link if link_type == :email
+      @format_link.call(link)
+    end
+  end
+
+  # @param [String] text
+  # @param [Hash] options
+  # @option options [Boolean] :multiline
+  # @option options [Boolean] :with_domains
+  # @option options [Boolean] :with_rel_me
+  # @option options [Array<Account>] :preloaded_accounts
+  # @option options [String] :content_type
+  def initialize(text, options = {})
+    content_type = options.delete(:content_type)
+    super(text, options)
+
+    @text = format_markdown(text) if content_type == 'text/markdown'
+  end
+
+  # Differs from TextFormatter by not messing with newline after parsing
+  def to_s
+    return ''.html_safe if text.blank?
+
+    html = rewrite do |entity|
+      if entity[:url]
+        link_to_url(entity)
+      elsif entity[:hashtag]
+        link_to_hashtag(entity)
+      elsif entity[:screen_name]
+        link_to_mention(entity)
+      end
+    end
+
+    html.html_safe # rubocop:disable Rails/OutputSafety
+  end
+
+  # Differs from `TextFormatter` by skipping HTML tags and entities
+  def entities
+    @entities ||= begin
+      gaps = []
+      total_offset = 0
+
+      escaped = text.gsub(/<[^>]*>|&#[0-9]+;/) do |match|
+        total_offset += match.length - 1
+        end_offset = Regexp.last_match.end(0)
+        gaps << [end_offset - total_offset, total_offset]
+        ' '
+      end
+
+      Extractor.extract_entities_with_indices(escaped, extract_url_without_protocol: false).map do |entity|
+        start_pos, end_pos = entity[:indices]
+        offset_idx = gaps.rindex { |gap| gap.first <= start_pos }
+        offset = offset_idx.nil? ? 0 : gaps[offset_idx].last
+        entity.merge(indices: [start_pos + offset, end_pos + offset])
+      end
+    end
+  end
+
+  private
+
+  # Differs from `TextFormatter` in that it keeps HTML; but it sanitizes at the end to remain safe
+  def rewrite
+    entities.sort_by! do |entity|
+      entity[:indices].first
+    end
+
+    result = ''.dup
+
+    last_index = entities.reduce(0) do |index, entity|
+      indices = entity[:indices]
+      result << text[index...indices.first]
+      result << yield(entity)
+      indices.last
+    end
+
+    result << text[last_index..-1]
+
+    Sanitize.fragment(result, Sanitize::Config::MASTODON_OUTGOING)
+  end
+
+  def format_markdown(html)
+    html = markdown_formatter.render(html)
+    html.delete("\r").delete("\n")
+  end
+
+  def markdown_formatter
+    extensions = {
+      autolink: true,
+      no_intra_emphasis: true,
+      fenced_code_blocks: true,
+      disable_indented_code_blocks: true,
+      strikethrough: true,
+      lax_spacing: true,
+      space_after_headers: true,
+      superscript: true,
+      underline: true,
+      highlight: true,
+      footnotes: false,
+    }
+
+    renderer = HTMLRenderer.new({
+      filter_html: false,
+      escape_html: false,
+      no_images: true,
+      no_styles: true,
+      safe_links_only: true,
+      hard_wrap: true,
+      link_attributes: { target: '_blank', rel: 'nofollow noopener' },
+    }) do |url|
+      link_to_url({ url: url })
+    end
+
+    Redcarpet::Markdown.new(renderer, extensions)
+  end
+end