Add markdown support

app/javascript/styles/application.scss

@@ -23,3 +23,4 @@
 @import 'mastodon/dashboard';
 @import 'mastodon/rtl';
 @import 'mastodon/accessibility';
+@import 'mastodon/rich_text';

app/javascript/styles/mastodon/rich_text.scss

@@ -0,0 +1,97 @@
+.account__header__bio,
+.status__content__text,
+.e-content,
+.reply-indicator__content {
+  pre,
+  blockquote {
+    margin-bottom: 20px;
+    white-space: pre-wrap;
+    unicode-bidi: plaintext;
+
+    &:last-child {
+      margin-bottom: 0;
+    }
+  }
+
+  code, pre {
+    border: 1px solid $ui-primary-color;
+    font-family: monospace;
+  }
+
+  code {
+    margin: 0 4px;
+  }
+
+  pre {
+    padding: 4px 8px;
+
+    span.ellipsis::after {
+      content: "";
+    }
+
+    span.invisible {
+      display: inline;
+      font-size: inherit;
+      line-height: inherit;
+      width: inherit;
+      height: inherit;
+      position: static;
+    }
+  }
+
+  blockquote {
+    padding-left: 10px;
+    border-left: 3px solid $darker-text-color;
+    color: $darker-text-color;
+    white-space: normal;
+
+    p:last-child {
+      margin-bottom: 0;
+    }
+  }
+
+  & > ul,
+  & > ol {
+    margin-bottom: 20px;
+  }
+
+  b,
+  strong {
+    font-weight: 700;
+  }
+
+  em,
+  i {
+    font-style: italic;
+  }
+
+  ul,
+  ol {
+    margin-left: 2em;
+
+    p {
+      margin: 0;
+    }
+  }
+
+  ul {
+    list-style-type: disc;
+  }
+
+  ol {
+    list-style-type: decimal;
+  }
+
+  mark {
+    background-color: $ui-highlight-color;
+    color: $ui-secondary-color;
+    padding: 0 2px;
+  }
+}
+
+.reply-indicator__content {
+  blockquote {
+    border-left-color: $inverted-text-color;
+    color: $inverted-text-color;
+  }
+}

app/lib/text_formatter.rb

@@ -43,7 +43,9 @@ class TextFormatter
       end
     end
 
-    html = simple_format(html, {}, sanitize: false).delete("\n") if multiline?
+    html = markdownify(html)
+
+    # html = simple_format(html, {}, sanitize: false).delete("\n") if multiline?
 
     html.html_safe # rubocop:disable Rails/OutputSafety
   end
@@ -155,4 +157,50 @@ class TextFormatter
   def preloaded_accounts?
     preloaded_accounts.present?
   end
+
+  def markdownify(html)
+    # not need filter_html because escape is already done
+    @htmlobj ||= MyMarkdownHTML.new(
+        filter_html: false,
+        hard_wrap: false,
+        no_styles: true
+      )
+    @markdown ||= Redcarpet::Markdown.new(@htmlobj,
+        autolink: false,
+        tables: false,
+        underline: true,
+        disable_indented_code_blocks: false,
+        fenced_code_blocks: true,
+        highlight: false
+      )
+    @markdown.render(html)
+  end
+
+  class MyMarkdownHTML < Redcarpet::Render::HTML
+    def link(link, title, content)
+      nil
+    end
+
+    def linebreak
+      nil
+    end
+
+    def block_code(code, language)
+      "<pre>#{code}</pre>"
+    end
+
+    def codespan(code)
+      "<code>#{escape_tags(code)}</code>"
+    end
+
+    def header(text, header_level)
+      "<p>#{text}</p>"
+    end
+
+    private
+
+    def escape_tags(code)
+      code.gsub(/</, '&lt;').gsub(/>/, '&gt;')
+    end
+  end
 end