render links with markdown in emails

app/views/submitter_mailer/_custom_content.html.erb

@@ -1 +1 @@
-<%= auto_link(simple_format(h(ReplaceEmailVariables.call(local_assigns[:content], submitter: local_assigns[:submitter], sig: local_assigns[:sig])))) %>
+<%= auto_link(simple_format(MarkdownToHtml.call(h(ReplaceEmailVariables.call(local_assigns[:content], submitter: local_assigns[:submitter], sig: local_assigns[:sig]))))) %>

lib/markdown_to_html.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module MarkdownToHtml
+  LINK_REGEXP = %r{\[([^\]]+)\]\((https?://[^)]+)\)}
+  LINK_REPLACE = '<a href="\2">\1</a>'
+
+  module_function
+
+  def call(text)
+    text.gsub(LINK_REGEXP, LINK_REPLACE)
+  end
+end