From 5214a74c0393d39e3358d8dd17537703b78ea1c1 Mon Sep 17 00:00:00 2001
From: Jorge Manrubia <jorge@37signals.com>
Date: Sun, 1 Jun 2025 21:51:26 +0200
Subject: [PATCH] Autolink emails and URLs at rendering time

---
 app/helpers/html_helper.rb                    | 46 +++++++++++++++++++
 .../action_text/contents/_content.html.erb    |  2 +-
 test/helpers/html_helper_test.rb              | 35 ++++++++++++++
 3 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 app/helpers/html_helper.rb
 create mode 100644 test/helpers/html_helper_test.rb

diff --git a/app/helpers/html_helper.rb b/app/helpers/html_helper.rb
new file mode 100644
index 000000000..b989adf12
--- /dev/null
+++ b/app/helpers/html_helper.rb
@@ -0,0 +1,46 @@
+module HtmlHelper
+  def format_html(html)
+    fragment = Nokogiri::HTML.fragment(html)
+
+    auto_link(fragment)
+
+    fragment.to_html.html_safe
+  end
+
+  private
+    EXCLUDED_ELEMENTS = %w[ a figcaption pre code ]
+    EMAIL_REGEXP = /\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b/
+    URL_REGEXP = URI::DEFAULT_PARSER.make_regexp(%w[http https])
+
+    def auto_link(fragment)
+      fragment.traverse do |node|
+        next unless auto_linkable_node?(node)
+
+        content = node.text
+        linked_content = content.dup
+
+        auto_link_urls(linked_content)
+        auto_link_emails(linked_content)
+
+        if linked_content != content
+          node.replace(Nokogiri::HTML.fragment(linked_content))
+        end
+      end
+    end
+
+    def auto_linkable_node?(node)
+      node.text? && node.ancestors.none? { |ancestor| EXCLUDED_ELEMENTS.include?(ancestor.name) }
+    end
+
+    def auto_link_urls(linked_content)
+      linked_content.gsub!(URL_REGEXP) do |match|
+        %(<a href="#{match}" rel="noreferrer">#{match}</a>)
+      end
+    end
+
+    def auto_link_emails(text)
+      text.gsub!(EMAIL_REGEXP) do |match|
+        %(<a href="mailto:#{match}">#{match}</a>)
+      end
+    end
+end
diff --git a/app/views/layouts/action_text/contents/_content.html.erb b/app/views/layouts/action_text/contents/_content.html.erb
index 0dec72775..b264733d7 100644
--- a/app/views/layouts/action_text/contents/_content.html.erb
+++ b/app/views/layouts/action_text/contents/_content.html.erb
@@ -1,3 +1,3 @@
 <div class="action-text-content">
-  <%= yield -%>
+  <%= format_html yield -%>
 </div>
diff --git a/test/helpers/html_helper_test.rb b/test/helpers/html_helper_test.rb
new file mode 100644
index 000000000..818ffa57b
--- /dev/null
+++ b/test/helpers/html_helper_test.rb
@@ -0,0 +1,35 @@
+require "test_helper"
+
+class HtmlHelperTest < ActionView::TestCase
+  test "converts URLs into anchor tags" do
+    assert_equal_html \
+      %(<p>Check this: <a href="https://example.com" rel="noreferrer">https://example.com</a></p>),
+      format_html("<p>Check this: https://example.com</p>")
+  end
+
+  test "respect existing links" do
+    assert_equal_html \
+      %(<p>Check this: <a href="https://example.com">https://example.com</a></p>),
+      format_html("<p>Check this: <a href=\"https://example.com\">https://example.com</a></p>")
+  end
+
+  test "converts email addresses into mailto links" do
+    assert_equal_html \
+      %(<p>Contact us at <a href="mailto:support@example.com">support@example.com</a></p>),
+      format_html("<p>Contact us at support@example.com</p>")
+  end
+
+  test "respect existing linked emails" do
+    assert_equal_html \
+      %(<p>Contact us at <a href="mailto:support@example.com">support@example.com</a></p>),
+      format_html(%(<p>Contact us at <a href="mailto:support@example.com">support@example.com</a></p>))
+  end
+
+  test "don't autolink content in excluded elements" do
+    %w[ figcaption pre code ].each do |element|
+      assert_equal_html \
+        "<#{element}>Check this: https://example.com</#{element}>",
+        format_html("<#{element}>Check this: https://example.com</#{element}>")
+    end
+  end
+end