From 38e38f4644b23031fb8a36105667ab776e234296 Mon Sep 17 00:00:00 2001
From: Anthony Shull <ashull@mbta.com>
Date: Fri, 31 Jan 2025 14:53:54 -0600
Subject: [PATCH] Maintain locale information when visiting MyCharlie (#2348)

---
 assets/js/translate-analytics.js      | 10 ++++++++++
 lib/dotcom/content_rewriter.ex        |  1 +
 lib/dotcom/content_rewriters/links.ex | 20 ++++++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/assets/js/translate-analytics.js b/assets/js/translate-analytics.js
index f4d7080bfc..e08d4beab5 100644
--- a/assets/js/translate-analytics.js
+++ b/assets/js/translate-analytics.js
@@ -14,6 +14,10 @@ export default () => {
   if (typeof MutationObserver === "function") {
     // Tell the observer to monitor for changes to HTML attributes
     const config = { attributes: true };
+
+    // Get the language of the page on load.
+    const oldLanguage = document.querySelector("html").getAttribute("lang");
+
     // Build the function to run when a change is observed
     const callback = mutationList => {
       // Loop through each observed change
@@ -36,6 +40,12 @@ export default () => {
               event: "translate",
               language: newLanguage && newLanguage !== "en" ? newLanguage : ""
             });
+
+            // If the page loaded with one language and switched to another, we have to reload the page.
+            // This is so that page content can be rendered differently with the added cookie information.
+            if (newLanguage !== oldLanguage) {
+              window.location.reload();
+            }
           }
         }
       }
diff --git a/lib/dotcom/content_rewriter.ex b/lib/dotcom/content_rewriter.ex
index 1bafe1810d..2752201046 100644
--- a/lib/dotcom/content_rewriter.ex
+++ b/lib/dotcom/content_rewriter.ex
@@ -94,6 +94,7 @@ defmodule Dotcom.ContentRewriter do
     element
     |> Links.add_target_to_redirect()
     |> Links.add_preview_params(conn)
+    |> Links.add_locale_params(conn)
     |> rewrite_children(conn, context)
   end
 
diff --git a/lib/dotcom/content_rewriters/links.ex b/lib/dotcom/content_rewriters/links.ex
index bc7068258e..481068fa03 100644
--- a/lib/dotcom/content_rewriters/links.ex
+++ b/lib/dotcom/content_rewriters/links.ex
@@ -40,4 +40,24 @@ defmodule Dotcom.ContentRewriters.Links do
         element
     end
   end
+
+  @doc """
+  If the user has used Google Translate on dotcom, we want to forward them to MyCharlie with the same language.
+  """
+  def add_locale_params({"a", attrs, children} = element, %{cookies: %{"googtrans" => languages}}) do
+    attr_map = Enum.into(attrs, %{})
+    href = Map.get(attr_map, "href", "")
+    locale = String.split(languages, "/") |> List.last()
+
+    if String.match?(href, ~r/mycharlie.mbta.com/) do
+      updated_href = "#{href}?locale=#{locale}"
+      updated_attrs = attr_map |> Map.replace!("href", updated_href) |> Map.to_list()
+
+      {"a", updated_attrs, children}
+    else
+      element
+    end
+  end
+
+  def add_locale_params(element, _conn), do: element
 end