From 136ed77dbfcbdb81745bb716fbb0bedb1f0c69ee Mon Sep 17 00:00:00 2001
From: Rob Hudson <robhudson@mozilla.com>
Date: Thu, 30 Nov 2023 15:06:58 -0800
Subject: [PATCH] Add statsd metrics for locale redirects (#13314)

---
 lib/l10n_utils/__init__.py        |  3 +++
 lib/l10n_utils/tests/test_base.py | 28 +++++++++++++++++-----------
 2 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/lib/l10n_utils/__init__.py b/lib/l10n_utils/__init__.py
index 00a14517e26..d5410a74fbb 100644
--- a/lib/l10n_utils/__init__.py
+++ b/lib/l10n_utils/__init__.py
@@ -13,6 +13,7 @@
 
 from product_details import product_details
 
+from bedrock.base import metrics
 from bedrock.base.urlresolvers import _get_language_map, split_path
 
 from .fluent import fluent_l10n, ftl_file_is_active, get_active_locales as ftl_active_locales
@@ -64,6 +65,8 @@ def redirect_to_best_locale(request, translations):
 def redirect_to_locale(request, locale, permanent=False):
     redirect_class = HttpResponsePermanentRedirect if permanent else HttpResponseRedirect
     response = redirect_class("/" + "/".join([locale, split_path(request.get_full_path())[1]]))
+    # Record count of redirects to this locale.
+    metrics.incr("locale.redirect", tags=[f"from_locale:{get_locale(request) or 'none'}", f"to_locale:{locale}"])
     # Add the Vary header to avoid wrong redirects due to a cache
     response["Vary"] = "Accept-Language"
     return response
diff --git a/lib/l10n_utils/tests/test_base.py b/lib/l10n_utils/tests/test_base.py
index 09d42652b2d..dee57071bf1 100644
--- a/lib/l10n_utils/tests/test_base.py
+++ b/lib/l10n_utils/tests/test_base.py
@@ -11,6 +11,7 @@
 
 import pytest
 from django_jinja.backend import Jinja2
+from markus.testing import MetricsMock
 
 from bedrock.base.urlresolvers import Prefixer
 from lib import l10n_utils
@@ -41,18 +42,23 @@ def _test(self, path, template, locale, accept_lang, status, destination=None, a
         if add_active_locales:
             ctx["add_active_locales"] = add_active_locales
 
-        response = l10n_utils.render(request, template, ctx)
-
-        if status == 302:
-            self.assertEqual(response.status_code, 302)
-            self.assertEqual(response["Location"], destination)
-            self.assertEqual(response["Vary"], "Accept-Language")
-        elif status == 404:
-            self.assertEqual(response.status_code, 404)
-        else:
-            self.assertEqual(response.status_code, 200)
-            if path == "/":
+        with MetricsMock() as mm:
+            response = l10n_utils.render(request, template, ctx)
+
+            if status == 302:
+                self.assertEqual(response.status_code, 302)
+                self.assertEqual(response["Location"], destination)
                 self.assertEqual(response["Vary"], "Accept-Language")
+                mm.assert_incr_once("locale.redirect", tags=[f"from_locale:{prefixer.locale or 'none'}", f"to_locale:{destination.split('/')[1]}"])
+
+            elif status == 404:
+                self.assertEqual(response.status_code, 404)
+                mm.assert_not_incr("locale.redirect")
+            else:
+                self.assertEqual(response.status_code, 200)
+                mm.assert_not_incr("locale.redirect")
+                if path == "/":
+                    self.assertEqual(response["Vary"], "Accept-Language")
 
     def test_no_accept_language_header(self):
         template = "firefox/new.html"