From e17aa809f082457c20cf48d68056b9d9efce5a3d Mon Sep 17 00:00:00 2001
From: Alexander Borsuk <me@alex.bio>
Date: Sat, 26 Nov 2022 14:59:49 +0100
Subject: [PATCH] Automatic language redirect

Signed-off-by: Alexander Borsuk <me@alex.bio>
---
 templates/base.html                      |  7 ++++++-
 templates/language_redirect.html         | 24 ++++++++++++++++++++++++
 templates/language_selector.html         | 10 ++++++++--
 templates/shortcodes/donate_buttons.html |  1 -
 4 files changed, 38 insertions(+), 4 deletions(-)
 create mode 100644 templates/language_redirect.html
diff --git a/templates/base.html b/templates/base.html
index d1525c1b..b908f224 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -57,6 +57,11 @@
   <link href="/main.css?h={{ get_file_hash(path='sass/main.scss', sha_type=256, base64=false) }}" rel="stylesheet" type="text/css">
 
   <title>{{ resource.title }}</title>
+
+  {# TODO: Replace 'en' with config.default_language after upgrading Zola #}
+  {%- if lang == 'en' %}
+  {% include 'language_redirect.html' %}
+  {% endif -%}
 </head>
 
 <body>
@@ -65,7 +70,7 @@
   </header>
 
   <main>
-    {% block content %} {% endblock %}
+    {% block content %}{% endblock %}
   </main>
 
   <footer>
diff --git a/templates/language_redirect.html b/templates/language_redirect.html
new file mode 100644
index 00000000..1b19763c
--- /dev/null
+++ b/templates/language_redirect.html
@@ -0,0 +1,24 @@
+<script>
+// Supports partially translated pages.
+// Redirects a user to his preferred language page translation only if
+// there were no previous redirects or explicit language selections before (see language_seletor.html)
+if (null === window.localStorage.getItem('lang')) {
+  // ["en", "ru", ...]
+  var pageTranslations = {{ resource.translations | map(attribute="lang") | json_encode() | safe }};
+  var userPreferredLanguages = navigator.languages ? navigator.languages : [navigator.language];
+  outerLoop:
+  for (var i = 0; i < userPreferredLanguages.length; i++) {
+    for (var j = 0; j < pageTranslations.length; j++) {
+      if (userPreferredLanguages[i].indexOf(pageTranslations[j]) == 0) {
+        window.localStorage.setItem('lang', pageTranslations[j]);
+        // Do not redirect the default 'en' language.
+        // TODO: Use config.default_language instead of hard-coding 'en' after Zola upgrade on CF.
+        if (pageTranslations[j] != 'en') {
+          window.location.pathname = '/' + pageTranslations[j] + window.location.pathname;
+        }
+        break outerLoop;
+      }
+    }
+  }
+}
+</script>
diff --git a/templates/language_selector.html b/templates/language_selector.html
index 48511204..a2ec1cb1 100644
--- a/templates/language_selector.html
+++ b/templates/language_selector.html
@@ -1,15 +1,21 @@
 <span>
+  <script>
+    function onLanguageClick(langCode) {
+      window.localStorage.setItem('lang', langCode);
+      return true;
+    }
+  </script>
   <!-- Hidden checkbox is used for pure CSS toggle menu. -->
   <input type="checkbox" id="menu_trigger" class="menu_trigger" />
   <label class="no-print" for="menu_trigger">
-     🌐 {{ lang | upper }} {# trans(key="language", lang=lang) #}
+     🌐 {{ lang | upper }}
   </label>
 
   <ul class="menu no-print" role="navigation">
     {% for translation in resource.translations %}
     {% if lang != translation.lang %}
     <li class="menu__item" role="menuitem">
-      <a class="menu__link" href="{{ translation.permalink }}">
+      <a class="menu__link" onclick="return onLanguageClick('{{translation.lang}}');" href="{{ translation.permalink }}">
         {{ trans(key="language", lang=translation.lang) }}
       </a>
     </li>
diff --git a/templates/shortcodes/donate_buttons.html b/templates/shortcodes/donate_buttons.html
index 1d19df11..efbcf586 100644
--- a/templates/shortcodes/donate_buttons.html
+++ b/templates/shortcodes/donate_buttons.html
@@ -41,5 +41,4 @@
     // Disable two unpopular methods to keep the number of methods constant
     document.getElementById('sofort').style.display = 'none';
   }
-  //
 </script>
