1 files changed, 107 insertions, 1 deletions
diff --git a/searx/locales.py b/searx/locales.py
index a4560aab7..ffa5e731c 100644
--- a/searx/locales.py
+++ b/searx/locales.py
@@ -4,7 +4,7 @@
 """Initialize :py:obj:`LOCALE_NAMES`, :py:obj:`RTL_LOCALES`.
 """
 
-from typing import Set
+from typing import Set, Optional, List
 import os
 import pathlib
 
@@ -177,6 +177,17 @@ def language_tag(locale: babel.Locale) -> str:
     return sxng_lang
 
 
+def get_locale(locale_tag: str) -> Optional[babel.Locale]:
+    """Returns a :py:obj:`babel.Locale` object parsed from argument
+    ``locale_tag``"""
+    try:
+        locale = babel.Locale.parse(locale_tag, sep='-')
+        return locale
+
+    except babel.core.UnknownLocaleError:
+        return None
+
+
 def get_offical_locales(
     territory: str, languages=None, regional: bool = False, de_facto: bool = True
 ) -> Set[babel.Locale]:
@@ -363,3 +374,98 @@ def get_engine_locale(searxng_locale, engine_locales, default=None):
         engine_locale = default
 
     return default
+
+
+def match_locale(searxng_locale: str, locale_tag_list: List[str], fallback: Optional[str] = None) -> Optional[str]:
+    """Return tag from ``locale_tag_list`` that best fits to ``searxng_locale``.
+
+    :param str searxng_locale: SearXNG's internal representation of locale (de,
+        de-DE, fr-BE, zh, zh-CN, zh-TW ..).
+
+    :param list locale_tag_list: The list of locale tags to select from
+
+    :param str fallback: fallback locale tag (if unset --> ``None``)
+
+    The rules to find a match are implemented in :py:obj:`get_engine_locale`,
+    the ``engine_locales`` is build up by :py:obj:`build_engine_locales`.
+
+    .. hint::
+
+       The *SearXNG locale* string and the members of ``locale_tag_list`` has to
+       be known by babel!  The :py:obj:`ADDITIONAL_TRANSLATIONS` are used in the
+       UI and are not known by babel --> will be ignored.
+    """
+
+    # searxng_locale = 'es'
+    # locale_tag_list = ['es-AR', 'es-ES', 'es-MX']
+
+    if not searxng_locale:
+        return fallback
+
+    locale = get_locale(searxng_locale)
+    if locale is None:
+        return fallback
+
+    # normalize to a SearXNG locale that can be passed to get_engine_locale
+
+    searxng_locale = language_tag(locale)
+    if locale.territory:
+        searxng_locale = region_tag(locale)
+
+    # clean up locale_tag_list
+
+    tag_list = []
+    for tag in locale_tag_list:
+        if tag in ('all', 'auto') or tag in ADDITIONAL_TRANSLATIONS:
+            continue
+        tag_list.append(tag)
+
+    # emulate fetch_traits
+    engine_locales = build_engine_locales(tag_list)
+    return get_engine_locale(searxng_locale, engine_locales, default=fallback)
+
+
+def build_engine_locales(tag_list: List[str]):
+    """From a list of locale tags a dictionary is build that can be passed by
+    argument ``engine_locales`` to :py:obj:`get_engine_locale`.  This function
+    is mainly used by :py:obj:`match_locale` and is similar to what the
+    ``fetch_traits(..)`` function of engines do.
+
+    If there are territory codes in the ``tag_list`` that have a *script code*
+    additional keys are added to the returned dictionary.
+
+    .. code:: python
+
+       >>> import locales
+       >>> engine_locales = locales.build_engine_locales(['en', 'en-US', 'zh', 'zh-CN', 'zh-TW'])
+       >>> engine_locales
+       {
+           'en': 'en', 'en-US': 'en-US',
+           'zh': 'zh', 'zh-CN': 'zh-CN', 'zh_Hans': 'zh-CN',
+           'zh-TW': 'zh-TW', 'zh_Hant': 'zh-TW'
+       }
+       >>> get_engine_locale('zh-Hans', engine_locales)
+       'zh-CN'
+
+    This function is a good example to understand the language/region model
+    of SearXNG:
+
+      SearXNG only distinguishes between **search languages** and **search
+      regions**, by adding the *script-tags*, languages with *script-tags* can
+      be assigned to the **regions** that SearXNG supports.
+
+    """
+    engine_locales = {}
+
+    for tag in tag_list:
+        locale = get_locale(tag)
+        if locale is None:
+            logger.warn("build_engine_locales: skip locale tag %s / unknown by babel", tag)
+            continue
+        if locale.territory:
+            engine_locales[region_tag(locale)] = tag
+            if locale.script:
+                engine_locales[language_tag(locale)] = tag
+        else:
+            engine_locales[language_tag(locale)] = tag
+    return engine_locales