web: basic Accept-Language HTTP negotiation

1 files changed, 26 insertions, 0 deletions

diff --git a/fatcat_scholar/hacks.py b/fatcat_scholar/hacks.py
index 710a25f..fc16564 100644
--- a/fatcat_scholar/hacks.py
+++ b/fatcat_scholar/hacks.py
@@ -51,3 +51,29 @@ class Jinja2Templates:
             media_type=media_type,
             background=background,
         )
+
+
+def parse_accept_lang(header: str, options: typing.List[str]) -> typing.Optional[str]:
+    """
+    Crude HTTP Accept-Language content negotiation.
+    Assumes that languages are specified in order of priority, etc.
+    """
+    if not header:
+        return None
+    chunks = [v.split(";")[0].split("-")[0] for v in header.split(",")]
+    for c in chunks:
+        if len(c) == 2 and c in options:
+            return c
+    return None
+
+
+def test_parse_accept_lang() -> None:
+    assert parse_accept_lang("", []) == None
+    assert parse_accept_lang("en,de", []) == None
+    assert parse_accept_lang("en,de", ["en"]) == "en"
+    assert parse_accept_lang("en-GB,de", ["en"]) == "en"
+    assert parse_accept_lang("en,de", ["de"]) == "de"
+    assert (
+        parse_accept_lang("en-ca,en;q=0.8,en-us;q=0.6,de-de;q=0.4,de;q=0.2", ["de"])
+        == "de"
+    )