+const MaxNbProblems = 20;
+
+const supportedLang = ["fr","en"];
+function selectLanguage(req, res)
+{
+ // If preferred language already set:
+ if (!!req.cookies["lang"])
+ return req.cookies["lang"];
+
+ // Else: search and set it
+ const langString = req.headers["accept-language"];
+ let langArray = langString
+ .replace(/;q=[0-9.]+/g, "") //priority
+ .replace(/-[A-Z]+/g, "") //region (skipped for now...)
+ .split(",") //may have some duplicates, but removal is too costly
+ let bestLang = "en"; //default: English
+ for (let lang of langArray)
+ {
+ if (supportedLang.includes(lang))
+ {
+ bestLang = lang;
+ break;
+ }
+ }
+ // Cookie expires in 183 days (expressed in milliseconds)
+ res.cookie('lang', bestLang, { maxAge: 183*24*3600*1000 });
+ return bestLang;
+}