1 files changed, 51 insertions, 0 deletions
diff --git a/util/util.go b/util/util.go
index c7816df..3e07e0f 100644
--- a/util/util.go
+++ b/util/util.go
@@ -4,6 +4,7 @@ package util
 
 import (
 	"net"
+	"strings"
 
 	"github.com/eduvpn/eduvpn-common/i18nerr"
 )
@@ -31,3 +32,53 @@ func CalculateGateway(cidr string) (string, error) {
 
 	return ret.String(), nil
 }
+
+// GetLanguageMatched uses a map from language tags to strings to extract the right language given the tag
+// It implements it according to https://github.com/eduvpn/documentation/blob/dc4d53c47dd7a69e95d6650eec408e16eaa814a2/SERVER_DISCOVERY.md#language-matching
+func GetLanguageMatched(langMap map[string]string, langTag string) string {
+	// If no map is given, return the empty string
+	if len(langMap) == 0 {
+		return ""
+	}
+	// Try to find the exact match
+	if val, ok := langMap[langTag]; ok {
+		return val
+	}
+	// Try to find a key that starts with the OS language setting
+	for k := range langMap {
+		if strings.HasPrefix(k, langTag) {
+			return langMap[k]
+		}
+	}
+	// Try to find a key that starts with the first part of the OS language (e.g. de-)
+	pts := strings.Split(langTag, "-")
+	// We have a "-"
+	if len(pts) > 1 {
+		for k := range langMap {
+			if strings.HasPrefix(k, pts[0]+"-") {
+				return langMap[k]
+			}
+		}
+	}
+	// search for just the language (e.g. de)
+	for k := range langMap {
+		if k == pts[0] {
+			return langMap[k]
+		}
+	}
+
+	// Pick one that is deemed best, e.g. en-US or en, but note that not all languages are always available!
+	// We force an entry that is english exactly or with an english prefix
+	for k := range langMap {
+		if k == "en" || strings.HasPrefix(k, "en-") {
+			return langMap[k]
+		}
+	}
+
+	// Otherwise just return one
+	for k := range langMap {
+		return langMap[k]
+	}
+
+	return ""
+}