2 files changed, 100 insertions, 1 deletions
diff --git a/internal/util/util.go b/internal/util/util.go
index b104476..e652779 100644
--- a/internal/util/util.go
+++ b/internal/util/util.go
@@ -83,3 +83,52 @@ func ReplaceWAYF(authTemplate string, authURL string, orgID string) string {
 	authTemplate = strings.Replace(authTemplate, "@ORG_ID@", WAYFEncode(orgID), 1)
 	return authTemplate
 }
+
+// https://github.com/eduvpn/documentation/blob/dc4d53c47dd7a69e95d6650eec408e16eaa814a2/SERVER_DISCOVERY.md#language-matching
+func GetLanguageMatched(languageMap map[string]string, languageTag string) string {
+	// If no or empty map is given, return the empty string
+	if languageMap == nil || len(languageMap) == 0 {
+		return ""
+	}
+	// Try to find the exact match
+	if val, ok := languageMap[languageTag]; ok {
+		return val
+	}
+	// Try to find a key that starts with the OS language setting
+	for k := range languageMap {
+		if strings.HasPrefix(k, languageTag) {
+			return languageMap[k]
+		}
+	}
+	// Try to find a key that starts with the first part of the OS language (e.g. de-)
+	splitted := strings.Split(languageTag, "-")
+	// We have a "-"
+	if len(splitted) > 1 {
+		for k := range languageMap {
+			if strings.HasPrefix(k, splitted[0]+"-") {
+				return languageMap[k]
+			}
+		}
+	}
+	// search for just the language (e.g. de)
+	for k := range languageMap {
+		if k == splitted[0] {
+			return languageMap[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 languageMap {
+		if k == "en" || strings.HasPrefix(k, "en-") {
+			return languageMap[k]
+		}
+	}
+
+	// Otherwise just return one
+	for k := range languageMap {
+		return languageMap[k]
+	}
+
+	return ""
+}
diff --git a/internal/util/util_test.go b/internal/util/util_test.go
index 9eda14e..31d01e7 100644
--- a/internal/util/util_test.go
+++ b/internal/util/util_test.go
@@ -80,7 +80,11 @@ func Test_WAYFEncode(t *testing.T) {
 func Test_ReplaceWAYF(t *testing.T) {
 	// We expect url encoding but the spaces to be correctly replace with a + instead of a %20
 	// And we expect that the return to and org_id are correctly replaced
-	replaced := ReplaceWAYF("@RETURN_TO@@ORG_ID@", "127.0.0.1:8000/&%$3#kM_-            ", "idp-test.nl.org/")
+	replaced := ReplaceWAYF(
+		"@RETURN_TO@@ORG_ID@",
+		"127.0.0.1:8000/&%$3#kM_-            ",
+		"idp-test.nl.org/",
+	)
 	wantReplaced := "127.0.0.1%3A8000%2F%26%25%243%23kM_-++++++++++++idp-test.nl.org%2F"
 	if replaced != wantReplaced {
 		t.Fatalf("Got: %s, want: %s", replaced, wantReplaced)
@@ -114,3 +118,49 @@ func Test_ReplaceWAYF(t *testing.T) {
 		t.Fatalf("Got: %s, want: %s", replaced, wantReplaced)
 	}
 }
+
+func Test_GetLanguageMatched(t *testing.T) {
+	// func GetLanguageMatched(languageMap map[string]string, languageTag string) string {
+
+	// exact match
+	returned := GetLanguageMatched(map[string]string{"en": "test", "de": "test2"}, "en")
+	if returned != "test" {
+		t.Fatalf("Got: %s, want: %s", returned, "test")
+	}
+
+	// starts with language tag
+	returned = GetLanguageMatched(map[string]string{"en-US-test": "test", "de": "test2"}, "en-US")
+	if returned != "test" {
+		t.Fatalf("Got: %s, want: %s", returned, "test")
+	}
+
+	// starts with en-
+	returned = GetLanguageMatched(map[string]string{"en-UK": "test", "en": "test2"}, "en-US")
+	if returned != "test" {
+		t.Fatalf("Got: %s, want: %s", returned, "test")
+	}
+
+	// exact match for en
+	returned = GetLanguageMatched(map[string]string{"de": "test", "en": "test2"}, "en-US")
+	if returned != "test2" {
+		t.Fatalf("Got: %s, want: %s", returned, "test2")
+	}
+
+	// We default to english
+	returned = GetLanguageMatched(map[string]string{"es": "test", "en": "test2"}, "nl-NL")
+	if returned != "test2" {
+		t.Fatalf("Got: %s, want: %s", returned, "test2")
+	}
+
+	// We default to english with a - as well
+	returned = GetLanguageMatched(map[string]string{"est": "test", "en-": "test2"}, "en-US")
+	if returned != "test2" {
+		t.Fatalf("Got: %s, want: %s", returned, "test2")
+	}
+
+	// None found just return one
+	returned = GetLanguageMatched(map[string]string{"es": "test"}, "en-US")
+	if returned != "test" {
+		t.Fatalf("Got: %s, want: %s", returned, "test")
+	}
+}