3 files changed, 269 insertions, 0 deletions
diff --git a/i18n/err/i18nerr.go b/i18n/err/i18nerr.go
new file mode 100644
index 0000000..8254dd4
--- /dev/null
+++ b/i18n/err/i18nerr.go
@@ -0,0 +1,168 @@
+// Package i18nerr implements errors with internationalization using gotext
+package i18nerr
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"sync"
+
+	"codeberg.org/eduVPN/eduvpn-common/internal/http"
+
+	"golang.org/x/text/language"
+	"golang.org/x/text/message"
+)
+
+var (
+	printers sync.Map
+	once     sync.Once
+)
+
+// TranslatedInner defines errors that are used as inner causes but are still translated because they can happen frequently
+func TranslatedInner(inner error) (string, bool) {
+	unwrapped := inner
+	for errors.Unwrap(unwrapped) != nil {
+		unwrapped = errors.Unwrap(unwrapped)
+	}
+
+	var tErr *http.TimeoutError
+	switch {
+	case errors.As(inner, &tErr):
+		return printerOrNew(language.English).Sprintf("Timeout reached contacting URL: '%s'", tErr.URL), false
+	case errors.Is(inner, context.Canceled):
+		return unwrapped.Error(), true
+	}
+	return unwrapped.Error(), false
+}
+
+// Error wraps an actual error with the translation key
+// This translation key is later used to lookup translation
+// The inner error always consists of the translation key and some formatting
+type Error struct {
+	key     message.Reference
+	args    []any
+	wrapped *Error
+	Misc    bool
+}
+
+func (e *Error) translated(t language.Tag) string {
+	once.Do(func() {
+		inititializeLangs()
+	})
+	msg := printerOrNew(t).Sprintf(e.key, e.args...)
+	if e.wrapped != nil {
+		return printerOrNew(t).Sprintf("%s. The cause of the error is: %s.", msg, e.wrapped.Error())
+	}
+	return msg
+}
+
+// Error gets the error string
+// it does this by simply forwarding the error method from the actual inner error
+func (e *Error) Error() string {
+	return e.translated(language.English)
+}
+
+// Translations returns all the translations for the error including the source translation (english)
+func (e *Error) Translations() map[string]string {
+	translations := make(map[string]string)
+	// add the source transltaion first
+	source := e.Error()
+	translations[language.English.String()] = source
+	for _, t := range message.DefaultCatalog.Languages() {
+		// already added
+		if t == language.English {
+			continue
+		}
+		// get the final translation string for the tag
+		// and add it if it's not equal to the english version
+		f := e.translated(t)
+		if f != source {
+			translations[t.String()] = f
+		}
+	}
+	return translations
+}
+
+// Unwrap returns the unwrapped error
+// it does this by unwrapping the inner error
+func (e *Error) Unwrap() error {
+	if e.wrapped == nil {
+		return nil
+	}
+	return e.wrapped.Unwrap()
+}
+
+// printerOrNew gets a message printer from the global printers map using the tag 'tag'
+// If the printer cannot be found in the sync map, we return a new printer
+func printerOrNew(tag language.Tag) *message.Printer {
+	v, ok := printers.Load(tag)
+	if !ok {
+		slog.Debug("i18n could not load printer from map", "tag", tag)
+		return message.NewPrinter(tag)
+	}
+	p, ok := v.(*message.Printer)
+	if !ok {
+		slog.Debug("i18n could not load printer from map with incorrect type", "tag", tag, "type", fmt.Sprintf("%T", p))
+		return message.NewPrinter(tag)
+	}
+	return p
+}
+
+// New creates a new i18n error using a message reference
+func New(key message.Reference) *Error {
+	_ = printerOrNew(language.English).Sprint(key)
+	return &Error{key: key}
+}
+
+// Newf creates a new i18n error using a message reference and arguments.
+// It formats this with fmt.Errorf
+func Newf(key message.Reference, args ...any) *Error {
+	_ = printerOrNew(language.English).Sprintf(key, args...)
+	return &Error{key: key, args: args}
+}
+
+// Wrap creates a new i18n error using an error to be wrapped 'err' and a prefix message reference 'key'.
+// It formats this with fmt.Errorf
+func Wrap(err error, key message.Reference) *Error {
+	_ = printerOrNew(language.English).Sprintf(key)
+	t, misc := TranslatedInner(err)
+	return &Error{key: key, wrapped: &Error{key: t, Misc: misc}, Misc: misc}
+}
+
+// Wrapf creates a new i18n error using an error to be wrapped 'err' and a prefix message reference 'key' with format arguments 'args'.
+// It formats this with fmt.Errorf
+func Wrapf(err error, key message.Reference, args ...any) *Error {
+	_ = printerOrNew(language.English).Sprintf(key, args...)
+	t, misc := TranslatedInner(err)
+	return &Error{key: key, args: args, wrapped: &Error{key: t, Misc: misc}, Misc: misc}
+}
+
+// NewInternal creates an internal localised error from a display string
+func NewInternal(disp string) *Error {
+	return Wrap(errors.New(disp), "An internal error occurred")
+}
+
+// NewInternalf creates an internal localised error from a display string and arguments
+func NewInternalf(disp string, args ...any) *Error {
+	return NewInternal(fmt.Sprintf(disp, args...))
+}
+
+// WrapInternal wraps an error and a display string into a localised internal error
+func WrapInternal(err error, disp string) *Error {
+	return Wrap(fmt.Errorf("%s with internal cause: %w", disp, err), "An internal error occurred")
+}
+
+// WrapInternalf wraps an error and a display string with args into a localised internal error
+func WrapInternalf(err error, disp string, args ...any) *Error {
+	return WrapInternal(err, fmt.Sprintf(disp, args...))
+}
+
+// initializeLangs initializes the printers from the default catalog into the sync map
+// we cannot do this in init() because this is too early
+func inititializeLangs() {
+	slog.Debug("i18n initializing languages")
+	for _, t := range message.DefaultCatalog.Languages() {
+		printers.Store(t, message.NewPrinter(t))
+	}
+}
diff --git a/i18n/i18n.go b/i18n/i18n.go
new file mode 100644
index 0000000..02b9028
--- /dev/null
+++ b/i18n/i18n.go
@@ -0,0 +1,54 @@
+// Package i18n implements utility functions for internationalization
+package i18n
+
+import "strings"
+
+// 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 ""
+}
diff --git a/i18n/i18n_test.go b/i18n/i18n_test.go
new file mode 100644
index 0000000..fc671a4
--- /dev/null
+++ b/i18n/i18n_test.go
@@ -0,0 +1,47 @@
+package i18n
+
+import "testing"
+
+func TestGetLanguageMatched(t *testing.T) {
+	// 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")
+	}
+}