Resolve the page UI language once and let each ExApp fill its own Phrases.

Co-authored-by: Cursor <cursoragent@cursor.com>

language.go

@@ -0,0 +1,163 @@
+package gonexapp
+
+import (
+	"context"
+	_ "embed"
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+//go:embed i18n/en.json
+var chromeENJSON []byte
+
+//go:embed i18n/de.json
+var chromeDEJSON []byte
+
+// chromeSets is the Library's own chrome. It is not part of the map the page script sees.
+var chromeSets = map[string]map[string]string{
+	"en": mustChrome(chromeENJSON),
+	"de": mustChrome(chromeDEJSON),
+}
+
+func mustChrome(raw []byte) map[string]string {
+	var m map[string]string
+	if err := json.Unmarshal(raw, &m); err != nil {
+		panic(err)
+	}
+	return m
+}
+
+type uiLanguageKey struct{}
+
+// UILanguage is the language of the Phrases for this request, "en" or "de".
+// It reads the Requesting user's language from the Provisioning OCS user
+// record and forwards the request's Accept-Language on that read.
+// The locale field is ignored. A more specific code uses the broader
+// language when this Library provides that language. Any other code, a
+// missing Requesting user, or a failed read is English, and the page still renders.
+// A second call with the request returned from a page render reuses that result.
+func (c Credentials) UILanguage(r *http.Request) string {
+	if r == nil {
+		return "en"
+	}
+	if lang, ok := r.Context().Value(uiLanguageKey{}).(string); ok {
+		return lang
+	}
+	return c.readUILanguage(r)
+}
+
+func (c Credentials) readUILanguage(r *http.Request) string {
+	if c.BaseURL == "" {
+		return "en"
+	}
+	userID, err := UserFromRequest(r)
+	if err != nil || userID == "" {
+		return "en"
+	}
+	ocs := OCSClient{Cred: c.WithUser(userID)}
+	if al := r.Header.Get("Accept-Language"); al != "" {
+		ocs.Header = http.Header{"Accept-Language": {al}}
+	}
+	raw, err := ocs.Call(http.MethodGet, "cloud/users/"+url.PathEscape(userID), nil)
+	if err != nil {
+		return "en"
+	}
+	return matchLanguage(userLanguage(raw), chromeHas)
+}
+
+func chromeHas(code string) bool {
+	_, ok := chromeSets[code]
+	return ok
+}
+
+// matchLanguage picks a Phrase set for the code Nextcloud returned.
+// The code itself wins when that set exists. Otherwise the part before "_"
+// wins when that set exists. Otherwise English.
+func matchLanguage(code string, has func(string) bool) string {
+	code = strings.TrimSpace(code)
+	if code != "" && has(code) {
+		return code
+	}
+	if i := strings.IndexByte(code, '_'); i > 0 {
+		if base := code[:i]; has(base) {
+			return base
+		}
+	}
+	return "en"
+}
+
+func userLanguage(raw []byte) string {
+	var parsed struct {
+		OCS struct {
+			Data struct {
+				Language string `json:"language"`
+			} `json:"data"`
+		} `json:"ocs"`
+	}
+	if err := json.Unmarshal(raw, &parsed); err != nil {
+		return ""
+	}
+	return parsed.OCS.Data.Language
+}
+
+func chromePhrase(lang, id string, holes map[string]string) string {
+	if _, ok := chromeSets[lang]; !ok {
+		lang = "en"
+	}
+	text := chromeSets[lang][id]
+	if text == "" && lang != "en" {
+		text = chromeSets["en"][id]
+	}
+	if text == "" {
+		return id
+	}
+	return fillHoles(text, holes)
+}
+
+// fillHoles replaces {name} with the plain-text value.
+// A hole with no value stays visible as {name}.
+// A value is not scanned for further holes.
+func fillHoles(text string, holes map[string]string) string {
+	if len(holes) == 0 || !strings.Contains(text, "{") {
+		return text
+	}
+	var b strings.Builder
+	b.Grow(len(text))
+	for i := 0; i < len(text); {
+		if text[i] != '{' {
+			b.WriteByte(text[i])
+			i++
+			continue
+		}
+		end := strings.IndexByte(text[i+1:], '}')
+		if end < 0 {
+			b.WriteByte(text[i])
+			i++
+			continue
+		}
+		name := text[i+1 : i+1+end]
+		value, ok := holes[name]
+		if !ok {
+			b.WriteByte(text[i])
+			i++
+			continue
+		}
+		b.WriteString(value)
+		i += end + 2
+	}
+	return b.String()
+}
+
+// rememberUILanguage returns r carrying lang so a later UILanguage call
+// on this page does not read Nextcloud again.
+func rememberUILanguage(r *http.Request, lang string) *http.Request {
+	if r == nil {
+		return nil
+	}
+	if _, ok := r.Context().Value(uiLanguageKey{}).(string); ok {
+		return r
+	}
+	return r.WithContext(context.WithValue(r.Context(), uiLanguageKey{}, lang))
+}