Add ServerInternationalization class for handling languages on the server side

Author: Simon Planinschek

src/ServerInternationalization.ts

@@ -0,0 +1,72 @@
+import { IncomingMessage } from 'http'
+import { getCookieFromRequest } from './utilities'
+import ClientInternationalization from './ClientInternationalization'
+
+class ServerInternationalization<
+  T extends string
+> extends ClientInternationalization<T> {
+  /**
+   * ServerInternationalization utility package for working with languages
+   *
+   *
+   * @param supportedLanguages { Array<string> } - List of all supported languages
+   * @param fallbackLanguage { string } - Fallback language if no language matches
+   * @param cookieName { string } - Optional: Set a preferred cookie name
+   */
+  constructor(
+    supportedLanguages: Array<T>,
+    fallbackLanguage: T,
+    cookieName: string
+  ) {
+    super(supportedLanguages, fallbackLanguage, cookieName)
+  }
+
+  /**
+   * Get the current language
+   * This method will first check if a language cookie is present.
+   * If no cookie was found the method will get the language form the browser
+   *
+   * @return { string } - Found language or fallback language
+   */
+  detectLanguage(request?: IncomingMessage): T {
+    // Check if request is not undefined
+    if (request) {
+      // Try to get language form cookie
+      const cookieFromRequest = getCookieFromRequest(this.cookieName, request)
+
+      if (cookieFromRequest) {
+        return cookieFromRequest as T
+      }
+
+      // Get accept language from request header
+      const acceptLanguage = request.headers['accept-language']
+
+      if (acceptLanguage) {
+        // Extract the locale string and the priority from header string
+        const requestedLocales = acceptLanguage.split(',').map((part) => {
+          const [locale, priority] = part.trim().split(';q=')
+
+          return { locale, priority: parseInt(priority) }
+        })
+
+        // Get the potential locale from requested locales array
+        const potentialLocale = requestedLocales
+          .sort((a, b) => b.priority - a.priority)
+          .find(
+            ({ locale }) =>
+              locale !== '*' &&
+              this.supportedLanguages.some((lang) => locale === lang)
+          )
+
+        // Check if the potential locale is not undefined else return the fallback language
+        return (potentialLocale
+          ? potentialLocale.locale
+          : this.fallbackLanguage) as T
+      }
+    }
+
+    return this.detectBrowserLanguage()
+  }
+}
+
+export default ServerInternationalization