Merge pull request #27 from nemphys/custom-detection

Implement custom locale detection using a new 'detectLocale' parameter

README.md

@@ -75,8 +75,9 @@ This is an extremely useful method if you are using `koa-better-error-handler` p
 This middleware uses custom locale detection (in order of priority):
 
 1. Check URL (e.g. if `/de` or `/de/` then it's a `de` locale - as long as `de` is a supported locale)
-2. Check the `"locale"` cookie value (or whatever the `cookie` option is defined as)
-3. Check `Accept-Language` header
+2. Use the custom function (if provided by the `detectLocale` parameter) for locale detection
+3. Check the `"locale"` cookie value (or whatever the `cookie` option is defined as)
+4. Check `Accept-Language` header
 
 It also exposes the following:
 
@@ -150,7 +151,9 @@ const i18n = new I18N({
     format: 'RFC1738',
     arrayFormat: 'indices'
   },
-  redirectTLDS: true
+  redirectTLDS: true,
+  // function that allows using a custom logic for locale detection (can return promise)
+  detectLocale: null
 });
 ```
 

index.js

@@ -49,6 +49,7 @@ class I18N {
         arrayFormat: 'indices'
       },
       redirectTLDS: true,
+      detectLocale: false,
       ...config
     };
 
@@ -112,7 +113,7 @@ class I18N {
     return err;
   }
 
-  middleware(ctx, next) {
+  async middleware(ctx, next) {
     const { locales, defaultLocale, phrases, cookie } = this.config;
 
     // expose api methods to `ctx.request` and `ctx.state`
@@ -128,9 +129,10 @@ class I18N {
     // in order of priority:
     //
     // 1. check the URL, if === `/de` or starts with `/de/` then locale is `de`
-    // 2. check the cookie
-    // 3. check Accept-Language last
-    // 4. check the user's lastLocale
+    // 2. use a custom function, if provided in parameters
+    // 3. check the cookie
+    // 4. check Accept-Language last
+    // 5. check the user's lastLocale
     //
     // also we need to expose `ctx.pathWithoutLocale`
     // as the path without locale
@@ -154,6 +156,12 @@ class I18N {
         ...new Set([defaultLocale, ...locales])
       ]);
       if (
+        this.config.detectLocale &&
+        typeof this.config.detectLocale === 'function'
+      ) {
+        locale = await this.config.detectLocale.call(this, ctx);
+        debug('found locale via custom function using %s', locale);
+      } else if (
         ctx.cookies.get(cookie) &&
         locales.includes(ctx.cookies.get(cookie))
       ) {