1 files changed, 93 insertions, 0 deletions
diff --git a/toolkit/modules/Locale.jsm b/toolkit/modules/Locale.jsm
new file mode 100644
index 000000000..886de9e3a
--- /dev/null
+++ b/toolkit/modules/Locale.jsm
@@ -0,0 +1,93 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+this.EXPORTED_SYMBOLS = ["Locale"];
+
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/Preferences.jsm");
+
+const PREF_MATCH_OS_LOCALE            = "intl.locale.matchOS";
+const PREF_SELECTED_LOCALE            = "general.useragent.locale";
+
+this.Locale = {
+  /**
+   * Gets the currently selected locale for display.
+   * @return  the selected locale or "en-US" if none is selected
+   */
+  getLocale() {
+    if (Preferences.get(PREF_MATCH_OS_LOCALE, false))
+      return Services.locale.getLocaleComponentForUserAgent();
+    try {
+      let locale = Preferences.get(PREF_SELECTED_LOCALE, null, Ci.nsIPrefLocalizedString);
+      if (locale)
+        return locale;
+    }
+    catch (e) {}
+    return Preferences.get(PREF_SELECTED_LOCALE, "en-US");
+  },
+
+  /**
+   * Selects the closest matching locale from a list of locales.
+   *
+   * @param  aLocales
+   *         An array of locales
+   * @return the best match for the currently selected locale
+   */
+  findClosestLocale(aLocales) {
+    let appLocale = this.getLocale();
+
+    // Holds the best matching localized resource
+    var bestmatch = null;
+    // The number of locale parts it matched with
+    var bestmatchcount = 0;
+    // The number of locale parts in the match
+    var bestpartcount = 0;
+
+    var matchLocales = [appLocale.toLowerCase()];
+    /* If the current locale is English then it will find a match if there is
+       a valid match for en-US so no point searching that locale too. */
+    if (matchLocales[0].substring(0, 3) != "en-")
+      matchLocales.push("en-us");
+
+    for (let locale of matchLocales) {
+      var lparts = locale.split("-");
+      for (let localized of aLocales) {
+        for (let found of localized.locales) {
+          found = found.toLowerCase();
+          // Exact match is returned immediately
+          if (locale == found)
+            return localized;
+
+          var fparts = found.split("-");
+          /* If we have found a possible match and this one isn't any longer
+             then we dont need to check further. */
+          if (bestmatch && fparts.length < bestmatchcount)
+            continue;
+
+          // Count the number of parts that match
+          var maxmatchcount = Math.min(fparts.length, lparts.length);
+          var matchcount = 0;
+          while (matchcount < maxmatchcount &&
+                 fparts[matchcount] == lparts[matchcount])
+            matchcount++;
+
+          /* If we matched more than the last best match or matched the same and
+             this locale is less specific than the last best match. */
+          if (matchcount > bestmatchcount ||
+              (matchcount == bestmatchcount && fparts.length < bestpartcount)) {
+            bestmatch = localized;
+            bestmatchcount = matchcount;
+            bestpartcount = fparts.length;
+          }
+        }
+      }
+      // If we found a valid match for this locale return it
+      if (bestmatch)
+        return bestmatch;
+    }
+    return null;
+  },
+};