DTG: Add notification service to display popup messages

unused for now

core/java/src/net/i2p/app/NotificationService.java

@@ -0,0 +1,54 @@
+package net.i2p.app;
+
+/**
+ *  A service to send messages to users.
+ *  This service is currently provided by desktopgui (when supported and enabled).
+ *  Other applications may support this interface in the future.
+ *
+ *  Example usage:
+ *
+ * <pre>
+ *     ClientAppManager cmgr = _context.clientAppManager();
+ *     if (cmgr != null) {
+ *         NotificationService ns = (NotificationService) cmgr.getRegisteredApp("desktopgui");
+ *         if (ns != null)
+ *             ns.notify("foo", null, Log.INFO, _t("foo"), _t("message"), "/foo/bar");
+ *     }
+ * <pre>
+ *
+ *  @since 0.9.53
+ */
+public interface NotificationService {
+
+    /**
+     *  Send a (possibly delayed) notification to the user.
+     *
+     *  @param source e.g. "i2psnark"
+     *  @param category may be null, probably unused
+     *  @param priority higher is higher, Log.INFO etc. recommended, probably unused
+     *  @param title for the popup, translated
+     *  @param message translated
+     *  @param path in console for more information, starting with /, must be URL-escaped, or null
+     *  @return an ID to use with cancel() or update(), or -1 on failure
+     */
+    public int notify(String source, String category, int priority, String title, String message, String path);
+
+    /**
+     *  Cancel a notification if possible.
+     *
+     *  @param id as received from notify()
+     *  @return success
+     */
+    public boolean cancel(int id);
+
+    /**
+     *  Update the text of a notification if possible.
+     *
+     *  @param id as received from notify()
+     *  @param title for the popup, translated
+     *  @param message translated
+     *  @param path in console starting with /, must be URL-escaped, or null
+     *  @return success
+     */
+    public boolean update(int id, String title, String message, String path);
+}