[FIX] router: properly handle popstate

It was not correct, the url was changed multiple times and back
navigation was broken.

Also, note that there are no tests because the history api is not
available in jsdom.

src/router/Router.ts

@@ -95,7 +95,7 @@ export class Router {
   //--------------------------------------------------------------------------
 
   async start() {
-    (this as any)._listener = () => this._navigate(this.currentPath());
+    (this as any)._listener = ev => this._navigate(this.currentPath(), ev);
     window.addEventListener("popstate", (this as any)._listener);
     if (this.mode === "hash") {
       window.addEventListener("hashchange", (this as any)._listener);
@@ -115,13 +115,16 @@ export class Router {
     const path = this.destToPath(to);
     return this._navigate(path);
   }
-  async _navigate(path: string): Promise<boolean> {
+  async _navigate(path: string, ev?: any): Promise<boolean> {
     const initialName = this.currentRouteName;
     const initialParams = this.currentParams;
     const result = await this.matchAndApplyRules(path);
     if (result.type === "match") {
       const finalPath = this.routeToPath(result.route, result.params);
-      this.setUrlFromPath(finalPath);
+      const isPopStateEvent = ev && ev instanceof PopStateEvent;
+      if (!isPopStateEvent) {
+        this.setUrlFromPath(finalPath);
+      }
       this.currentRoute = result.route;
       this.currentParams = result.params;
     } else if (result.type === "nomatch") {
@@ -151,8 +154,11 @@ export class Router {
   //--------------------------------------------------------------------------
 
   private setUrlFromPath(path: string) {
-    const url = location.origin + path;
+    const separator = this.mode === "hash" ? "/" : "";
-    window.history.pushState({}, path, url);
+    const url = location.origin + separator + path;
+    if (url !== window.location.href) {
+      window.history.pushState({}, path, url);
+    }
   }
 
   private validateDestination(dest: Destination) {