fix(theme): save theme in local storage after theme changing

src/app/@core/utils/theme.service.ts

@@ -1,6 +1,7 @@
 import {Injectable, OnDestroy} from '@angular/core';
 import {Observable} from 'rxjs';
 import {takeWhile} from 'rxjs/operators';
+import {environment} from '../../../environments/environment';
 
 @Injectable()
 export class CurrentThemeService implements OnDestroy {
@@ -10,6 +11,22 @@ export class CurrentThemeService implements OnDestroy {
     subscriber.next(localStorage.theme);
   }).pipe(takeWhile(() => this.alive));
 
+  setCurrentTheme(themeName: string): void {
+    const currentTheme = {
+      themeName: themeName,
+      expires_in: this.calculateExpiration(environment.currentThemeLife),
+    };
+
+    localStorage.setItem('theme', JSON.stringify(currentTheme));
+  }
+
+  calculateExpiration(iat: number): number {
+    const currentDate = new Date().getTime();
+    const timestamp = iat || Math.floor(Date.now() / 1000);
+
+    return Math.floor(timestamp + currentDate);
+  }
+
   ngOnDestroy(): void {
     this.alive = false;
   }