feat: disable polling by default and add visibility-based flag refresh

- Change DEFAULT_POLL_INTERVAL from 30000ms to 0 (polling disabled by default)
- Add visibility change detection to re-fetch flags when page/app becomes visible
- Add _visibilityChangeHandler property and _onVisibilityChange() method
- Register/unregister visibility change listener in initialize/onClose
- Re-fetches respect Retry-After rate limit headers
- Emits ConfigurationChanged or Stale events based on fetch results

Author: marcozabel

libs/providers/ofrep-web/src/lib/ofrep-web-provider.ts

@@ -36,7 +36,7 @@ import type { FlagCache, MetadataCache } from './model/in-memory-cache';
 import type { OFREPWebProviderOptions } from './model/ofrep-web-provider-options';
 
 export class OFREPWebProvider implements Provider {
-  DEFAULT_POLL_INTERVAL = 30000;
+  DEFAULT_POLL_INTERVAL = 0;
 
   readonly metadata = {
     name: 'OpenFeature Remote Evaluation Protocol Web Provider',
@@ -57,6 +57,7 @@ export class OFREPWebProvider implements Provider {
   private _flagSetMetadataCache?: MetadataCache;
   private _context: EvaluationContext | undefined;
   private _pollingIntervalId?: number;
+  private _visibilityChangeHandler = this._onVisibilityChange.bind(this);
 
   constructor(options: OFREPWebProviderOptions, logger?: Logger) {
     this._options = options;
@@ -86,6 +87,11 @@ export class OFREPWebProvider implements Provider {
         this.startPolling();
       }
 
+      // Listen for page/app visibility changes to refetch flags when becoming visible
+      if (typeof document !== 'undefined') {
+        document.addEventListener('visibilitychange', this._visibilityChangeHandler);
+      }
+
       this._logger?.debug(`${this.metadata.name} initialized successfully`);
     } catch (error) {
       if (error instanceof OFREPApiUnauthorizedError || error instanceof OFREPForbiddenError) {
@@ -166,6 +172,9 @@ export class OFREPWebProvider implements Provider {
    */
   onClose?(): Promise<void> {
     this.stopPolling();
+    if (typeof document !== 'undefined') {
+      document.removeEventListener('visibilitychange', this._visibilityChangeHandler);
+    }
     this._ofrepAPI.close();
     return Promise.resolve();
   }
@@ -319,4 +328,30 @@ export class OFREPWebProvider implements Provider {
       clearInterval(this._pollingIntervalId);
     }
   }
+
+  /**
+   * Handler for visibility changes (page/app becoming visible)
+   * Re-fetches flags when the document becomes visible
+   * @private
+   */
+  private async _onVisibilityChange() {
+    // Only re-fetch when the page becomes visible, not when it's hidden
+    if (typeof document !== 'undefined' && document.visibilityState === 'visible') {
+      try {
+        const now = new Date();
+        if (this._retryPollingAfter !== undefined && this._retryPollingAfter > now) {
+          return;
+        }
+        const res = await this._fetchFlags(this._context);
+        if (res.status === BulkEvaluationStatus.SUCCESS_WITH_CHANGES) {
+          this.events?.emit(ClientProviderEvents.ConfigurationChanged, {
+            message: 'Flags updated after visibility change',
+            flagsChanged: res.flags,
+          });
+        }
+      } catch (error) {
+        this.events?.emit(ClientProviderEvents.Stale, { message: `Error while fetching after visibility change: ${error}` });
+      }
+    }
+  }
 }