fix(web): keep app awake after returning from the background (#48)

* feat: handle visibility change in web

* chore: format the code

src/web.ts

@@ -11,6 +11,10 @@ export class KeepAwakeWeb extends WebPlugin implements KeepAwakePlugin {
   private readonly _isSupported =
     typeof navigator !== 'undefined' && 'wakeLock' in navigator;
 
+  private handleVisibilityChange = () => {
+    if (document.visibilityState === 'visible') this.keepAwake();
+  };
+
   public async keepAwake(): Promise<void> {
     if (!this._isSupported) {
       this.throwUnsupportedError();
@@ -19,6 +23,8 @@ export class KeepAwakeWeb extends WebPlugin implements KeepAwakePlugin {
       await this.allowSleep();
     }
     this.wakeLock = await navigator.wakeLock.request('screen');
+    document.addEventListener('visibilitychange', this.handleVisibilityChange);
+    document.addEventListener('fullscreenchange', this.handleVisibilityChange);
   }
 
   public async allowSleep(): Promise<void> {
@@ -27,6 +33,14 @@ export class KeepAwakeWeb extends WebPlugin implements KeepAwakePlugin {
     }
     this.wakeLock?.release();
     this.wakeLock = null;
+    document.removeEventListener(
+      'visibilitychange',
+      this.handleVisibilityChange,
+    );
+    document.removeEventListener(
+      'fullscreenchange',
+      this.handleVisibilityChange,
+    );
   }
 
   public async isSupported(): Promise<IsSupportedResult> {