Improve offline/online detection

src/app/service/api.service.ts

@@ -45,27 +45,103 @@ export class ApiService {
       protected db: DatabaseService,
       protected connection: ConnectionService,
   ) {
-    connection.monitor().subscribe(isConnected => {
-      if ( !isConnected ) {
-        this.makeOffline();
-      } else {
-        this.checkOnline().then(isOnline => {
-          if ( isOnline ) {
-            this.makeOnline();
-          } else {
-            this.makeOffline();
+    this.startOfflineObserver();
   }
-        });
+
+  protected stopOfflineObserverClosure?: any;
+
+  public stopOfflineObserver() {
+    if ( this.stopOfflineObserverClosure ) {
+      this.stopOfflineObserverClosure();
     }
+  }
+
+  protected startOfflineObserver() {
+    const passiveCheckTime = 5;
+    const checkTimes = [5, 5, 10, 10, 15, 15, 20, 20, 30, 30, 30, 60, 60, 500];
+    let currentCheckTimeIndex = 0;
+    let hasNetConnection = true;
+    let hasServerConnection = true;
+    let online = true;
+    let passiveCheckInterval;
+    let activeCheckInterval;
+    let stopped = false;
+
+    this.stopOfflineObserverClosure = () => {
+      stopped = true;
+      clearInterval(passiveCheckInterval);
+      clearInterval(activeCheckInterval);
+    };
+
+    const checkServerConnection = async () => {
+      if ( !hasNetConnection ) {
+        return false;
+      }
+
+      return this.checkOnline();
+    };
+
+    const startPassiveCheck = () => {
+      passiveCheckInterval = setInterval(async () => {
+        if ( hasNetConnection ) {
+          const server = await checkServerConnection();
+          if ( server !== hasServerConnection ) {
+            hasServerConnection = server;
+            await handleNetConnectionEvent();
+          }
+        }
+      }, passiveCheckTime * 1000);
+    };
+
+    const doActiveCheck = async () => {
+      if ( activeCheckInterval ) {
+        clearInterval(activeCheckInterval);
+        if ( currentCheckTimeIndex < (checkTimes.length - 1) ) {
+          currentCheckTimeIndex += 1;
+        }
+      }
+
+      if ( hasNetConnection ) {
+        const server = await checkServerConnection();
+        if ( server !== hasServerConnection ) {
+          hasServerConnection = server;
+          await handleNetConnectionEvent();
+        } else {
+          if ( activeCheckInterval ) {
+            activeCheckInterval = setInterval(doActiveCheck, checkTimes[currentCheckTimeIndex] * 1000);
+          }
+        }
+      }
+    };
+
+    const handleNetConnectionEvent = async () => {
+      if ( stopped ) {
+        return;
+      }
+
+      if ( online && (!hasNetConnection || !hasServerConnection) ) {
+        online = false;
+        await this.makeOffline();
+        clearInterval(passiveCheckInterval);
+        activeCheckInterval = setInterval(doActiveCheck, checkTimes[currentCheckTimeIndex] * 1000);
+      } else if ( !online && (hasNetConnection && hasServerConnection) ) {
+        if ( activeCheckInterval ) {
+          clearInterval(activeCheckInterval);
+        }
+
+        online = true;
+        currentCheckTimeIndex = 0;
+        await this.makeOnline();
+        startPassiveCheck();
+      }
+    };
+
+    this.connection.monitor().subscribe(isConnected => {
+      hasNetConnection = isConnected;
+      handleNetConnectionEvent();
     });
 
-    this.checkOnline().then(isConnected => {
-      if ( !isConnected ) {
-        this.makeOffline();
-      } else {
-        this.makeOnline();
-      }
-    });
+    startPassiveCheck();
   }
 
   public checkOnline(): Promise<boolean> {