Avoid disconnect during flash. (#252)

Somewhat speculative fix as I can't get the visibilitychange event to trigger during flash anymore. It seems to occur at the end of flash. But given there's async work in the flash it makes sense that it can occur.

I've added logging for the visibility change work.

I think we'd like to drop all this if we could fix the underlying cause of #89.

Fixes #223

Author: microbit-matt-hillsdon

src/device/device.ts

@@ -203,21 +203,33 @@ export class MicrobitWebUSBConnection
     this.emit(EVENT_SERIAL_DATA, data);
   };
 
+  private flashing: boolean = false;
+  private disconnectAfterFlash: boolean = false;
   private visibilityReconnect: boolean = false;
   private visibilityChangeListener = () => {
     if (document.visibilityState === "visible") {
       if (
         this.visibilityReconnect &&
         this.status !== ConnectionStatus.CONNECTED
       ) {
+        this.disconnectAfterFlash = false;
         this.visibilityReconnect = false;
-        this.connect();
+        if (!this.flashing) {
+          this.log("Reconnecting visible tab");
+          this.connect();
+        }
       }
     } else {
       if (!this.unloading && this.status === ConnectionStatus.CONNECTED) {
-        this.disconnect().then(() => {
-          this.visibilityReconnect = true;
-        });
+        if (!this.flashing) {
+          this.log("Disconnecting hidden tab");
+          this.disconnect().then(() => {
+            this.visibilityReconnect = true;
+          });
+        } else {
+          this.log("Scheduling disconnect of hidden tab for after flash");
+          this.disconnectAfterFlash = true;
+        }
       }
     }
   };
@@ -311,20 +323,25 @@ export class MicrobitWebUSBConnection
       progress: (percentage: number | undefined) => void;
     }
   ): Promise<void> {
-    const startTime = new Date().getTime();
+    this.flashing = true;
+    try {
+      const startTime = new Date().getTime();
 
-    await this.withEnrichedErrors(() =>
-      this.flashInternal(dataSource, options)
-    );
+      await this.withEnrichedErrors(() =>
+        this.flashInternal(dataSource, options)
+      );
 
-    const flashTime = new Date().getTime() - startTime;
-    this.logging.event({
-      type: "WebUSB-time",
-      detail: {
-        flashTime,
-      },
-    });
-    this.logging.log("Flash complete");
+      const flashTime = new Date().getTime() - startTime;
+      this.logging.event({
+        type: "WebUSB-time",
+        detail: {
+          flashTime,
+        },
+      });
+      this.logging.log("Flash complete");
+    } finally {
+      this.flashing = false;
+    }
   }
 
   private async flashInternal(
@@ -356,12 +373,19 @@ export class MicrobitWebUSBConnection
     } finally {
       progress(undefined);
 
-      // This might not strictly be "reinstating". We should make this
-      // behaviour configurable when pulling out a library.
-      this.log("Reinstating serial after flash");
-      if (this.connection.daplink) {
-        await this.connection.daplink.connect();
-        await this.startSerialInternal();
+      if (this.disconnectAfterFlash) {
+        this.log("Disconnecting after flash due to tab visibility");
+        this.disconnectAfterFlash = false;
+        await this.disconnect();
+        this.visibilityReconnect = true;
+      } else {
+        // This might not strictly be "reinstating". We should make this
+        // behaviour configurable when pulling out a library.
+        this.log("Reinstating serial after flash");
+        if (this.connection.daplink) {
+          await this.connection.daplink.connect();
+          await this.startSerialInternal();
+        }
       }
     }
   }