From 4c00805a8e9cd3e58c36256f6501013be709ec2e Mon Sep 17 00:00:00 2001
From: Matt Hillsdon <44397098+microbit-matt-hillsdon@users.noreply.github.com>
Date: Fri, 23 Feb 2024 10:09:36 +0000
Subject: [PATCH] Older Safari: Handle speech sample rate errors, reuse audio
 context (#111)

- Workaround for https://github.com/microbit-foundation/micropython-microbit-v2-simulator/issues/110 where we've observed that the sample rate of 19000 isn't supported. We'll aim to increase the sample rate in a separate PR but this will at least mean the simulator isn't put in a bad state.
- Reuse the audio context created after the user interaction, as there are limits to how many you can create on Safari 13 (4 in my BrowserStack testing). I think we always intended to do this, but careful review needed as this is a more significant change than I was anticipating. We already had clean up code for the nodes when the board stops. We never cleaned up the context. So I think we were assuming it lived forever. If this doesn't work out then an alternative is to try closing the old one before creating the new one.
---
 src/board/audio/index.ts | 10 ++++++----
 src/jshal.js             | 20 ++++++++++++++------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/src/board/audio/index.ts b/src/board/audio/index.ts
index 3b14dd53..9bb7f5f9 100644
--- a/src/board/audio/index.ts
+++ b/src/board/audio/index.ts
@@ -67,10 +67,12 @@ export class Audio {
   }
 
   async createAudioContextFromUserInteraction(): Promise<void> {
-    this.context = new (window.AudioContext || window.webkitAudioContext)({
-      // The highest rate is the sound expression synth.
-      sampleRate: 44100,
-    });
+    this.context =
+      this.context ??
+      new (window.AudioContext || window.webkitAudioContext)({
+        // The highest rate is the sound expression synth.
+        sampleRate: 44100,
+      });
     if (this.context.state === "suspended") {
       return this.context.resume();
     }
diff --git a/src/jshal.js b/src/jshal.js
index 39d3cf08..3cc18cd1 100644
--- a/src/jshal.js
+++ b/src/jshal.js
@@ -240,14 +240,22 @@ mergeInto(LibraryManager.library, {
     /** @type {number} */ buf,
     /** @type {number} */ num_samples
   ) {
+    /** @type {AudioBuffer | undefined} */ let webAudioBuffer;
+    try {
+      // @ts-expect-error
+      webAudioBuffer = Module.board.audio.speech.createBuffer(num_samples);
+    } catch (e) {
+      // Swallow error on older Safari to keep the sim in a good state.
+      // @ts-expect-error
+      if (e.name === "NotSupportedError") {
+        return;
+      } else {
+        throw e;
+      }
+    }
     // @ts-expect-error
     Module.board.audio.speech.writeData(
-      Module.conversions.convertAudioBuffer(
-        Module.HEAPU8,
-        buf,
-        // @ts-expect-error
-        Module.board.audio.speech.createBuffer(num_samples)
-      )
+      Module.conversions.convertAudioBuffer(Module.HEAPU8, buf, webAudioBuffer)
     );
   },