refactor(live-atc): extract encodeWav to shared/utils, add tests

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/pages/live-atc.vue

@@ -1525,6 +1525,7 @@ import { createNoiseGenerators, getReadabilityProfile } from '../../shared/utils
 import { createAtisAudioLoop, type AtisAudioLoop } from '../../shared/utils/atisAudioLoop'
 import { normalizeManualFreq } from '../../shared/utils/frequency'
 import { normalizeSimFreq, normalizeBridgeTelemetry, telemetrySignature } from '../../shared/utils/bridgeTelemetry'
+import { encodeWav } from '../../shared/utils/wavEncoder'
 import type {
   CandidateTraceElimination,
   CandidateTraceEntry,
@@ -4037,35 +4038,6 @@ const snapshotPrerecPCM = (): Float32Array => {
   return out
 }
 
-const encodeWav = (pcm: Float32Array, sampleRate: number): Blob => {
-  const length = pcm.length
-  const buffer = new ArrayBuffer(44 + length * 2)
-  const view = new DataView(buffer)
-  const writeStr = (off: number, s: string) => {
-    for (let i = 0; i < s.length; i++) view.setUint8(off + i, s.charCodeAt(i))
-  }
-  writeStr(0, 'RIFF')
-  view.setUint32(4, 36 + length * 2, true)
-  writeStr(8, 'WAVE')
-  writeStr(12, 'fmt ')
-  view.setUint32(16, 16, true)
-  view.setUint16(20, 1, true)
-  view.setUint16(22, 1, true)
-  view.setUint32(24, sampleRate, true)
-  view.setUint32(28, sampleRate * 2, true)
-  view.setUint16(32, 2, true)
-  view.setUint16(34, 16, true)
-  writeStr(36, 'data')
-  view.setUint32(40, length * 2, true)
-  let off = 44
-  for (let i = 0; i < length; i++) {
-    const s = Math.max(-1, Math.min(1, pcm[i]))
-    view.setInt16(off, s < 0 ? s * 0x8000 : s * 0x7FFF, true)
-    off += 2
-  }
-  return new Blob([buffer], { type: 'audio/wav' })
-}
-
 const stopPrerecCapture = () => {
   prerecLiveCapture = false
   prerecLiveChunks = []

shared/utils/wavEncoder.ts

@@ -0,0 +1,28 @@
+export const encodeWav = (pcm: Float32Array, sampleRate: number): Blob => {
+  const length = pcm.length
+  const buffer = new ArrayBuffer(44 + length * 2)
+  const view = new DataView(buffer)
+  const writeStr = (off: number, s: string) => {
+    for (let i = 0; i < s.length; i++) view.setUint8(off + i, s.charCodeAt(i))
+  }
+  writeStr(0, 'RIFF')
+  view.setUint32(4, 36 + length * 2, true)
+  writeStr(8, 'WAVE')
+  writeStr(12, 'fmt ')
+  view.setUint32(16, 16, true)
+  view.setUint16(20, 1, true)
+  view.setUint16(22, 1, true)
+  view.setUint32(24, sampleRate, true)
+  view.setUint32(28, sampleRate * 2, true)
+  view.setUint16(32, 2, true)
+  view.setUint16(34, 16, true)
+  writeStr(36, 'data')
+  view.setUint32(40, length * 2, true)
+  let off = 44
+  for (let i = 0; i < length; i++) {
+    const s = Math.max(-1, Math.min(1, pcm[i]))
+    view.setInt16(off, s < 0 ? s * 0x8000 : s * 0x7FFF, true)
+    off += 2
+  }
+  return new Blob([buffer], { type: 'audio/wav' })
+}

tests/shared/wavEncoder.test.ts

@@ -0,0 +1,36 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { encodeWav } from '../../shared/utils/wavEncoder.ts'
+
+test('encodeWav produces a valid RIFF/WAVE header', async () => {
+  const pcm = new Float32Array([0, 0.5, -0.5, 1, -1])
+  const blob = encodeWav(pcm, 16000)
+  const buf = new Uint8Array(await blob.arrayBuffer())
+  const ascii = (start: number, len: number) =>
+    String.fromCharCode(...buf.slice(start, start + len))
+  assert.equal(ascii(0, 4), 'RIFF')
+  assert.equal(ascii(8, 4), 'WAVE')
+  assert.equal(ascii(12, 4), 'fmt ')
+  // sample rate is little-endian at byte offset 24
+  const view = new DataView(buf.buffer)
+  assert.equal(view.getUint32(24, true), 16000)
+})
+
+test('encodeWav clamps out-of-range samples instead of wrapping', async () => {
+  const pcm = new Float32Array([2, -2])
+  const blob = encodeWav(pcm, 16000)
+  const buf = new Uint8Array(await blob.arrayBuffer())
+  const view = new DataView(buf.buffer)
+  // 16-bit PCM data starts at byte 44 in a standard WAV header
+  assert.equal(view.getInt16(44, true), 32767)
+  assert.equal(view.getInt16(46, true), -32768)
+})
+
+test('encodeWav sets the correct data chunk size', async () => {
+  const pcm = new Float32Array(10)
+  const blob = encodeWav(pcm, 8000)
+  const buf = new Uint8Array(await blob.arrayBuffer())
+  assert.equal(buf.length, 44 + 20)
+  const view = new DataView(buf.buffer)
+  assert.equal(view.getUint32(40, true), 20)
+})