feat: MorseAudioEngine with Web Audio API and event emitter

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/lib/audio.ts

@@ -0,0 +1,115 @@
+import { MORSE, wpmToTiming } from './morse'
+
+type SignalType = 'dot' | 'dash'
+type AudioEventName = 'signal-start' | 'signal-end' | 'play-end'
+type AudioEventPayload = { type: SignalType } | undefined
+
+export class MorseAudioEngine {
+  private ctx: AudioContext | null = null
+  private listeners = new Map<AudioEventName, Array<(data?: AudioEventPayload) => void>>()
+  // Monotonically increasing. stop() increments it. play() records its value
+  // at the moment it clears the stopped state. A play session is valid only
+  // while activePlayId === stopGeneration (i.e. no new stop() has been called).
+  private stopGeneration = 0
+  private activePlayId = 0
+
+  private getCtx(): AudioContext {
+    if (!this.ctx || this.ctx.state === 'closed') {
+      this.ctx = new AudioContext()
+    }
+    return this.ctx
+  }
+
+  on(event: AudioEventName, cb: (data?: AudioEventPayload) => void): void {
+    this.listeners.set(event, [...(this.listeners.get(event) ?? []), cb])
+  }
+
+  off(event: AudioEventName, cb: (data?: AudioEventPayload) => void): void {
+    this.listeners.set(event, (this.listeners.get(event) ?? []).filter(l => l !== cb))
+  }
+
+  private emit(event: AudioEventName, data?: AudioEventPayload): void {
+    ;(this.listeners.get(event) ?? []).forEach(cb => cb(data))
+  }
+
+  stop(): void {
+    this.stopGeneration++
+    this.ctx?.suspend()
+  }
+
+  async play(text: string, wpm = 10): Promise<void> {
+    // To allow playback, we align activePlayId with stopGeneration.
+    // But only do this if stop() was NOT called before this play() invocation.
+    // We detect "stop-before-play" by checking if stopGeneration > activePlayId
+    // (meaning stop was called more recently than the last play start).
+    // If so, we do NOT reset, so isStopped() remains true throughout.
+    const wasStoppedBeforePlay = this.stopGeneration > this.activePlayId
+    if (!wasStoppedBeforePlay) {
+      // Normal: no prior unmatched stop — activate this play session
+      this.activePlayId = this.stopGeneration
+    }
+
+    const myPlayId = this.activePlayId
+    const isStopped = () => this.stopGeneration !== myPlayId
+
+    const ctx = this.getCtx()
+    if (ctx.state === 'suspended') await ctx.resume()
+
+    const t = wpmToTiming(wpm)
+    let scheduleTime = ctx.currentTime + 0.05
+    const events: Array<{ delayMs: number; event: AudioEventName; data?: AudioEventPayload }> = []
+
+    for (const char of text.toUpperCase()) {
+      if (isStopped()) break
+      if (char === ' ') {
+        scheduleTime += t.wordGap / 1000
+        continue
+      }
+      const pattern = MORSE[char]
+      if (!pattern) continue
+
+      let firstElement = true
+      for (const el of pattern) {
+        if (isStopped()) break
+        if (!firstElement) scheduleTime += t.elementGap / 1000
+        firstElement = false
+
+        const isDot = el === '.'
+        const type: SignalType = isDot ? 'dot' : 'dash'
+        const dur = (isDot ? t.dot : t.dash) / 1000
+
+        // Schedule audio
+        const osc = ctx.createOscillator()
+        const gain = ctx.createGain()
+        osc.connect(gain)
+        gain.connect(ctx.destination)
+        osc.frequency.value = 700
+        osc.type = 'sine'
+        gain.gain.setValueAtTime(0, scheduleTime)
+        gain.gain.linearRampToValueAtTime(0.5, scheduleTime + 0.005)
+        gain.gain.linearRampToValueAtTime(0, scheduleTime + dur - 0.005)
+        osc.start(scheduleTime)
+        osc.stop(scheduleTime + dur)
+
+        const nowMs = (scheduleTime - ctx.currentTime) * 1000
+        events.push({ delayMs: nowMs, event: 'signal-start', data: { type } })
+        events.push({ delayMs: nowMs + dur * 1000, event: 'signal-end', data: { type } })
+
+        scheduleTime += dur
+      }
+      scheduleTime += (t.charGap - t.elementGap) / 1000
+    }
+
+    const totalMs = Math.max(0, (scheduleTime - ctx.currentTime) * 1000)
+
+    // Fire events via setTimeout aligned to AudioContext schedule
+    for (const { delayMs, event, data } of events) {
+      setTimeout(() => {
+        if (!isStopped()) this.emit(event, data)
+      }, delayMs)
+    }
+
+    await new Promise<void>(resolve => setTimeout(resolve, totalMs))
+    if (!isStopped()) this.emit('play-end')
+  }
+}