petal/web/src/audio/sounds.ts

// Petal's cute sound palette. These are hand-picked mp3 effects (warm bubble
// pops, a wooden "tok", rolling baoding balls, a Chinese fanfare for milestones,
// and a playful "haiya" for errors) living as assets in ./assets/sounds. Vite
// fingerprints and bundles them into dist, so they ride along inside the single
// Go binary; here we just fetch + decode them once and play them through a Web
// Audio bus with a soft master volume. The whole thing is opt-out-able and the
// mute choice persists in localStorage so it survives reloads.

import pop1Url from '../assets/sounds/pop1.mp3'
import pop2Url from '../assets/sounds/pop2.mp3'
import tokUrl from '../assets/sounds/tok.mp3'
import blockUrl from '../assets/sounds/block.mp3'
import baodingUrl from '../assets/sounds/baoding.mp3'
import milestoneUrl from '../assets/sounds/milestone.mp3'
import errorUrl from '../assets/sounds/error.mp3'

const STORAGE_KEY = 'petal.sound'

// Master volume — deliberately gentle. These are background delights, not alerts.
const MASTER_GAIN = 0.5

export type SoundName =
  | 'pop1' // a soft bubble pop
  | 'pop2' // a second bubble pop, slightly different
  | 'tok' // a light wooden "tok"
  | 'block' // a quick Chinese wood-block tap
  | 'baoding' // rolling baoding-ball shimmer
  | 'milestone' // a happy Chinese fanfare (word-count milestones)
  | 'error' // a playful "haiya" — something went wrong

const SOURCES: Record<SoundName, string> = {
  pop1: pop1Url,
  pop2: pop2Url,
  tok: tokUrl,
  block: blockUrl,
  baoding: baodingUrl,
  milestone: milestoneUrl,
  error: errorUrl,
}

// The pool of light "something happened" notification sounds. We rotate through
// these (skipping the one just played) so the same blip never repeats back to
// back — a batch of suggestions or a run of tips stays lively instead of
// hammering one note. milestone/error are deliberately NOT in the pool: they're
// reserved for their specific moments.
const POP_POOL: SoundName[] = ['pop1', 'pop2', 'tok', 'block', 'baoding']
let lastPop = -1

let ctx: AudioContext | null = null
let master: GainNode | null = null
const buffers = new Map<SoundName, AudioBuffer>()
let enabled = readEnabled()
const listeners = new Set<(on: boolean) => void>()

function readEnabled(): boolean {
  try {
    return localStorage.getItem(STORAGE_KEY) !== 'off'
  } catch {
    return true
  }
}

export function isSoundEnabled(): boolean {
  return enabled
}

export function setSoundEnabled(on: boolean): void {
  enabled = on
  try {
    localStorage.setItem(STORAGE_KEY, on ? 'on' : 'off')
  } catch {
    /* private mode — choice just won't persist */
  }
  listeners.forEach((fn) => fn(on))
  // Touching the context on enable doubles as a user-gesture unlock + warm-up.
  if (on) void ensureContext()
}

export function onSoundEnabledChange(fn: (on: boolean) => void): () => void {
  listeners.add(fn)
  return () => listeners.delete(fn)
}

// Lazily create the AudioContext (browsers require a user gesture before audio
// can play; the first play() after a click will succeed, earlier ones resume).
async function ensureContext(): Promise<AudioContext | null> {
  if (typeof window === 'undefined') return null
  const AC: typeof AudioContext | undefined =
    window.AudioContext ??
    (window as unknown as { webkitAudioContext?: typeof AudioContext }).webkitAudioContext
  if (!AC) return null
  if (!ctx) {
    ctx = new AC()
    master = ctx.createGain()
    master.gain.value = MASTER_GAIN
    // A gentle soft-clip so stacked sounds never crackle.
    const shaper = ctx.createWaveShaper()
    shaper.curve = softClipCurve()
    master.connect(shaper)
    shaper.connect(ctx.destination)
  }
  if (ctx.state === 'suspended') {
    try {
      await ctx.resume()
    } catch {
      /* will retry on the next gesture */
    }
  }
  return ctx
}

function softClipCurve(): Float32Array<ArrayBuffer> {
  const n = 1024
  const curve = new Float32Array(new ArrayBuffer(n * 4))
  for (let i = 0; i < n; i++) {
    const x = (i / (n - 1)) * 2 - 1
    curve[i] = Math.tanh(x * 1.2)
  }
  return curve
}

// Fetch + decode one sound, caching the decoded buffer for instant replay.
async function load(name: SoundName, audio: AudioContext): Promise<AudioBuffer | null> {
  const cached = buffers.get(name)
  if (cached) return cached
  try {
    const res = await fetch(SOURCES[name])
    const bytes = await res.arrayBuffer()
    const buf = await audio.decodeAudioData(bytes)
    buffers.set(name, buf)
    return buf
  } catch {
    return null // asset missing / decode failed — sound just won't play
  }
}

// Warm the cache so the first real play is instant.
async function prime(): Promise<void> {
  const audio = await ensureContext()
  if (!audio) return
  await Promise.all((Object.keys(SOURCES) as SoundName[]).map((n) => load(n, audio)))
}

// Fire a sound. No-op when muted or audio is unavailable. Never throws — a
// delight that fails should fail silently.
export function playSound(name: SoundName): void {
  if (!enabled) return
  void (async () => {
    const audio = await ensureContext()
    if (!audio || !master || audio.state !== 'running') return
    const buf = await load(name, audio)
    if (!buf) return
    try {
      const src = audio.createBufferSource()
      src.buffer = buf
      src.connect(master)
      src.start()
    } catch {
      /* audio glitch — ignore */
    }
  })()
}

// Play the next notification pop from the pool, never repeating the last one, so
// consecutive blips always sound different. This is the everyday "something
// arrived" voice for suggestions, tips, and gentle cheers.
export function playPop(): void {
  let i = lastPop
  // Tiny pool, so a short scan to pick anything but the last is plenty.
  for (let tries = 0; tries < POP_POOL.length && i === lastPop; tries++) {
    i = Math.floor(Math.random() * POP_POOL.length)
  }
  lastPop = i
  playSound(POP_POOL[i])
}

// Each freshly-surfaced suggestion just gets a rotating pop — the variety comes
// from the pool, not from the suggestion type, so a batch of same-type fixes
// still sounds lively.
export function playSuggestionSound(_type: string): void {
  playPop()
}

// Unlock + warm audio on the first user gesture so the very first sound isn't
// dropped by the browser's autoplay policy. Self-removing.
if (typeof window !== 'undefined') {
  const unlock = () => {
    void prime()
    window.removeEventListener('pointerdown', unlock)
    window.removeEventListener('keydown', unlock)
  }
  window.addEventListener('pointerdown', unlock)
  window.addEventListener('keydown', unlock)
}