// Binaural beats — slightly different frequencies in each ear.
// Run: node examples/binaural-beats.js 200 10 10s
// Run: node examples/binaural-beats.js freq=200 beat=10 -d 10s
// Keys: ←/→ ±0.5 Hz beat · ↑/↓ ±semitone carrier · q quit

import { AudioContext } from 'web-audio-api'
import { init } from './graphs/binaural-beats.js'
import { args, num, sec, keys, status, clearLine, pausedTag, help } from './utils.js'

help({
  description: 'create a binaural difference tone (headphones required)',
  usage: ['', '[carrier] [beat] [duration]', 'freq=200 beat=10 dur=10s'],
  options: [
    ['freq=<hz|note>', 'left-ear carrier frequency (default: 200)'],
    ['beat=<hz>', 'right-ear frequency offset (default: 10)'],
    ['-d, --duration <time>', 'run time with optional s/m/h suffix (default: 60s)'],
  ],
  controls: [['Space', 'pause/resume'], ['← / →', 'change beat by 0.5 Hz'], ['↑ / ↓', 'move carrier one semitone'], ['Q / Esc', 'quit']],
  notes: ['Use headphones; speakers do not isolate the left and right tones.'],
})

let { pos, $ } = args()
let nums = pos.filter(t => /^\d/.test(t) && !/[smh]$/.test(t) || /^[A-G][#b]?\d$/i.test(t))
let f = num(nums[0] || $('freq', 200))
let beat = +(nums[1] || $('beat', 10))
let dur = sec(pos.find(t => /\d[smh]$/.test(t)) || $('dur', '60'))

let ctx = new AudioContext()
await ctx.resume()

let demo = init(ctx, { frequency: f, difference: beat, duration: dur, gain: 0.3 })
let [oscL, oscR] = demo.sources

let retune = () => {
  let t = ctx.currentTime
  oscL.frequency.setTargetAtTime(f, t, 0.02)
  oscR.frequency.setTargetAtTime(f + beat, t, 0.02)
}

let render = status()
let ui = setInterval(() => render(`L ${f.toFixed(2)}Hz · R ${(f + beat).toFixed(2)}Hz · beat ${beat.toFixed(2)}Hz · space pause · ←→ beat · ↑↓ carrier · q quit${pausedTag(ctx)}`), 80)

keys({
  left: () => { beat = Math.max(0.1, beat - 0.5); retune() },
  right: () => { beat += 0.5; retune() },
  up: () => { f *= 2 ** (1/12); retune() },
  down: () => { f *= 2 ** (-1/12); retune() },
}, () => { clearInterval(ui); clearLine(); ctx.close() }, ctx)

console.log(`L: ${f}Hz  R: ${f + beat}Hz  beat: ${beat}Hz — use headphones  (${dur}s)`)

setTimeout(() => { clearInterval(ui); clearLine(); ctx.close(); process.exit(0) }, dur * 1000)