import {Ticker, withResolvers} from '@/util/promise.js';

const Modulators = {
  flat: () => 0.5,
  random: () => Math.random(),
  sawtooth: (unit) => unit,
  sine: (unit) => 0.5 * (1 + Math.sin(unit * Math.PI * 2)),
  square: (unit) => (unit < 0.5 ? 0 : 1),
  triangle: (unit) => 2 * Math.abs(((unit + 0.75) % 1) - 0.5),
};

export default function lfo(object, properties) {
  const oscillators = {};
  const promises = [];
  for (const key in properties) {
    const property = properties[key];
    const oscillator = {
      count: Infinity,
      elapsed: 0,
      offset: 0,
      ...property,
    };
    if (!('median' in oscillator)) {
      oscillator.median = oscillator.magnitude / 2;
    }
    if (!oscillator.modulators) {
      oscillator.modulators = [Modulators.triangle];
    }
    else {
      const {modulators} = oscillator;
      for (const i in modulators) {
        if ('string' === typeof modulators[i]) {
          modulators[i] = Modulators[modulators[i]];
        }
      }
    }
    oscillator.low = oscillator.median - oscillator.magnitude / 2;
    ({promise: oscillator.promise, resolve: oscillator.stop} = withResolvers());
    oscillator.promise.then(() => {
      delete oscillators[key];
    });
    promises.push(oscillator.promise);
    oscillators[key] = oscillator;
  }
  let stop;
  const promise = new Ticker(
    (resolve) => {
      stop = resolve;
      Promise.all(promises).then(resolve);
    },
    (elapsed) => {
      for (const key in oscillators) {
        const oscillator = oscillators[key];
        oscillator.elapsed += elapsed;
        if (oscillator.elapsed >= oscillator.frequency) {
          if (0 === --oscillator.count) {
            oscillator.stop();
            return;
          }
          oscillator.elapsed = oscillator.elapsed % oscillator.frequency;
        }
        const x = (oscillator.offset + (oscillator.elapsed / oscillator.frequency)) % 1;
        let y = 0;
        for (const modulator of oscillator.modulators) {
          y += modulator(x);
        }
        object[key] = oscillator.low + oscillator.magnitude * (y / oscillator.modulators.length);
      }
    },
  );
  return {stop, oscillators, promise};
}