/**
 * Everything in SI: metres, seconds, hertz, metres per second.
 *
 * The app used to be dimensionless — a domain two units across, a background
 * speed of one — which is tidy but leaves every number needing a translation
 * before it means anything, and leaves the microphone's recording with no
 * honest playback rate. In physical units all of that falls out: a wavelength
 * is a length you can compare to the room, a timestep is a real duration, and
 * the recorded trace plays back in real time at the pitch a microphone there
 * would have heard.
 *
 * It also makes the method's limits visible rather than hidden. A grid solver
 * resolves a wavelength with some number of cells, so a fixed grid over a
 * fixed domain is a low-frequency method: at 512 points across ten metres,
 * 700 Hz is 25 cells per wavelength and 2 kHz is nine. That ratio is now on
 * screen, because it is the number that decides whether what you are watching
 * is physics or grid dispersion.
 */

/** Speed of sound in air at about 20 °C, m/s. */
export const C_AIR = 343;

/** Side of the square domain, metres. Hall-sized: big enough for a room with
 *  air around it, small enough that a wavefront crosses it in 30 ms. */
export const DOMAIN = 10;

/** Cells per wavelength below which what is on screen is as much grid
 *  dispersion as it is sound. */
export const POOR_RESOLUTION = 8;

/** A length in metres, written the way a person would say it. */
export const fmtLength = (m: number): string =>
  Math.abs(m) < 1 ? `${(1000 * m).toPrecision(3)} mm` : `${m.toPrecision(3)} m`;

/** A duration in seconds, likewise. */
export const fmtTime = (s: number): string => {
  const a = Math.abs(s);
  if (a > 0 && a < 1e-3) return `${(1e6 * s).toPrecision(3)} µs`;
  if (a < 1) return `${(1e3 * s).toPrecision(3)} ms`;
  return `${s.toPrecision(3)} s`;
};