/**
 * Everything in SI: metres, seconds, hertz, metres per second.
 *
 * Physical units are what make the numbers here mean something. The string's
 * fundamental is a real pitch, the box is a real size you could build, the
 * timestep is a real duration, and the microphone's trace plays back at the
 * pitch a microphone there would have heard. They also keep the method's
 * limits visible: a grid solver resolves a wavelength with some number of
 * cells, so a fixed grid is a low-frequency method, and how low is a number
 * the app can show rather than hide.
 */

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

/** The domain, metres: a box around the instrument, twice as long along the
 *  string (x) as across (y) and up (z), centred on the origin. The top plate
 *  of the dulcimer body sits at z = 0 and the string runs along x just above
 *  it. */
export const DOMAIN_X = 1.0;
export const DOMAIN_YZ = 0.5;

/** Fraction of the stability limit the timestep is taken at. Fixed rather
 *  than a control: everything downstream (the string grid, the recording's
 *  sample rate) follows from dt, and one good value is worth more here than a
 *  slider. */
export const CFL = 0.5;

/** Cells per wavelength below which what is on screen (and in the recording)
 *  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`;
};