// The parameters of the modal bank for the configuration currently being designed.
//
// A modes file is computed for one shape at a reference material and listener. The material and
// the damping enter analytically (see precompute/pipeline.ts), so they are applied here, on every
// slider move, without touching the eigensolve. The listener enters through the gains, which are
// a separate and slower computation done in the worker.
import type { SimulationConfig } from "./config/schema.ts";
import type { ModesData } from "./modes.ts";

export interface Derived {
  freq: Float64Array; // [Hz]
  sigma: Float64Array; // [1/s]
  phiFactor: number; // mode-shape rescaling for a density change
  overdamped: number; // modes whose loss had to be clamped below critical
  t60Low: number; // 60 dB decay of the lowest mode [s]
  t60High: number; // 60 dB decay of the highest mode [s]
}

export function derive(data: ModesData, cfg: SimulationConfig): Derived {
  const { E0, rho0 } = data.meta;
  const sE = cfg.material.E / E0, sRho = cfg.material.rho / rho0;
  const fScale = Math.sqrt(sE / sRho);
  const Nm = data.nModes;
  const freq = new Float64Array(Nm), sigma = new Float64Array(Nm);
  let overdamped = 0;
  for (let m = 0; m < Nm; m++) {
    const f = data.freq[m] * fScale;
    freq[m] = f;
    const s = cfg.material.sigma0 + cfg.material.sigma1 * data.dampQ[m];
    const crit = 0.999 * 2 * Math.PI * f;
    if (s > crit) overdamped++;
    sigma[m] = Math.min(s, crit);
  }
  return {
    freq, sigma, phiFactor: 1 / Math.sqrt(sRho), overdamped,
    t60Low: 6.907755 / sigma[0],
    t60High: 6.907755 / sigma[Nm - 1],
  };
}

/** The live quantities the gains depend on, as a comparable string. The gains are a sum over
 * elements at the mode frequencies, so they go stale when the listener moves and when the
 * material changes the frequencies. */
export function gainState(cfg: SimulationConfig): string {
  return JSON.stringify([cfg.material.E, cfg.material.rho, cfg.listener]);
}

/** The same string for the state a freshly loaded modes file was computed at. */
export function storedGainState(data: ModesData): string {
  const stored = data.meta.config as unknown as SimulationConfig;
  return JSON.stringify([data.meta.E0, data.meta.rho0, stored.listener]);
}