/*
 * Philip Crotwell
 * University of South Carolina, 2019
 * https://www.seis.sc.edu
 */
import { Seismogram } from "./seismogram";

/**
 * Applies a time domain taper of the given type.
 *
 * @param   seis      Seismogram to taper
 * @param   width     width as a fraction of seismogram length, default is 0.05
 * @param   taperType taper type, default is HANNING, others are HAMMING and COSINE
 * @returns            copy of seismogram with taper applied.
 */
export function taper(
  seis: Seismogram,
  width = 0.05,
  taperType: string = HANNING,
): Seismogram {
  if (width > 0.5) {
    throw new Error(`Taper width cannot be larger than 0.5, width=${width}`);
  }

  if (seis.isContiguous()) {
    const data = seis.y;
    const outData = Float32Array.from(data);
    const w = Math.floor(data.length * width);
    const coeff = getCoefficients(taperType, w);
    const omega = coeff[0];
    const f0 = coeff[1];
    const f1 = coeff[2];

    for (let i = 0; i < w; i++) {
      const taperFactor = f0 - f1 * Math.cos(omega * i);
      outData[i] = outData[i] * taperFactor;
      outData[outData.length - i - 1] =
        outData[outData.length - i - 1] * taperFactor;
    }

    return seis.cloneWithNewData(outData);
  } else {
    throw new Error(
      `Cannot take taper of non-contiguous seismogram: ${seis.segments.length}`,
    );
  }
}

/**
 * Calculates the coefficients for tapering, [omega, f0, f1]
 *
 * @param type HANNING, HAMMING or COSINE
 * @param length number of data points
 * @returns tapering coefficients as an array of length 3
 */
export function getCoefficients(type: string, length: number): Array<number> {
  let omega, f0, f1;

  if (type === HANNING) {
    omega = Math.PI / length;
    f0 = 0.5;
    f1 = 0.5;
  } else if (type === HAMMING) {
    omega = Math.PI / length;
    f0 = 0.54;
    f1 = 0.46;
  } else {
    // cosine
    omega = Math.PI / 2 / length;
    f0 = 1;
    f1 = 1;
  }

  return [omega, f0, f1];
}
export const HANNING = "HANNING";
export const HAMMING = "HAMMING";
export const COSINE = "COSINE";