/* eslint-disable no-param-reassign */
/* eslint-disable no-plusplus */
/* eslint-disable @typescript-eslint/no-use-before-define */

import { TEasingBezier } from '../types';

export function easingByBezier(progress: number, bezier: TEasingBezier) {
  const [x1, y1, x2, y2] = bezier;

  if (x1 === y1 && x2 === y2) {
    return progress;
  }

  const val = [];
  for (let i = 0; i < 11; ++i) {
    val[i] = bezierCalc(i * 0.1, x1, x2);
  }

  if (progress === 0) {
    return 0;
  }
  if (progress === 1) {
    return 1;
  }

  return bezierCalc(bezierX(bezier, progress, val), y1, y2);
}

function bezierCalc(progress: number, x1: number, x2: number) {
  return (
    ((bezierA(x1, x2) * progress + bezierB(x1, x2)) * progress + bezierC(x1)) *
    progress
  );
}

function bezierA(x1: number, x2: number) {
  return 1.0 - 3.0 * x2 + 3.0 * x1;
}

function bezierB(x1: number, x2: number) {
  return 3.0 * x2 - 6.0 * x1;
}

function bezierC(x1: number) {
  return 3.0 * x1;
}

function bezierX(bezier: number[], progress: number, val: number[]) {
  // eslint-disable-next-line no-unused-vars
  const x1 = bezier[0];
  const x2 = bezier[2];

  let start = 0;
  let current = 1;

  for (; current !== 10 && val[current] <= progress; ++current) {
    start += 0.1;
  }
  --current;

  const dist = (progress - val[current]) / (val[current + 1] - val[current]);
  const guessForT = start + dist * 0.1;

  const initialSlope = bezierSlope(guessForT, x1, x2);
  if (initialSlope >= 0.001) {
    return bezierNewtonRaphsonIterate(progress, guessForT, x1, x2);
  }
  if (initialSlope === 0.0) {
    return guessForT;
  }

  return bezierBinarySubdivide(progress, start, start + 0.1, x1, x2);
}

function bezierSlope(progress: number, x1: number, x2: number) {
  return (
    3.0 * bezierA(x1, x2) * progress * progress +
    2.0 * bezierB(x1, x2) * progress +
    bezierC(x1)
  );
}

function bezierNewtonRaphsonIterate(
  progress: number,
  guessForT: number,
  x1: number,
  x2: number,
) {
  for (let i = 0; i < 4; ++i) {
    const currentSlope = bezierSlope(guessForT, x1, x2);
    if (currentSlope === 0.0) {
      return guessForT;
    }
    const currentX = bezierCalc(guessForT, x1, x2) - progress;
    guessForT -= currentX / currentSlope;
  }

  return guessForT;
}

function bezierBinarySubdivide(
  progress: number,
  a: number,
  b: number,
  x1: number,
  x2: number,
) {
  let currentX;
  let currentT;
  let i = 0;

  do {
    currentT = a + (b - a) / 2.0;
    currentX = bezierCalc(currentT, x1, x2) - progress;
    if (currentX > 0.0) {
      b = currentT;
    } else {
      a = currentT;
    }
  } while (Math.abs(currentX) > 0.0000001 && ++i < 10);

  return currentT;
}