'use strict';

var noop = require('../noop.js');

/*
  Bezier function generator
  This has been modified from Gaëtan Renaudeau's BezierEasing
  https://github.com/gre/bezier-easing/blob/master/src/index.js
  https://github.com/gre/bezier-easing/blob/master/LICENSE
  
  I've removed the newtonRaphsonIterate algo because in benchmarking it
  wasn't noticeably faster than binarySubdivision, indeed removing it
  usually improved times, depending on the curve.
  I also removed the lookup table, as for the added bundle size and loop we're
  only cutting ~4 or so subdivision iterations. I bumped the max iterations up
  to 12 to compensate and this still tended to be faster for no perceivable
  loss in accuracy.
  Usage
    const easeOut = cubicBezier(.17,.67,.83,.67);
    const x = easeOut(0.5); // returns 0.627...
*/
// Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
const calcBezier = (t, a1, a2) => (((1.0 - 3.0 * a2 + 3.0 * a1) * t + (3.0 * a2 - 6.0 * a1)) * t + 3.0 * a1) *
    t;
const subdivisionPrecision = 0.0000001;
const subdivisionMaxIterations = 12;
function binarySubdivide(x, lowerBound, upperBound, mX1, mX2) {
    let currentX;
    let currentT;
    let i = 0;
    do {
        currentT = lowerBound + (upperBound - lowerBound) / 2.0;
        currentX = calcBezier(currentT, mX1, mX2) - x;
        if (currentX > 0.0) {
            upperBound = currentT;
        }
        else {
            lowerBound = currentT;
        }
    } while (Math.abs(currentX) > subdivisionPrecision &&
        ++i < subdivisionMaxIterations);
    return currentT;
}
function cubicBezier(mX1, mY1, mX2, mY2) {
    // If this is a linear gradient, return linear easing
    if (mX1 === mY1 && mX2 === mY2)
        return noop.noop;
    const getTForX = (aX) => binarySubdivide(aX, 0, 1, mX1, mX2);
    // If animation is at start/end, return t without easing
    return (t) => t === 0 || t === 1 ? t : calcBezier(getTForX(t), mY1, mY2);
}

exports.cubicBezier = cubicBezier;
