charts/src/js/utils/draw-utils.js

import { fillArray } from './helpers';

export function getBarHeightAndYAttr(yTop, zeroLine) {
	let height, y;
	if (yTop <= zeroLine) {
		height = zeroLine - yTop;
		y = yTop;
	} else {
		height = yTop - zeroLine;
		y = zeroLine;
	}

	return [height, y];
}

export function equilizeNoOfElements(array1, array2,
	extraCount = array2.length - array1.length) {

	// Doesn't work if either has zero elements.
	if(extraCount > 0) {
		array1 = fillArray(array1, extraCount);
	} else {
		array2 = fillArray(array2, extraCount);
	}
	return [array1, array2];
}

export function truncateString(txt, len) {
	if (!txt) {
		return;
	}
	if (txt.length > len) {
		return txt.slice(0, len-3) + '...';
	} else {
		return txt;
	}
}

export function shortenLargeNumber(label) {
	let number;
	if (typeof label === 'number') number = label;
	else if (typeof label === 'string') {
		number = Number(label);
		if (Number.isNaN(number)) return label;
	}

	// Using absolute since log wont work for negative numbers
	let p = Math.floor(Math.log10(Math.abs(number)));
	if (p <= 2) return number; // Return as is for a 3 digit number of less
	let	l = Math.floor(p / 3);
	let shortened = (Math.pow(10, p - l * 3) * +(number / Math.pow(10, p)).toFixed(1));

	// Correct for floating point error upto 2 decimal places
	return Math.round(shortened*100)/100 + ' ' + ['', 'K', 'M', 'B', 'T'][l];
}

// cubic bezier curve calculation (from example by François Romain)
export function getSplineCurvePointsStr(xList, yList) {

	let points=[];
	for(let i=0;i<xList.length;i++){
		points.push([xList[i], yList[i]]);
	}

	let smoothing = 0.2;
	let line = (pointA, pointB) => {
		let lengthX = pointB[0] - pointA[0];
		let lengthY = pointB[1] - pointA[1];
		return {
			length: Math.sqrt(Math.pow(lengthX, 2) + Math.pow(lengthY, 2)),
			angle: Math.atan2(lengthY, lengthX)
		};
	};
    
	let controlPoint = (current, previous, next, reverse) => {
		let p = previous || current;
		let n = next || current;
		let o = line(p, n);
		let angle = o.angle + (reverse ? Math.PI : 0);
		let length = o.length * smoothing;
		let x = current[0] + Math.cos(angle) * length;
		let y = current[1] + Math.sin(angle) * length;
		return [x, y];
	};
    
	let bezierCommand = (point, i, a) => {
		let cps = controlPoint(a[i - 1], a[i - 2], point);
		let cpe = controlPoint(point, a[i - 1], a[i + 1], true);
		return `C ${cps[0]},${cps[1]} ${cpe[0]},${cpe[1]} ${point[0]},${point[1]}`;
	};
    
	let pointStr = (points, command) => {
		return points.reduce((acc, point, i, a) => i === 0
			? `${point[0]},${point[1]}`
			: `${acc} ${command(point, i, a)}`, '');
	};
    
	return pointStr(points, bezierCommand);
}