vega-lite/src/compile/mark/encode/scaledZeroOrMinOrMax.ts

Vega-Lite is a concise high-level language for interactive visualization.

import {VgValueRef} from '../../../vega.schema.js';
import {ScaleComponent} from '../../scale/component.js';

export interface ScaledZeroOrMinOrMaxProps {
  scaleName: string;
  scale: ScaleComponent;
  mode: 'zeroOrMin' | {zeroOrMax: {widthSignal: string; heightSignal: string}};
}

export function scaledZeroOrMinOrMax({scaleName, scale, mode}: ScaledZeroOrMinOrMaxProps): VgValueRef | undefined {
  const domain = `domain('${scaleName}')`;

  if (!scale || !scaleName) {
    return undefined;
  }
  const min = `${domain}[0]`;
  const max = `peek(${domain})`; // peek = the last item of the array

  // If there is a scale (and hence its name)
  const domainHasZero = scale.domainHasZero();
  // zeroOrMin or zeroOrMax mode
  if (domainHasZero === 'definitely') {
    return {
      scale: scaleName,
      value: 0,
    };
  } else if (domainHasZero === 'maybe') {
    const nonZeroValue = mode === 'zeroOrMin' ? min : max;
    return {signal: `scale('${scaleName}', inrange(0, ${domain}) ? 0 : ${nonZeroValue})`};
  } else {
    // domainHasZero === 'definitely-not'
    return {signal: `scale('${scaleName}', ${mode === 'zeroOrMin' ? min : max})`};
  }
}