postcss-calc/src/lib/simplify/fold.js

PostCSS plugin to reduce calc()

import { num, dim } from '../node.js';
import { baseOf, convert } from '../convertUnits.js';

/** @typedef {import('../node.js').Node} Node */
/** @typedef {import('../node.js').Num} Num */
/** @typedef {import('../node.js').Dim} Dim */
/** @typedef {import('../convertUnits.js').BaseType} BaseType */

/**
 * Construct a Num or Dim node from a folded result.
 * @param {{ unit: string }} fold
 * @param {number} value
 * @return {Num | Dim}
 */
function foldResult(fold, value) {
  return fold.unit === '' ? num(value) : dim(value, fold.unit);
}

/**
 * Return the argument that produced a folded min/max/clamp value, so the
 * result keeps its own unit, spelling and zero sign. Falls back to a fresh
 * node when no argument matches (NaN).
 * @param {Node[]} args
 * @param {{ values: number[], unit: string }} fold
 * @param {number} value
 * @return {Node}
 */
function chosenArg(args, fold, value) {
  const index = fold.values.findIndex((v) => Object.is(v, value));
  return index === -1 ? foldResult(fold, value) : args[index];
}

/**
 * @param {Node[]} args
 * @return {{ values: number[], unit: string } | null}
 */
function foldConstArgs(args) {
  if (args.length === 0) {
    return null;
  }

  const first = args[0];
  if (first.type === 'Num') {
    return foldNumberArgs(args);
  }
  if (first.type === 'Dim') {
    const b = first.unit === '%' ? null : baseOf(first.unit);
    if (!b) {
      return null;
    }
    return foldDimArgs(args, first.unit, b);
  }
  return null;
}

/**
 * @param {Node[]} args
 * @return {{ values: number[], unit: '' } | null}
 */
function foldNumberArgs(args) {
  /** @type {number[]} */ const values = [];
  for (const a of args) {
    if (a.type !== 'Num') {
      return null;
    }
    values.push(a.value);
  }
  return { values, unit: '' };
}

/**
 * @param {Node[]} args
 * @param {string} unit
 * @param {BaseType} base
 * @return {{ values: number[], unit: string } | null}
 */
function foldDimArgs(args, unit, base) {
  /** @type {number[]} */ const values = [];
  for (const a of args) {
    if (a.type !== 'Dim' || a.unit === '%' || baseOf(a.unit) !== base) {
      return null;
    }
    const converted = convert(a.value, a.unit, unit);
    if (converted === null) {
      return null;
    }
    values.push(converted);
  }
  return { values, unit };
}

export { foldConstArgs, foldResult, chosenArg };