@fractorysolutions/safe-units/src/measure/format.ts

Type-safe TypeScript units of measure

import {
  getExponentValue,
  negateExponent,
} from "../exponent/exponentValueArithmetic";
import { SymbolAndExponent, UnitWithSymbols } from "./unitTypeArithmetic";

export function defaultFormatUnit(unit: UnitWithSymbols): string {
  const dimensions = Object.keys(unit)
    .map((dimension) => unit[dimension])
    .filter(isDimensionPresent)
    .sort(orderDimensions);

  if (dimensions.length === 0) {
    return "";
  }

  const positive = dimensions.filter(([_, dim]) => getExponentValue(dim) > 0);
  const negative = dimensions.filter(([_, dim]) => getExponentValue(dim) < 0);

  if (positive.length === 0) {
    return formatDimensions(negative);
  }

  const numerator = formatDimensions(positive);
  if (negative.length === 0) {
    return numerator;
  }

  const denominator = formatDimensions(negative.map(negateDimension));
  return `${numerator} / ${maybeParenthesize(
    denominator,
    negative.length !== 1,
  )}`;
}

function isDimensionPresent(
  dimension: SymbolAndExponent | undefined,
): dimension is SymbolAndExponent {
  return dimension !== undefined && dimension[1] !== "0";
}

function orderDimensions(
  [leftSymbol]: SymbolAndExponent,
  [rightSymbol]: SymbolAndExponent,
): number {
  return leftSymbol < rightSymbol ? -1 : 1;
}

function formatDimensions(dimensions: SymbolAndExponent[]): string {
  return dimensions
    .map(([symbol, exponent]) => {
      const exponentStr = exponent !== "1" ? `^${exponent}` : "";
      return `${symbol}${exponentStr}`;
    })
    .join(" * ");
}

function negateDimension([
  symbol,
  exponent,
]: SymbolAndExponent): SymbolAndExponent {
  return [symbol, negateExponent(exponent)];
}

function maybeParenthesize(text: string, parenthesize: boolean): string {
  return parenthesize ? `(${text})` : text;
}