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

Type-safe TypeScript units of measure

import { Exponent, PositiveExponent } from "../exponent";
import {
  addExponents,
  divideExponents,
  multiplyExponents,
} from "../exponent/exponentValueArithmetic";
import {
  AllowedExponents,
  DivideUnits,
  DivisorUnit,
  ExponentiateUnit,
  MultiplicandUnit,
  MultiplyUnits,
  NthRootUnit,
  RadicandUnit,
  SymbolAndExponent,
  Unit,
  UnitWithSymbols,
} from "./unitTypeArithmetic";

export function dimension<Dim extends string>(
  dim: Dim,
  symbol?: string,
): UnitWithSymbols<{ [D in Dim]: "1" }> {
  return { [dim]: [symbol || dim, "1"] } as any;
}

export function multiplyUnits<L extends Unit, R extends MultiplicandUnit<L>>(
  left: UnitWithSymbols<L>,
  right: UnitWithSymbols<R>,
): UnitWithSymbols<MultiplyUnits<L, R>> {
  const result: UnitWithSymbols = {};
  for (const dimension in left) {
    const symbolAndExponent = copySymbolAndExponent(left, dimension);
    if (symbolAndExponent !== undefined && symbolAndExponent[1] !== "0") {
      result[dimension] = symbolAndExponent;
    }
  }
  for (const dimension in right) {
    const symbolAndExponent = copySymbolAndExponent(right, dimension);
    if (symbolAndExponent === undefined) {
      continue;
    }
    const [, exponent] = symbolAndExponent;
    const resultValue: SymbolAndExponent | undefined = result[dimension];
    if (resultValue !== undefined) {
      const newExponent = addExponents(resultValue[1], exponent);
      if (newExponent === "0") {
        delete result[dimension];
      } else {
        resultValue[1] = newExponent;
      }
    } else if (exponent !== "0") {
      result[dimension] = symbolAndExponent;
    }
  }
  return result as any;
}

function copySymbolAndExponent(
  unit: UnitWithSymbols,
  dimension: string,
): SymbolAndExponent | undefined {
  const result = unit[dimension];
  if (result === undefined) {
    return undefined;
  }
  const [symbol, exponent] = result;
  return [symbol, exponent];
}

export function divideUnits<L extends Unit, R extends DivisorUnit<L>>(
  left: UnitWithSymbols<L>,
  right: UnitWithSymbols<R>,
): UnitWithSymbols<DivideUnits<L, R>> {
  const rightInverse = exponentiateUnit(right, "-1") as any;
  return multiplyUnits(left, rightInverse) as any;
}

export function exponentiateUnit<U extends Unit, N extends AllowedExponents<U>>(
  unit: UnitWithSymbols<U>,
  power: N,
): UnitWithSymbols<ExponentiateUnit<U, N>> {
  return expAndRootImpl(unit, (exponent) => multiplyExponents(exponent, power));
}

export function nthRootUnit<
  U extends RadicandUnit<N>,
  N extends PositiveExponent,
>(unit: UnitWithSymbols<U>, root: N): UnitWithSymbols<NthRootUnit<U, N>> {
  return expAndRootImpl(unit, (exponent) => divideExponents(exponent, root));
}

function expAndRootImpl(
  unit: UnitWithSymbols,
  updateExponent: (exp: Exponent) => Exponent,
): any {
  const result: UnitWithSymbols = {};
  for (const dimension in unit) {
    const symbolAndExponent = unit[dimension];
    if (symbolAndExponent === undefined) {
      continue;
    }
    const [symbol, exponent] = symbolAndExponent;
    const newExponent = updateExponent(exponent);
    if (newExponent !== "0") {
      result[dimension] = [symbol, newExponent];
    }
  }
  return result;
}