/** Serializable representation of a ratio. */
export type RatioData = [numerator: number, denominator: number];

/** Representation of a ratio for performing fractional artithmetic. */
export default class Ratio {
  readonly #numerator: number;
  readonly #denominator: number;

  get numerator(): number {
    return this.#numerator;
  }

  get denominator(): number {
    return this.#denominator;
  }

  constructor(numerator: number, denominator: number) {
    if (!Number.isInteger(numerator) || !Number.isInteger(denominator)) {
      throw new TypeError(
        `Ratio must have integer parts: ${numerator} / ${denominator}`,
      );
    }

    if (denominator === 0) {
      throw new RangeError("Ratio demnominator cannot be zero");
    }

    this.#numerator = numerator;
    this.#denominator = denominator;
  }

  multiplyRatio(other: Ratio): Ratio {
    return new Ratio(
      this.numerator * other.numerator,
      this.denominator * other.denominator,
    );
  }

  divideRatio(other: Ratio): Ratio {
    return new Ratio(
      this.numerator * other.denominator,
      this.denominator * other.numerator,
    );
  }

  add(other: Ratio): Ratio {
    return new Ratio(
      this.numerator * other.denominator + other.numerator * this.denominator,
      this.denominator * other.denominator,
    );
  }

  subtract(other: Ratio): Ratio {
    return new Ratio(
      this.numerator * other.denominator - other.numerator * this.denominator,
      this.denominator * other.denominator,
    );
  }

  compare(other: Ratio): number {
    const left = this.numerator * other.denominator;
    const right = other.numerator * this.denominator;
    return left < right ? -1 : left > right ? 1 : 0;
  }

  toNumber(): number {
    return this.numerator / this.denominator;
  }

  static fromInteger(n: number): Ratio {
    return new Ratio(n, 1);
  }

  toData(): RatioData {
    return [this.numerator, this.denominator];
  }

  static fromData(ratio: RatioData): Ratio {
    return new Ratio(ratio[0], ratio[1]);
  }
}