10.4_ReplaceConditionalWithPolymorphism_refactring.ts

/**
 * 第一步：函数组合成类
 */
function rating(voyage, history) {
  return createRating(voyage, history).value;
}

class Rating {
  _voyage;
  _history;

  constructor(voyage, history) {
    this._voyage = voyage;
    this._history = history;
  }

  get value() {
    const vpf = this.voyageProfitFactor;
    const vr = this.voyageRisk;
    const chr = this.captainHistoryRisk;
    if (vpf * 3 > vr + chr * 2) return 'A';
    else return 'B';
  }

  get voyageRisk() {
    let result = 1;
    if (this._voyage.length > 4) result += 4;
    if (this._voyage.length > 8) result += this._voyage.length - 8;
    if (this.isSpecialZone) result += 4;
    return Math.max(result, 0);
  }

  get captainHistoryRisk() {
    let result = 1;
    if (this._history.length < 5) result += 4;
    result += this._history.filter((v) => v.profit < 0).length;
    return Math.max(result, 0);
  }

  get voyageProfitFactor() {
    let result = 2;
    if (this.isSpecialZone) result += 1;
    result += this.historyLengthFactor;
    result += this.voyageLengthFactor;
    return result;
  }

  get voyageLengthFactor(): number{
    return this._voyage.length > 14 ? -1 : 0;
  }

  get historyLengthFactor() {
    return this._history.length > 8 ? 1 : 0;
  }

  get isSpecialZone() {
    return ['china', 'east-indies'].includes(this._voyage.zone);
  }
}

class ExperiencedChinaRating extends Rating {
  get captainHistoryRisk() {
    const result = super.captainHistoryRisk - 2;
    return Math.max(result, 0);
  }

  get voyageLengthFactor() {
    let result = 0;
    if (this._voyage.length > 12) result += 1;
    if (this._voyage.length > 18) result -= 1;
    return result;
  }

  get historyLengthFactor() {
    return this._history.length > 10 ? 1 : 0;
  }

  get voyageProfitFactor() {
    return super.voyageProfitFactor + 3;
  }
}

function createRating(voyage, history) {
  if (voyage.zone === 'china' && history.some((v) => 'china' === v.zone))
    return new ExperiencedChinaRating(voyage, history);
  else return new Rating(voyage, history);
}