Dependency Inversion Example

gistfile1.ts

type IApplicableFeeMap = Map<string, IApplicableFee>

class ApplicableFeesCooridinator {
  protected applicableFees: IApplicableFee[]

  constructor(protected Models: IModels, prices: IOfferingPriceDerivedBase[]) {
    ...
    this.applicableFees = this.generateApplicableFees(prices)
  }

  public isApplicable(fee: IFeeDerived, price: IOfferingPriceDerivedBase): boolean {
    const result = _.filter(
      this.applicableFees,
      (applicableFee) => applicableFee.feeId === fee.feeId && applicableFee.sourceOfferingId === price.offeringId
    )
    return result.length > 0
  }

  private generateApplicableFees(prices: IOfferingPriceDerivedBase[]): IApplicableFee[] {
    ...
    return Array.from(applicableFeesMap.values())
  }

  private isFeeAlwaysApplied(fee: IFeeDerived): boolean {
    return (
      fee.feeTypeId === this.Models.FeeType.ID.OTHER && !fee.isAppliedOnce
    ) || (
      fee.feeTypeId !== this.Models.FeeType.ID.OTHER &&
      fee.feeType.feeTypeApplicableRuleTypeId === this.Models.FeeTypeApplicableRuleType.ID.APPLY_ALL
    )
  }

  private isFeeApplyLowest(fee: IFeeDerived): boolean {
    return fee.feeType.feeTypeApplicableRuleTypeId === this.Models.FeeTypeApplicableRuleType.ID.APPLY_LOWEST
  }

  private generateApplicableFeeHash (fee: IFeeDerived, offeringId: number) {
    if (fee.feeTypeId === this.Models.FeeType.ID.OTHER)
      return `applyOncePerFee?feeId=${fee.feeId}`  // only one fee should be included
    else
      ...
    }
}

export default class FeePriceCalculator {
  protected className: string

  constructor(protected Connectors: IConnectors, protected Models: IModels, protected useMaster: boolean) {
    this.className = this.constructor.name
  }

  public mutatingReapplyFeesAndFeeDiscounts(prices: IOfferingPriceDerivedBase[]) {
    const applicableFeesCoordinator = new ApplicableFeesCooridinator(this.Models, prices)
    ...
    
    _.forEach(prices, (price) => {
      // mutate fees
      price.fees = _.filter(price.fees, (fee) => applicableFeesCoordinator.isApplicable(fee, price))

      ...
    })
  }
}