functor exercise 1

functorExercise1.js

public async isValidEndDateFantasy (offeringId: number, endDate: string) {
    // doLoadOffering :: number -> Promise(Either(AppError, Offering))
    const loadOffering = new Task((reject, result) => {
      this.Models.Offering.load(offeringId)
        .then((offering) => {
          if (isNil(offering)) {
            return reject(new AppError(`OfferingId ${offeringId} did not correspond to an offering`))
          }

          return result(offering)
        })
    })

    const isBefore = curry((dateA, dateB) => moment.utc(dateA).isBefore(dateB))

    // isBefore =
    const forgivingIsBefore = (dateA) => maybe(true, isBefore(dateA))

    // getAvailabilityEnd :: Offering -> Maybe(string)
    const getAvailabilityEnd = (offering) => {
      return Maybe.of(offering.availabilityEnd)
    }

    // getAvailabilityEndDate :: Offering -> Maybe(Date)
    const getAvailabilityEndDate = compose(
      moment.utc,
      getAvailabilityEnd
    )

    // doIt :: number -> Task(AppError, Offering) -> Maybe(Date) -> boolean
    const doIt = compose(
      forgivingIsBefore(dateA),
      map(getAvailabilityEndDate) ,
      loadOffering
    )

    return doIt(offering)
  }