How do I go about implementing circular interfaces with purify-ts?

[justinemmanuelmercado]

Specifically for this line, it needs a reference to itself.

https://github.com/ScaleLeap/amazon-mws-api-sdk/blob/ee978e0955a6b127d02e836d96b9a8f9a9f1c2dd/src/sections/products.ts#L142-L143

I've tried using lazy like this

import { lazy } from 'purify-ts'

//...

interface FeeDetail {
  FeeType: AvailableFeeTypes
  FeeAmount: MoneyType
  FeePromotion?: MoneyType
  TaxAmount?: MoneyType
  FinalFee: MoneyType
  IncludedFeeDetailList?: FeeDetail
}

const FeeDetail: Codec<FeeDetail> = Codec.interface({
  FeeType: oneOf(Object.values(FeeType).map((x) => exactly(x))),
  FeeAmount: MoneyType,
  FeePromotion: optional(MoneyType),
  TaxAmount: optional(MoneyType),
  FinalFee: MoneyType,
  IncludedFeeDetailList: optional(lazy(() => ensureArray('IncludedFeeDetail', FeeDetail))),
})

But typescript nags me about FeeDetail the interface not being equal to what's beeing calculated by Codec

Any help appreciated, @gigobyte

[gigobyte]

Try putting the lazy codec last:

IncludedFeeDetailList: optional(ensureArray('IncludedFeeDetail', lazy(() =>FeeDetail)))

[justinemmanuelmercado]

TS is complaining :/

Type 'Codec<{ FeeType: string; FeeAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; FeePromotion: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; TaxAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; FinalFee: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; IncludedFeeDetailList: FeeDetail[] | undefined; }>' is not assignable to type 'Codec<FeeDetail>'.
  The types returned by 'decode(...)' are incompatible between these types.
    Type 'Either<string, { FeeType: string; FeeAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; FeePromotion: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; TaxAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; FinalFee: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; IncludedFeeDetailList: FeeDetail[] | undefined; }>' is not assignable to type 'Either<string, FeeDetail>'.
      Type '{ FeeType: string; FeeAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; FeePromotion: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; TaxAmount: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; } | undefined; FinalFee: { Amount: number | undefined; CurrencyCode: CurrencyCodeEnum; }; IncludedFeeDetailList: FeeDetail[] | undefined; }' is not assignable to type 'FeeDetail'.ts(2322)

Any ideas? If none, it's probably alright as an unknown array. Since Amazon's own API doesn't seem to follow the docs itself. Thanks for the help!

[gigobyte]

Your interface is wrong though, it says IncludedFeeDetailList?: FeeDetail but the codec is IncludedFeeDetailList?: FeeDetail[], as mentioned in the error you posted. That is because of ensureArray.

[justinemmanuelmercado]

Ohh yeah you're right! I don't know why I didn't see that earlier.

TS still complained after though so I just copy pasted whatever was in the error and weirdly enough this is what worked for TS

interface FeeDetail {
  FeePromotion: MoneyType | undefined
  TaxAmount: MoneyType | undefined
  FinalFee: MoneyType
  FeeType: string
  FeeAmount: MoneyType
  IncludedFeeDetailList: FeeDetail[] | undefined
}

const FeeDetail: Codec<FeeDetail> = Codec.interface({
  FeeType: string,
  FeeAmount: MoneyType,
  FeePromotion: optional(MoneyType),
  TaxAmount: optional(MoneyType),
  FinalFee: MoneyType,
  IncludedFeeDetailList: optional(
    ensureArray(
      'IncludedFeeDetail',
      lazy(() => FeeDetail),
    ),
  ),
})

If I tried replacing TaxAmount: MoneyType | undefined with TaxAmount?: MoneyType TS complained that they weren't equal.

Here's the commit to the fix if you're interested https://github.com/ScaleLeap/amazon-mws-api-sdk/pull/45/commits/0ed9e9f7db0fd16dc9d6a4abefd18bb8b50e1713

Thank you for the help 👍