ResultAsync through methods

class ResultAsync<T, E> {
  andThrough<F>(
    f: (t: T) => Result<unknown, F> | ResultAsync<unknown, F>
  ): ResultAsync<T, E | F>
}

const result = await fetchUser(id)
  .andThrough(user => {
    if (user.age < 18) {
      return err('User must be 18 or older')
    }
    return ok(undefined)
  })
  .andThen(saveUser)

// Type: ResultAsync<User, FetchError | string | SaveError>
// Value is still User, not undefined

const processOrder = (order: Order) => {
  return okAsync(order)
    .andThrough(validatePaymentMethod)
    .andThrough(checkInventory)
    .andThrough(verifyAddress)
    .andThen(submitOrder)
}

// Each validation can fail, but order is preserved through the chain

const result = await createUser(data)
  .andThrough(async user => {
    // Send welcome email - must succeed
    return ResultAsync.fromPromise(
      sendEmail(user.email, 'Welcome!'),
      (e) => new Error('Failed to send welcome email')
    )
  })
  .andThen(user => okAsync(user.id))

// If email fails, whole chain fails
// If email succeeds, user object continues through chain

// andTee - logging that can't fail the operation
const teeResult = await okAsync(user)
  .andTee(user => logToAnalytics(user))  // Log error ignored
  .andThen(saveUser)
// Type: ResultAsync<User, SaveError>

// andThrough - validation that can fail the operation
const throughResult = await okAsync(user)
  .andThrough(user => validateUser(user))  // Validation error propagates
  .andThen(saveUser)
// Type: ResultAsync<User, ValidationError | SaveError>