def _report(self, posts: AccrualPostings, index: int) -> Iterable[str]:

        meta = posts[0].meta

        date_s = meta.date.strftime('%Y-%m-%d')

        entity_s = meta.get('entity', '<no entity>')

        invoice_s = meta.get('invoice', '<no invoice>')

        balance_s = posts.balance_at_cost().format(zero="Zero balance")

        if index:

            yield ""

        yield f"{entity_s} {invoice_s}:"

        yield f"  {balance_s} outstanding since {date_s}"

class OutgoingReport(BaseReport):

    class PaymentMethods(enum.Enum):

        ach = 'ACH'

        check = 'Check'

        creditcard = 'Credit Card'

        debitcard = 'Debit Card'

        paypal = 'PayPal'

        vendorportal = 'Vendor Portal'

        wire = 'Wire'

        fxwire = wire

        uswire = wire

    def __init__(self, rt_wrapper: rtutil.RT, out_file: TextIO) -> None:

        super().__init__(out_file)

        self.rt_wrapper = rt_wrapper

        self.rt_client = rt_wrapper.rt

    def _primary_rt_id(self, posts: AccrualPostings) -> rtutil.TicketAttachmentIds:

        rt_ids = posts.first_meta_links('rt-id')

        rt_id = next(rt_ids, None)

        rt_id2 = next(rt_ids, None)

        if rt_id is None:

            raise ValueError("no rt-id links found")

        elif rt_id2 is not None:

            raise ValueError("multiple rt-id links found")

        parsed = rtutil.RT.parse(rt_id)

        if parsed is None:

            raise ValueError("rt-id is not a valid RT reference")

        else:

            return parsed

    def _get_payment_method(self, posts: AccrualPostings, ticket_id: str) -> Optional[str]:

        payment_methods = posts.meta_values('payment-method')

        payment_methods.discard(None)

        if all(isinstance(s, str) for s in payment_methods):

            payment_methods = {s.strip().lower() for s in payment_methods}  # type:ignore[union-attr]

        log_prefix = f"cannot set payment-method for rt:{ticket_id}:"

        payment_method_count = len(payment_methods)

        if payment_method_count != 1:

            self.logger.warning("%s %s metadata values found",

                                log_prefix, payment_method_count)

            return None

        payment_method = payment_methods.pop()

        if not isinstance(payment_method, str):

            self.logger.warning("%s %r is not a string value",

                                log_prefix, payment_method)

            return None

        try:

            currency, method_key = payment_method.split(None, 1)

        except ValueError:

            self.logger.warning("%s no method specified in %r",

                                log_prefix, payment_method)

            return None

        curr_match = re.fullmatch(r'[a-z]{3}', currency)

        if curr_match is None:

            self.logger.warning("%s invalid currency %r",

                                log_prefix, currency)

        try:

            method_enum = self.PaymentMethods[method_key]

        except KeyError:

            self.logger.warning("%s invalid method %r",

                                log_prefix, method_key)

            curr_match = None

        if curr_match is None:

            return None

        else:

            return f'{currency.upper()} {method_enum.value}'

    def _report(self, posts: AccrualPostings, index: int) -> Iterable[str]:

        try:

            ticket_id, _ = self._primary_rt_id(posts)

            ticket = self.rt_client.get_ticket(ticket_id)

            # Note we only use this when ticket is None.

            errmsg = f"ticket {ticket_id} not found"

        except (ValueError, rt.RtError) as error:

            ticket = None

            errmsg = error.args[0]

        if ticket is None:

            meta = posts[0].meta

            self.logger.error(

                "can't generate outgoings report for %s %s %s because no RT ticket available: %s",

                meta.date.isoformat(),

                meta.get('entity', '<no entity>'),