// What the billing overview may say about money still owed. A figure is only stated when every
// sent invoice, and every payment ledger that could reduce one, was actually read.
import type { Invoice, PaymentReconciliation } from 'fhir/r4';
import { readInvoiceAllowPartialPay, readInvoiceTotalCents } from '../../../utils/invoiceTransform';
import { remainingCents } from '../../../utils/paymentModel';
import { sumCents } from '../../../utils/money';
import { pastDue, pastDueWithRemaining } from './invoiceDisplay';

export type Ledgers = Map<string, PaymentReconciliation[] | 'unreadable'>;

export interface OutstandingSummary {
    // null when the issued set itself is incomplete: a truncated fetch makes a count that LOOKS whole
    // but is not, which is the same defect as a wrong dollar figure that looks read.
    sent: number | null;
    pastDue: number | null;
    // null when some part could not be read: an unknown balance is never shown as a number.
    outstandingCents: number | null;
}

/** Only an invoice that allows part payment can carry payments while still sent. */
export const needsLedger = (invoice: Invoice): boolean =>
    invoice.status === 'issued' && Boolean(invoice.id) && readInvoiceAllowPartialPay(invoice);

export function summarizeOutstanding(
    issued: Invoice[],
    ledgers: Ledgers,
    complete: boolean,
    today?: string,
): OutstandingSummary {
    let unknownAmount = !complete;
    let unknownPastDue = false;
    const remaining = issued.map((invoice) => {
        const amount = readInvoiceTotalCents(invoice);
        if (amount === null) {
            unknownAmount = true;
            if (pastDue(invoice, today)) unknownPastDue = true;
            return 0;
        }
        if (!needsLedger(invoice)) return amount;
        const ledger = ledgers.get(invoice.id as string);
        if (!ledger || ledger === 'unreadable') {
            unknownAmount = true;
            return amount;
        }
        return remainingCents(invoice, ledger);
    });
    return {
        sent: complete ? issued.length : null,
        pastDue: !complete || unknownPastDue
            ? null
            : issued.filter((invoice, index) => pastDueWithRemaining(invoice, remaining[index], today)).length,
        outstandingCents: unknownAmount ? null : sumCents(remaining),
    };
}