import type { Invoice, PaymentReconciliation } from 'fhir/r4';
import { invoiceTotalCents } from './invoiceTransform';

/** A payment ledger that could not be read in full: its payments are a subset, so nothing is worked out from them. */
export class IncompleteLedgerError extends Error {
    constructor() {
        super('The payments on this invoice could not be read in full.');
        this.name = 'IncompleteLedgerError';
    }
}

export const isIncompleteLedger = (error: unknown): boolean =>
    error instanceof IncompleteLedgerError || (error as { name?: unknown } | null)?.name === 'IncompleteLedgerError';

// Pure, React/HTTP-free model deriving paid/remaining/partial-payment state from an invoice's
// PaymentReconciliation ledger (server: GET /R4/PaymentReconciliation?invoice=<id>). Kept dependency-free
// (no services import) so it unit-tests in isolation and is reusable by any invoice surface (list, detail,
// pay UI) without dragging in HTTP.

/** Sum of every payment's `paymentAmount.value`, in integer cents. A missing paymentAmount counts as 0. */
export const paidCents = (recs: PaymentReconciliation[]): number =>
    Math.round(recs.reduce((total, rec) => total + (rec.paymentAmount?.value ?? 0), 0) * 100);

/** Frozen invoice total minus paid-to-date, in integer cents. Never negative (an overpay clamps to 0). */
export const remainingCents = (invoice: Invoice, recs: PaymentReconciliation[]): number =>
    Math.max(0, invoiceTotalCents(invoice) - paidCents(recs));

// Partial-paid is only meaningful for an ISSUED invoice with money down but not fully covered - a draft
// or balanced (fully paid/settled some other way) invoice is never "partially paid", regardless of what
// its ledger shows.
export const isPartiallyPaid = (invoice: Invoice, recs: PaymentReconciliation[]): boolean =>
    invoice.status === 'issued' && paidCents(recs) > 0 && remainingCents(invoice, recs) > 0;

export interface PaymentHistoryEntry {
    dateISO: string;
    amountCents: number;
}

/** Maps the ledger to a display-ready history, most-recent-first. Prefers `created`, falls back to `paymentDate`. */
export const paymentHistory = (recs: PaymentReconciliation[]): PaymentHistoryEntry[] =>
    recs
        .map((rec) => ({
            dateISO: rec.created ?? rec.paymentDate ?? '',
            amountCents: Math.round((rec.paymentAmount?.value ?? 0) * 100),
        }))
        .sort((a, b) => (a.dateISO < b.dateISO ? 1 : a.dateISO > b.dateISO ? -1 : 0));