import { useEffect, useState } from 'react';
import type { Invoice } from 'fhir/r4';
import { usePatientServiceContext } from '../../../services';
import { formatFhirHumanName } from '../../../utils/fhirHumanName';
import { UNREADABLE_BILL_FIELD } from './invoiceDisplay';

const subjectId = (invoice: Invoice) => invoice.subject?.reference?.split('/')[1];

export const useInvoicePatientNames = (invoices: Invoice[]): Record<string, string> => {
    const { patientList, fetchPatient } = usePatientServiceContext();
    const [fetched, setFetched] = useState<Record<string, string>>({});
    const [failed, setFailed] = useState<Record<string, true>>({});

    const names: Record<string, string> = {};
    for (const invoice of invoices) {
        const id = subjectId(invoice);
        const frozen = invoice.subject?.display?.trim();
        if (id && frozen) names[id] = frozen;
    }
    const ids = [...new Set(invoices.map(subjectId).filter((id): id is string => Boolean(id)))];
    for (const patient of patientList) {
        const name = patient.id && ids.includes(patient.id) ? formatFhirHumanName(patient.name, { emptyText: '' }) : '';
        if (name) names[patient.id as string] = name;
    }
    for (const id of ids) {
        if (!names[id] && fetched[id]) names[id] = fetched[id];
        if (!names[id] && failed[id]) names[id] = UNREADABLE_BILL_FIELD;
    }

    useEffect(() => {
        let cancelled = false;
        const dropGone = <T extends Record<string, unknown>>(prev: T): T => {
            const extra = Object.keys(prev).filter((id) => !ids.includes(id));
            if (extra.length === 0) return prev;
            const next = { ...prev };
            for (const id of extra) delete next[id];
            return next as T;
        };
        setFetched(dropGone);
        setFailed(dropGone);
        const missing = ids.filter((id) => !names[id] && !failed[id] && !fetched[id]);
        if (missing.length === 0 || typeof fetchPatient !== 'function') return;
        void Promise.all(missing.map(async (id) => {
            try {
                const patient = await fetchPatient(id);
                const name = formatFhirHumanName(patient.name, { emptyText: '' });
                if (cancelled) return;
                if (name) setFetched((prev) => (prev[id] ? prev : { ...prev, [id]: name }));
                else setFailed((prev) => (prev[id] ? prev : { ...prev, [id]: true }));
            } catch {
                if (!cancelled) setFailed((prev) => (prev[id] ? prev : { ...prev, [id]: true }));
            }
        }));
        return () => { cancelled = true; };
    }, [ids.join(','), fetchPatient]);

    return names;
};

export const invoiceSubjectId = subjectId;