import { useChartRecordStanding, useFreshAfterReauthorization, type RecordAccessStanding, type RecordFreshness } from './useRecordAccessStanding';
import { isAsOfIncomplete, isServedAtCutoff } from '../utils/searchTruncation';
import { useEffect, useState, useCallback, useRef } from 'react';
import { usePatientServiceContext, useMedicationRequestServiceContext } from '../services';

import { describeFetchFailure, isRefusedRead } from '../utils/fetchFailureMessage';
import { patientCacheGuard } from '../utils/cacheOwner';

interface UseFhirMedicationRequestsOptions {
    /** The record standing to answer to; the open chart's when not given. */
    standing?: RecordAccessStanding;
    autoLoad?: boolean;
    errorMessage?: string;
    forceReload?: boolean;
}

interface UseFhirMedicationRequestsReturn {
    /** After a reauthorization, whether this list has been read again under it. */
    freshness: RecordFreshness;
    /** Served as of a cutoff and not in full: what it left out is unknown, never none. */
    incomplete: boolean;
    loading: boolean;
    error: string | undefined;
    /** The last load was answered with a 403: refused, not lost. */
    refused: boolean;
    /** The error and refusal are this patient's read, not an earlier patient's. */
    failureIsThisPatients: boolean;
    /** The service's list is this patient's. Anything else is another patient's, never this one's data. */
    listIsThisPatients: boolean;
    /** This patient's read has answered, one way or the other. Until then an empty list is unknown. */
    answered: boolean;
    /**
 * WAS THE SERVER ACTUALLY ASKED? The effect early-returns when `patientState` is unresolved, so the
 * caller is left holding `loading: false` and `error: undefined` over an empty list - byte-identical to
 * a load that succeeded and found nothing. Only the hook knows which of the two it is in, so it reports
 * it. The four sibling hooks on the patient summary already did; this one did not, and that asymmetry
 * would have left medicines as the one section still able to claim None recorded about a question
 * nobody asked.
 */
    attempted: boolean;
    loadMedicationRequests: () => Promise<void>;
    clearError: () => void;
    medicationRequestsBundle: ReturnType<typeof useMedicationRequestServiceContext>['medicationRequestsBundle'];
    medicationRequestsList: ReturnType<typeof useMedicationRequestServiceContext>['medicationRequestsList'];
}

export const useFhirMedicationRequests = (options: UseFhirMedicationRequestsOptions = {}): UseFhirMedicationRequestsReturn => {
    const {
        autoLoad = true,
        errorMessage = "Failed to load medication requests",
        forceReload = false
    } = options;

    const { patientState } = usePatientServiceContext();
    const {
        fetchMedicationRequestsWithPolling,
        listRead,
        medicationRequestsBundle,
        medicationRequestsList,
        cachedForPatientId
    } = useMedicationRequestServiceContext();
    // After a reauthorization this list is read again past every cache; until then it is not taken for current.
    const chartStanding = useChartRecordStanding().standing;
    const freshness = useFreshAfterReauthorization(options.standing ?? chartStanding, () => (
        patientState ? fetchMedicationRequestsWithPolling(patientState, true) : Promise.reject(new Error('No patient to read.'))),
        { resource: 'MedicationRequest', patientId: patientState?.id, listRead, servedAtCutoff: isServedAtCutoff(medicationRequestsBundle) });

    const [loading, setLoading] = useState(false);
    const [error, setError] = useState<string | undefined>();
    const [refused, setRefused] = useState(false);
    const [failedFor, setFailedFor] = useState<string | undefined>();
    // The latest patient asked for; a slower read for an earlier patient must not write over it.
    const askingFor = useRef<string | undefined>(undefined);

    const loadMedicationRequests = useCallback(async () => {
        if (!patientState) {
            return;
        }

        setLoading(true);
        setError(undefined);
        setRefused(false);
        askingFor.current = patientState.id;

        try {
            await fetchMedicationRequestsWithPolling(patientState);
        } catch (err) {
            if (askingFor.current !== patientState.id) return;
            console.error('Failed to load medication requests:', err);
            setFailedFor(patientState.id);
            setRefused(isRefusedRead(err));
            setError(describeFetchFailure(err, errorMessage));
        } finally {
            if (askingFor.current === patientState.id) setLoading(false);
        }
    }, [patientState, fetchMedicationRequestsWithPolling, errorMessage]);

    const clearError = useCallback(() => {
        setError(undefined);
        setRefused(false);
    }, []);

    useEffect(() => {
        if (!autoLoad) return;
        if (!patientState) return;

        // A bundle belonging to SOMEBODY ELSE is not a reason not to ask. This used to fire only when
        // there was no bundle at all, so moving between two charts left the previous patient's
        // medication list in place, with no request and nothing on screen to say it was not theirs.
        // NOT a refetch on every navigation: same patient, bundle loaded, no request.
        if (!medicationRequestsBundle || cachedForPatientId !== patientState.id || forceReload) {
            loadMedicationRequests();
        }
    }, [autoLoad, patientState, medicationRequestsBundle, cachedForPatientId, forceReload, loadMedicationRequests]);

    // The cache outlives a change of patient: hand out only the patient asked about.
    const guard = patientCacheGuard(cachedForPatientId, patientState?.id);

    return {
        freshness,
        loading: guard.loading(loading, Boolean(error) || refused),
        error,
        refused,
        failureIsThisPatients: failedFor !== undefined && failedFor === patientState?.id,
        listIsThisPatients: cachedForPatientId !== undefined && cachedForPatientId === patientState?.id,
        answered: Boolean(error) || (Boolean(medicationRequestsBundle) && cachedForPatientId === patientState?.id),
        // Derived from the SAME condition the early returns above test, never tracked separately: a
        // hand-set flag goes stale the first time somebody adds a third reason to bail, and silently.
        attempted: Boolean(patientState),
        loadMedicationRequests,
        clearError,
        // Served as of a cutoff and not in full: what it left out is unknown, never none.
        incomplete: isAsOfIncomplete(guard.bundle(medicationRequestsBundle, null)),
        medicationRequestsBundle: guard.bundle(medicationRequestsBundle, null),
        medicationRequestsList: guard.list(medicationRequestsList)
    };
};