import { isAsOfIncomplete } from '../utils/searchTruncation';
import { useEffect, useState, useCallback, useRef } from 'react';
import { usePatientServiceContext, useEncounterServiceContext, useFhirServiceContext } from '../services';
import { Encounter, Bundle } from 'fhir/r4';

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

interface UseFhirEncountersOptions {
    autoLoad?: boolean;
    errorMessage?: string;
    forceReload?: boolean;
}

interface UseFhirEncountersReturn {
    /** 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;
    /**
 * - was the server actually asked?
 *
 * This hook early-returns while `patientState` is unresolved, so `setLoading(true)` never runs and
 * the effect never fires. The caller is then holding `loading: false` - `error: undefined` - an
 * empty list - **indistinguishable from a load that succeeded and found nothing** - and
 * `ResourceListStatus` says *"No X found."* about a question nobody asked.
 * Only the hook knows which of the two it is in, so it reports it.
 */
    attempted: boolean;
    loadEncounters: () => Promise<void>;
    clearError: () => void;
    encountersBundle: ReturnType<typeof useEncounterServiceContext>['encountersBundle'];
    encountersList: ReturnType<typeof useEncounterServiceContext>['encountersList'];
    tempEncountersBundle: Bundle<Encounter> | null;
    tempEncountersList: Encounter[];
    loadTempEncounters: () => Promise<void>;
    clearTempEncounters: () => void;
}

export const useFhirEncounters = (options: UseFhirEncountersOptions = {}): UseFhirEncountersReturn => {
    const {
        autoLoad = true,
        errorMessage = 'Failed to load encounters',
        forceReload = false
    } = options;

    const { patientState, tempPatientState } = usePatientServiceContext();
    const {
        cachedForPatientId,
        fetchEncountersWithPolling,
        fetchEncounters,
        encountersBundle,
        encountersList
    } = useEncounterServiceContext();
    const { unpackBundle } = useFhirServiceContext();

    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 [tempEncountersBundle, setTempEncountersBundle] = useState<Bundle<Encounter> | null>(null);
    const [tempEncountersList, setTempEncountersList] = useState<Encounter[]>([]);

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

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

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

    const loadTempEncounters = useCallback(async () => {
        if (!tempPatientState) {
            return;
        }

        setLoading(true);
        setError(undefined);

        try {
            const bundle = await fetchEncounters({ patient: tempPatientState });

            setTempEncountersBundle(bundle);
            setTempEncountersList(unpackBundle(bundle));
        } catch (err) {
            console.error('Failed to load encounters:', err);
            setError(describeFetchFailure(err, `${errorMessage} for selected patient`));
        } finally {
            setLoading(false);
        }
    }, [tempPatientState, fetchEncounters, unpackBundle, errorMessage]);

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

    const clearTempEncounters = useCallback(() => {
        setTempEncountersBundle(null);
        setTempEncountersList([]);
    }, []);

    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 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 (!encountersBundle || cachedForPatientId !== patientState.id || forceReload) {
            loadEncounters();
        }
    }, [autoLoad, patientState, encountersBundle, cachedForPatientId, forceReload, loadEncounters]);

    useEffect(() => {
        if (tempPatientState) {
            loadTempEncounters();
        } else {
            clearTempEncounters();
        }
    }, [tempPatientState, loadTempEncounters, clearTempEncounters]);

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

    return {
        loading: guard.loading(loading, Boolean(error) || refused),
        error,
        refused,
        failureIsThisPatients: failedFor !== undefined && failedFor === patientState?.id,
        listIsThisPatients: cachedForPatientId !== undefined && 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),
        loadEncounters,
        clearError,
        // Served as of a cutoff and not in full: what it left out is unknown, never none.
        incomplete: isAsOfIncomplete(guard.bundle(encountersBundle, null)),
        encountersBundle: guard.bundle(encountersBundle, null),
        encountersList: guard.list(encountersList),
        tempEncountersBundle,
        tempEncountersList,
        loadTempEncounters,
        clearTempEncounters
    };
};