import { isAsOfIncomplete } from '../utils/searchTruncation';
import { useEffect, useState, useCallback, useRef } from 'react';
import { usePatientServiceContext, useDiagnosticReportServiceContext } from '../services';

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

/**
 * THE RESULTS HALF OF *My Visits & Results* -.
 *
 * Deliberately the SAME SHAPE as its eleven siblings (`useFhirObservations`, `useFhirConditions`,...)
 * down to the `attempted` flag and its reasoning. The service and its provider have been mounted all
 * along; only the hook was missing, which is why the stream could carry visits and prescriptions and
 * not the results the screen is half named after.
 */

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

interface UseFhirDiagnosticReportsReturn {
    /** 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 would say
 * *"no results"* about a question nobody asked.
 * Only the hook knows which of the two it is in, so it reports it.
 */
    attempted: boolean;
    loadDiagnosticReports: () => Promise<void>;
    /** Re-reads past the cache without a loading state; a failure is reported like a load's. */
    refreshDiagnosticReports: () => Promise<void>;
    clearError: () => void;
    diagnosticReportsBundle: ReturnType<typeof useDiagnosticReportServiceContext>['diagnosticReportsBundle'];
    diagnosticReportsList: ReturnType<typeof useDiagnosticReportServiceContext>['diagnosticReportsList'];
}

export const useFhirDiagnosticReports = (
    options: UseFhirDiagnosticReportsOptions = {},
): UseFhirDiagnosticReportsReturn => {
    const {
        autoLoad = true,
        errorMessage = 'Failed to load results',
        forceReload = false
    } = options;

    const { patientState } = usePatientServiceContext();
    const {
        cachedForPatientId,
        fetchDiagnosticReportsWithPolling,
        diagnosticReportsBundle,
        diagnosticReportsList
    } = useDiagnosticReportServiceContext();

    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);
    // Whether this view has read the list since it opened, by a load or by the quiet re-read below.
    const readSinceOpened = useRef(false);

    const read = useCallback(async (quiet: boolean) => {
        if (!patientState) {
            return;
        }

        if (!quiet) {
            setLoading(true);
            setError(undefined);
            setRefused(false);
        }
        askingFor.current = patientState.id;

        try {
            await fetchDiagnosticReportsWithPolling(patientState, quiet);
            if (askingFor.current !== patientState.id) return;
            setError(undefined);
            setRefused(false);
        } catch (err) {
            if (askingFor.current !== patientState.id) return;
            console.error('Failed to load diagnostic reports:', err);
            setFailedFor(patientState.id);
            setRefused(isRefusedRead(err));
            setError(describeFetchFailure(err, errorMessage));
        } finally {
            if (!quiet && askingFor.current === patientState.id) setLoading(false);
        }
    }, [patientState, fetchDiagnosticReportsWithPolling, errorMessage]);
    const loadDiagnosticReports = useCallback(() => read(false), [read]);
    const refreshDiagnosticReports = useCallback(() => read(true), [read]);

    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 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 (!diagnosticReportsBundle || cachedForPatientId !== patientState.id || forceReload) {
            readSinceOpened.current = true;
            loadDiagnosticReports();
            return;
        }
        // A view opening on this patient's cached list re-reads it once, without a loading state, so a
        // result corrected since the list loaded shows the next time a results view opens.
        if (readSinceOpened.current) return;
        readSinceOpened.current = true;
        refreshDiagnosticReports();
    }, [autoLoad, patientState, diagnosticReportsBundle, cachedForPatientId, forceReload, loadDiagnosticReports, refreshDiagnosticReports]);

    // 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),
        loadDiagnosticReports,
        refreshDiagnosticReports,
        clearError,
        // Served as of a cutoff and not in full: what it left out is unknown, never none.
        incomplete: isAsOfIncomplete(guard.bundle(diagnosticReportsBundle, null)),
        diagnosticReportsBundle: guard.bundle(diagnosticReportsBundle, null),
        diagnosticReportsList: guard.list(diagnosticReportsList)
    };
};