import { useEffect, useState, useCallback } from 'react';
import { usePatientServiceContext, useDeviceServiceContext } from '../services';

import { describeFetchFailure } from '../utils/fetchFailureMessage';

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

interface UseFhirDevicesReturn {
    loading: boolean;
    error: string | undefined;
    loadDevices: () => Promise<void>;
    clearError: () => void;
    /** This patient's read has answered, one way or the other. Until then an empty list is unknown. */
    answered: boolean;
    /** The read could be asked at all: there is a patient to ask about. */
    attempted: boolean;
    devicesBundle: ReturnType<typeof useDeviceServiceContext>['devicesBundle'];
    devicesList: ReturnType<typeof useDeviceServiceContext>['devicesList'];
}

export const useFhirDevices = (options: UseFhirDevicesOptions = {}): UseFhirDevicesReturn => {
    const {
        autoLoad = true,
        errorMessage = "Failed to load devices",
        forceReload = false
    } = options;

    const { patientState } = usePatientServiceContext();
    const {
        cachedForPatientId,
        fetchDevicesWithPolling,
        devicesBundle,
        devicesList
    } = useDeviceServiceContext();

    const [loading, setLoading] = useState(false);
    const [error, setError] = useState<string | undefined>();

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

        setLoading(true);
        setError(undefined);

        try {
            await fetchDevicesWithPolling(patientState);
        } catch (err) {
            console.error('Failed to load devices:', err);
            setError(describeFetchFailure(err, errorMessage));
        } finally {
            setLoading(false);
        }
    }, [patientState, fetchDevicesWithPolling, errorMessage]);

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

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

    return {
        loading,
        error,
        loadDevices,
        clearError,
        answered: Boolean(error) || (Boolean(devicesBundle) && cachedForPatientId === patientState?.id),
        attempted: Boolean(patientState),
        devicesBundle,
        devicesList
    };
};