import { useEffect } from 'react';
import { Observation } from 'fhir/r4';
import {
    useObservationServiceContext,
    useFhirServiceContext,
    usePatientServiceContext,
    useWebSocketServiceContext
} from '../services';
import { isArchived } from '../utils/archivedResource';
import { useNoticeFence } from './useNoticeFence';

export const useFhirObservationBroadcast = () => {
    const { subscribe, unsubscribe } = useWebSocketServiceContext();
    const { observationsList, setObservationsList, fetchObservation } = useObservationServiceContext();
    const { patientState } = usePatientServiceContext();
    const { extractReferenceId } = useFhirServiceContext();
    const fence = useNoticeFence(patientState?.id);

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

        const handleObservationEvent = (cloudEvent: any) => {
            const observation: Observation = cloudEvent.data;
            const eventType = cloudEvent.type;
            const patientId = extractReferenceId(observation.subject);

            // The patient's own channel names which result changed and nothing of it: what may be shown is read
            // again through the gated GET, and a result that read no longer returns leaves the list.
            // Every event about a result retires a reread still pending for it, and so does a change of patient.
            const stands = patientState.id === patientId && observation.id ? fence.claim(observation.id) : () => false;
            if (patientState.id === patientId && cloudEvent.data?.invalidated === true && observation.id) {
                const id = observation.id;
                if (eventType === 'com.akashichealthrecords.fhir.observation.deleted') {
                    setObservationsList(prev => prev.filter(p => p.id !== id));
                    return;
                }
                fetchObservation(id, true)
                    .then((fresh) => {
                        if (!stands()) return;
                        setObservationsList(prev => (isArchived(fresh)
                            ? prev.filter(p => p.id !== id)
                            : prev.some(p => p.id === id) ? prev.map(p => p.id === id ? fresh : p) : [...prev, fresh]));
                    })
                    .catch(() => {
                        if (stands()) setObservationsList(prev => prev.filter(p => p.id !== id));
                    });
                return;
            }

            if (patientState.id === patientId) {
                switch (eventType) {
                    case 'com.akashichealthrecords.fhir.observation.created':
                        // The list has two writers: this broadcast, and the service's own refetch after a write
                        // (several of which POLL until the new id appears). Refetch first and the list already holds
                        // the record, so an unconditional append put a SECOND copy of it on screen - observed on a
                        // patient's questionnaire answers, where one submission rendered as two completed forms.
                        // Keeping the broadcast's copy rather than skipping: its body is at least as fresh.
                        setObservationsList(prev =>
                            prev.some(p => p.id === observation.id)
                                ? prev.map(p => p.id === observation.id ? observation : p)
                                : [...prev, observation]
                        );
                        break;
                    case 'com.akashichealthrecords.fhir.observation.updated':
                        setObservationsList(prev =>
                            isArchived(observation)
                                ? prev.filter(p => p.id !== observation.id)
                                : prev.map(p => p.id === observation.id ? observation : p)
                        );
                        break;
                    case 'com.akashichealthrecords.fhir.observation.deleted':
                        setObservationsList(prev => prev.filter(p => p.id !== observation.id));
                        break;
                }
            }
        };

        subscribe('com.akashichealthrecords.fhir.observation.created', handleObservationEvent);
        subscribe('com.akashichealthrecords.fhir.observation.updated', handleObservationEvent);
        subscribe('com.akashichealthrecords.fhir.observation.deleted', handleObservationEvent);

        return () => {
            unsubscribe('com.akashichealthrecords.fhir.observation.created', handleObservationEvent);
            unsubscribe('com.akashichealthrecords.fhir.observation.updated', handleObservationEvent);
            unsubscribe('com.akashichealthrecords.fhir.observation.deleted', handleObservationEvent);
        };
    }, [patientState, subscribe, unsubscribe, extractReferenceId, observationsList, setObservationsList, fetchObservation, fence]);
};