import { useEffect } from 'react';
import { AllergyIntolerance } from 'fhir/r4';
import {
    useAllergyIntoleranceServiceContext,
    useFhirServiceContext,
    usePatientServiceContext,
    useWebSocketServiceContext
} from '../services';
import { isArchived } from '../utils/archivedResource';
import { olderThan } from '../utils/versionOrder';

export const useFhirAllergyIntoleranceBroadcast = () => {
    const { subscribe, unsubscribe } = useWebSocketServiceContext();
    const { setAllergyIntolerancesList, allergyFloor } = useAllergyIntoleranceServiceContext();
    const { patientState } = usePatientServiceContext();
    const { extractReferenceId } = useFhirServiceContext();
    // THE NEWEST VERSION KNOWN OF EACH RECORD, KEPT THROUGH ITS REMOVAL - the service's, per patient, so its own answers
    // (an archive or delete acknowledged before its event) and these events both count. Without it a delayed older
    // event (the create echo, an earlier update) would put a removed row back.

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

        const handleAllergyIntoleranceEvent = (cloudEvent: any) => {
            const allergyIntolerance: AllergyIntolerance = cloudEvent.data;
            // A deleted record does not come back, and nothing older than what is known of it is published.
            if (!allergyFloor.admits(allergyIntolerance)) return;
            if (cloudEvent.type === 'com.akashichealthrecords.fhir.allergyintolerance.deleted') allergyFloor.remove(allergyIntolerance, true);
            else if (isArchived(allergyIntolerance)) allergyFloor.remove(allergyIntolerance);
            else allergyFloor.learn(allergyIntolerance);
            // EVENTS CAN ARRIVE OUT OF ORDER. One older than the version the list holds (a delayed v4 after v5) is not
            // published - not as the row, and not as the archive that removes it - so an editor opening from the list
            // never starts from an older record than one already seen.
            const newest = (held: AllergyIntolerance) => (olderThan(allergyIntolerance, held) ? held : allergyIntolerance);
            const olderThanHeld = (list: AllergyIntolerance[]) =>
                list.some((held) => held.id === allergyIntolerance.id && olderThan(allergyIntolerance, held));
            const eventType = cloudEvent.type;
            const patientId = extractReferenceId(allergyIntolerance.patient);

            if (patientState.id === patientId) {
                switch (eventType) {
                    case 'com.akashichealthrecords.fhir.allergyintolerance.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.
                        setAllergyIntolerancesList(prev =>
                            prev.some(p => p.id === allergyIntolerance.id)
                                ? prev.map(p => p.id === allergyIntolerance.id ? newest(p) : p)
                                : [...prev, allergyIntolerance]
                        );
                        break;
                    case 'com.akashichealthrecords.fhir.allergyintolerance.updated':
                        setAllergyIntolerancesList(prev =>
                            olderThanHeld(prev)
                                ? prev
                                : isArchived(allergyIntolerance)
                                    ? prev.filter(p => p.id !== allergyIntolerance.id)
                                    : prev.map(p => p.id === allergyIntolerance.id ? allergyIntolerance : p)
                        );
                        break;
                    case 'com.akashichealthrecords.fhir.allergyintolerance.deleted':
                        setAllergyIntolerancesList(prev => prev.filter(p => p.id !== allergyIntolerance.id));
                        break;
                }
            }
        };

        subscribe('com.akashichealthrecords.fhir.allergyintolerance.created', handleAllergyIntoleranceEvent);
        subscribe('com.akashichealthrecords.fhir.allergyintolerance.updated', handleAllergyIntoleranceEvent);
        subscribe('com.akashichealthrecords.fhir.allergyintolerance.deleted', handleAllergyIntoleranceEvent);

        return () => {
            unsubscribe('com.akashichealthrecords.fhir.allergyintolerance.created', handleAllergyIntoleranceEvent);
            unsubscribe('com.akashichealthrecords.fhir.allergyintolerance.updated', handleAllergyIntoleranceEvent);
            unsubscribe('com.akashichealthrecords.fhir.allergyintolerance.deleted', handleAllergyIntoleranceEvent);
        };
    }, [patientState, subscribe, unsubscribe, extractReferenceId, allergyFloor]);
};