import type { ReadOptions } from '../hooks/anchorView/readOptions';
import { isHeld, overlayHeldBundle, refersToPatient, writtenSince } from '../utils/writeThroughHold';
import { useState, useCallback, createContext, useContext, ReactNode, useEffect, useRef } from 'react';
import {
    Bundle,
    Flag,
    Patient,
    Practitioner,
    Encounter
} from 'fhir/r4';
import { environment } from '../environments/environment.ts';
import { useFhirServiceContext } from './FhirService.tsx';
import { useHttpService } from './HttpService.tsx';
import { formatFhirHumanName } from '../utils/fhirHumanName.tsx';
import { usePatientServiceContext } from './PatientService.tsx';
import { applyArchive, isArchived, type ArchiveReason } from '../utils/archivedResource';
import { fetchAllPagesAsBundle } from '../utils/fetchAllPagesAsBundle';
import { searchPageSize } from '../utils/pageSizeOverride';
import { useCacheOwner } from '../utils/cacheOwner';

const API_URL = environment.fhirBaseApi;

export const useFlagService = () => {
    const { get, post, put, delete: del } = useHttpService();
    const { patientState } = usePatientServiceContext();
    const {
        transformToCodeableConcept,
        transformFromCodeableConcept,
        createReferenceObject,
        unpackBundle,
        addFhirPeriodIfApplicable,
        addPeriodControlsIfApplicable
    } = useFhirServiceContext();

    const [flagsList, setFlagsList] = useState<Flag[]>([]);
    const [shouldReload, setShouldReload] = useState<boolean>(false);
    const [lastUpserted, setLastUpserted] = useState<string | null | undefined>(null);
    const [unsaved, setUnsaved] = useState<boolean>(false);

    const [flagsBundle, setFlagsBundle] = useState<Bundle<Flag> | null>(null);
    const flagsBundleRef = useRef<Bundle<Flag> | null>(null);
    const lastFetchTimeRef = useRef<number>(0);

    useEffect(() => {
        flagsBundleRef.current = flagsBundle;
    }, [flagsBundle]);

    // WHOSE RECORDS ARE THESE? The reset below fires only when there is NO patient, which moving
    // between two charts never is - so the previous patient's bundle survived the switch and was
    // served as a cache hit, with no request and nothing on screen to say the list was not theirs.
    const cacheOwner = useCacheOwner('Flag', () => {
        setLastUpserted(null);
        setFlagsBundle(null);
        setFlagsList([]);
        lastFetchTimeRef.current = 0;
    });

    useEffect(() => {
        if (!patientState) {
            setFlagsBundle(null);
            setFlagsList([]);
            lastFetchTimeRef.current = 0;
            cacheOwner.release();
        }
    }, [patientState, cacheOwner.release]);

    const fetchFlags = useCallback(async (patient: Patient, options?: ReadOptions): Promise<Bundle<Flag>> => {
        return overlayHeldBundle('Flag', await fetchAllPagesAsBundle<Flag>((pageParam) => {
            let params = new URLSearchParams();

            params.append('_count', searchPageSize('100'));
            params.append('subject', patient.id as string);
            if (pageParam) params.set('page', pageParam);

            return get<Bundle<Flag>>(`${API_URL}/Flag?${params.toString()}`, options);
        }), (resource) => refersToPatient(resource, patient.id)) as Bundle<Flag>;
    }, [get]);

    const fetchFlagsWithPolling = useCallback(async (patient: Patient, forceReload = false): Promise<Bundle<Flag>> => {
        const now = Date.now();
        const cacheAge = now - lastFetchTimeRef.current;
        const cacheFresh = cacheAge < 5 * 60 * 1000;

        // cacheOwner.isFor is the load-bearing clause: a fresh bundle belonging to the PREVIOUS
        // patient satisfies every other condition here and would be returned as a hit.
        if (!forceReload && !shouldReload && !writtenSince('Flag', lastFetchTimeRef.current) && flagsBundleRef.current && cacheFresh && cacheOwner.isCurrentFor(patient.id)) {
            return flagsBundleRef.current;
        }

        const operation = cacheOwner.begin();

        let retries = 10;
        const delay = 3000;
        let found = false;
        let bundle: Bundle<Flag> | null = null;
        let entries: Flag[];

        do {
            bundle = await fetchFlags(patient);
            entries = unpackBundle(bundle);
            found = lastUpserted ? entries.some(e => e.id === lastUpserted) || isHeld('Flag', lastUpserted) : true;

            if (!found) {
                await new Promise(resolve => setTimeout(resolve, delay));
            }
            retries--;
        } while (!found && retries > 0 && cacheOwner.publishes(operation));


        if (!cacheOwner.publishes(operation)) return cacheOwner.answerFor(operation, bundle);
        setFlagsBundle(bundle);
        setFlagsList(entries.filter((r) => !isArchived(r)));
        setLastUpserted(null);
        setShouldReload(false);
        lastFetchTimeRef.current = now;
        // Stamped WITH the data, never before it - on a throw the owner must still name the list
        // that is actually in state.
        cacheOwner.claim(patient.id, operation);

        return bundle;
    }, [fetchFlags, unpackBundle, lastUpserted, shouldReload]);

    const fetchFlag = useCallback(async (id: string): Promise<Flag> => {
        const cachedFlag = cacheOwner.isCurrent(cacheOwner.claimed) ? flagsList.find(flag => flag.id === id) : undefined;
        if (cachedFlag) {
            return cachedFlag;
        }

        return get<Flag>(`${API_URL}/Flag/${id}`);
    }, [get, flagsList]);

    const fetchFlagHistory = useCallback(async (id: string, options?: ReadOptions): Promise<Bundle<Flag>> => {
        return get<Bundle<Flag>>(`${API_URL}/Flag/${id}/_history`, options);
    }, [get]);

    const createFlag = useCallback(async (flag: Flag): Promise<Flag> => {
        return post<Flag>(`${API_URL}/Flag`, flag);
    }, [post]);

    const updateFlag = useCallback(async (flag: Flag): Promise<Flag> => {
        return put<Flag>(`${API_URL}/Flag/${flag.id}`, flag);
    }, [put]);

    const deleteFlag = useCallback(async (flag: Flag): Promise<Flag> => {
        return del<Flag>(`${API_URL}/Flag/${flag.id}`);
    }, [del]);

    const archiveFlag = useCallback(async (flag: Flag, reason: ArchiveReason, note?: string): Promise<Flag> => {
        return put<Flag>(`${API_URL}/Flag/${flag.id}`, applyArchive(flag, reason, note));
    }, [put]);

    const transformToFhirFlag = useCallback((item: any, subjectType?: 'Patient', newSubject?: Patient, authorType?: 'Practitioner', newAuthor?: Practitioner, newEncounter?: Encounter): Flag => {
        const {
            status,
            category,
            code,
            subject,
            encounter,
            author
        } = item;
        
        const flag: Flag = {
            resourceType: 'Flag',
            status: status,
            code: transformToCodeableConcept(code),
            ...(category && { category: transformToCodeableConcept(category) }),
            ...((subject || newSubject) && { subject: newSubject ? createReferenceObject(subjectType as string, newSubject.id as string, formatFhirHumanName((newSubject as Patient).name)) : subject }),
            ...((author || newAuthor) && { author: newAuthor ? createReferenceObject(authorType as string, newAuthor.id as string, formatFhirHumanName((newAuthor as Practitioner).name)) : author }),
            ...((encounter || newEncounter) && { encounter: newEncounter ? createReferenceObject('Encounter', encounter.id as string) : encounter }),
        };

        return addFhirPeriodIfApplicable(flag, item, 'period');
    }, [createReferenceObject, transformToCodeableConcept, addFhirPeriodIfApplicable]);

    const transformFromFhirFlag = useCallback((flag: Flag): any => {
        const {
            status,
            category,
            code,
            subject,
            encounter,
            author
        } = flag;

        const formData = {
            status: status,
            category: transformFromCodeableConcept(category),
            code: transformFromCodeableConcept(code),
            subject,
            encounter,
            author
        };

        return addPeriodControlsIfApplicable(formData, flag);
    }, [transformFromCodeableConcept, addPeriodControlsIfApplicable]);

    return {
        // WHO THE CACHED LIST IS FOR, so a consumer can ask whether it belongs to the patient on
        // screen rather than trusting an app-wide context with no patient in its name.
        cachedForPatientId: cacheOwner.ownerId,
        flagsBundle,
        flagsList,
        setFlagsList,
        shouldReload,
        setShouldReload,
        lastUpserted,
        setLastUpserted,
        unsaved,
        setUnsaved,

        fetchFlags,
        fetchFlagsWithPolling,
        fetchFlag,
        fetchFlagHistory,
        createFlag,
        updateFlag,
        deleteFlag,
        archiveFlag,

        transformToFhirFlag,
        transformFromFhirFlag
    };
};

const FlagServiceContext = createContext<ReturnType<typeof useFlagService> | undefined>(undefined);

export const FlagServiceProvider: React.FC<{ children: ReactNode }> = ({ children }) => {
    const flagService = useFlagService();

    return (
        <FlagServiceContext.Provider value={flagService}>
            {children}
        </FlagServiceContext.Provider>
    );
};

export const useFlagServiceContext = () => {
    const context = useContext(FlagServiceContext);

    if (context === undefined) {
        throw new Error('useFlagServiceContext must be used within a FlagServiceProvider');
    }

    return context;
};