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,
    DetectedIssue,
    Patient,
    Reference,
    DetectedIssueEvidence,
    PractitionerRole
} 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 { usePractitionerRoleServiceContext } from './PractitionerRoleService.tsx';
import { formatFhirCodeableConcept } from '../utils/fhirCodeableConcept.tsx';
import { usePatientServiceContext } from './PatientService.tsx';
import { formatFhirPeriod } from '../utils/fhirPeriod.tsx';
import { applyArchive, isArchived, type ArchiveReason } from '../utils/archivedResource';
import { statusLabel } from '../utils/fhirStatusVocabulary';
import { fetchAllPagesAsBundle } from '../utils/fetchAllPagesAsBundle';
import { searchPageSize } from '../utils/pageSizeOverride';
import { useCacheOwner } from '../utils/cacheOwner';

const API_URL = environment.fhirClinicalApi;

export const useDetectedIssueService = () => {
    const { get, post, put, delete: del } = useHttpService();
    const { patientState } = usePatientServiceContext();
    const {
        transformToCodeableConcept,
        transformFromCodeableConcept,
        createReferenceObject,
        formatDateTime,
        formatDateTimeForInput,
        formatDateTimeForDisplay,
        unpackBundle,
        addFhirPeriodIfApplicable,
        addPeriodControlsIfApplicable,
        extractReferenceId
    } = useFhirServiceContext();
    const { getPractitionerRoleDisplay } = usePractitionerRoleServiceContext();

    const [detectedIssuesList, setDetectedIssuesList] = useState<DetectedIssue[]>([]);
    const [shouldReload, setShouldReload] = useState<boolean>(false);
    const [lastUpserted, setLastUpserted] = useState<string | null | undefined>(null);
    const [unsaved, setUnsaved] = useState<boolean>(false);

    const [detectedIssuesBundle, setDetectedIssuesBundle] = useState<Bundle<DetectedIssue> | null>(null);
    const detectedIssuesBundleRef = useRef<Bundle<DetectedIssue> | null>(null);
    const lastFetchTimeRef = useRef<number>(0);

    useEffect(() => {
        detectedIssuesBundleRef.current = detectedIssuesBundle;
    }, [detectedIssuesBundle]);

    // 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('DetectedIssue', () => {
        setLastUpserted(null);
        setDetectedIssuesBundle(null);
        setDetectedIssuesList([]);
        lastFetchTimeRef.current = 0;
    });

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

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

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

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

    const fetchDetectedIssuesWithPolling = useCallback(async (patient: Patient, forceReload = false): Promise<Bundle<DetectedIssue>> => {
        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('DetectedIssue', lastFetchTimeRef.current) && detectedIssuesBundleRef.current && cacheFresh && cacheOwner.isCurrentFor(patient.id)) {
            return detectedIssuesBundleRef.current;
        }

        const operation = cacheOwner.begin();

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

        do {
            bundle = await fetchDetectedIssues(patient);
            entries = unpackBundle(bundle).filter((r) => !isArchived(r));
            found = lastUpserted ? entries.some(e => e.id === lastUpserted) || isHeld('DetectedIssue', 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);
        setDetectedIssuesBundle(bundle);
        setDetectedIssuesList(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;
    }, [fetchDetectedIssues, unpackBundle, lastUpserted, shouldReload]);

    const fetchDetectedIssue = useCallback(async (id: string): Promise<DetectedIssue> => {
        const cachedIssue = cacheOwner.isCurrent(cacheOwner.claimed) ? detectedIssuesList.find(issue => issue.id === id) : undefined;
        if (cachedIssue) {
            return cachedIssue;
        }

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

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

    const createDetectedIssue = useCallback(async (detectedIssue: DetectedIssue): Promise<DetectedIssue> => {
        let params = new URLSearchParams();

        params.append('patient', extractReferenceId(detectedIssue.patient) as string);

        return post<DetectedIssue>(`${API_URL}/DetectedIssue?${params.toString()}`, detectedIssue);
    }, [post, extractReferenceId]);

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

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

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

    const transformToFhirDetectedIssue = useCallback((item: any, patient: Patient, author?: PractitionerRole): DetectedIssue => {
        const {
            status,
            code,
            severity,
            identifiedType,
            identifiedDateTime,
            evidence,
            detail,
            reference,
            mitigation
        } = item;

        const patientReference: Reference = createReferenceObject('Patient', patient.id as string, formatFhirHumanName(patient.name));

        let detectedIssue: DetectedIssue = {
            resourceType: 'DetectedIssue',
            status: status,
            ...(patient && { patient: patientReference }),
            ...(code && { code: transformToCodeableConcept(code) }),
            ...(severity && { severity }),
            ...(identifiedType === 'dateTime' && identifiedDateTime && { identifiedDateTime: formatDateTime(identifiedDateTime) }),
            ...(author && { author: createReferenceObject('PractitionerRole', author.id as string, getPractitionerRoleDisplay(author)) }),
            ...(evidence && evidence.length !== 0 && {
                evidence: evidence.map((ev: any) => {
                    const evidenceItem: DetectedIssueEvidence = {
                        ...(ev.code && ev.code.length !== 0 && { code: transformToCodeableConcept(ev.code) })
                    };

                    return evidenceItem;
                })
            }),
            ...(detail && { detail }),
            ...(reference && { reference }),
            ...(mitigation && mitigation.length !== 0 && {
                mitigation: mitigation.map((mit: any) => ({
                    action: transformToCodeableConcept(mit.action),
                    ...(mit.date && { date: formatDateTime(mit.date) })
                }))
            })
        };

        if (identifiedType === 'period') {
            delete detectedIssue.identifiedDateTime;
            return addFhirPeriodIfApplicable(detectedIssue, item, 'identifiedPeriod');
        }

        return detectedIssue;
    }, [createReferenceObject, transformToCodeableConcept, formatDateTime, addFhirPeriodIfApplicable]);

    const transformFromFhirDetectedIssue = useCallback((detectedIssue: DetectedIssue): any => {
        const {
            identifier,
            status,
            code,
            severity,
            identifiedDateTime,
            identifiedPeriod,
            evidence,
            detail,
            mitigation
        } = detectedIssue;

        const formData = {
            identifier: identifier || [],
            status: status,
            code: transformFromCodeableConcept(code),
            severity: severity,
            identifiedType: identifiedDateTime ? 'dateTime' : identifiedPeriod ? 'period' : '',
            identifiedDateTime: formatDateTimeForInput(identifiedDateTime),
            evidence: (evidence ?? []).map(ev => ({
                code: transformFromCodeableConcept(ev.code ?? [])
            })),
            detail: detail ?? '',
            mitigation: (mitigation ?? []).map(mit => ({
                action: transformFromCodeableConcept(mit.action),
                date: formatDateTimeForInput(mit.date),
            }))
        };

        return addPeriodControlsIfApplicable(formData, detectedIssue, 'identifiedPeriod');
    }, [transformFromCodeableConcept, formatDateTime]);

    const getDetectedIssueDisplay = (detectedIssue: DetectedIssue): string => {
        if (!detectedIssue) {
            return 'Unknown Detected Issue';
        }

        const issueCode = formatFhirCodeableConcept(detectedIssue.code) || 'Detected Issue';
        // - the human label, never the code. `statusLabel` returns `undefined` for a code we
        // have no words for, and this omits the status entirely in that case rather than falling back to
        // the raw value - the fallback IS the defect. `utils/fhirStatusVocabulary.ts`
        const statusText = statusLabel(detectedIssue.status);
        const status = statusText ? ` · ${statusText}` : '';

        let dateSuffix = '';
        if (detectedIssue.identifiedDateTime) {
            dateSuffix = ` (${formatDateTimeForDisplay(detectedIssue.identifiedDateTime)})`;
        } else if (detectedIssue.identifiedPeriod) {
            dateSuffix = ` (${formatFhirPeriod(detectedIssue.identifiedPeriod)})`;
        }

        return `${issueCode}${status}${dateSuffix}`;
    };

    return {
        detectedIssuesBundle,
        // 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,
        detectedIssuesList,
        setDetectedIssuesList,
        shouldReload,
        setShouldReload,
        lastUpserted,
        setLastUpserted,
        unsaved,
        setUnsaved,

        fetchDetectedIssues,
        fetchDetectedIssuesWithPolling,
        fetchDetectedIssue,
        fetchDetectedIssueHistory,
        createDetectedIssue,
        updateDetectedIssue,
        deleteDetectedIssue,
        archiveDetectedIssue,

        transformToFhirDetectedIssue,
        transformFromFhirDetectedIssue,
        getDetectedIssueDisplay,
    };
};

const DetectedIssueServiceContext = createContext<ReturnType<typeof useDetectedIssueService> | undefined>(undefined);

export const DetectedIssueServiceProvider: React.FC<{ children: ReactNode }> = ({ children }) => {
    const detectedIssueService = useDetectedIssueService();

    return (
        <DetectedIssueServiceContext.Provider value={detectedIssueService}>
            {children}
        </DetectedIssueServiceContext.Provider>
    );
};

export const useDetectedIssueServiceContext = () => {
    const context = useContext(DetectedIssueServiceContext);

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

    return context;
};