import { useCallback, createContext, useContext, ReactNode } from 'react';
import { environment } from '../environments/environment.ts';
import { HttpError, useHttpService } from './HttpService.tsx';
import type { SaveTransport } from '../utils/saveOperation';
import { buildBillingExportQuery, exportFilename, type BillingExportFilters } from '../pages/DashboardPage/BillingPage/billingExportQuery';

// (Billing-Aware Export), Task 9 - the CLIENT half of the export flow. Mirrors
// PaymentService.tsx: same fhirBaseApi base (the org-scoped FHIR-adjacent API, NOT apiUrl) and the
// same hook + Provider/Context pair shape.
const API_URL = environment.fhirBaseApi;

// Result shape the download resolves to - the caller (an export dialog) turns this into a browser
// download via a Blob URL + <a download={filename}>.
export type BillingExportResult = { blob: Blob; filename: string };
export type BillingExportTransport = SaveTransport & { organizationId?: string };

export const BILLING_EXPORT_UNAVAILABLE = 'The billing export could not be fully loaded. Please try again.';

export const useBillingExportService = () => {
    const { fetchWithAuth } = useHttpService();

    // GET {fhirBaseApi}/BillingExport?start=...&end=...&format=csv|json[&provider=...][&encounterType=...]
    // Deliberately uses fetchWithAuth (not the `get()` helper) because `get()` unconditionally calls
    // response.json() - that would corrupt a CSV body (and even for JSON, this endpoint returns a
    // downloadable file, not a typed resource). fetchWithAuth already attaches Authorization and the
    // X-Organization-ID/X-Organization-Context headers, so no org/issuer query param is sent here -
    // the server org-scopes off the trusted header, not a client-supplied value.
    const downloadBillingExport = useCallback(
        async (f: BillingExportFilters, transport?: BillingExportTransport): Promise<BillingExportResult> => {
            transport?.admit();
            const filters = { ...f };
            const accept = filters.format === 'csv' ? 'text/csv' : 'application/json';
            const res = await fetchWithAuth(`${API_URL}/BillingExport?${buildBillingExportQuery(filters)}`, {
                headers: { Accept: accept },
                admit: transport?.admit,
                signal: transport?.signal,
                organizationId: transport?.organizationId,
            });
            transport?.admit();
            if (!res.ok) {
                const message = res.status === 401 || res.status === 403
                    ? 'You do not have access to this billing export.'
                    : BILLING_EXPORT_UNAVAILABLE;
                throw new HttpError(res.status, message, { message });
            }
            const contentType = res.headers.get('Content-Type')?.split(';')[0].trim().toLowerCase();
            if (contentType !== accept) throw new Error(BILLING_EXPORT_UNAVAILABLE);
            const blob = await res.blob();
            transport?.admit();
            if (blob.size === 0) throw new Error(BILLING_EXPORT_UNAVAILABLE);
            return { blob, filename: exportFilename(filters, filters.format) };
        },
        [fetchWithAuth],
    );

    return { downloadBillingExport };
};

const BillingExportServiceContext = createContext<ReturnType<typeof useBillingExportService> | undefined>(undefined);

export const BillingExportServiceProvider = ({ children }: { children: ReactNode }) => {
    const billingExportService = useBillingExportService();
    return (
        <BillingExportServiceContext.Provider value={billingExportService}>
            {children}
        </BillingExportServiceContext.Provider>
    );
};

export const useBillingExportServiceContext = () => {
    const context = useContext(BillingExportServiceContext);
    if (context === undefined) {
        throw new Error('useBillingExportServiceContext must be used within a BillingExportServiceProvider');
    }
    return context;
};