import type { Bundle, Composition } from 'fhir/r4';

const FALLBACK_PATIENT = 'unknown-patient';
const FALLBACK_DATE = 'unknown-date';

/** Filesystem-safe token: strip everything but alphanumerics/underscore/hyphen, collapse runs, trim edges. */
function safeToken(value: string, fallback: string): string {
    const cleaned = value
        .replace(/[^A-Za-z0-9_-]+/g, '-')
        .replace(/-+/g, '-')
        .replace(/^-|-$/g, '');
    return cleaned || fallback;
}

/** The Bundle's `entry[0]` per the B3 FHIR-document contract, if it's actually a Composition. */
function compositionOf(bundle: Bundle): Composition | undefined {
    const first = bundle.entry?.[0]?.resource;
    return first?.resourceType === 'Composition' ? (first as Composition) : undefined;
}

/** Derive the `{patient}` filename token from `Composition.subject` (`Patient/{pid}`). */
function patientToken(composition: Composition | undefined): string {
    const ref = composition?.subject?.reference;
    const pid = ref?.startsWith('Patient/') ? ref.slice('Patient/'.length) : ref;
    return pid ? safeToken(pid, FALLBACK_PATIENT) : FALLBACK_PATIENT;
}

/**
 * Derive the `{anchorDate}` filename token. The signed Bundle carries no separate structured field
 * for the anchor's own pinned date - `buildLegalExportDocument` (infra
 * `aws/sam/services/api/src/utils/legal-export-document.ts`) only embeds it as the trailing
 * " - {date}" segment of `Composition.title` (`Care-View Legal Record - Patient/{pid} -
 * {anchor.date ?? nowIso}`). Falls back to `Composition.date` (the export's own generation time)
 * if the title doesn't parse as expected - never throws.
 */
function anchorDateToken(composition: Composition | undefined): string {
    const title = composition?.title ?? '';
    const parts = title.split(' — ');
    const trailing = parts.length >= 3 ? parts[parts.length - 1]?.trim() : undefined;
    return safeToken(trailing || composition?.date || FALLBACK_DATE, FALLBACK_DATE);
}

/**
 * Downloads a signed B3 legal-export Bundle as pretty-printed FHIR JSON - the authoritative
 * artifact (`LegalRecordPrintView` is only a human-readable convenience copy of the same data).
 *
 * Filename: `akashic-legal-record-{patient}-{anchorDate}.json`, both tokens derived from the
 * Bundle's own `Composition` (entry[0]) so this stays a pure, single-argument, side-effecting
 * util with no dependency on caller-tracked state.
 *
 * Mirrors the existing Blob -> createObjectURL -> anchor-click -> revoke pattern already used by
 * `FhirDocumentReferenceDisplay`'s attachment download (no new browser API surface).
 */
export function downloadBundleJson(bundle: Bundle): void {
    const composition = compositionOf(bundle);
    const filename = `akashic-legal-record-${patientToken(composition)}-${anchorDateToken(composition)}.json`;

    const blob = new Blob([JSON.stringify(bundle, null, 2)], { type: 'application/fhir+json' });
    const url = URL.createObjectURL(blob);

    const link = document.createElement('a');
    link.href = url;
    link.download = filename;
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
    URL.revokeObjectURL(url);
}

export default downloadBundleJson;