/**
 * Global FHIR version context provider.
 *
 * Initialized once per generation run via {@link initVersionContext}.
 * All emitters, parsers, and generators call {@link ctx} (or the typed
 * helpers below) instead of hard-coding version-specific imports.
 *
 * This is intentionally a singleton; generation is single-threaded.
 */

import type { FhirRules, FhirVersionContext, FhirVersionSlug } from './types.js';
import { resolveVersionContext, DEFAULT_FHIR_VERSION } from './types.js';

let _current: FhirVersionContext | null = null;

/**
 * Resolve and set the global version context.
 * Must be called before any generation work begins.
 */
export async function initVersionContext(
  slug: FhirVersionSlug = DEFAULT_FHIR_VERSION,
): Promise<FhirVersionContext> {
  _current = await resolveVersionContext(slug);
  return _current;
}

/**
 * Return the active version context.
 * Throws if {@link initVersionContext} has not been called.
 */
export function ctx(): FhirVersionContext {
  if (!_current) {
    throw new Error(
      'FHIR version context not initialised. Call initVersionContext() first.',
    );
  }
  return _current;
}

/** Shorthand – the rules object from the active context. */
export function getRules(): FhirRules {
  return ctx().rules;
}

/** The `fhir/<slug>` import specifier for generated output code. */
export function fhirModuleSpecifier(): string {
  return `fhir/${ctx().versionSlug}`;
}

/** FHIR version slug (e.g. 'r4', 'r4b') */
export function versionSlug(): FhirVersionSlug {
  return ctx().versionSlug;
}

/**
 * FHIRPath model slug for the active version.
 *
 * `fhirpath` only ships `fhir-context/` models for dstu2, stu3, r4 and r5 —
 * there is no r4b model. R4B is a maintenance release of R4 whose FHIRPath
 * type model is unchanged, so R4B validators load the r4 model.
 *
 * Emitted as `fhirpath/fhir-context/<slug>/index.js`; the trailing filename is
 * required because fhirpath >= 5 declares an `exports` map and extensionless
 * deep paths no longer resolve.
 */
export function fhirpathModelSlug(): string {
  return ctx().versionSlug === 'r4b' ? 'r4' : ctx().versionSlug;
}

/** Full semver version (e.g. '4.0.1', '4.3.0') */
export function versionString(): string {
  return ctx().version;
}

/**
 * Reset the provider (for testing).
 * @internal
 */
export function resetVersionContext(): void {
  _current = null;
}