/**
 * The facts about this host that decide whether a native Module Package v1 can run on it
 * (ADR 0049): operating system, CPU, C library family and version, and Node-API version.
 *
 * Everything comes from Node.js itself (`process.platform`, `process.arch`, `process.versions`, and
 * the diagnostic report's `glibcVersionRuntime`), never from running a system command. A fact Node
 * cannot report is left undefined, and every check that needs it fails closed.
 */
export interface ModulePackageHost {
  readonly platform: string;
  readonly arch: string;
  /** The C library on Linux: glibc with its runtime version, or undefined when it cannot be proven
   * to be glibc (musl reports none). */
  readonly libc?: { readonly family: "glibc"; readonly version: string };
  /** `process.versions.napi`: the highest Node-API version this Node.js provides. */
  readonly nodeApi?: number;
  /** `process.versions.modules`: the ABI an ABI-specific addon must have been built for. */
  readonly nodeAbi?: string;
}

function glibcVersion(): string | undefined {
  try {
    const header = (process.report?.getReport() as { header?: { glibcVersionRuntime?: unknown } })
      ?.header;
    const version = header?.glibcVersionRuntime;
    return typeof version === "string" && /^\d+\.\d+(?:\.\d+)?$/u.test(version)
      ? version
      : undefined;
  } catch {
    return undefined;
  }
}

export function currentModulePackageHost(): ModulePackageHost {
  const libc = process.platform === "linux" ? glibcVersion() : undefined;
  const nodeApi = Number(process.versions.napi);
  return Object.freeze({
    arch: process.arch,
    ...(libc === undefined
      ? {}
      : { libc: Object.freeze({ family: "glibc" as const, version: libc }) }),
    ...(Number.isInteger(nodeApi) && nodeApi > 0 ? { nodeApi } : {}),
    ...(typeof process.versions.modules === "string" ? { nodeAbi: process.versions.modules } : {}),
    platform: process.platform,
  });
}

/** The native targets this platform can verify, with what each requires of a host. */
export const MODULE_PACKAGE_NATIVE_TARGETS: ReadonlyMap<
  string,
  {
    readonly platform: string;
    readonly arch: string;
    readonly libc: "glibc";
    readonly elfMachine: number;
  }
> = new Map([
  ["linux-x64-glibc", { arch: "x64", elfMachine: 62, libc: "glibc", platform: "linux" }],
]);