import { createRequire } from "node:module";

import * as sys from "../sys.mjs";

const __require = createRequire(import.meta.url);
const cwd = sys.cwd();

export default function rootModule(root) {
  if (!root || root?.startsWith("virtual:")) return null;
  const [module, name] = root.split("#");
  const rootModule = __require.resolve(module, { paths: [cwd] });

  return {
    name: "react-server:root-module",
    transform: {
      filter: {
        id: new RegExp(rootModule.replace(/([/.])/g, "\\$1")),
      },
      handler(code, id) {
        if (id === rootModule) {
          const ast = this.parse(code, { sourceType: "module" });

          const defaultExport = ast.body.find(
            (node) => node.type === "ExportDefaultDeclaration"
          );
          const namedExports = ast.body
            .filter(
              (node) =>
                node.type === "ExportNamedDeclaration" && node.declaration
            )
            .map((node) => node.declaration.id?.name);
          const allExports = ast.body
            .filter(
              (node) =>
                node.type === "ExportNamedDeclaration" &&
                node.specifiers.length > 0
            )
            .flatMap((node) => node.specifiers)
            .map((node) => node.exported.name);

          const rootName = name ?? "default";
          if (
            (rootName === "default" &&
              !defaultExport &&
              !allExports?.find((name) => name === "default")) ||
            (rootName !== "default" &&
              !namedExports.find((name) => name === rootName) &&
              !allExports?.find((name) => name === rootName))
          ) {
            throw new Error(
              `Module "${rootModule}" does not export "${rootName}"`
            );
          }

          if (name && name !== "default") {
            return {
              code: `${code}\nexport { ${name} as default };`,
              map: null,
            };
          }
        }
      },
    },
  };
}