import { existsSync, readFileSync, writeFileSync } from "node:fs";
import { join } from "node:path";

/**
 * Throws if a core package directory already exists. Used as the first action
 * in every per-package generator so re-running is safe.
 */
export function assertOptionalPackageNotPresent(
  name: string,
  cwd: string = process.cwd(),
): void {
  const pkgRoot = join(cwd, "packages", name);
  if (existsSync(pkgRoot)) {
    throw new Error(
      `packages/${name}/ already exists — refusing to scaffold (delete it first if intentional)`,
    );
  }
}

/**
 * Inserts a package name into the transpilePackages array of a Next.js config
 * file, preserving alphabetical order. Idempotent.
 */
export function addToTranspilePackages(
  nextConfigPath: string,
  pkgName: string,
): void {
  const source = readFileSync(nextConfigPath, "utf8");
  if (source.includes(`"${pkgName}"`)) return;
  const updated = source.replace(
    /(transpilePackages:\s*\[\s*)([\s\S]*?)(\s*\])/,
    (_match, open: string, body: string, close: string) => {
      const entries = body
        .split(",")
        .map((e) => e.trim())
        .filter(Boolean);
      entries.push(`"${pkgName}"`);
      entries.sort();
      const formatted = entries.map((e) => `    ${e}`).join(",\n");
      return `${open}\n${formatted},${close}`;
    },
  );
  writeFileSync(nextConfigPath, updated);
}