/**
 * Constructs the environment variables for the child process.
 *
 * @param customEnv - Custom environment variables to merge with default environment variables.
 * @returns The environment variables for the child process.
 */
export function getEnvironment(
  customEnv?: Record<string, string>,
): Record<string, string> {
  const isWindows = globalThis.process.platform === 'win32';
  const DEFAULT_INHERITED_ENV_VARS = isWindows
    ? [
        'APPDATA',
        'HOMEDRIVE',
        'HOMEPATH',
        'LOCALAPPDATA',
        'PATH',
        'PROCESSOR_ARCHITECTURE',
        'SYSTEMDRIVE',
        'SYSTEMROOT',
        'TEMP',
        'USERNAME',
        'USERPROFILE',
      ]
    : ['HOME', 'LOGNAME', 'PATH', 'SHELL', 'TERM', 'USER'];

  const env: Record<string, string> = customEnv ? { ...customEnv } : {};
  const customEnvKeys = new Set(
    Object.keys(env).map(key => (isWindows ? key.toUpperCase() : key)),
  );

  for (const key of DEFAULT_INHERITED_ENV_VARS) {
    if (customEnvKeys.has(key)) {
      continue;
    }

    const value = globalThis.process.env[key];
    if (value === undefined) {
      continue;
    }

    if (value.startsWith('()')) {
      continue;
    }

    env[key] = value;
  }

  return env;
}