import { Provider } from "@smithy/types";

import { ProviderError } from "./ProviderError";

/**
 * @internal
 *
 * Compose a single credential provider function from multiple credential
 * providers. The first provider in the argument list will always be invoked;
 * subsequent providers in the list will be invoked in the order in which the
 * were received if the preceding provider did not successfully resolve.
 *
 * If no providers were received or no provider resolves successfully, the
 * returned promise will be rejected.
 */
export const chain = <T>(...providers: Array<Provider<T>>): Provider<T> => async () => {
  if (providers.length === 0) {
    throw new ProviderError("No providers in chain");
  }

  let lastProviderError: Error | undefined;
  for (const provider of providers) {
    try {
      const credentials = await provider();
      return credentials;
    } catch (err) {
      lastProviderError = err;
      if (err?.tryNextLink) {
        continue;
      }
      throw err;
    }
  }
  throw lastProviderError;
};