import { filter, pipe, tap } from 'wonka';
import type { ExchangeIO, ExchangeInput } from '../types';

/** Used by the `Client` as the last exchange to warn about unhandled operations.
 *
 * @remarks
 * In a normal setup, some operations may go unhandled when a {@link Client} isn’t set up
 * with the right exchanges.
 * For instance, a `Client` may be missing a fetch exchange, or an exchange handling subscriptions.
 * This {@link Exchange} is added by the `Client` automatically to log warnings about unhandled
 * {@link Operaiton | Operations} in development.
 */
export const fallbackExchange: ({
  dispatchDebug,
}: Pick<ExchangeInput, 'dispatchDebug'>) => ExchangeIO =
  ({ dispatchDebug }) =>
  ops$ => {
    if (process.env.NODE_ENV !== 'production') {
      ops$ = pipe(
        ops$,
        tap(operation => {
          if (
            operation.kind !== 'teardown' &&
            process.env.NODE_ENV !== 'production'
          ) {
            const message = `No exchange has handled operations of kind "${operation.kind}". Check whether you've added an exchange responsible for these operations.`;

            dispatchDebug({
              type: 'fallbackCatch',
              message,
              operation,
            });
            console.warn(message);
          }
        })
      );
    }

    // All operations that skipped through the entire exchange chain should be filtered from the output
    return filter((_x): _x is never => false)(ops$);
  };