// writing code is the easy bit

const newFiltersetToUrl = ({
  newFilterset,
  categoryApplicableFilters,
  oldMatchParams = {},
  alwaysIncludeBaseUrl = false,
}) => {
  const newUrlOfQueryParams = parseFilterSetToShopQueryParams(newFilterset);
  /* see if we have just one top level category requiredId
   * in which case we'll ditch it as a requiredID param
   * and take the user to the nice URL for that category
   */
  const { fromId } = whitelistedUrlsForCategories(categoryApplicableFilters);

  const requiredIdsThatAreCategories = Array.from(
    newFilterset.requiredIds
  ).filter(id => fromId.has(id));

  const hadBrowseList = oldMatchParams.browseListId;
  const newFiltersetHasBrowseList = newFilterset.requiredIds.has(
    oldMatchParams.browseListId
  );

  const shouldSwapToNiceCategoryUrl =
    newFiltersetHasBrowseList === false &&
    requiredIdsThatAreCategories.length === 1;

  const generateUrlToReturn = () => {
    if (shouldSwapToNiceCategoryUrl) {
      return generateUrlForMatchedCategory({
        filterset: newFilterset,
        fromId,
        categoryId: requiredIdsThatAreCategories[0],
      });
    } else if (hadBrowseList && newFiltersetHasBrowseList) {
      return generateUrlForBrowseList({
        filterset: newFilterset,
        browseListId: oldMatchParams.browseListId,
      });
    } else if (oldMatchParams.niceUrl || oldMatchParams.browseListId) {
      // we had a nice URL before and now we don't
      // so we need to put the baseUrl in here
      return baseUrl + newUrlOfQueryParams;
    } else {
      /* but if we're here and are not sure how to deal with the URL change
       * in a way that maintains the "nice" URLs
       * let's just use query params, which will work totally fine
       */
      return newUrlOfQueryParams;
    }
  };

  const url = generateUrlToReturn();

  if (url.includes(baseUrl) || alwaysIncludeBaseUrl === false) {
    return url;
  } else {
    return baseUrl + url;
  }
};

const generateUrlForBrowseList = ({ filterset, browseListId }) => {
  const newUrlForBrowseList = urlForBrowseList(browseListId);
  const filtersetWithBrowseListRemoved = mapFilterset(filterset, filterset => {
    filterset.requiredIds = filterSet(
      filterset.requiredIds,
      id => id !== browseListId
    );
    return filterset;
  });
  const newQueryParams = parseFilterSetToShopQueryParams(
    filtersetWithBrowseListRemoved
  );

  return newUrlForBrowseList + (newQueryParams === '?' ? '' : newQueryParams);
};

const generateUrlForMatchedCategory = ({ filterset, fromId, categoryId }) => {
  // take the user to the nice URL for this category
  const newUrlForCategory = baseUrl + fromId.get(categoryId);

  // now we remove that requiredId
  const filtersetWithCategoryIdRemoved = mapFilterset(filterset, filterset => {
    return {
      ...filterset,
      requiredIds: filterSet(filterset.requiredIds, id => id !== categoryId),
    };
  });
  const newQueryParams = parseFilterSetToShopQueryParams(
    filtersetWithCategoryIdRemoved
  );

  return newUrlForCategory + (newQueryParams === '?' ? '' : newQueryParams);
};

export default newFiltersetToUrl;