import React from "react";
import gql from "graphql-tag";
import { Box, Text, VisuallyHidden } from "@chakra-ui/react";
import { useQuery } from "@apollo/client";

import { Delay, useDebounce } from "../util";
import { emptySearchQuery } from "./SearchToolbar";
import Item, { ItemListContainer, ItemListSkeleton } from "./Item";
import { itemAppearanceFragment } from "../components/useOutfitAppearance";

/**
 * SearchPanel shows item search results to the user, so they can preview them
 * and add them to their outfit!
 *
 * It's tightly coordinated with SearchToolbar, using refs to control special
 * keyboard and focus interactions.
 */
function SearchPanel({
  query,
  outfitState,
  dispatchToOutfit,
  scrollContainerRef,
  searchQueryRef,
  firstSearchResultRef,
}) {
  // Whenever the search query changes, scroll back up to the top!
  React.useEffect(() => {
    if (scrollContainerRef.current) {
      scrollContainerRef.current.scrollTop = 0;
    }
  }, [query, scrollContainerRef]);

  // Sometimes we want to give focus back to the search field!
  const onMoveFocusUpToQuery = (e) => {
    if (searchQueryRef.current) {
      searchQueryRef.current.focus();
      e.preventDefault();
    }
  };

  return (
    <Box
      onKeyDown={(e) => {
        // This will catch any Escape presses when the user's focus is inside
        // the SearchPanel.
        if (e.key === "Escape") {
          onMoveFocusUpToQuery(e);
        }
      }}
    >
      <SearchResults
        // When the query changes, replace the SearchResults component with a
        // new instance, to reset `itemIdsToReconsider`. That way, if you find
        // an item you like in one search, then immediately do a second search
        // and try a conflicting item, we'll restore the item you liked from
        // your first search!
        //
        // NOTE: I wonder how this affects things like state. This component
        //       also tries to gracefully handle changes in the query, but tbh
        //       I wonder whether that's still necessary...
        key={serializeQuery(query)}
        query={query}
        outfitState={outfitState}
        dispatchToOutfit={dispatchToOutfit}
        scrollContainerRef={scrollContainerRef}
        firstSearchResultRef={firstSearchResultRef}
        onMoveFocusUpToQuery={onMoveFocusUpToQuery}
      />
    </Box>
  );
}

/**
 * SearchResults loads the search results from the user's query, renders them,
 * and tracks the scroll container for infinite scrolling.
 *
 * For each item, we render a <label> with a visually-hidden checkbox and the
 * Item component (which will visually reflect the radio's state). This makes
 * the list screen-reader- and keyboard-accessible!
 */
function SearchResults({
  query,
  outfitState,
  dispatchToOutfit,
  scrollContainerRef,
  firstSearchResultRef,
  onMoveFocusUpToQuery,
}) {
  const { loading, loadingMore, error, items, fetchMore } = useSearchResults(
    query,
    outfitState
  );
  useScrollTracker(scrollContainerRef, 300, fetchMore);

  // This will save the `wornItemIds` when the SearchResults first mounts, and
  // keep it saved even after the outfit changes. We use this to try to restore
  // these items after the user makes changes, e.g., after they try on another
  // Background we want to restore the previous one!
  const [itemIdsToReconsider] = React.useState(outfitState.wornItemIds);

  // You can use UpArrow/DownArrow to navigate between items, and even back up
  // to the search field!
  const goToPrevItem = React.useCallback(
    (e) => {
      const prevLabel = e.target.closest("label").previousSibling;
      if (prevLabel) {
        prevLabel.querySelector("input[type=checkbox]").focus();
        prevLabel.scrollIntoView({ block: "center" });
        e.preventDefault();
      } else {
        // If we're at the top of the list, move back up to the search box!
        onMoveFocusUpToQuery(e);
      }
    },
    [onMoveFocusUpToQuery]
  );
  const goToNextItem = React.useCallback((e) => {
    const nextLabel = e.target.closest("label").nextSibling;
    if (nextLabel) {
      nextLabel.querySelector("input[type=checkbox]").focus();
      nextLabel.scrollIntoView({ block: "center" });
      e.preventDefault();
    }
  }, []);

  // If the results aren't ready, we have some special case UI!
  if (loading) {
    return (
      <Delay ms={500}>
        <ItemListSkeleton count={8} />
      </Delay>
    );
  } else if (error) {
    return (
      <Text>
        We hit an error trying to load your search results{" "}
        <span role="img" aria-label="(sweat emoji)">
          😓
        </span>{" "}
        Try again?
      </Text>
    );
  } else if (items.length === 0) {
    return (
      <Text>
        We couldn't find any matching items{" "}
        <span role="img" aria-label="(thinking emoji)">
          🤔
        </span>{" "}
        Try again?
      </Text>
    );
  }

  // Finally, render the item list, with checkboxes and Item components!
  // We also render some extra skeleton items at the bottom during infinite
  // scroll loading.
  return (
    <>
      <ItemListContainer>
        {items.map((item, index) => (
          <SearchResultItem
            key={item.id}
            item={item}
            itemIdsToReconsider={itemIdsToReconsider}
            isWorn={outfitState.wornItemIds.includes(item.id)}
            isInOutfit={outfitState.allItemIds.includes(item.id)}
            dispatchToOutfit={dispatchToOutfit}
            checkboxRef={index === 0 ? firstSearchResultRef : null}
            goToPrevItem={goToPrevItem}
            goToNextItem={goToNextItem}
          />
        ))}
      </ItemListContainer>
      {loadingMore && <ItemListSkeleton count={8} />}
    </>
  );
}

function SearchResultItem({
  item,
  itemIdsToReconsider,
  isWorn,
  isInOutfit,
  dispatchToOutfit,
  checkboxRef,
  goToPrevItem,
  goToNextItem,
}) {
  // It's important to use `useCallback` for `onRemove`, to avoid re-rendering
  // the whole list of <Item>s!
  const onRemove = React.useCallback(
    () =>
      dispatchToOutfit({
        type: "removeItem",
        itemId: item.id,
        itemIdsToReconsider,
      }),
    [item.id, itemIdsToReconsider, dispatchToOutfit]
  );

  return (
    <label>
      <VisuallyHidden
        as="input"
        type="checkbox"
        aria-label={`Wear "${item.name}"`}
        value={item.id}
        checked={isWorn}
        ref={checkboxRef}
        onChange={(e) => {
          const itemId = e.target.value;
          const willBeWorn = e.target.checked;
          if (willBeWorn) {
            dispatchToOutfit({ type: "wearItem", itemId, itemIdsToReconsider });
          } else {
            dispatchToOutfit({
              type: "unwearItem",
              itemId,
              itemIdsToReconsider,
            });
          }
        }}
        onKeyDown={(e) => {
          if (e.key === "Enter") {
            e.target.click();
          } else if (e.key === "ArrowUp") {
            goToPrevItem(e);
          } else if (e.key === "ArrowDown") {
            goToNextItem(e);
          }
        }}
      />
      <Item
        item={item}
        isWorn={isWorn}
        isInOutfit={isInOutfit}
        onRemove={onRemove}
      />
    </label>
  );
}

/**
 * useSearchResults manages the actual querying and state management of search!
 * It's hefty, infinite-scroll pagination is a bit of a thing!
 */
function useSearchResults(query, outfitState) {
  const { speciesId, colorId } = outfitState;
  const [isEndOfResults, setIsEndOfResults] = React.useState(false);

  // We debounce the search query, so that we don't resend a new query whenever
  // the user types anything.
  const debouncedQuery = useDebounce(query, 300, {
    waitForFirstPause: true,
    initialValue: emptySearchQuery,
  });

  // When the query changes, we should update our impression of whether we've
  // reached the end!
  React.useEffect(() => {
    setIsEndOfResults(false);
  }, [query]);

  // NOTE: This query should always load ~instantly, from the client cache.
  const { data: zoneData } = useQuery(gql`
    query SearchPanelZones {
      allZones {
        id
        label
      }
    }
  `);
  const allZones = zoneData?.allZones || [];
  const filterToZones = query.filterToZoneLabel
    ? allZones.filter((z) => z.label === query.filterToZoneLabel)
    : [];
  const filterToZoneIds = filterToZones.map((z) => z.id);

  // Here's the actual GQL query! At the bottom we have more config than usual!
  const {
    loading: loadingGQL,
    error,
    data,
    fetchMore: fetchMoreGQL,
  } = useQuery(
    gql`
      query SearchPanel(
        $query: String!
        $fitsPet: FitsPetSearchFilter
        $itemKind: ItemKindSearchFilter
        $currentUserOwnsOrWants: OwnsOrWants
        $zoneIds: [ID!]!
        $speciesId: ID!
        $colorId: ID!
        $offset: Int!
      ) {
        itemSearch(
          query: $query
          fitsPet: $fitsPet
          itemKind: $itemKind
          currentUserOwnsOrWants: $currentUserOwnsOrWants
          zoneIds: $zoneIds
          offset: $offset
          limit: 50
        ) {
          query
          zones {
            id
          }
          items {
            # TODO: De-dupe this from useOutfitState?
            id
            name
            thumbnailUrl
            isNc
            isPb
            currentUserOwnsThis
            currentUserWantsThis

            appearanceOn(speciesId: $speciesId, colorId: $colorId) {
              # This enables us to quickly show the item when the user clicks it!
              ...ItemAppearanceForOutfitPreview

              # This is used to group items by zone, and to detect conflicts when
              # wearing a new item.
              layers {
                zone {
                  id
                  label @client
                }
              }
              restrictedZones {
                id
                label @client
                isCommonlyUsedByItems @client
              }
            }
          }
        }
      }
      ${itemAppearanceFragment}
    `,
    {
      variables: {
        query: debouncedQuery.value,
        fitsPet: { speciesId, colorId },
        itemKind: debouncedQuery.filterToItemKind,
        currentUserOwnsOrWants: debouncedQuery.filterToCurrentUserOwnsOrWants,
        zoneIds: filterToZoneIds,
        offset: 0,
        speciesId,
        colorId,
      },
      context: { sendAuth: true },
      skip:
        !debouncedQuery.value &&
        !debouncedQuery.filterToItemKind &&
        !debouncedQuery.filterToZoneLabel &&
        !debouncedQuery.filterToCurrentUserOwnsOrWants,
      notifyOnNetworkStatusChange: true,
      onCompleted: (d) => {
        // This is called each time the query completes, including on
        // `fetchMore`, with the extended results. But, on the first time, this
        // logic can tell us whether we're at the end of the list, by counting
        // whether there was <30. We also have to check in `fetchMore`!
        const items = d && d.itemSearch && d.itemSearch.items;
        if (items && items.length < 30) {
          setIsEndOfResults(true);
        }
      },
      onError: (e) => {
        console.error("Error loading search results", e);
      },
    }
  );

  // Smooth over the data a bit, so that we can use key fields with confidence!
  const result = data?.itemSearch;
  const resultValue = result?.query;
  const zoneStr = [...filterToZoneIds].sort().join(",");
  const resultZoneStr = (result?.zones || [])
    .map((z) => z.id)
    .sort()
    .join(",");
  const queriesMatch = resultValue === query.value && resultZoneStr === zoneStr;
  const items = result?.items || [];

  // Okay, what kind of loading state is this?
  let loading;
  let loadingMore;
  if (loadingGQL && items.length > 0 && queriesMatch) {
    // If we already have items for this query, but we're also loading GQL,
    // then we're `loadingMore`.
    loading = false;
    loadingMore = true;
  } else if (loadingGQL || query !== debouncedQuery) {
    // Otherwise, if we're loading GQL or the user has changed the query, we're
    // just `loading`.
    loading = true;
    loadingMore = false;
  } else {
    // Otherwise, we're not loading at all!
    loading = false;
    loadingMore = false;
  }

  // When SearchResults calls this, we'll resend the query, with the `offset`
  // increased. We'll append the results to the original query!
  const fetchMore = React.useCallback(() => {
    if (!loadingGQL && !error && !isEndOfResults) {
      fetchMoreGQL({
        variables: {
          offset: items.length,
        },
        updateQuery: (prev, { fetchMoreResult }) => {
          // Note: This is a bit awkward because, if the results count ends on
          // a multiple of 30, the user will see a flash of loading before
          // getting told it's actually the end. Ah well :/
          //
          // We could maybe make this more rigorous later with
          // react-virtualized to have a better scrollbar anyway, and then
          // we'd need to return the total result count... a bit annoying to
          // potentially double the query runtime? We'd need to see how slow it
          // actually makes things.
          if (fetchMoreResult.itemSearch.items.length < 30) {
            setIsEndOfResults(true);
          }

          return {
            ...prev,
            itemSearch: {
              ...(prev?.itemSearch || {}),
              items: [
                ...(prev?.itemSearch?.items || []),
                ...(fetchMoreResult?.itemSearch?.items || []),
              ],
            },
          };
        },
      }).catch((e) => {
        console.error("Error loading more search results pages", e);
      });
    }
  }, [loadingGQL, error, isEndOfResults, fetchMoreGQL, items.length]);

  return { loading, loadingMore, error, items, fetchMore };
}

/**
 * useScrollTracker watches for the given scroll container to scroll near the
 * bottom, then fires a callback. We use this to fetch more search results!
 */
function useScrollTracker(scrollContainerRef, threshold, onScrolledToBottom) {
  const onScroll = React.useCallback(
    (e) => {
      const topEdgeScrollPosition = e.target.scrollTop;
      const bottomEdgeScrollPosition =
        topEdgeScrollPosition + e.target.clientHeight;
      const remainingScrollDistance =
        e.target.scrollHeight - bottomEdgeScrollPosition;
      if (remainingScrollDistance < threshold) {
        onScrolledToBottom();
      }
    },
    [onScrolledToBottom, threshold]
  );

  React.useLayoutEffect(() => {
    const scrollContainer = scrollContainerRef.current;

    if (!scrollContainer) {
      return;
    }

    scrollContainer.addEventListener("scroll", onScroll);

    return () => {
      if (scrollContainer) {
        scrollContainer.removeEventListener("scroll", onScroll);
      }
    };
  }, [onScroll, scrollContainerRef]);
}

/**
 * serializeQuery stably converts a search query object to a string, for easier
 * JS comparison.
 */
function serializeQuery(query) {
  return `${JSON.stringify([
    query.value,
    query.filterToItemKind,
    query.filterToZoneLabel,
    query.filterToCurrentUserOwnsOrWants,
  ])}`;
}

export default SearchPanel;