import { ApolloClient, createHttpLink, InMemoryCache } from "@apollo/client";
import { loadErrorMessages, loadDevMessages } from "@apollo/client/dev";
import { createPersistedQueryLink } from "apollo-link-persisted-queries";

import { buildImpress2020Url } from "./impress-2020-config";

// Use Apollo's error messages in development.
if (process.env["NODE_ENV"] === "development") {
  loadErrorMessages();
  loadDevMessages();
}

// Teach Apollo to load certain fields from the cache, to avoid extra network
// requests. This happens a lot - e.g. reusing data from item search on the
// outfit immediately!
const typePolicies = {
  Query: {
    fields: {
      closetList: (_, { args, toReference }) => {
        return toReference({ __typename: "ClosetList", id: args.id }, true);
      },
      items: (_, { args, toReference }) => {
        return args.ids.map((id) =>
          toReference({ __typename: "Item", id }, true),
        );
      },
      item: (_, { args, toReference }) => {
        return toReference({ __typename: "Item", id: args.id }, true);
      },
      petAppearanceById: (_, { args, toReference }) => {
        return toReference({ __typename: "PetAppearance", id: args.id }, true);
      },
      species: (_, { args, toReference }) => {
        return toReference({ __typename: "Species", id: args.id }, true);
      },
      color: (_, { args, toReference }) => {
        return toReference({ __typename: "Color", id: args.id }, true);
      },
      outfit: (_, { args, toReference }) => {
        return toReference({ __typename: "Outfit", id: args.id }, true);
      },
      user: (_, { args, toReference }) => {
        return toReference({ __typename: "User", id: args.id }, true);
      },
    },
  },

  Item: {
    fields: {
      appearanceOn: (appearance, { args, readField, toReference }) => {
        // If we already have this exact appearance in the cache, serve it!
        if (appearance) {
          return appearance;
        }

        const { speciesId, colorId, altStyleId } = args;
        console.debug(
          "[appearanceOn] seeking cached appearance",
          speciesId,
          colorId,
          altStyleId,
          readField("id"),
        );

        // If this is an alt style, don't try to mess with clever caching.
        // (Note that, if it's already in the cache, the first condition will
        // catch that! This won't *always* force a fresh load!)
        if (altStyleId != null) {
          return undefined;
        }

        // Otherwise, we're going to see if this is a standard color, in which
        // case we can reuse the standard color appearance if we already have
        // it! This helps for fast loading when switching between standard
        // colors.
        const speciesStandardBodyId = readField(
          "standardBodyId",
          toReference({ __typename: "Species", id: speciesId }),
        );
        const colorIsStandard = readField(
          "isStandard",
          toReference({ __typename: "Color", id: colorId }),
        );
        if (speciesStandardBodyId == null || colorIsStandard == null) {
          // We haven't loaded all the species/colors into cache yet. We might
          // be loading them, depending on the page? Either way, return
          // `undefined`, meaning we don't know how to serve this from cache.
          // This will cause us to start loading it from the server.
          console.debug("[appearanceOn] species/colors not loaded yet");
          return undefined;
        }

        if (colorIsStandard) {
          const itemId = readField("id");
          console.debug(
            "[appearanceOn] standard color, will read:",
            `item-${itemId}-body-${speciesStandardBodyId}`,
          );
          return toReference({
            __typename: "ItemAppearance",
            id: `item-${itemId}-body-${speciesStandardBodyId}`,
          });
        } else {
          console.debug("[appearanceOn] non-standard color, failure");
          // This isn't a standard color, so we don't support special
          // cross-color caching for it. Return `undefined`, meaning we don't
          // know how to serve this from cache. This will cause us to start
          // loading it from the server.
          return undefined;
        }
      },

      currentUserOwnsThis: (cachedValue, { readField }) => {
        if (cachedValue != null) {
          return cachedValue;
        }

        // Do we know what items this user owns? If so, scan for this item.
        const currentUserRef = readField("currentUser", {
          __ref: "ROOT_QUERY",
        });
        if (!currentUserRef) {
          return undefined;
        }
        const thisItemId = readField("id");
        const itemsTheyOwn = readField("itemsTheyOwn", currentUserRef);
        if (!itemsTheyOwn) {
          return undefined;
        }

        const theyOwnThisItem = itemsTheyOwn.some(
          (itemRef) => readField("id", itemRef) === thisItemId,
        );
        return theyOwnThisItem;
      },
      currentUserWantsThis: (cachedValue, { readField }) => {
        if (cachedValue != null) {
          return cachedValue;
        }

        // Do we know what items this user owns? If so, scan for this item.
        const currentUserRef = readField("currentUser", {
          __ref: "ROOT_QUERY",
        });
        if (!currentUserRef) {
          return undefined;
        }
        const thisItemId = readField("id");
        const itemsTheyWant = readField("itemsTheyWant", currentUserRef);
        if (!itemsTheyWant) {
          return undefined;
        }

        const theyWantThisItem = itemsTheyWant.some(
          (itemRef) => readField("id", itemRef) === thisItemId,
        );
        return theyWantThisItem;
      },
    },
  },

  ClosetList: {
    fields: {
      // When loading the updated contents of a list, replace it entirely.
      items: { merge: false },
    },
  },
};

const cache = new InMemoryCache({ typePolicies });

const httpLink = createHttpLink({
  uri: buildImpress2020Url("/api/graphql"),
});

const link = createPersistedQueryLink({
  useGETForHashedQueries: true,
}).concat(httpLink);

/**
 * apolloClient is the global Apollo Client instance we use for GraphQL
 * queries. This is how we communicate with the server!
 */
const apolloClient = new ApolloClient({
  link,
  cache,
  connectToDevTools: true,
});

export default apolloClient;