From 1f817c8a79c5cb669d2f410c45dea4297d841058 Mon Sep 17 00:00:00 2001
From: MTG2000 <mtg0987654321@gmail.com>
Date: Mon, 18 Apr 2022 16:37:59 +0300
Subject: [PATCH] feat: added infinite scroll to feed page

---
 .../Posts/Components/PostsList/PostsList.tsx  | 11 ++----
 .../Posts/pages/FeedPage/FeedPage.tsx         | 18 +++++++--
 .../Posts/pages/FeedPage/feed.graphql         |  4 +-
 src/graphql/index.tsx                         | 11 ++++--
 src/mocks/data/posts.ts                       |  8 ++--
 src/mocks/handlers.ts                         |  7 ++--
 src/mocks/resolvers.ts                        |  8 ++--
 src/utils/apollo.ts                           | 39 ++++++++++++++++++-
 src/utils/hooks/index.ts                      |  2 +
 src/utils/hooks/useInfiniteQuery.ts           | 34 ++++++++++++++++
 src/utils/hooks/useReachedBottom.ts           | 17 +++++---
 src/utils/interfaces/misc.interfaces.ts       |  2 +-
 12 files changed, 125 insertions(+), 36 deletions(-)
 create mode 100644 src/utils/hooks/useInfiniteQuery.ts

diff --git a/src/features/Posts/Components/PostsList/PostsList.tsx b/src/features/Posts/Components/PostsList/PostsList.tsx
index 383f97a..d983037 100644
--- a/src/features/Posts/Components/PostsList/PostsList.tsx
+++ b/src/features/Posts/Components/PostsList/PostsList.tsx
@@ -1,19 +1,14 @@
 import { useCallback } from "react"
 import { Post } from "src/features/Posts/types"
 import { useReachedBottom } from "src/utils/hooks/useReachedBottom"
-import { ListProps } from "src/utils/interfaces"
+import { ListComponentProps } from "src/utils/interfaces"
 import PostCard, { PostCardSkeleton } from "../PostCard"
 
-type Props = ListProps<Post>
+type Props = ListComponentProps<Post>
 
 export default function PostsList(props: Props) {
 
-
-    const reachedBottom = useCallback(() => {
-        console.log("NEW FETCH")
-    }, [])
-
-    const { ref } = useReachedBottom<HTMLDivElement>(reachedBottom)
+    const { ref } = useReachedBottom<HTMLDivElement>(props.onReachedBottom)
 
     if (props.isLoading)
         return <div className="flex flex-col gap-24">
diff --git a/src/features/Posts/pages/FeedPage/FeedPage.tsx b/src/features/Posts/pages/FeedPage/FeedPage.tsx
index 81c2c89..c72d99d 100644
--- a/src/features/Posts/pages/FeedPage/FeedPage.tsx
+++ b/src/features/Posts/pages/FeedPage/FeedPage.tsx
@@ -1,15 +1,22 @@
 
 import { useFeedQuery } from 'src/graphql'
-import { MOCK_DATA } from 'src/mocks/data'
+import { useInfiniteQuery } from 'src/utils/hooks'
 import PostsList from '../../Components/PostsList/PostsList'
 import TrendingCard from '../../Components/TrendingCard/TrendingCard'
 import PopularCategories from './PopularCategories/PopularCategories'
 import SortBy from './SortBy/SortBy'
 import styles from './styles.module.css'
 
+
 export default function FeedPage() {
 
-    const feedQuery = useFeedQuery()
+    const feedQuery = useFeedQuery({
+        variables: {
+            take: 10,
+            skip: 0
+        }
+    })
+    const { fetchMore, isFetchingMore } = useInfiniteQuery(feedQuery, 'getFeed')
 
     return (
         <div
@@ -22,7 +29,12 @@ export default function FeedPage() {
                     <PopularCategories />
                 </div>
             </aside>
-            <PostsList isLoading={feedQuery.loading} items={feedQuery.data?.getFeed} />
+            <PostsList
+                isLoading={feedQuery.loading}
+                items={feedQuery.data?.getFeed}
+                isFetching={isFetchingMore}
+                onReachedBottom={fetchMore}
+            />
             <aside>
                 <div className="sticky top-16">
                     <TrendingCard />
diff --git a/src/features/Posts/pages/FeedPage/feed.graphql b/src/features/Posts/pages/FeedPage/feed.graphql
index d012632..5bdbfa7 100644
--- a/src/features/Posts/pages/FeedPage/feed.graphql
+++ b/src/features/Posts/pages/FeedPage/feed.graphql
@@ -1,5 +1,5 @@
-query Feed {
-  getFeed {
+query Feed($skip: Int, $take: Int) {
+  getFeed(skip: $skip, take: $take) {
     ... on Story {
       id
       title
diff --git a/src/graphql/index.tsx b/src/graphql/index.tsx
index e354914..faff981 100644
--- a/src/graphql/index.tsx
+++ b/src/graphql/index.tsx
@@ -254,7 +254,10 @@ export type SearchProjectsQueryVariables = Exact<{
 
 export type SearchProjectsQuery = { __typename?: 'Query', searchProjects: Array<{ __typename?: 'Project', id: number, thumbnail_image: string, title: string, category: { __typename?: 'Category', title: string, id: number } }> };
 
-export type FeedQueryVariables = Exact<{ [key: string]: never; }>;
+export type FeedQueryVariables = Exact<{
+  skip: InputMaybe<Scalars['Int']>;
+  take: InputMaybe<Scalars['Int']>;
+}>;
 
 
 export type FeedQuery = { __typename?: 'Query', getFeed: Array<{ __typename?: 'Bounty', id: number, title: string, date: string, excerpt: string, votes_count: number, type: string, cover_image: string, deadline: string, reward_amount: number, applicants_count: number, author: { __typename?: 'User', id: number, name: string, image: string }, tags: Array<{ __typename?: 'Tag', id: number, title: string }> } | { __typename?: 'Question', id: number, title: string, date: string, excerpt: string, votes_count: number, type: string, cover_image: string, deadline: string, reward_amount: number, answers_count: number, author: { __typename?: 'User', id: number, name: string, image: string }, tags: Array<{ __typename?: 'Tag', id: number, title: string }>, comments: Array<{ __typename?: 'PostComment', id: number, date: string, body: string, author: { __typename?: 'User', id: number, name: string, image: string } }> } | { __typename?: 'Story', id: number, title: string, date: string, excerpt: string, votes_count: number, type: string, cover_image: string, comments_count: number, author: { __typename?: 'User', id: number, name: string, image: string }, tags: Array<{ __typename?: 'Tag', id: number, title: string }> }> };
@@ -391,8 +394,8 @@ export type SearchProjectsQueryHookResult = ReturnType<typeof useSearchProjectsQ
 export type SearchProjectsLazyQueryHookResult = ReturnType<typeof useSearchProjectsLazyQuery>;
 export type SearchProjectsQueryResult = Apollo.QueryResult<SearchProjectsQuery, SearchProjectsQueryVariables>;
 export const FeedDocument = gql`
-    query Feed {
-  getFeed {
+    query Feed($skip: Int, $take: Int) {
+  getFeed(skip: $skip, take: $take) {
     ... on Story {
       id
       title
@@ -480,6 +483,8 @@ export const FeedDocument = gql`
  * @example
  * const { data, loading, error } = useFeedQuery({
  *   variables: {
+ *      skip: // value for 'skip'
+ *      take: // value for 'take'
  *   },
  * });
  */
diff --git a/src/mocks/data/posts.ts b/src/mocks/data/posts.ts
index 6aae6b7..0157339 100644
--- a/src/mocks/data/posts.ts
+++ b/src/mocks/data/posts.ts
@@ -87,9 +87,7 @@ posts.bounties = posts.bounties.map(b => ({ ...b, __typename: "Bounty" }))
 posts.questions = posts.questions.map(b => ({ ...b, __typename: "Question" }))
 posts.stories = posts.stories.map(b => ({ ...b, __typename: "Story" }))
 
-export const feed: Post[] = [
-    ...posts.stories,
-    ...posts.bounties,
-    ...posts.questions,
-]
+export const feed: Post[] = Array(30).fill(0).map((_, idx) => {
+    return { ...posts.stories[0], id: idx + 1, title: `Post Title ${idx + 1}` }
+})
 
diff --git a/src/mocks/handlers.ts b/src/mocks/handlers.ts
index 5b19143..26f95df 100644
--- a/src/mocks/handlers.ts
+++ b/src/mocks/handlers.ts
@@ -17,6 +17,7 @@ import {
     FeedQuery,
     PostDetailsQuery,
     PostDetailsQueryVariables,
+    FeedQueryVariables,
 } from 'src/graphql'
 
 const delay = (ms = 1000) => new Promise((res) => setTimeout(res, ms))
@@ -99,12 +100,12 @@ export const handlers = [
         )
     }),
 
-    graphql.query<FeedQuery>('Feed', async (req, res, ctx) => {
+    graphql.query<FeedQuery, FeedQueryVariables>('Feed', async (req, res, ctx) => {
         await delay()
-
+        const { take, skip } = req.variables;
         return res(
             ctx.data({
-                getFeed: getFeed()
+                getFeed: getFeed({ take, skip })
             })
         )
     }),
diff --git a/src/mocks/resolvers.ts b/src/mocks/resolvers.ts
index b432d25..04a9525 100644
--- a/src/mocks/resolvers.ts
+++ b/src/mocks/resolvers.ts
@@ -1,6 +1,6 @@
 import ASSETS from "src/assets";
 import { MOCK_DATA } from "./data";
-import { Query } from 'src/graphql'
+import { Query, QueryGetFeedArgs } from 'src/graphql'
 
 export function getCategory(id: number) {
 
@@ -42,8 +42,10 @@ export function hottestProjects() {
     return MOCK_DATA.projects.sort((p1, p2) => p2.votes_count - p1.votes_count).slice(0, 20)
 }
 
-export function getFeed(): Query['getFeed'] {
-    return MOCK_DATA.feed as any;
+export function getFeed(config: QueryGetFeedArgs): Query['getFeed'] {
+    const take = config.take ?? 10
+    const skip = config.skip ?? 0
+    return MOCK_DATA.feed.slice(skip, skip + take) as any;
 }
 
 export function getPostById(postId: number): Query['getPostById'] {
diff --git a/src/utils/apollo.ts b/src/utils/apollo.ts
index 7486911..7d7cc47 100644
--- a/src/utils/apollo.ts
+++ b/src/utils/apollo.ts
@@ -1,4 +1,4 @@
-import { ApolloClient, HttpLink, InMemoryCache, from } from "@apollo/client";
+import { ApolloClient, HttpLink, InMemoryCache, from, Reference, FieldPolicy } from "@apollo/client";
 import { onError } from "@apollo/client/link/error";
 import { RetryLink } from "@apollo/client/link/retry";
 
@@ -45,5 +45,40 @@ export const apolloClient = new ApolloClient({
         errorLink,
         httpLink
     ]),
-    cache: new InMemoryCache()
+    cache: new InMemoryCache({
+        typePolicies: {
+            Query: {
+                fields: {
+                    getFeed: offsetLimitPagination()
+                },
+            },
+        },
+    })
 });
+
+type KeyArgs = FieldPolicy<any>["keyArgs"];
+
+function offsetLimitPagination<T = Reference>(
+    keyArgs: KeyArgs = false,
+): FieldPolicy<T[]> {
+    return {
+        keyArgs,
+        merge(existing, incoming, { args }) {
+            const merged = existing ? existing.slice(0) : [];
+            if (args) {
+                // Assume an skip of 0 if args.skip omitted.
+                const { skip = 0 } = args;
+                for (let i = 0; i < incoming.length; ++i) {
+                    merged[skip + i] = incoming[i];
+                }
+            } else {
+                // It's unusual (probably a mistake) for a paginated field not
+                // to receive any arguments, so you might prefer to throw an
+                // exception here, instead of recovering by appending incoming
+                // onto the existing array.
+                merged.push.apply(merged, [...incoming]);
+            }
+            return merged;
+        },
+    };
+}
\ No newline at end of file
diff --git a/src/utils/hooks/index.ts b/src/utils/hooks/index.ts
index 14a37bb..498027e 100644
--- a/src/utils/hooks/index.ts
+++ b/src/utils/hooks/index.ts
@@ -1,3 +1,5 @@
 export * from "./storeHooks";
 export * from "./useResizeListener";
 export * from "./usePressHolder";
+export * from "./useInfiniteQuery";
+export * from "./useReachedBottom";
diff --git a/src/utils/hooks/useInfiniteQuery.ts b/src/utils/hooks/useInfiniteQuery.ts
new file mode 100644
index 0000000..d3f9cb9
--- /dev/null
+++ b/src/utils/hooks/useInfiniteQuery.ts
@@ -0,0 +1,34 @@
+import { QueryResult } from "@apollo/client";
+import { useCallback, useState } from "react";
+
+export const useInfiniteQuery = (query: QueryResult, dataField: string) => {
+    const [fetchingMore, setFetchingMore] = useState(false)
+    const [reachedLastPage, setReachedLastPage] = useState(false)
+
+
+    const fetchMore = useCallback(
+        () => {
+            if (!fetchingMore && !reachedLastPage) {
+                setFetchingMore(true);
+                // console.log(feedQuery.variables?.skip);
+
+                query.fetchMore({
+                    variables: {
+                        skip: query.data?.[dataField].length,
+                    }
+                }).then((d) => {
+                    if (d.data?.[dataField].length === 0)
+                        setReachedLastPage(true)
+
+                    setFetchingMore(false)
+                })
+            }
+        }
+        , [dataField, fetchingMore, query, reachedLastPage]
+    )
+
+    return {
+        isFetchingMore: fetchingMore,
+        fetchMore: fetchMore
+    }
+}
diff --git a/src/utils/hooks/useReachedBottom.ts b/src/utils/hooks/useReachedBottom.ts
index 1837ef6..2426921 100644
--- a/src/utils/hooks/useReachedBottom.ts
+++ b/src/utils/hooks/useReachedBottom.ts
@@ -6,25 +6,30 @@ export const useReachedBottom = <T extends HTMLElement>(cb?: () => void, options
     const { offset = window.innerHeight, throttle = 600 } = options
 
     const ref = useRef<T>(null);
+    const callbackHandler = useRef<Function>();
+
+    useEffect(() => {
+        if (!cb)
+            callbackHandler.current = undefined;
+        else {
+            callbackHandler.current = _debounce(cb, throttle)
+        }
+    }, [cb, throttle])
 
 
     useEffect(() => {
-        if (!cb) return;
-
-        const cbDebounced = _debounce(cb, throttle)
         const listener = () => {
             if (!ref.current) return;
             const curWindowPosition = window.scrollY + window.innerHeight;
             const elTriggerPosition = ref.current.offsetTop + ref.current.scrollHeight - offset;
-            if (curWindowPosition > elTriggerPosition) cbDebounced();
+            if (curWindowPosition > elTriggerPosition) callbackHandler.current?.();
         }
-
         document.addEventListener('scroll', listener)
 
         return () => {
             document.removeEventListener('scroll', listener)
         }
-    }, [cb, offset, throttle])
+    }, [offset, throttle])
 
     return { ref }
 }
\ No newline at end of file
diff --git a/src/utils/interfaces/misc.interfaces.ts b/src/utils/interfaces/misc.interfaces.ts
index 2831c9c..b8cd2b3 100644
--- a/src/utils/interfaces/misc.interfaces.ts
+++ b/src/utils/interfaces/misc.interfaces.ts
@@ -5,7 +5,7 @@ export type Tag = {
 }
 
 
-export type ListProps<T> = {
+export type ListComponentProps<T> = {
     items?: T[]
     isLoading?: boolean;
     isFetching?: boolean;