feat: add pagination to topic's posts

packages/concordia-app/src/components/PostList/index.jsx

@@ -51,11 +51,13 @@ const PostList = (props) => {
   }, [focusOnPost, getPostCallHashes, loading, postIds]);
 
   return (
+      <>
           <Dimmer.Dimmable as={Feed} blurring dimmed={loading} id="post-list" size="large">
               <Loader active={loading} />
               {posts}
-          <PaginationComponent onPageChange={onPageChange} numberOfItems={numberOfItems} />
           </Dimmer.Dimmable>
+          <PaginationComponent onPageChange={onPageChange} numberOfItems={numberOfItems} />
+      </>
   );
 };
 

packages/concordia-app/src/views/Topic/TopicView/TopicPostList/index.jsx

@@ -0,0 +1,82 @@
+import React, {
+  useEffect, useMemo, useState,
+} from 'react';
+import { useSelector } from 'react-redux';
+import { FORUM_CONTRACT } from 'concordia-shared/src/constants/contracts/ContractNames';
+import PostList from '../../../../components/PostList';
+import { ITEMS_PER_PAGE } from '../../../../components/PaginationComponent';
+import { drizzle } from '../../../../redux/store';
+
+const {
+  contracts: {
+    [FORUM_CONTRACT]: {
+      methods: {
+        getTopicPostCount: { cacheCall: getTopicPostCountChainData },
+        getTopicPosts: { cacheCall: getTopicPostsChainData },
+      },
+    },
+  },
+} = drizzle;
+
+const TopicPostList = (props) => {
+  const {
+    topicId, loading, focusOnPost,
+  } = props;
+  const [pageNumber, setPageNumber] = useState(1);
+
+  const [topicPostCount, setTopicPostCount] = useState(null);
+  const [postIds, setPostIds] = useState([]);
+
+  const [getTopicPostCountCallHash, setGetTopicPostCountCallHash] = useState(null);
+  const [getTopicPostsCallHash, setGetTopicPostsCallHash] = useState(null);
+
+  const getTopicPostCountResult = useSelector((state) => state.contracts[FORUM_CONTRACT].getTopicPostCount[getTopicPostCountCallHash]);
+  const getTopicPostsResult = useSelector((state) => state.contracts[FORUM_CONTRACT].getTopicPosts[getTopicPostsCallHash]);
+
+  useEffect(() => {
+    if (getTopicPostCountCallHash === null) {
+      setGetTopicPostCountCallHash(getTopicPostCountChainData(topicId));
+    }
+  }, [getTopicPostCountCallHash, topicId]);
+
+  useEffect(() => {
+    if (topicPostCount !== null && topicPostCount !== 0) {
+      const startIndex = Math.max(topicPostCount - ITEMS_PER_PAGE * pageNumber, 0);
+      const endIndex = topicPostCount - ITEMS_PER_PAGE * (pageNumber - 1) - 1;
+      setGetTopicPostsCallHash(getTopicPostsChainData(topicId, startIndex, endIndex));
+    }
+  }, [pageNumber, topicId, topicPostCount]);
+
+  useEffect(() => {
+    if (getTopicPostCountResult) {
+      setTopicPostCount(parseInt(getTopicPostCountResult.value, 10));
+    }
+  }, [getTopicPostCountResult, topicPostCount]);
+
+  useEffect(() => {
+    if (getTopicPostsResult) {
+      setPostIds(getTopicPostsResult.value.slice().reverse().map(Number));
+    }
+  }, [getTopicPostsResult, topicPostCount]);
+
+  const handlePageChange = (event, data) => {
+    setPageNumber(data.activePage);
+  };
+
+  return useMemo(() => {
+    if (postIds.length && postIds.length !== 0) {
+      return (
+          <PostList
+            postIds={postIds}
+            numberOfItems={topicPostCount}
+            onPageChange={handlePageChange}
+            loading={loading}
+            focusOnPost={focusOnPost}
+          />
+      );
+    }
+    return null;
+  }, [postIds, topicPostCount, loading, focusOnPost]);
+};
+
+export default TopicPostList;

packages/concordia-app/src/views/Topic/TopicView/index.jsx

@@ -11,7 +11,7 @@ import { TOPICS_DATABASE, USER_DATABASE } from 'concordia-shared/src/constants/o
 import { breeze, drizzle } from '../../../redux/store';
 import { FETCH_USER_DATABASE } from '../../../redux/actions/peerDbReplicationActions';
 import './styles.css';
-import PostList from '../../../components/PostList';
+import TopicPostList from './TopicPostList';
 import determineKVAddress from '../../../utils/orbitUtils';
 import { TOPIC_SUBJECT } from '../../../constants/orbit/TopicsDatabaseKeys';
 import PostCreate from '../../../components/PostCreate';
@@ -24,8 +24,6 @@ const TopicView = (props) => {
     topicId, topicAuthorAddress: initialTopicAuthorAddress, topicAuthor: initialTopicAuthor,
     timestamp: initialTimestamp, postIds: initialPostIds, focusOnPost,
   } = props;
-  const drizzleInitialized = useSelector((state) => state.drizzleStatus.initialized);
-  const drizzleInitializationFailed = useSelector((state) => state.drizzleStatus.failed);
   const userAddress = useSelector((state) => state.user.address);
   const hasSignedUp = useSelector((state) => state.user.hasSignedUp);
   const getTopicResults = useSelector((state) => state.contracts[FORUM_CONTRACT].getTopic);
@@ -47,12 +45,10 @@ const TopicView = (props) => {
         || timestamp === null
         || postIds === null;
 
-    if (drizzleInitialized && !drizzleInitializationFailed && shouldGetTopicDataFromChain) {
+    if (shouldGetTopicDataFromChain) {
       setGetTopicCallHash(getTopicChainData(topicId));
     }
-  }, [
-    drizzleInitializationFailed, drizzleInitialized, postIds, timestamp, topicAuthor, topicAuthorAddress, topicId,
-  ]);
+  }, [postIds, timestamp, topicAuthor, topicAuthorAddress, topicId]);
 
   useEffect(() => {
     if (getTopicCallHash && getTopicResults && getTopicResults[getTopicCallHash]) {
@@ -149,7 +145,7 @@ const TopicView = (props) => {
                   </div>
                   <Divider />
               </Dimmer.Dimmable>
-              <PostList postIds={postIds || []} loading={postIds === null} focusOnPost={focusOnPost} />
+              <TopicPostList topicId={topicId} loading={postIds === null} focusOnPost={focusOnPost} />
           </Segment>
 
           {topicSubject !== null && postIds !== null && hasSignedUp && (

packages/concordia-app/src/views/Topic/TopicView/styles.css

@@ -1,5 +1,6 @@
 #topic-container {
     height: auto !important;
+    text-align: center;
 }
 
 #topic-header {

packages/concordia-contracts/contracts/Forum.sol

@@ -188,9 +188,22 @@ contract Forum {
         );
     }
 
-    function getTopicPosts(uint topicID) public view returns (uint[] memory) {
+    function getTopicPostCount(uint topicID) public view returns (uint) {
         require(topicExists(topicID), TOPIC_DOES_NOT_EXIST);
-        return topics[topicID].postIDs;
+        return topics[topicID].postIDs.length;
+    }
+
+    function getTopicPosts(uint topicID, uint startIndex, uint endIndex) public view returns (uint[] memory) {
+        require(topicExists(topicID), TOPIC_DOES_NOT_EXIST);
+        require(startIndex <= endIndex && topics[topicID].postIDs.length > endIndex, INVALID_RANGE);
+        uint length = endIndex - startIndex + 1;
+        uint[] memory topicPosts = new uint[](length);
+        uint counter = 0;
+        for (uint i = startIndex; i <= endIndex; i++) {
+            topicPosts[counter] = topics[topicID].postIDs[i];
+            counter++;
+        }
+        return topicPosts;
     }
 
     function getTopicAuthor(uint topicID) public view returns (address) {