Optimize tags and followedTags

followedTags:
- Moved the filtering to the reducer side, so that we don't do it every time. We can't rely on `createSelector` because the store will be invalidated on each `USER_STATE_POPULATE`, unfortunately.

tags:
- Memoize via re-reselect for the "ForUri" selector.

ui/component/claimTags/index.js

@@ -1,10 +1,10 @@
 import { connect } from 'react-redux';
-import { makeSelectTagsForUri } from 'redux/selectors/claims';
+import { selectTagsForUri } from 'redux/selectors/claims';
 import { selectFollowedTags } from 'redux/selectors/tags';
 import ClaimTags from './view';
 
 const select = (state, props) => ({
-  tags: makeSelectTagsForUri(props.uri)(state),
+  tags: selectTagsForUri(state, props.uri),
   followedTags: selectFollowedTags(state),
 });
 

ui/redux/reducers/tags.js

@@ -65,11 +65,22 @@ export default handleActions(
     [ACTIONS.USER_STATE_POPULATE]: (state: TagState, action: { data: { tags: ?Array<string> } }) => {
       const { tags } = action.data;
       if (Array.isArray(tags)) {
+        const next = tags && tags.filter((tag) => typeof tag === 'string');
+        const prev = state.followedTags;
+
+        if (next && prev && prev.length === next.length && prev.every((value, index) => value === next[index])) {
+          // No changes
+          return state;
+        }
+
+        // New state
         return {
           ...state,
-          followedTags: tags,
+          followedTags: next || [],
         };
       }
+
+      // Purge 'followedTags'
       return {
         ...state,
       };

ui/redux/selectors/claims.js

@@ -267,6 +267,11 @@ export const makeSelectTotalPagesInChannelSearch = (uri: string) =>
     return byChannel['pageCount'];
   });
 
+export const selectMetadataForUri = createCachedSelector(selectClaimForUri, (claim, uri) => {
+  const metadata = claim && claim.value;
+  return metadata || (claim === undefined ? undefined : null);
+})((state, uri) => uri);
+
 export const makeSelectMetadataForUri = (uri: string) =>
   createSelector(makeSelectClaimForUri(uri), (claim) => {
     const metadata = claim && claim.value;
@@ -534,6 +539,10 @@ export const makeSelectMyChannelPermUrlForName = (name: string) =>
     return matchingClaim ? matchingClaim.permanent_url : null;
   });
 
+export const selectTagsForUri = createCachedSelector(selectMetadataForUri, (metadata: ?GenericMetadata) => {
+  return (metadata && metadata.tags) || [];
+})((state, uri) => uri);
+
 export const makeSelectTagsForUri = (uri: string) =>
   createSelector(makeSelectMetadataForUri(uri), (metadata: ?GenericMetadata) => {
     return (metadata && metadata.tags) || [];

ui/redux/selectors/tags.js

@@ -1,16 +1,16 @@
 // @flow
 import { createSelector } from 'reselect';
 
-const selectState = (state: { tags: TagState }) => state.tags || {};
+type State = { tags: TagState };
+
+const selectState = (state: State) => state.tags || {};
 
 export const selectKnownTagsByName = createSelector(selectState, (state: TagState): KnownTags => state.knownTags);
 
-export const selectFollowedTagsList = createSelector(selectState, (state: TagState): Array<string> =>
-  state.followedTags.filter(tag => typeof tag === 'string')
-);
+export const selectFollowedTagsList = (state: State) => selectState(state).followedTags;
 
 export const selectFollowedTags = createSelector(selectFollowedTagsList, (followedTags: Array<string>): Array<Tag> =>
-  followedTags.map(tag => ({ name: tag.toLowerCase() })).sort((a, b) => a.name.localeCompare(b.name))
+  followedTags.map((tag) => ({ name: tag.toLowerCase() })).sort((a, b) => a.name.localeCompare(b.name))
 );
 
 export const selectUnfollowedTags = createSelector(
@@ -19,7 +19,7 @@ export const selectUnfollowedTags = createSelector(
   (tagsByName: KnownTags, followedTags: Array<string>): Array<Tag> => {
     const followedTagsSet = new Set(followedTags);
     let tagsToReturn = [];
-    Object.keys(tagsByName).forEach(key => {
+    Object.keys(tagsByName).forEach((key) => {
       if (!followedTagsSet.has(key)) {
         const { name } = tagsByName[key];
         tagsToReturn.push({ name: name.toLowerCase() });
@@ -31,6 +31,6 @@ export const selectUnfollowedTags = createSelector(
 );
 
 export const makeSelectIsFollowingTag = (tag: string) =>
-  createSelector(selectFollowedTags, followedTags => {
-    return followedTags.some(followedTag => followedTag.name === tag.toLowerCase());
+  createSelector(selectFollowedTags, (followedTags) => {
+    return followedTags.some((followedTag) => followedTag.name === tag.toLowerCase());
   });