Add listing of followed hashtags (#21773)

* Add followed_tags route.

This at least gets us to the point where the page can actually be
rendered, although it doesn't display any hashtags (yet?).

Attempting to implement #20763.

* Fix minor issues.

* I've got the followed tags data partially working

But the Hashtag component errors for some reason. Something about the
value of the history attribute being invalid.

* Fix a mistake in the code

* Minor change.

* Get the followed hashtags list fully working.

Still need to add the Follow/Unfollow buttons, though.

* Resolve JS linter issues.

* Add pagination logic to followed tags list view.

However, it currently loads further pages immediately on page load, so
that's not ideal. Need to figure that one out.

* Appease the linter.

* Apply suggestions from code review

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

* Fixes and resolve some other feedback.

* Use set/update instead of setIn/updateIn.

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/mastodon/actions/tags.js

@@ -1,9 +1,17 @@
-import api from '../api';
+import api, { getLinks } from '../api';
 
 export const HASHTAG_FETCH_REQUEST = 'HASHTAG_FETCH_REQUEST';
 export const HASHTAG_FETCH_SUCCESS = 'HASHTAG_FETCH_SUCCESS';
 export const HASHTAG_FETCH_FAIL    = 'HASHTAG_FETCH_FAIL';
 
+export const FOLLOWED_HASHTAGS_FETCH_REQUEST = 'FOLLOWED_HASHTAGS_FETCH_REQUEST';
+export const FOLLOWED_HASHTAGS_FETCH_SUCCESS = 'FOLLOWED_HASHTAGS_FETCH_SUCCESS';
+export const FOLLOWED_HASHTAGS_FETCH_FAIL    = 'FOLLOWED_HASHTAGS_FETCH_FAIL';
+
+export const FOLLOWED_HASHTAGS_EXPAND_REQUEST = 'FOLLOWED_HASHTAGS_EXPAND_REQUEST';
+export const FOLLOWED_HASHTAGS_EXPAND_SUCCESS = 'FOLLOWED_HASHTAGS_EXPAND_SUCCESS';
+export const FOLLOWED_HASHTAGS_EXPAND_FAIL    = 'FOLLOWED_HASHTAGS_EXPAND_FAIL';
+
 export const HASHTAG_FOLLOW_REQUEST = 'HASHTAG_FOLLOW_REQUEST';
 export const HASHTAG_FOLLOW_SUCCESS = 'HASHTAG_FOLLOW_SUCCESS';
 export const HASHTAG_FOLLOW_FAIL    = 'HASHTAG_FOLLOW_FAIL';
@@ -37,6 +45,78 @@ export const fetchHashtagFail = error => ({
   error,
 });
 
+export const fetchFollowedHashtags = () => (dispatch, getState) => {
+  dispatch(fetchFollowedHashtagsRequest());
+
+  api(getState).get('/api/v1/followed_tags').then(response => {
+    const next = getLinks(response).refs.find(link => link.rel === 'next');
+    dispatch(fetchFollowedHashtagsSuccess(response.data, next ? next.uri : null));
+  }).catch(err => {
+    dispatch(fetchFollowedHashtagsFail(err));
+  });
+};
+
+export function fetchFollowedHashtagsRequest() {
+  return {
+    type: FOLLOWED_HASHTAGS_FETCH_REQUEST,
+  };
+};
+
+export function fetchFollowedHashtagsSuccess(followed_tags, next) {
+  return {
+    type: FOLLOWED_HASHTAGS_FETCH_SUCCESS,
+    followed_tags,
+    next,
+  };
+};
+
+export function fetchFollowedHashtagsFail(error) {
+  return {
+    type: FOLLOWED_HASHTAGS_FETCH_FAIL,
+    error,
+  };
+};
+
+export function expandFollowedHashtags() {
+  return (dispatch, getState) => {
+    const url = getState().getIn(['followed_tags', 'next']);
+
+    if (url === null) {
+      return;
+    }
+
+    dispatch(expandFollowedHashtagsRequest());
+
+    api(getState).get(url).then(response => {
+      const next = getLinks(response).refs.find(link => link.rel === 'next');
+      dispatch(expandFollowedHashtagsSuccess(response.data, next ? next.uri : null));
+    }).catch(error => {
+      dispatch(expandFollowedHashtagsFail(error));
+    });
+  };
+};
+
+export function expandFollowedHashtagsRequest() {
+  return {
+    type: FOLLOWED_HASHTAGS_EXPAND_REQUEST,
+  };
+};
+
+export function expandFollowedHashtagsSuccess(followed_tags, next) {
+  return {
+    type: FOLLOWED_HASHTAGS_EXPAND_SUCCESS,
+    followed_tags,
+    next,
+  };
+};
+
+export function expandFollowedHashtagsFail(error) {
+  return {
+    type: FOLLOWED_HASHTAGS_EXPAND_FAIL,
+    error,
+  };
+};
+
 export const followHashtag = name => (dispatch, getState) => {
   dispatch(followHashtagRequest(name));