Display followed hashtags on the home header

Display the followed hashtags on the home header, allowing for easier
access to them. Listed from most recent to oldest, and with 2 dedicated
buttons.

Co-authored-by: Tiago Peralta <tiagofilipeperalta@tecnico.ulisboa.pt>

app/javascript/mastodon/components/__tests__/__snapshots__/button_scroll_list-test.jsx.snap

@@ -0,0 +1,258 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`<ButtonScrollList /> handles a large number of children correctly 1`] = `
+<div
+  className="button-scroll-list-container"
+>
+  <button
+    aria-label="Scroll left"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+  <div
+    className="button-scroll-list"
+  >
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+  </div>
+  <button
+    aria-label="Scroll right"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+</div>
+`;
+
+exports[`<ButtonScrollList /> handles a single child correctly 1`] = `
+<div
+  className="button-scroll-list-container"
+>
+  <button
+    aria-label="Scroll left"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+  <div
+    className="button-scroll-list"
+  >
+    <div>
+      <div />
+    </div>
+  </div>
+  <button
+    aria-label="Scroll right"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+</div>
+`;
+
+exports[`<ButtonScrollList /> renders an empty button scroll list element 1`] = `null`;
+
+exports[`<ButtonScrollList /> renders the children 1`] = `
+<div
+  className="button-scroll-list-container"
+>
+  <button
+    aria-label="Scroll left"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+  <div
+    className="button-scroll-list"
+  >
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+    <div>
+      <div />
+    </div>
+  </div>
+  <button
+    aria-label="Scroll right"
+    className="icon-button column-header__setting-btn"
+    onClick={[Function]}
+  >
+    <div>
+      MockIcon
+    </div>
+  </button>
+</div>
+`;

app/javascript/mastodon/components/__tests__/button_scroll_list-test.jsx

@@ -0,0 +1,119 @@
+import renderer from 'react-test-renderer';
+
+import { render, screen } from 'mastodon/test_helpers';
+
+import ButtonScrollList from '../button_scroll_list';
+
+jest.mock('mastodon/components/icon', () => {
+  return {
+    Icon: () => <div>MockIcon</div>,
+  };
+});
+
+describe('<ButtonScrollList />', () => {
+  it('renders an empty button scroll list element', () => {
+    const children = [];
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const tree = component.toJSON();
+
+    expect(tree).toMatchSnapshot();
+  });
+
+  it('renders the children', () => {
+    const children = Array.from({ length: 5 }, (_, i) => (
+      <div key={i} ref={jest.fn()} />
+    ));
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const tree = component.toJSON();
+
+    expect(tree).toMatchSnapshot();
+  });
+
+  it('scrolls left', () => {
+    const children = Array.from({ length: 5 }, (_, i) => (
+      <div key={i} ref={jest.fn()} />
+    ));
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const instance = component.getInstance();
+    instance.scrollLeft();
+  });
+
+  it('scrolls right', () => {
+    const children = Array.from({ length: 5 }, (_, i) => (
+      <div key={i} ref={jest.fn()} />
+    ));
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const instance = component.getInstance();
+    instance.scrollRight();
+  });
+
+  it('scrolls left and right correctly', () => {
+    const children = Array.from({ length: 10 }, (_, i) => (
+      <div key={i}>{i}</div>
+    ));
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+
+    setTimeout(() => {
+      let instance = component.getInstance();
+      instance.scrollRight();
+      expect(instance.slide).toBe(1);
+    }, 1000);
+
+    setTimeout(() => {
+      let instance = component.getInstance();
+      instance.scrollLeft();
+      expect(instance.slide).toBe(0);
+    }, 2000);
+  });
+
+  it('handles a single child correctly', () => {
+    const children = [<div key={0} ref={jest.fn()} />];
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const tree = component.toJSON();
+
+    expect(tree).toMatchSnapshot();
+  });
+
+  it('handles a large number of children correctly', () => {
+    const children = Array.from({ length: 50 }, (_, i) => (
+      <div key={i} ref={jest.fn()} />
+    ));
+    const component = renderer.create(
+      <ButtonScrollList>{children}</ButtonScrollList>,
+    );
+    const tree = component.toJSON();
+
+    expect(tree).toMatchSnapshot();
+  });
+
+  it('checks if scroll buttons are accessible', () => {
+    const children = Array.from({ length: 5 }, (_, i) => (
+      <div key={i} ref={jest.fn()} />
+    ));
+    render(<ButtonScrollList>{children}</ButtonScrollList>);
+
+    const leftButton = screen.getByRole('button', { name: /scroll left/i });
+    const rightButton = screen.getByRole('button', { name: /scroll right/i });
+
+    expect(leftButton).toBeTruthy();
+    expect(rightButton).toBeTruthy();
+
+    leftButton.focus();
+    expect(document.activeElement).toBe(leftButton);
+
+    rightButton.focus();
+    expect(document.activeElement).toBe(rightButton);
+  });
+});

app/javascript/mastodon/components/button_scroll_list.jsx

@@ -0,0 +1,87 @@
+import PropTypes from 'prop-types';
+import React, { Component } from 'react';
+
+import ChevronLeftIcon from '@/material-icons/400-24px/chevron_left.svg?react';
+import ChevronRightIcon from '@/material-icons/400-24px/chevron_right.svg?react';
+import { Icon } from 'mastodon/components/icon';
+
+class ButtonScrollList extends Component {
+  static propTypes = {
+    children: PropTypes.node.isRequired,
+  };
+
+  constructor(props) {
+    super(props);
+    this.scrollRef = React.createRef();
+    this.slide = 0;
+    this.childrenLength = React.Children.count(props.children);
+  }
+
+  componentDidMount() {
+    setTimeout(() => {
+      if (this.scrollRef && this.scrollRef.current) {
+        const container = this.scrollRef.current;
+        container.scrollTo({ left: 0, behavior: 'auto' });
+        this.slide = 0;
+      }
+    }, 500);
+  }
+
+  scrollLeft = () => {
+    if (this.scrollRef && this.scrollRef.current) {
+      this.scrollRef.current.scrollBy({ left: -200, behavior: 'smooth' });
+      this.slide = Math.max(0, this.slide - 1);
+    }
+  };
+
+  scrollRight = () => {
+    if (this.scrollRef && this.scrollRef.current) {
+      const { children } = this.props;
+      const container = this.scrollRef.current;
+      const maxScrollLeft = container.scrollWidth - container.clientWidth;
+
+      if (container.scrollLeft < maxScrollLeft) {
+        container.scrollBy({ left: 200, behavior: 'smooth' });
+        this.slide = Math.min(
+          React.Children.count(children) - 1,
+          this.slide + 1,
+        );
+      } else {
+      }
+    }
+  };
+
+  render() {
+    const { children } = this.props;
+
+    if (React.Children.count(children) === 0) {
+      return null;
+    }
+
+    return (
+      <div className='button-scroll-list-container'>
+        <button
+          className='icon-button column-header__setting-btn'
+          aria-label='Scroll left'
+          onClick={this.scrollLeft}
+        >
+          <Icon id='chevron-left' icon={ChevronLeftIcon} />
+        </button>
+        <div className='button-scroll-list' ref={this.scrollRef}>
+          {React.Children.map(children, (child, index) => (
+            <div key={index}>{child}</div>
+          ))}
+        </div>
+        <button
+          className='icon-button column-header__setting-btn'
+          aria-label='Scroll right'
+          onClick={this.scrollRight}
+        >
+          <Icon id='chevron-right' icon={ChevronRightIcon} />
+        </button>
+      </div>
+    );
+  }
+}
+
+export default ButtonScrollList;

app/javascript/mastodon/components/column_header.jsx

@@ -12,12 +12,12 @@ import ChevronLeftIcon from '@/material-icons/400-24px/chevron_left.svg?react';
 import ChevronRightIcon from '@/material-icons/400-24px/chevron_right.svg?react';
 import CloseIcon from '@/material-icons/400-24px/close.svg?react';
 import SettingsIcon from '@/material-icons/400-24px/settings.svg?react';
+import FollowedTagsList from 'mastodon/components/followed_tags_list';
 import { Icon }  from 'mastodon/components/icon';
 import { ButtonInTabsBar } from 'mastodon/features/ui/util/columns_context';
 import { identityContextPropShape, withIdentity } from 'mastodon/identity_context';
 import { WithRouterPropTypes } from 'mastodon/utils/react_router';
 
-
 import { useAppHistory } from './router';
 
 const messages = defineMessages({
@@ -194,13 +194,17 @@ class ColumnHeader extends PureComponent {
             <>
               {backButton}
 
-              <button onClick={this.handleTitleClick} className='column-header__title'>
+              <button onClick={this.handleTitleClick} className='column-header__title' style={{ overflow: 'visible', paddingRight: '15px' }}>
                 {!backButton && <Icon id={icon} icon={iconComponent} className='column-header__icon' />}
                 {title}
               </button>
             </>
           )}
 
+          { icon === 'home' ? (
+            <FollowedTagsList />
+          ) : null }
+
           {!hasTitle && backButton}
 
           <div className='column-header__buttons'>

app/javascript/mastodon/components/followed_tags_list.jsx

@@ -0,0 +1,67 @@
+import PropTypes from 'prop-types';
+import { PureComponent } from 'react';
+
+import { injectIntl } from 'react-intl';
+
+import ImmutablePropTypes from 'react-immutable-proptypes';
+import { connect } from 'react-redux';
+
+import debounce from 'lodash/debounce';
+
+import {
+  expandFollowedHashtags,
+  fetchFollowedHashtags,
+} from 'mastodon/actions/tags';
+import ButtonScrollList from 'mastodon/components/button_scroll_list';
+import { Hashtag } from 'mastodon/components/hashtag';
+import { WithRouterPropTypes } from 'mastodon/utils/react_router';
+
+const mapStateToProps = (state) => ({
+  hashtags: state.getIn(['followed_tags', 'items']),
+  isLoading: state.getIn(['followed_tags', 'isLoading'], true),
+  hasMore: !!state.getIn(['followed_tags', 'next']),
+});
+
+class FollowedTagsList extends PureComponent {
+  static propTypes = {
+    hashtags: ImmutablePropTypes.list.isRequired,
+    isLoading: PropTypes.bool.isRequired,
+    hasMore: PropTypes.bool.isRequired,
+    ...WithRouterPropTypes,
+  };
+
+  componentDidMount() {
+    this.props.dispatch(fetchFollowedHashtags());
+  }
+
+  handleLoadMore = debounce(
+    () => {
+      this.props.dispatch(expandFollowedHashtags());
+    },
+    300,
+    { leading: true },
+  );
+
+  render() {
+    const { hashtags } = this.props;
+
+    return (
+      <div className='followed-tags-list'>
+        <ButtonScrollList>
+          {hashtags.map((hashtag) => (
+            <div className='hashtag-wrapper' key={hashtag.get('name')}>
+              <Hashtag
+                name={hashtag.get('name')}
+                showSkeleton={false}
+                to={`/tags/${hashtag.get('name')}`}
+                withGraph={false}
+              />
+            </div>
+          ))}
+        </ButtonScrollList>
+      </div>
+    );
+  }
+}
+
+export default connect(mapStateToProps)(injectIntl(FollowedTagsList));

app/javascript/mastodon/components/hashtag.tsx

@@ -85,6 +85,7 @@ export interface HashtagProps {
   description?: React.ReactNode;
   history?: number[];
   name: string;
+  showSkeleton?: boolean;
   people: number;
   to: string;
   uses?: number;
@@ -93,6 +94,7 @@ export interface HashtagProps {
 
 export const Hashtag: React.FC<HashtagProps> = ({
   name,
+  showSkeleton = true,
   to,
   people,
   uses,
@@ -113,13 +115,15 @@ export const Hashtag: React.FC<HashtagProps> = ({
         )}
       </Link>
 
-      {description ? (
-        <span>{description}</span>
-      ) : typeof people !== 'undefined' ? (
-        <ShortNumber value={people} renderer={accountsCountRenderer} />
-      ) : (
-        <Skeleton width={100} />
-      )}
+      {showSkeleton ? (
+        description ? (
+          <span>{description}</span>
+        ) : typeof people !== 'undefined' ? (
+          <ShortNumber value={people} renderer={accountsCountRenderer} />
+        ) : (
+          <Skeleton width={100} />
+        )
+      ) : null}
     </div>
 
     {typeof uses !== 'undefined' && (

app/javascript/styles/mastodon/components.scss

@@ -3541,6 +3541,42 @@ $ui-header-logo-wordmark-width: 99px;
   }
 }
 
+.button-scroll-list-container {
+  display: flex;
+  align-items: center;
+  max-width: 100%;
+  overflow: hidden;
+}
+
+.icon-button {
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 0;
+}
+
+.button-scroll-list {
+  display: flex;
+  overflow-x: auto;
+  scrollbar-width: none;
+  -ms-overflow-style: none;
+  flex-grow: 1;
+  white-space: nowrap;
+}
+
+.button-scroll-list::-webkit-scrollbar {
+  display: none;
+}
+
+.followed-tags-list {
+  overflow: hidden;
+  flex: 0 1 auto;
+}
+
+.hashtag-wrapper {
+  border-bottom: none;
+}
+
 .column-back-button {
   box-sizing: border-box;
   width: 100%;