Increment an existing reaction

This allows you to increment an existing reaction below a message by clicking on
it.

At the moment, this is not linked to the action bar, so they each are using
local state. We'll likely want to add some mechanism so that we can local echo
to both of these UI areas at the same time, but that can be done separately.

Fixes element-hq/element-web#9486

res/css/views/messages/_ReactionsRowButton.scss

@@ -23,8 +23,14 @@ limitations under the License.
     border: 1px solid $reaction-row-button-border-color;
     border-radius: 10px;
     background-color: $reaction-row-button-bg-color;
+    cursor: pointer;
 
     &:hover {
         border-color: $reaction-row-button-hover-border-color;
     }
+
+    &.mx_ReactionsRowButton_selected {
+        background-color: $reaction-row-button-selected-bg-color;
+        border-color: $reaction-row-button-selected-border-color;
+    }
 }

res/themes/dark/css/_dark.scss

@@ -154,6 +154,8 @@ $message-action-bar-hover-border-color: $header-panel-text-primary-color;
 $reaction-row-button-bg-color: $header-panel-bg-color;
 $reaction-row-button-border-color: #616b7f;
 $reaction-row-button-hover-border-color: $header-panel-text-primary-color;
+$reaction-row-button-selected-bg-color: #1f6954;
+$reaction-row-button-selected-border-color: $accent-color;
 
 // ***** Mixins! *****
 

res/themes/light/css/_light.scss

@@ -262,6 +262,8 @@ $message-action-bar-hover-border-color: #b8c1d2;
 $reaction-row-button-bg-color: $header-panel-bg-color;
 $reaction-row-button-border-color: #e9edf1;
 $reaction-row-button-hover-border-color: #bebebe;
+$reaction-row-button-selected-bg-color: #e9fff9;
+$reaction-row-button-selected-border-color: $accent-color;
 
 // ***** Mixins! *****
 

src/components/views/messages/ReactionsRowButton.js

@@ -16,18 +16,50 @@ limitations under the License.
 
 import React from 'react';
 import PropTypes from 'prop-types';
+import classNames from 'classnames';
 
 export default class ReactionsRowButton extends React.PureComponent {
     static propTypes = {
         content: PropTypes.string.isRequired,
         count: PropTypes.number.isRequired,
     }
 
+    constructor(props) {
+        super(props);
+
+        // TODO: This should be derived from actual reactions you may have sent
+        // once we have some API to read them.
+        this.state = {
+            selected: false,
+        };
+    }
+
+    onClick = (ev) => {
+        const state = this.state.selected;
+        this.setState({
+            selected: !state,
+        });
+        // TODO: Send the reaction event
+    };
+
     render() {
         const { content, count } = this.props;
+        const { selected } = this.state;
+
+        const classes = classNames({
+            mx_ReactionsRowButton: true,
+            mx_ReactionsRowButton_selected: selected,
+        });
+
+        let adjustedCount = count;
+        if (selected) {
+            adjustedCount++;
+        }
 
-        return <span className="mx_ReactionsRowButton">
-            {content} {count}
+        return <span className={classes}
+            onClick={this.onClick}
+        >
+            {content} {adjustedCount}
         </span>;
     }
 }