feat: improve chat UX

lang/main.json

     },
     "chat": {
         "error": "Error: your message was not sent. Reason: {{error}}",
+        "fieldPlaceHolder": "Type your message here",
         "messagebox": "Type a message",
         "messageTo": "Private message to {{recipient}}",
+        "noMessagesMessage": "There are no messages in the meeting yet. Start a conversation here!",
         "nickname": {
             "popover": "Choose a nickname",
             "title": "Enter a nickname to use chat"

react/features/chat/components/AbstractMessageContainer.js

  *
  * @extends PureComponent
  */
-export default class AbstractMessageContainer extends PureComponent<Props> {
+export default class AbstractMessageContainer<P: Props> extends PureComponent<P> {
     static defaultProps = {
         messages: []
     };
             }
         }
 
-        groups.push(currentGrouping);
+        currentGrouping.length && groups.push(currentGrouping);
 
         return groups;
     }

react/features/chat/components/native/ChatInputBar.js

 import React, { Component } from 'react';
 import { TextInput, TouchableOpacity, View } from 'react-native';
 
+import { translate } from '../../../base/i18n';
 import { Icon, IconChatSend } from '../../../base/icons';
 import { Platform } from '../../../base/react';
 
     /**
      * Callback to invoke on message send.
      */
-    onSend: Function
+    onSend: Function,
+
+    /**
+     * Function to be used to translate i18n labels.
+     */
+    t: Function
 };
 
 type State = {
 /**
  * Implements the chat input bar with text field and action(s).
  */
-export default class ChatInputBar extends Component<Props, State> {
+class ChatInputBar extends Component<Props, State> {
     /**
      * Instantiates a new instance of the component.
      *
         };
 
         this._onChangeText = this._onChangeText.bind(this);
+        this._onFieldReferenceAvailable = this._onFieldReferenceAvailable.bind(this);
         this._onFocused = this._onFocused.bind(this);
         this._onSubmit = this._onSubmit.bind(this);
     }
                     onChangeText = { this._onChangeText }
                     onFocus = { this._onFocused(true) }
                     onSubmitEditing = { this._onSubmit }
+                    placeholder = { this.props.t('chat.fieldPlaceHolder') }
+                    ref = { this._onFieldReferenceAvailable }
                     returnKeyType = 'send'
                     style = { styles.inputField }
                     value = { this.state.message } />
         });
     }
 
+    _onFieldReferenceAvailable: Object => void;
+
+    /**
+     * Callback to be invoked when the field reference is available.
+     *
+     * @param {Object} field - The reference to the field.
+     * @returns {void}
+     */
+    _onFieldReferenceAvailable(field) {
+        field && field.focus();
+    }
+
     _onFocused: boolean => Function;
 
     /**
         });
     }
 }
+
+export default translate(ChatInputBar);

react/features/chat/components/native/MessageContainer.js

 // @flow
 
 import React from 'react';
-import { FlatList } from 'react-native';
+import { FlatList, Text, View } from 'react-native';
 
-import AbstractMessageContainer, { type Props }
+import { ColorSchemeRegistry } from '../../../base/color-scheme';
+import { translate } from '../../../base/i18n';
+import { connect } from '../../../base/redux';
+import { StyleType } from '../../../base/styles';
+
+import AbstractMessageContainer, { type Props as AbstractProps }
     from '../AbstractMessageContainer';
 
 import ChatMessageGroup from './ChatMessageGroup';
 import styles from './styles';
 
+type Props = AbstractProps & {
+
+    /**
+     * The color-schemed stylesheet of the feature.
+     */
+    _styles: StyleType,
+
+    /**
+     * Function to be used to translate i18n labels.
+     */
+    t: Function
+};
+
 /**
  * Implements a container to render all the chat messages in a conference.
  */
-export default class MessageContainer extends AbstractMessageContainer {
+class MessageContainer extends AbstractMessageContainer<Props> {
     /**
      * Instantiates a new instance of the component.
      *
         super(props);
 
         this._keyExtractor = this._keyExtractor.bind(this);
+        this._renderListEmptyComponent = this._renderListEmptyComponent.bind(this);
         this._renderMessageGroup = this._renderMessageGroup.bind(this);
     }
 
      * @inheritdoc
      */
     render() {
+        const data = this._getMessagesGroupedBySender();
+
         return (
             <FlatList
-                data = { this._getMessagesGroupedBySender() }
-                inverted = { true }
+                ListEmptyComponent = { this._renderListEmptyComponent }
+                data = { data }
+
+                // Workaround for RN bug:
+                // https://github.com/facebook/react-native/issues/21196
+                inverted = { Boolean(data.length) }
                 keyExtractor = { this._keyExtractor }
                 keyboardShouldPersistTaps = 'always'
                 renderItem = { this._renderMessageGroup }
         return `key_${index}`;
     }
 
-    _renderMessageGroup: Object => React$Element<*>;
+    _renderListEmptyComponent: () => React$Element<any>;
+
+    /**
+     * Renders a message when there are no messages in the chat yet.
+     *
+     * @returns {React$Element<any>}
+     */
+    _renderListEmptyComponent() {
+        const { _styles, t } = this.props;
+
+        return (
+            <View style = { styles.emptyComponentWrapper }>
+                <Text style = { _styles.emptyComponentText }>
+                    { t('chat.noMessagesMessage') }
+                </Text>
+            </View>
+        );
+    }
+
+    _renderMessageGroup: Object => React$Element<any>;
 
     /**
      * Renders a single chat message.
         return <ChatMessageGroup messages = { messages } />;
     }
 }
+
+/**
+ * Maps part of the redux state to the props of this component.
+ *
+ * @param {Object} state - The Redux state.
+ * @returns {Props}
+ */
+function _mapStateToProps(state) {
+    return {
+        _styles: ColorSchemeRegistry.get(state, 'Chat')
+    };
+}
+
+export default translate(connect(_mapStateToProps)(MessageContainer));

react/features/chat/components/native/styles.js

         flexDirection: 'column'
     },
 
+    emptyComponentWrapper: {
+        alignSelf: 'center',
+        flex: 1,
+        padding: BoxModel.padding,
+        paddingTop: '10%'
+    },
+
     /**
      * A special padding to avoid issues on some devices (such as Android devices with custom suggestions bar).
      */
         fontSize: 13
     },
 
+    emptyComponentText: {
+        color: schemeColor('displayName'),
+        textAlign: 'center'
+    },
+
     localMessageBubble: {
         backgroundColor: schemeColor('localMsgBackground'),
         borderTopRightRadius: 0

react/features/chat/components/web/MessageContainer.js

  *
  * @extends AbstractMessageContainer
  */
-export default class MessageContainer extends AbstractMessageContainer {
+export default class MessageContainer extends AbstractMessageContainer<Props> {
     /**
      * Whether or not chat has been scrolled to the bottom of the screen. Used
      * to determine if chat should be scrolled automatically to the bottom when