Chat/src/reducers/chat.js

function chatReducer(state = {}, { type, chat_id, title, createdAt, lastModified, avatar, members, messages, msg_id, msg_text, msg_createdAt, msg_owner, msg_media, msg_replyTo, socket = false }) {
    if (type === 'CHAT') {
        if (Object.keys(state).filter(id => id === chat_id).length === 0) { //новый чат
            return {
                ...state,

                [chat_id]: {
                    title,
                    createdAt,
                    lastModified,
                    avatar,
                    messages,
                    members
                }
            }
        }

        if (Object.keys(state).filter(id => id === chat_id).length === 1) { //измененный чат
            return {
                ...state,

                [chat_id]: {
                    ...state[chat_id],
                    title: title,
                    avatar: avatar,
                    members: members
                }
            }
        }
    }

    if (type === "MESSAGE") {
        if ((state[chat_id]?.messages?.filter(msg => msg._id === msg_id).length === 0)) { //новое сообщение
            return {
                ...state,

                [chat_id]: {
                    title: state[chat_id].title,
                    createdAt: state[chat_id].createdAt,
                    lastModified: state[chat_id].lastModified > msg_createdAt ? state[chat_id].lastModified : msg_createdAt,
                    avatar: state[chat_id].avatar,
                    messages: socket ? [...state[chat_id].messages, { _id: msg_id, text: msg_text, createdAt: msg_createdAt, owner: msg_owner, media: msg_media, replyTo: msg_replyTo }] : [{ _id: msg_id, text: msg_text, createdAt: msg_createdAt, owner: msg_owner, media: msg_media, replyTo: msg_replyTo }, ...state[chat_id].messages],
                    members: state[chat_id].members
                }
            }
        }

        if ((state[chat_id]?.messages?.filter(msg => msg._id === msg_id).length === 1)) { //измененное сообщение
            let order;

            for (let key in state[chat_id].messages) {
                if (state[chat_id].messages[key]._id === msg_id) {
                    order = key
                }
            }

            let newMessages = [...state[chat_id].messages]
            newMessages[order].text = msg_text

            return {
                ...state,

                [chat_id]: {
                    title: state[chat_id].title,
                    createdAt: state[chat_id].createdAt,
                    lastModified: state[chat_id].lastModified,
                    avatar: state[chat_id].avatar,
                    messages: newMessages,
                    members: state[chat_id].members
                }
            }
        }
    }

    return state
}

export default chatReducer