status-web/packages/status-communities/src/chat.ts

import { idToContentTopic } from "./contentTopic";
import { createSymKeyFromPassword } from "./encryption";
import { ChatMessage, Content } from "./wire/chat_message";

/**
 * Represent a chat room. Only public chats are currently supported.
 */
export class Chat {
  private lastClockValue?: number;
  private lastMessage?: ChatMessage;

  private constructor(public id: string, public symKey: Uint8Array) {}

  /**
   * Create a public chat room.
   */
  public static async create(id: string): Promise<Chat> {
    const symKey = await createSymKeyFromPassword(id);

    return new Chat(id, symKey);
  }

  public get contentTopic(): string {
    return idToContentTopic(this.id);
  }

  public createMessage(content: Content): ChatMessage {
    const { timestamp, clock } = this._nextClockAndTimestamp();

    const message = ChatMessage.createMessage(
      clock,
      timestamp,
      this.id,
      content
    );

    this._updateClockFromMessage(message);

    return message;
  }

  public handleNewMessage(message: ChatMessage): void {
    this._updateClockFromMessage(message);
  }

  private _nextClockAndTimestamp(): { clock: number; timestamp: number } {
    let clock = this.lastClockValue;
    const timestamp = Date.now();

    if (!clock || clock < timestamp) {
      clock = timestamp;
    } else {
      clock += 1;
    }

    return { clock, timestamp };
  }

  private _updateClockFromMessage(message: ChatMessage): void {
    if (
      !this.lastMessage ||
      !this.lastMessage.clock ||
      (message.clock && this.lastMessage.clock <= message.clock)
    ) {
      this.lastMessage = message;
    }

    if (
      !this.lastClockValue ||
      (message.clock && this.lastClockValue < message.clock)
    ) {
      this.lastClockValue = message.clock;
    }
  }
}