import { Client, WebhookEvent, Message } from '@line/bot-sdk';

export type Sender = {
  // send (or reply) message
  send: (message: Message) => Promise<void>;
  // flush the reply message queue
  flush: () => Promise<void>;
};

// messages will be sent by replyMessage during this period
const REPLY_TIMEOUT = 10 * 1000;

function getSourceId(event: WebhookEvent): string {
  if (event.source.type === 'user') {
    return event.source.userId;
  } else if (event.source.type === 'group') {
    return event.source.groupId;
  } else if (event.source.type === 'room') {
    return event.source.roomId;
  } else {
    throw new Error('unreachable');
  }
}

export function createSender(client: Client, event: WebhookEvent): Sender {
  const sourceId = getSourceId(event);
  const replyToken: string | undefined = (event as any).replyToken;

  if (replyToken) {
    // return replyable sender with replyMessage timeout
    let flushed = false;
    let messages: Array<Message> = [];

    const now = Date.now();

    const sender: Sender = {
      async send(message) {
        if (flushed) {
          await client.pushMessage(sourceId, message);
        } else {
          messages.push(message);
        }
      },
      async flush() {
        if (flushed) return;
        flushed = true;

        if (messages.length === 0) {
          return;
        }

        try {
          await client.replyMessage(replyToken, messages);
        } catch (err) {
          console.error(err);
        } finally {
          messages = [];
        }
      },
    };

    setTimeout(() => sender.flush(), REPLY_TIMEOUT);

    return sender;
  } else {
    // return trivial sender for non-replyable event
    return {
      send: message => client.pushMessage(sourceId, message),
      flush: () => Promise.resolve(),
    };
  }
}