notify_live_channels.ts

import AWS = require("aws-sdk");
import got = require("got");
import {
  Context,
  DynamoDBStreamEvent,
  StreamRecord,
  AttributeValue,
} from "aws-lambda";
import { uniq, keyBy } from "lodash";

import { LiveChannelRecord } from "./util/types";
import { getKnownChannelInfos } from "./util/channelInfo";

const kTwitchPurpleInDecimal = 7506394;
const kViewCountThreshold = 5000;
const kWebhook = "{your discord webhook url}";

const executeWebhook = async (webhook: string, body): Promise<void> => {
  await got.post(webhook, {
    json: true,
    body,
  });
};

/**
 * Called by DynamoDB Stream
 * On newly live users, publish a notification to discord.
 */
export const handler = main(
  async (event: DynamoDBStreamEvent, context: Context): Promise<any> => {
    // build `LiveChannelRecord`s from INSERT operations
    const inserts = event.Records.filter(r => r.eventName === "INSERT")
      .map(r => r.dynamodb)
      .filter((d): d is StreamRecord => !!d)
      .map(d => d.NewImage)
      .filter((i): i is { [_: string]: AttributeValue } => !!i)
      .map(
        item => AWS.DynamoDB.Converter.unmarshall(item) as LiveChannelRecord,
      );

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

    const ids = uniq(inserts.map(image => image.id));
    console.log(`fetching ids: ${ids}`);
    const infoById = keyBy(
      await getKnownChannelInfos(ids, ["id", "login"]),
      "id",
    );

    const messages = inserts
      .filter(image => !!infoById[image.id])
      // ^ filter only people we have information about
      .filter(image => {
        try {
          const count = parseInt(image.view_count, 10);
          return count > kViewCountThreshold;
        } catch {
          return false;
        }
      })
      // ^ filter by view_count
      .map(async image => {
        console.log(
          `Posting Notification: ${image.id}/${image.username} went live (${
            image.game
          })`,
        );
        const { login } = infoById[image.id];
        const url = `https://twitch.tv/${login}`;

        // NOTE: don't have to worry about throwing because of filter above
        const viewCount = parseInt(image.view_count, 10).toLocaleString();

        await executeWebhook(kWebhook, {
          content: `${image.username} is live with Stickers`,
          embeds: [
            {
              author: { name: image.username },
              color: kTwitchPurpleInDecimal,
              title: image.title,
              url,
              fields: [
                {
                  name: "Playing",
                  value: image.game,
                  inline: true,
                },
                {
                  name: "View Count",
                  value: viewCount,
                  inline: true,
                },
              ],
              image: {
                url: `https://static-cdn.jtvnw.net/previews-ttv/live_user_${login}-1280x720.jpg`,
              },
            },
          ],
        });
      });

    await Promise.all(messages);
  },
);