get_live_channels.ts

import { Context } from "aws-lambda";
import AWS = require("aws-sdk");
import { orderBy, uniq } from "lodash";

import dynamodb from "./dynamodb";
import { kLiveChannelsTable } from "./environment";
import { LiveChannelInfo, LiveChannelRecord } from "./types";
import { InternalError } from "./errors";
import { getKnownChannelInfos } from "./channelInfo";

const kLiveChannelConstantPartitionKey = "constant";

export const handler = main(
  async (event, context): Promise<LiveChannelInfo[]> => {
    const results = await dynamodb
      .query({
        TableName: kLiveChannelsTable,
        IndexName: "by_view_count",
        KeyConditionExpression: "#key = :constant",
        ExpressionAttributeNames: {
          "#key": "key",
        },
        ExpressionAttributeValues: {
          ":constant": { S: kLiveChannelConstantPartitionKey },
        },
        ScanIndexForward: true,
        Limit: 20,
      })
      .promise();

    if (!results.Items) {
      throw new InternalError(`No Items Returned: ${JSON.stringify(results)}`);
    }

    const items = (results.Items || []).map(
      item => AWS.DynamoDB.Converter.unmarshall(item) as LiveChannelRecord,
    );

    const ids = uniq(items.map(le => le.id));

    const channelInfos = await getKnownChannelInfos(ids, [
      "id",
      "login",
      "display_name",
      "profile_image_url",
      "view_count",
    ]);

    const liveChannelInfos = channelInfos.map<LiveChannelInfo>(ei => ({
      ...(items.find(le => le.id === ei.id) as LiveChannelRecord),
      ...ei,
    }));

    return orderBy(liveChannelInfos, ["view_count"], ["desc"]);
  },
);