index.js

const core = require("@actions/core");
const github = require("@actions/github");
const { WebClient } = require("@slack/web-api");
const { buildSlackAttachments, formatChannelName } = require("./src/utils");

(async () => {
  try {
    const channel = core.getInput("channel");
    const status = core.getInput("status");
    const color = core.getInput("color");
    const messageId = core.getInput("message_id");
    const token = process.env.SLACK_BOT_TOKEN;
    const slack = new WebClient(token);

    if (!channel && !core.getInput("channel_id")) {
      core.setFailed(`You must provider either a 'channel' or a 'channel_id'.`);
      return;
    }

    const attachments = buildSlackAttachments({ status, color, github });
    const channelId =
      core.getInput("channel_id") ||
      (await lookUpChannelId({ slack, channel }));

    if (!channelId) {
      core.setFailed(`Slack channel ${channel} could not be found.`);
      return;
    }

    const apiMethod = Boolean(messageId) ? "update" : "postMessage";

    const args = {
      channel: channelId,
      attachments,
    };

    if (messageId) {
      args.ts = messageId;
    }

    const response = await slack.chat[apiMethod](args);

    core.setOutput("message_id", response.ts);
  } catch (error) {
    core.setFailed(error);
  }
})();

async function lookUpChannelId({ slack, channel }) {
  let result;
  const formattedChannel = formatChannelName(channel);

  // Async iteration is similar to a simple for loop.
  // Use only the first two parameters to get an async iterator.
  for await (const page of slack.paginate("conversations.list", {
    types: "public_channel, private_channel",
  })) {
    // You can inspect each page, find your result, and stop the loop with a `break` statement
    const match = page.channels.find((c) => c.name === formattedChannel);
    if (match) {
      result = match.id;
      break;
    }
  }

  return result;
}