slack_handler.ts

callback(null, { body: "OK", statusCode: 200 });

const message = mentionEvent.text;
const parts = repoRegExp.exec(message);
if (parts) {
    const repo = parts[1];

    const params = {
        FunctionName: `${stage}-getContributorStatsImage`,
        InvocationType: "RequestResponse",
        LogType: "Tail",
        Payload: JSON.stringify({
            repo
        })
    };

    const response = await lambda.invoke(params).promise();
    const payload = JSON.parse(response.Payload);

    const message = {
        channel: mentionEvent.channel,
        text: "Contributor stats",
        attachments: [
            {
                title: `Contributor stats for ${repo} repository`,
                image_url: payload.imageUri
            }
        ]
    };

    await request({
        url: "https://slack.com/api/chat.postMessage",
        method: "post",
        json: true,
        headers: {
            Authorization: `Bearer ${slackToken}`,
            "User-Agent": "Stats Bot for Slack"
        },
        body: message
    });
} else {
    throw new Error("Can not recognize repository name");
}