index.js

const core = require('@actions/core');
const github = require('@actions/github');

const validEvents = ['push', 'pull_request'];

function getBranchName(eventName, payload) {
    let branchName;
    switch (eventName) {
        case 'push':
            branchName = payload.ref.replace('refs/heads/', '');
            break;
        case 'pull_request':
            branchName = payload.pull_request.head.ref;
            break;
        default:
            throw new Error(`Invalid event name: ${eventName}`);
    }
    return branchName;
}


// most @actions toolkit packages have async methods
async function run() {
  try {
    const eventName = github.context.eventName;
    core.info(`Event name: ${eventName}`);
    if (validEvents.indexOf(eventName) < 0) {
        core.setFailed(`Invalid event: ${eventName}`);
        return;
    }

    const branch = getBranchName(eventName, github.context.payload);
    core.info(`Branch name: ${branch}`);
    // Check if branch is to be ignored
    const ignore = core.getInput('ignore');
    if (ignore.length > 0 && ignore.split(',').some((el) => branch === el)) {
        core.info(`Skipping checks since ${branch} is in the ignored list - ${ignore}`);
        return
    }

    // Check if branch pass regex
    const regex = RegExp(core.getInput('regex'));
    core.info(`Regex: ${regex}`);
    if (!regex.test(branch)) {
        core.setFailed(`Branch ${branch} failed to pass match regex - ${regex}`);
        return
    }

    // Check if branch starts with a prefix
    const prefixes = core.getInput('allowed_prefixes');
    core.info(`Allowed Prefixes: ${prefixes}`);
    if (prefixes.length > 0 && !prefixes.split(',').some((el) => branch.startsWith(el))) {
        core.setFailed(`Branch ${branch} failed did not match any of the prefixes - ${prefixes}`);
        return
    }

    // Check min length
    const minLen = parseInt(core.getInput('min_length'));
    if (branch.length < minLen) {
        core.setFailed(`Branch ${branch} is smaller than min length specified - ${minLen}`);
        return
    }

    // Check max length
    const maxLen = parseInt(core.getInput('max_length'));
    if (maxLen > 0 && branch.length > maxLen) {
        core.setFailed(`Branch ${branch} is greater than max length specified - ${maxLen}`);
        return
    }
  } catch (error) {
      core.setFailed(error.message);
  }
}

run();