index.js

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

async function run() {
  try {
    const tokenRegex = new RegExp('%branch%', "g");

    const inputs = {
      token: core.getInput('repo-token', {required: true}),
      branchRegex: core.getInput('branch-regex', {required: true}),
      lowercaseBranch: (core.getInput('lowercase-branch').toLowerCase() === 'true'),
      titleTemplate: core.getInput('title-template', {required: true}),
      replaceTitle: (core.getInput('replace-title').toLowerCase() === 'true'),
      titlePrefixSpace: (core.getInput('title-prefix-space').toLowerCase() === 'true'),
      uppercaseTitle: (core.getInput('uppercase-title').toLowerCase() === 'true'),
      bodyTemplate: core.getInput('body-template', {required: true}),
      replaceBody: (core.getInput('replace-body').toLowerCase() === 'true'),
      bodyPrefixNewlineCount: parseInt(core.getInput('body-prefix-newline-count', {required: true})),
      uppercaseBody: (core.getInput('uppercase-body').toLowerCase() === 'true'),
    }

    const branchName = github.context.payload.pull_request.head.ref;
    const branch = inputs.lowercaseBranch ? branchName.toLowerCase() : branchName;
    core.debug(`branch: ${branch}`);

    const matches = branch.match(new RegExp(inputs.branchRegex));
    if (!matches) {
      core.setFailed('Branch name does not match given regex');
      return;
    }

    const match = (upperCase) => upperCase ? matches[0].toUpperCase() : matches[0];
    core.info(`Matched branch text: ${match(false)}`);

    const request = {
      owner: github.context.repo.owner,
      repo: github.context.repo.repo,
      pull_number: github.context.payload.pull_request.number,
    }

    const title = github.context.payload.pull_request.title || '';
    const processedTitle = inputs.titleTemplate.replace(tokenRegex, match(inputs.uppercaseTitle));
    core.debug(`processedTitle: ${processedTitle}`);

    const updateTitle = inputs.replaceTitle
      ? title.toLowerCase() !== processedTitle.toLowerCase()
      : !title.toLowerCase().startsWith(processedTitle.toLowerCase());

    if (updateTitle) {
      request.title = inputs.replaceTitle
      ? processedTitle
      : processedTitle.concat(inputs.titlePrefixSpace ? ' ': '', title);
      core.debug(`new title: ${request.title}`);
    } else {
      core.warning('PR title is up to date already - no updates made');
    }

    const body = github.context.payload.pull_request.body || '';
    const processedBody = inputs.bodyTemplate.replace(tokenRegex, match(inputs.uppercaseBody));
    core.debug(`processedBody: ${processedBody}`);

    const updateBody = inputs.replaceBody
      ? body.toLowerCase() !== processedBody.toLowerCase()
      : !body.toLowerCase().startsWith(processedBody.toLowerCase());

    if (updateBody) {
      request.body = inputs.replaceBody
      ? processedBody
      : processedBody.concat('\n'.repeat(inputs.bodyPrefixNewlineCount), body);
      core.debug(`new body: ${request.body}`);
    } else {
      core.warning('PR body is up to date already - no updates made');
    }

    if (!updateTitle && !updateBody) {
      return;
    }

    const client = new github.GitHub(inputs.token);
    const response = await client.pulls.update(request);

    core.info(`response: ${response.status}`);
    if (response.status !== 200) {
      core.error('Updating the pull request has failed');
    }
  }
  catch (error) {
    core.error(error);
    core.setFailed(error.message);
  }
}

run()