name: Update Base Branch

# Run every 20 mins or manually
on:
  schedule:
    - cron: '*/20 * * * *'
  workflow_dispatch:

jobs:
  update:
    runs-on: ubuntu-20.04
    steps:
      - uses: actions/github-script@v3
        with:
          github-token: ${{secrets.GITHUB_TOKEN}}
          script: |
            const updateLabel = 'update-base';
            const owner = context.repo.owner;
            const repo = context.repo.repo;

            const response = await github.repos.get({ owner, repo })
            const base = response.data.default_branch

            async function updateBase(pull) {
                const pull_number = issue_number = pull.number;

                if (pull.base.ref == base) {
                    await github.issues.createComment({ owner, repo, issue_number, body: '🚨 Target branch is already set to ' + base });
                    await github.issues.removeLabel({ owner, repo, issue_number, name: updateLabel });
                    return;
                }

                // Update target PR branch
                await github.pulls.update({ owner, repo, pull_number, base });
                // Updates the pull request with the latest upstream changes.
                await github.pulls.updateBranch({ owner, repo, pull_number, });
                await github.issues.createComment({ owner, repo, issue_number, body: '🚀 Target branch has been updated to ' + base });
                await github.issues.removeLabel({ owner, repo, issue_number, name: updateLabel });
            }

            // Query all of the open pull requests
            const pulls = await github.pulls.list({
                owner,
                repo,
                state: 'open'
            });

            // Loop all of the pull requests, finding any with the target label.
            for (const pull of pulls.data) {
                const requiresUpdate = pull.labels.some((label) => label.name === updateLabel);

                if (requiresUpdate) {
                    await updateBase(pull);
                }
            }