name: Block if prerelease is present

on:
  pull_request:

permissions:
  contents: read

jobs:
  check-latest-release:
    runs-on: ubuntu-latest
    steps:
      - name: "Check latest published release isn't a prerelease"
        uses: actions/github-script@d7906e4ad0b1822421a7e6a35d5ca353c962f410 # v6
        with:
          script: |
            const tags = await github.rest.repos.listTags({
              owner: context.repo.owner,
              repo: context.repo.repo,
              per_page: 1
            });

            if (!tags.data || tags.data.length === 0) {
              core.info('No tags found for this repository; skipping prerelease check.');
              return;
            }

            const latestTag = tags.data[0].name;
            core.info(`Latest tag found: ${latestTag}`);

            try {
              const { data } = await github.rest.repos.getReleaseByTag({
                owner: context.repo.owner,
                repo: context.repo.repo,
                tag: latestTag
              });

              if (data.prerelease) {
                core.setFailed(`Release for tag ${latestTag} (${data.tag_name}) is a prerelease. Blocking merges to main as we need to wait for the prerelease to become stable.`);
              } else {
                core.info(`Release for tag ${latestTag} (${data.tag_name}) is not a prerelease.`);
              }

            } catch (err) {
              if (err.status === 404) {
                core.info(`No release found for tag ${latestTag}; skipping prerelease check.`);
              } else {
                throw err;
              }
            }