name: Populate PR commits

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  update-body:
    name: Inject commit list into PR body
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write

    steps:
      - uses: actions/github-script@v7
        with:
          script: |
            const { data: commits } = await github.rest.pulls.listCommits({
              owner: context.repo.owner,
              repo: context.repo.repo,
              pull_number: context.payload.pull_request.number,
            });

            const commitLines = commits
              .map(c => `- ${c.commit.message.split('\n')[0]} (${c.sha.slice(0, 7)})`)
              .join('\n');

            const currentBody = context.payload.pull_request.body ?? '';

            // Replace everything between the Commits header and the next ## header
            const updated = currentBody.replace(
              /(## Commits\n)[\s\S]*?(\n## )/,
              `$1\n${commitLines}\n$2`
            );

            if (updated === currentBody) return;

            await github.rest.pulls.update({
              owner: context.repo.owner,
              repo: context.repo.repo,
              pull_number: context.payload.pull_request.number,
              body: updated,
            });