name: Auto PR description

# Dogfoods our own Action: when a PR is opened with an empty body, run the
# pr-description-writer skill on the diff and fill it in. A living demo of
# `uses: ./action`. Requires the ANTHROPIC_API_KEY repo secret; skips quietly
# without it (and on forks, which can't read secrets).

on:
  pull_request:
    types: [opened]

permissions:
  contents: read
  pull-requests: write

jobs:
  describe:
    if: github.event.pull_request.head.repo.full_name == github.repository
    runs-on: ubuntu-latest
    env:
      ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
    steps:
      - name: Check for API key and an empty PR body
        id: gate
        uses: actions/github-script@v7
        with:
          script: |
            const hasKey = !!process.env.ANTHROPIC_API_KEY;
            const body = (context.payload.pull_request.body || '').trim();
            if (!hasKey) core.info('ANTHROPIC_API_KEY not set — skipping.');
            if (body) core.info('PR already has a description — skipping.');
            core.setOutput('go', String(hasKey && !body));

      - name: Checkout
        if: steps.gate.outputs.go == 'true'
        uses: actions/checkout@v4
        with: { fetch-depth: 0 }

      - name: Collect the diff
        if: steps.gate.outputs.go == 'true'
        id: diff
        run: |
          {
            echo "text<<DIFF_EOF"
            echo "Title: ${{ github.event.pull_request.title }}"
            echo "Commits:"; git log --oneline origin/${{ github.base_ref }}..HEAD | head -30
            echo; echo "Changed files:"; git diff --stat origin/${{ github.base_ref }}...HEAD | tail -40
            echo "DIFF_EOF"
          } >> "$GITHUB_OUTPUT"

      - name: Write the PR description with the skill
        if: steps.gate.outputs.go == 'true'
        id: skill
        uses: ./action
        with:
          skill: pr-description-writer
          input: ${{ steps.diff.outputs.text }}
          api_key: ${{ secrets.ANTHROPIC_API_KEY }}

      - name: Update the PR body
        if: steps.gate.outputs.go == 'true'
        uses: actions/github-script@v7
        env:
          BODY: ${{ steps.skill.outputs.result }}
        with:
          script: |
            await github.rest.pulls.update({
              owner: context.repo.owner, repo: context.repo.repo,
              pull_number: context.issue.number,
              body: process.env.BODY + '\n\n<sub>✍️ Drafted by the pm-claude-skills GitHub Action (pr-description-writer).</sub>',
            });