name: Read the Docs PR preview

on:
  pull_request_target:
    types:
      - opened
      - synchronize

permissions:
  contents: read
  pull-requests: write

concurrency:
  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
  cancel-in-progress: true

jobs:
  documentation-links:
    runs-on: ubuntu-latest
    if: github.event.repository.fork == false
    steps:
      - uses: actions/checkout@v5

      - name: Check for docs changes
        id: docs_changes
        run: |
          # Fetch the PR head
          git fetch origin pull/${{ github.event.pull_request.number }}/head:pr-head

          # Show diff between base (current checkout) and PR head
          if git diff --name-only HEAD pr-head | grep -q '^docs/'; then
            echo "docs_changed=true" >> "$GITHUB_OUTPUT"
          else
            echo "docs_changed=false" >> "$GITHUB_OUTPUT"
          fi

      - uses: readthedocs/actions/preview@v1
        if: steps.docs_changes.outputs.docs_changed == 'true'
        with:
          project-slug: "pybind11"
          single-version: "true"