name: Notebook Check Pull Request

on:
  pull_request_target:
    types: [opened, reopened]

permissions:
  contents: read

jobs:
  comment-welcome:
    permissions:
      contents: read
      pull-requests: write

    runs-on: ubuntu-latest
    steps:
    - name: Fetch pull request branch
      uses: actions/checkout@v4
      with:
        repository: ${{ github.event.pull_request.head.repo.full_name }}
        ref: ${{ github.event.pull_request.head.sha }}
    - name: Fetch base develop branch
      run: git fetch -u "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY" develop:develop
    - name: Create message
      env:
        HEAD_REPOSITORY: ${{ github.event.pull_request.head.repo.full_name }}
        HEAD_REF: ${{ github.event.pull_request.head.ref }}
        PR_NUM: ${{ github.event.pull_request.number }}
      run: |
        # Preview links and tool usage only needed for notebook changes.
        readarray -t changed_notebooks < <(git diff --name-only develop | grep '\.ipynb$' || true)
        if [[ ${#changed_notebooks[@]} == 0 ]]; then
          echo "No notebooks modified in this pull request."
        else
          msg="<h4>Preview</h4>\n"
          msg+="Preview and run these notebook edits with Google Colab:\n<ul>\n"
          # Link to PR branch in user's fork that is always current.
          for fp in "${changed_notebooks[@]}"; do
            gh_path="${HEAD_REPOSITORY}/blob/${HEAD_REF}/${fp}"
            colab_url="https://colab.research.google.com/github/${gh_path}"
            msg+="<li><a href='${colab_url}'>${fp}</a></li>\n"
          done
          msg+="</ul>\n"

          reviewnb_url="https://app.reviewnb.com/${GITHUB_REPOSITORY}/pull/${PR_NUM}/files/"
          msg+="Rendered <a href='${reviewnb_url}'>notebook diffs</a> available on ReviewNB.com.\n"

          msg+="If commits are added to the pull request, synchronize your local branch: <code>git pull origin $HEAD_REF</code>\n"
        fi
        echo "MESSAGE=$msg" >> $GITHUB_ENV
    - name: Post comment
      env:
        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        ISSUE_URL: ${{ github.event.pull_request.issue_url }}
      run: |
        # Env var defined in previous step. Escape string for JSON.
        body="$(echo -n -e $MESSAGE | python3 -c 'import json,sys; print(json.dumps(sys.stdin.read()))')"
        # Add comment to pull request.
        curl -X POST \
          -H "Accept: application/vnd.github.v3+json" \
          -H "Authorization: token $GITHUB_TOKEN" \
          "${ISSUE_URL}/comments" \
          --data "{\"body\": $body}"