name: diff-pr

on:
  pull_request:

permissions:
  contents: read
  pull-requests: write

concurrency:
  group: diff-pr-${{ github.event.pull_request.number }}
  cancel-in-progress: true

jobs:
  dix:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: cachix/install-nix-action@v31
        with:
          extra_nix_config: |
            experimental-features = nix-command flakes

      - name: worktree base for diff
        run: git worktree add "$RUNNER_TEMP/base" "${{ github.event.pull_request.base.sha }}"

      - name: build closures and render diff
        run: |
          nix run .#ci -- diff "$RUNNER_TEMP/base" . \
            "### System closure diff vs \`${{ github.event.pull_request.base.ref }}\`" \
            > "$RUNNER_TEMP/comment.md"
          nix run .#ci -- inspect-diff "$RUNNER_TEMP/base" . \
            "### Inspection diff vs \`${{ github.event.pull_request.base.ref }}\`" \
            >> "$RUNNER_TEMP/comment.md"

      - name: post/update PR comment
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          API: ${{ github.api_url }}
          REPO: ${{ github.repository }}
          PR: ${{ github.event.pull_request.number }}
        run: nix run .#ci -- post-comment "<!-- dix-diff -->" "$RUNNER_TEMP/comment.md"