name: Build LaTeX PDF

on:
  push:
    paths:
      - '**/*.tex'

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 2   # need previous commit to diff against

      - name: Find changed .tex root files
        id: changed
        run: |
          apt-get update -qq && apt-get install -y -qq git > /dev/null
          git config --global --add safe.directory "$GITHUB_WORKSPACE"

          # root files = .tex files that contain \documentclass
          CHANGED=$(git diff --name-only "${{ github.event.before }}" "${{ github.sha }}" -- '*.tex' || true)
          ROOTS=""
          for f in $CHANGED; do
            if [ -f "$f" ] && grep -q '\\documentclass' "$f"; then
              ROOTS="$ROOTS $f"
            fi
          done
          echo "roots=$ROOTS" >> "$GITHUB_OUTPUT"
          echo "Root files to build: $ROOTS"

      - name: Compile changed root files
        if: steps.changed.outputs.roots != ''
        uses: docker://texlive/texlive:latest
        run: |
          mkdir -p pdf aux
          for f in ${{ steps.changed.outputs.roots }}; do
            echo "== Building $f =="
            latexmk -pdf -interaction=nonstopmode -halt-on-error \
              -outdir=pdf -auxdir=aux "$f"
          done
          # keep pdf/ containing only pdfs
          find pdf -type f ! -name '*.pdf' -delete

      - name: Upload built PDFs
        if: steps.changed.outputs.roots != ''
        uses: actions/upload-artifact@v4
        with:
          name: pdf-output
          path: pdf/*.pdf

      - name: Commit PDFs back to repo
        if: steps.changed.outputs.roots != ''
        run: |
          git config user.name "gitea-actions"
          git config user.email "actions@gitea.local"
          git remote set-url origin "https://Domipoke:${{ secrets.GITEA_PUSH_TOKEN }}@gitea.egregge.eg/Domipoke/SharedLaTeX.git"          
          git add pdf/*.pdf
          git diff --cached --quiet || git commit -m "CI: rebuild PDF(s) [skip ci]"
          git push origin HEAD:${{ github.ref_name }}