name: Deploy Pages

# Publishes docs/ to GitHub Pages through Actions rather than by serving the branch
# directly, so the page is rebuilt from src/ and checked before it goes live instead
# of after.
#
# REQUIRES A ONE-TIME SETTING. Settings → Pages → Build and deployment → Source must
# be "GitHub Actions", not "Deploy from a branch". Until it is, the deploy job fails
# with "Resource not accessible by integration" — the workflow is correct, the
# repository is still configured to serve the branch. The switch cannot be made from
# here: it needs a token with administration:write, which GITHUB_TOKEN is not.
#
# It is reversible. Setting Source back to a branch restores the old behaviour and
# this workflow simply stops being able to deploy.

on:
  push:
    branches: [ main ]
    # docs/ holds both the page and its generated bundle, so a src/ change only
    # matters here once it has been rebuilt into docs/ — which is what CI enforces.
    paths:
      - 'docs/**'
      - '.github/workflows/pages.yml'
  workflow_dispatch:

permissions:
  contents: read
  pages: write
  id-token: write

# Never cancel a deploy in flight: a half-published site is worse than a stale one.
# Queue instead, so the last push wins without interrupting the one already going out.
concurrency:
  group: pages
  cancel-in-progress: false

jobs:
  build:
    name: Build and check
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with:
        node-version: 22.x
        cache: 'npm'
    - name: Install dependencies
      run: npm ci
    - name: Rebuild the page bundle from src/
      run: npm run build:docs
    - name: The committed page is in sync with src/
      run: |
        git diff --exit-code -- docs/ \
          || (echo "docs/ is stale — run 'npm run build:docs' and commit the result" && exit 1)
    - name: The page loads nothing from the network
      run: npm run check:docs
    - uses: actions/configure-pages@v5
    - uses: actions/upload-pages-artifact@v3
      with:
        path: ./docs

  deploy:
    name: Deploy
    needs: build
    runs-on: ubuntu-latest
    environment:
      name: github-pages
      url: ${{ steps.deployment.outputs.page_url }}
    steps:
    - name: Deploy to GitHub Pages
      id: deployment
      uses: actions/deploy-pages@v5