build-gallery.yml

# .github/workflows/build-gallery.yml
#
# Auto-generate the example gallery (index.html) on push to main.
# The generated file is committed back to the branch, and GitHub Pages
# serves it via the normal "Deploy from a branch" setting.

name: Build Gallery

on:
  push:
    branches: [main]
  workflow_dispatch:

permissions:
  contents: write        # needed to push the generated index.html back

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.12"

      - name: Set up Node
        uses: actions/setup-node@v4
        with:
          node-version: "20"
          cache: npm

      - name: Install Node dependencies
        run: npm ci

      - name: Install ffmpeg
        run: sudo apt-get update && sudo apt-get install -y ffmpeg

      # Cache Playwright's bundled Chromium across runs, keyed on the lockfile
      # (which pins the Playwright version).
      - name: Cache Playwright browsers
        uses: actions/cache@v4
        with:
          path: ~/.cache/ms-playwright
          key: playwright-${{ runner.os }}-${{ hashFiles('package-lock.json') }}

      - name: Install Playwright Chromium
        run: npx playwright install --with-deps chromium

      # Regenerate thumbnails (animated WebP + poster). The script content-hashes
      # each example and skips unchanged ones, so this is cheap when nothing
      # changed — only edited examples are re-captured.
      - name: Generate previews
        run: node scripts/capture_previews.mjs

      - name: Generate gallery index.html
        run: python scripts/build_gallery.py

      - name: Commit and push if changed
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"
          git add index.html previews
          git diff --cached --quiet || git commit -m "Auto-generate gallery + previews [skip ci]"
          git push