name: Documentation

# Built on every push, and published from main.
#
# The publishing used to wait for a manual dispatch, with a note saying it would
# run "once Pages is enabled". Pages was enabled — and the condition was never
# changed, so the site was built forty times and published none of them. What it
# showed was a Verdande from before v0.43: /links/, /beacon/ and /notifications/
# all answered 404, months after they were written. Nothing failed, because
# building *is* what the job was asked to do.
#
# The lesson is not about this line. It is that "publish later" needs something
# that fails when later arrives — a switch that is off and silent looks exactly
# like a switch that is on.
#
# Pull requests still build and never publish: `mkdocs build --strict` fails on a
# link to a page that does not exist, and building only after the merge means
# finding that out on `main`.
on:
  push:
    branches: [main]
    paths:
      - 'docs/**'
      - 'mkdocs.yml'
      - '.github/workflows/docs.yml'
  pull_request:
    paths:
      - 'docs/**'
      - 'mkdocs.yml'
      - '.github/workflows/docs.yml'
  workflow_dispatch:

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

concurrency:
  group: pages
  cancel-in-progress: false

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

      - uses: actions/setup-python@v5
        with:
          python-version: '3.12'
          cache: pip
          cache-dependency-path: docs/requirements.txt

      - run: pip install -r docs/requirements.txt

      - run: mkdocs build --strict

      - uses: actions/upload-pages-artifact@v3
        with:
          path: site_build

  deploy:
    needs: build
    runs-on: ubuntu-latest
    # From main, and by hand. Never from a pull request — a fork could otherwise
    # publish over the site by opening one.
    if: github.event_name != 'pull_request'
    environment:
      name: github-pages
      url: ${{ steps.deploy.outputs.page_url }}
    steps:
      - id: deploy
        uses: actions/deploy-pages@v4