name: Synchronise README

on:
  pull_request:
    paths:
      - 'lru-cache.wiki'
      - 'scripts/wiki2html.scm'

permissions:
  contents: read

jobs:

  generate:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout PR branch
        uses: actions/checkout@v6
        with:
          ref: ${{ github.head_ref }}

      - name: Install Nix
        uses: cachix/install-nix-action@v31
        with:
          nix_path: nixpkgs=channel:nixpkgs-unstable

      - name: Generate README
        run: nix run .#generate-readme -- lru-cache.wiki > README.md

      - name: Upload README artefact
        uses: actions/upload-artifact@v4
        with:
          name: readme
          path: README.md

  commit:
    needs: generate
    runs-on: ubuntu-latest

    permissions:
      contents: write

    steps:
      - name: Checkout PR branch
        uses: actions/checkout@v6
        with:
          ref: ${{ github.head_ref }}

      - name: Download README artefact
        uses: actions/download-artifact@v4
        with:
          name: readme

      - name: Commit generated README changes
        if: github.event.pull_request.head.repo.fork == false
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"
          git add README.md
          git commit -m "Generate README.md from lru-cache.wiki"
          git push

      - name: Check for drift (forks only)
        if: github.event.pull_request.head.repo.fork == true
        run: |
          git add README.md
          if ! git diff --staged --quiet; then
            echo "::error::README.md is out of date. Please regenerate it locally by running: nix run .#generate-readme -- lru-cache.wiki > README.md"
            exit 1
          fi