build-and-preview-site.yml

name: PR Preview Deployment (Gatsby + GitHub Pages)

on:
  pull_request_target:
    branches: [master]
    types: [opened, synchronize, reopened, closed]

permissions:
  contents: write
  pull-requests: write

concurrency:
  group: preview-${{ github.event.pull_request.number || github.run_id }}
  cancel-in-progress: true

defaults:
  run:
    shell: bash

jobs:
  preview:
    runs-on: ubuntu-latest
    outputs:
      removed_prs_json: ${{ steps.prune-previews.outputs.removed_prs_json }}
    env:
      PREVIEW_RETENTION_LIMIT: 6

    steps:

      - name: Checkout PR
        if: github.event.action != 'closed'
        uses: actions/checkout@v6
        with:
          ref: ${{ github.event.pull_request.head.sha }}

      - name: Checkout gh-pages for cleanup
        if: github.event.action == 'closed'
        uses: actions/checkout@v6
        with:
          ref: gh-pages

      - name: Setup Node
        if: github.event.action != 'closed'
        uses: actions/setup-node@v6
        with:
          node-version: "20"

      - name: Install dependencies
        if: github.event.action != 'closed'
        run: npm ci

      - name: Set PATH_PREFIX for preview
        if: github.event.action != 'closed'
        run: |
          echo "PATH_PREFIX=pr-preview/pr-${{ github.event.pull_request.number }}" >> $GITHUB_ENV

      - name: Build PR preview
        if: github.event.action != 'closed'
        env:
          GATSBY_PREVIEW: "true"
          GATSBY_SITE_URL: https://${{ github.repository_owner }}.github.io
        run: |
          PATH_PREFIX=$PATH_PREFIX npm run build:preview

          # Prevent indexing
          echo -e "User-agent: *\nDisallow: /" > public/robots.txt

      - name: Deploy PR preview
        if: github.event.action != 'closed'
        uses: rossjrw/pr-preview-action@v1.6.3
        with:
          source-dir: ./public
          preview-branch: gh-pages
          umbrella-dir: pr-preview
          action: auto
          comment: false

      - name: Checkout gh-pages for preview retention
        if: github.event.action != 'closed'
        uses: actions/checkout@v6
        with:
          ref: gh-pages
          fetch-depth: 0
          filter: blob:none
          sparse-checkout: |
            pr-preview
          path: gh-pages-maintenance

      - name: Prune old PR previews
        id: prune-previews
        if: github.event.action != 'closed'
        run: |
          cd gh-pages-maintenance
          mkdir -p pr-preview
          removed_prs=()

          mapfile -t previews < <(
            while IFS= read -r preview; do
              timestamp="$(git log -1 --format=%ct -- "pr-preview/$preview" 2>/dev/null || echo 0)"
              printf '%s %s\n' "$timestamp" "$preview"
            done < <(find pr-preview -mindepth 1 -maxdepth 1 -type d -name 'pr-*' -printf '%f\n') \
              | sort -nr \
              | awk '{print $2}'
          )

          if (( ${#previews[@]} <= PREVIEW_RETENTION_LIMIT )); then
            echo "removed_prs_json=[]" >> "$GITHUB_OUTPUT"
            exit 0
          fi

          for preview in "${previews[@]:PREVIEW_RETENTION_LIMIT}"; do
            rm -rf "pr-preview/$preview"
            removed_prs+=("${preview#pr-}")
          done

          if git diff --quiet -- pr-preview; then
            echo "removed_prs=" >> "$GITHUB_OUTPUT"
            echo "removed_prs_json=[]" >> "$GITHUB_OUTPUT"
            exit 0
          fi

          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"
          git add pr-preview
          git commit -m "Prune old PR previews"
          git push

          echo "removed_prs=$(IFS=,; echo "${removed_prs[*]}")" >> "$GITHUB_OUTPUT"
          echo "removed_prs_json=$(printf '%s\n' "${removed_prs[@]}" | jq -R . | jq -sc .)" >> "$GITHUB_OUTPUT"

      - name: Comment PR with Preview URL
        if: github.event.action != 'closed'
        uses: marocchino/sticky-pull-request-comment@v2
        with:
          header: pr-preview
          message: |
            🚀 Preview deployment: https://layer5.io/pr-preview/pr-${{ github.event.pull_request.number }}/
            > *Note: Preview may take a moment (GitHub Pages deployment in progress). Please wait and refresh. Track deployment [here](https://github.com/${{ github.repository }}/actions/workflows/pages/pages-build-deployment)*

      - name: Comment on pruned previews
        if: github.event.action != 'closed' && steps.prune-previews.outputs.removed_prs_json != '[]'
        uses: actions/github-script@v7
        env:
          REMOVED_PRS_JSON: ${{ steps.prune-previews.outputs.removed_prs_json }}
          PREVIEW_RETENTION_LIMIT: ${{ env.PREVIEW_RETENTION_LIMIT }}
        with:
          script: |
            const removedPrs = JSON.parse(process.env.REMOVED_PRS_JSON);
            const retentionLimit = process.env.PREVIEW_RETENTION_LIMIT;
            const header = "pr-preview";
            const marker = `<!-- Sticky Pull Request Comment${header} -->`;

            for (const prNumber of removedPrs) {
              const body =
                `Preview deployment for PR #${prNumber} removed.\n\n` +
                `This PR preview was automatically pruned because we keep only the ${retentionLimit} most recently updated previews on GitHub Pages to stay within deployment size limits.\n\n` +
                `If needed, push a new commit to this PR to generate a fresh preview.\n` +
                `${marker}`;

              const { data: comments } = await github.rest.issues.listComments({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: Number(prNumber),
                per_page: 100,
              });

              const existingComment = [...comments].reverse().find((comment) =>
                comment.user?.login === "github-actions[bot]" &&
                comment.body?.includes(marker)
              );

              if (existingComment) {
                await github.rest.issues.updateComment({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  comment_id: existingComment.id,
                  body,
                });
                continue;
              }

              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: Number(prNumber),
                body,
              });
            }

      - name: Cleanup PR preview on close
        if: github.event.action == 'closed'
        uses: rossjrw/pr-preview-action@v1.6.3
        with:
          preview-branch: gh-pages
          umbrella-dir: pr-preview
          action: remove