Add GH action to push hydrogen theme to external repo

.github/workflows/push-to-external-repo.yml

@@ -0,0 +1,78 @@
+name: (main) push to external repo
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - "templates/hydrogen-theme/**"
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  push-to-external-repo:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Determine branch
+        id: branch
+        run: |
+          if [ "${{ github.event_name }}" == "pull_request" ]; then
+            pr_number="${{ github.event.number }}"
+            echo "branch=pull-request-${pr_number}" >> $GITHUB_OUTPUT
+          else
+            echo "branch=main" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Publish to external repository
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          deploy_key: ${{ secrets.SSH_DEPLOY_KEY }}
+          publish_dir: ./templates/hydrogen-theme
+          external_repository: ${{ vars.EXTERNAL_REPO }}
+          publish_branch: ${{ steps.branch.outputs.branch }}
+          allow_empty_commit: true
+
+      - name: Generate pull request comment
+        id: pr_comment
+        run: |
+          if [ "${{ github.event_name }}" == "pull_request" ]; then
+            preview_url="https://headless-clone-git-${{ steps.branch.outputs.branch }}-thomaskn1.vercel.app"
+            echo "body=A preview URL is being deployed to test this PR. It should be live in a short moment: ${preview_url}" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Check Existing Comments
+        id: check-comments
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const existingComments = await github.rest.issues.listComments({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo
+            });
+
+            const marker = "${{ steps.pr_comment.outputs.body }}"
+            const existingComment = existingComments.data.find(comment => comment.body.includes(marker));
+            console.log(existingComment ? 'Existing comment found' : 'No existing comment found');
+
+            // Set an output to pass information to subsequent steps
+            core.setOutput("existingCommentFound", existingComment ? 'true' : 'false');
+            core.setOutput("existingCommentId", existingComment ? existingComment.id : '');
+
+      - name: Comment on Pull Request
+        if: steps.check-comments.outputs.existingCommentFound != 'true'
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `${{ steps.pr_comment.outputs.body }}`
+            });