use a single deployment workflow that is aware of PR vs merge

.github/workflows/build-and-stage.yml

@@ -3,38 +3,56 @@ name: Build and stage
 env:
   AZURE_WEBAPP_PACKAGE_PATH: '.'
   DOTNET_VERSION: '8.0'
-  SLOT_NAME: staging
 
 on:
   push:
     branches: [ "main" ]
+  pull_request:
+    branches:
+    - main
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 permissions:
   contents: read
 
 jobs:
+  set-environment:
+    name: Determine workflow environment
+    runs-on: ubuntu-latest
+    outputs:
+      Slot_Name: ${{ steps.set-name.outputs.name }}
+    steps:
+    - id: set-name
+      run: echo "Slot_Name=${{ github.event_name == 'pull_request' && format('pr-', github.event.number) || vars.STAGING_SLOT_NAME }}" >> "$GITHUB_OUTPUT"
+
   build:
     name: Build and publish app
     runs-on: ubuntu-latest
-
     steps:
       - uses: actions/checkout@v4
 
       - name: Set up .NET Core
         uses: actions/setup-dotnet@v4
         with:
           dotnet-version: ${{ env.DOTNET_VERSION }}
+
       - name: Set up dependency caching for faster builds
         uses: actions/cache@v4
         with:
           path: ~/.nuget/packages
           key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
           restore-keys: |
             ${{ runner.os }}-nuget-
-      - name: Build with dotnet
+
+      - name: dotnet build
         run: dotnet build src/Client --configuration Release
+
       - name: dotnet publish
         run: dotnet publish src/Client -c Release -o ${{ env.DOTNET_ROOT }}/mainsite
+
       - name: Upload artifact for deployment job
         uses: actions/upload-artifact@v4
         with:
@@ -48,8 +66,10 @@ jobs:
     runs-on: ubuntu-latest
     needs: build
     environment:
-      name: 'Staging'
+      name: ${{ needs.set-environment.outputs.Slot_Name }}
       url: ${{ steps.deploy-to-webapp.outputs.webapp-url }}
+    env:
+      SLOT_NAME: ${{ needs.set-environment.outputs.Slot_Name }}
 
     steps:
       - name: Download artifact from build job
@@ -62,10 +82,28 @@ jobs:
         with:
           creds: ${{ secrets.AZURE_CREDENTIALS }}
 
+      - name: If PR, create a new staging slot
+        if: ${{ github.event_name == 'pull_request' }}
+        run: az webapp deployment slot create --resource-group ${{ vars.AZURE_RESOURCE_GROUP }} --name ${{ vars.AZURE_WEBAPP_NAME}} --slot ${{ env.SLOT_NAME }}
+
       - name: Deploy to Azure Web App
         id: deploy-to-webapp
         uses: azure/webapps-deploy@v3
         with:
           app-name: ${{ vars.AZURE_WEBAPP_NAME }}
           package: ${{ env.AZURE_WEBAPP_PACKAGE_PATH }}
           slot-name: ${{ env.SLOT_NAME }}
+
+      - name: If PR, comment with the preview link
+        if: ${{ github.event_name == 'pull_request' }}
+        uses: mshick/add-pr-comment@v2
+        with:
+          message: |
+            ## Preview link: https://${{ vars.AZURE_WEBAPP_NAME }}-${{ env.SLOT_NAME }}.azurewebsites.net 
+            
+            - Your changes have been deployed to the preview site. The preview site will update as you add more commits to this branch.
+            - The preview link is shareable, but will be deleted when the pull request is merged or closed.
+
+            > *This is an automated message.*
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+

.github/workflows/pr-cleanup.yml

@@ -1,4 +1,3 @@
-
 name: Delete a preview environment
 
 on: