Validate inputs are set (#12)

action.yml

@@ -33,6 +33,29 @@ runs:
   using: "composite"
   steps:
       - uses: actions/checkout@v3.5.3 # checkout the repository in which this GitHub Action is being used.
+      - name: Validate inputs
+        shell: bash
+        run: |
+          if  [ -z "${{ inputs.speckle_token }}" ]; then
+            echo "ERROR: speckle_token secret is required"
+            exit 1
+          fi
+          if  [ -z "${{ inputs.speckle_automate_url }}" ]; then
+            echo "ERROR: speckle_automate_url input value is required"
+            exit 1
+          fi
+          if  [ -z "${{ inputs.speckle_function_id }}" ]; then
+            echo "ERROR: speckle_function_id input value is required"
+            exit 1
+          fi
+          if  [ -z "${{ inputs.speckle_function_input_schema_file_path }}" ]; then
+            echo "ERROR: speckle_function_input_schema_file_path input value is required"
+            exit 1
+          fi
+          if  [ -z "${{ inputs.speckle_function_command }}" ]; then
+            echo "ERROR: speckle_function_command input value is required"
+            exit 1
+          fi
       - name: Set Version tag
         shell: bash
         run: |
@@ -60,7 +83,17 @@ runs:
         run: |
           AUTOMATE_HOST=$(python -c 'from urllib.parse import urlparse; print(urlparse("${{ inputs.speckle_automate_url }}").netloc)')
           echo "Parsed automate host: ${AUTOMATE_HOST}"
-          echo "automateHost=${AUTOMATE_HOST}"" >>"$GITHUB_ENV"
+          echo "automateHost=${AUTOMATE_HOST}" >>"$GITHUB_ENV"
+      - name: Ensure image doesn't exist in registry
+        shell: bash
+        run: |
+          set +e
+          docker manifest inspect ${{ env.automateHost }}/${{ inputs.speckle_function_id }}:${{ env.releaseTag }}
+          if [[ $? == 0 ]]
+          then
+            echo "Cannot override the existing release tag ${{ env.releaseTag }}. Please publish a new release!"
+            exit 1
+          fi
       - name: Build and push Docker image
         uses: docker/build-push-action@v4.1.1
         with: