ci: add file-checker.yml (#119)

We want to enforce the existence
of the files contained within the
userstyles template directory.

This will eliminate PRs getting
merged that may have deleted
existing files or may have missing
preview images.

.github/workflows/file-checker.yml

@@ -0,0 +1,49 @@
+name: Required Files Checker
+
+on:
+  workflow_dispatch:
+  pull_request_target:
+
+jobs:
+  file-checker:
+    name: Check for Missing Files
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Check
+        run: |
+          MISSING_FILES=0
+          echo "# Missing Files Found 😠" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+
+          required_files=(
+            "catppuccin.user.css"
+            "assets/mocha.webp"
+            "assets/macchiato.webp"
+            "assets/frappe.webp"
+            "assets/latte.webp"
+            "assets/catwalk.webp"
+          )
+
+          find_files() {
+            local path=$1
+            for file in "${required_files[@]}"; do
+              if [ ! -f "$path/$file" ]; then
+                MISSING_FILES=1
+                echo "- $path/$file" >> $GITHUB_STEP_SUMMARY
+              fi
+            done
+          }
+
+          for dir in styles/*; do
+            if [ -d "$dir" ]; then
+              find_files "$dir"
+            fi
+          done
+
+          if [ $MISSING_FILES -eq 0 ]; then
+            echo "# No Missing Files 🙌" > $GITHUB_STEP_SUMMARY
+          fi
+
+          exit $MISSING_FILES
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json