Check if user is banned, log them out and then flash them with a funny message which is handled by error modals

main.py

@@ -1,4 +1,4 @@
-from flask import Flask, redirect, url_for, render_template, request, Response, send_from_directory, g
+from flask import Flask, redirect, url_for, render_template, request, Response, send_from_directory, g, flash
 from dotenv import load_dotenv
 from constants import RICKROLL_LINK, UPLOAD_DIR, MINIMUM_COSINE_SIMILARITY, MINIMUM_OCR_SIMILARITY, DATABASE_FILE
 from PIL import Image
@@ -82,6 +82,20 @@ def user_loader(user_id):
 def unauthorized_handler():
     return redirect(url_for("login"))
 
+@app.before_request
+def check_banned():
+    username = flask_login.current_user.id
+    
+    cur = get_db().cursor()
+    cur.execute("SELECT banned FROM Users WHERE username = ?", (username))
+    row = cur.fetchone()
+    cur.close()
+
+    if row is None or row[0]:
+        flash("Imagine forgetting to touch grass so you get banned from my app. Such a discord moderator you are. You have no life. Just go outside.")
+        flask_login.logout_user()
+        return redirect("/")
+
 def resize_image_file(path, max_side=256, fmt="JPEG"):
     img = Image.open(path)
     scale = max_side / max(img.size)

templates/base.jinja2

@@ -18,5 +18,37 @@
     For more information, please visit <a href="/info" class="alert-link">the unofficial safety guide</a>!
     </div>
     {% block body %}{% endblock %}
+    <div class="modal fade" id="errorModal" tabindex="-1" aria-labelledby="errorModalLabel" aria-hidden="true">
+    <div class="modal-dialog">
+        <div class="modal-content">
+        <div class="modal-header bg-danger text-white">
+            <h5 class="modal-title" id="errorModalLabel">Error</h5>
+            <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="Close"></button>
+        </div>
+        <div class="modal-body" id="errorModalBody">
+        </div>
+        <div class="modal-footer">
+            <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Close</button>
+        </div>
+        </div>
+    </div>
+    </div>
+    <script>
+        document.addEventListener("DOMContentLoaded", function() {
+            {% with messages = get_flashed_messages(with_categories=true) %}
+                {% if messages %}
+                    {% for category, message in messages %}
+                        {% if category == 'error' %}
+                            const modalBody = document.getElementById("errorModalBody");
+                            modalBody.textContent = "{{ message|escapejs }}";
+
+                            const errorModal = new bootstrap.Modal(document.getElementById('errorModal'));
+                            errorModal.show();
+                        {% endif %}
+                    {% endfor %}
+                {% endif %}
+            {% endwith %}
+        });
+    </script>
 </body>
 </html>