Refactor API endpoints and modularize controllers and models

public/js/networkUtils.js

@@ -0,0 +1,31 @@
+export function sendRequest(url, method = "GET", data = null, customHeaders = {}) {
+  const options = {
+    method,
+    credentials: 'include',
+    headers: {}
+  };
+
+  // Merge custom headers
+  Object.assign(options.headers, customHeaders);
+
+  // If data is provided and is not FormData, assume JSON.
+  if (data && !(data instanceof FormData)) {
+    if (!options.headers["Content-Type"]) {
+      options.headers["Content-Type"] = "application/json";
+    }
+    options.body = JSON.stringify(data);
+  } else if (data instanceof FormData) {
+    options.body = data;
+  }
+
+  return fetch(url, options)
+    .then(response => {
+      if (!response.ok) {
+        return response.text().then(text => {
+          throw new Error(`HTTP error ${response.status}: ${text}`);
+        });
+      }
+      const clonedResponse = response.clone();
+      return response.json().catch(() => clonedResponse.text());
+    });
+}