Now supports running under a sub path

Just set the SPOOLMAN_BASE_PATH environment variable and it should work.

Resolves #95

client/src/utils/url.ts

@@ -0,0 +1,35 @@
+declare global {
+  interface Window {
+    SPOOLMAN_BASE_PATH: string;
+  }
+}
+
+/**
+ * Returns the base path of the application.
+ *
+ * If a base path is set, this returns e.g. "/spoolman". If none is set, it returns "".
+ *
+ * @return {string} The base path of the application. If the `SPOOLMAN_BASE_PATH`
+ * window variable is set and not empty, it is returned. Otherwise, the
+ * default base path "" is returned.
+ */
+export function getBasePath(): string {
+  if (window.SPOOLMAN_BASE_PATH && window.SPOOLMAN_BASE_PATH.length > 0) {
+    return window.SPOOLMAN_BASE_PATH;
+  } else {
+    return "";
+  }
+}
+
+/**
+ * A function that returns the Spoolman API URL
+ * This returns e.g. "/spoolman/api/v1" if the base path is "/spoolman"
+ *
+ * @return {string} The API URL
+ */
+export function getAPIURL(): string {
+  if (!import.meta.env.VITE_APIURL) {
+    throw new Error("VITE_APIURL is not set");
+  }
+  return getBasePath() + import.meta.env.VITE_APIURL;
+}