Update map filtering

frontend/src/lib/index.ts

@@ -252,3 +252,22 @@ export function typeToString(type: string) {
 		return 'Unknown';
 	}
 }
+
+/**
+ * Checks if an adventure has been visited.
+ *
+ * This function determines if the `adventure.visits` array contains at least one visit
+ * with a `start_date` that is before the current date.
+ *
+ * @param adventure - The adventure object to check.
+ * @returns `true` if the adventure has been visited, otherwise `false`.
+ */
+export function isAdventureVisited(adventure: Adventure) {
+	const currentTime = Date.now();
+
+	// Check if any visit's start_date is before the current time.
+	return adventure.visits.some((visit) => {
+		const visitStartTime = new Date(visit.start_date).getTime();
+		return visit.start_date && visitStartTime <= currentTime;
+	});
+}