Validate and deduplicate custom difficulty presets

lib/service-error.ts

@@ -7,10 +7,28 @@ export class ServiceError extends Error {
   }
 }
 
-export function checkServiceError(error: { message: string; code?: string } | null) {
+export function checkDifficultyPresetError(
+  error: { message: string; code?: string } | null,
+) {
+  if (error?.code === "23505")
+    throw new ServiceError("A difficulty with that name already exists", 409);
+  if (error?.code === "23514")
+    throw new ServiceError(
+      "Use a name with 2–40 characters and a round time of 15–600 seconds in 15-second steps",
+      400,
+    );
+  checkServiceError(error);
+}
+
+export function checkServiceError(
+  error: { message: string; code?: string } | null,
+) {
   if (!error) return;
   if (error.code === "P0001") throw new Error(error.message);
-  if (error.code === "PGRST116") throw new ServiceError("Record not found", 404);
+  if (error.code === "PGRST116")
+    throw new ServiceError("Record not found", 404);
   console.error("Supabase request failed:", error.code, error.message);
-  throw new ServiceError("MineGeo could not reach its data service. Please try again.");
+  throw new ServiceError(
+    "MineGeo could not reach its data service. Please try again.",
+  );
 }