Refactor: Modularize Scoring Engine, Unify Persistence Pipeline, and Streamline Comparison State

src/app/api/compare/route.ts

@@ -1,43 +1,14 @@
 import { NextResponse } from "next/server";
 import {
-  CompareUserFetchError,
   calculateWinner,
   compareUsers,
   createComparisonInsights,
-  parseSelectedLanguagesFromSearchParams,
   resolveLocale,
 } from "@/features/comparison/services";
-import { toSafeApiError } from "@/lib/github";
-import type { ClientSafeError, SafeApiError } from "@/types/api";
+import { formatApiErrorResponse, parseSelectedLanguagesFromSearchParams } from "@/lib/api";
 
 export const runtime = "nodejs";
 
-function toApiErrorStatus(code: ReturnType<typeof toSafeApiError>["code"]): number {
-  switch (code) {
-    case "RATE_LIMITED":
-    case "TEMPORARY_THROTTLE":
-      return 429;
-    case "GITHUB_TIMEOUT":
-    case "GITHUB_RESOURCE_LIMIT":
-    case "GITHUB_AUTH":
-      return code === "GITHUB_AUTH" ? 401 : 503;
-    case "GITHUB_NOT_FOUND":
-      return 404;
-    case "NETWORK":
-      return 503;
-    default:
-      return 500;
-  }
-}
-
-function toClientSafeError(error: SafeApiError): ClientSafeError {
-  return {
-    code: error.code,
-    message: error.message,
-    targetUsernames: error.targetUsernames,
-  };
-}
-
 export async function GET(request: Request) {
   const { searchParams } = new URL(request.url);
   const usernames = searchParams
@@ -61,40 +32,6 @@ export async function GET(request: Request) {
     return NextResponse.json({ success: true, users, ...winnerData, insights });
   } catch (error: unknown) {
     console.error("GitHub score error:", error);
-
-    let safeError: SafeApiError;
-
-    if (error instanceof CompareUserFetchError) {
-      const mappedCause = toSafeApiError(error.causeError);
-      if (
-        mappedCause.code === "GITHUB_NOT_FOUND" ||
-        (error.causeError instanceof Error && error.causeError.message === "User not found")
-      ) {
-        safeError = {
-          code: "GITHUB_NOT_FOUND",
-          message: "GitHub user not found",
-          targetUsernames: [error.username],
-          rateLimit: mappedCause.rateLimit,
-        };
-      } else {
-        safeError = mappedCause;
-      }
-    } else {
-      safeError =
-        error instanceof Error && error.message === "User not found"
-          ? { code: "GITHUB_NOT_FOUND", message: "GitHub user not found" }
-          : toSafeApiError(error);
-    }
-
-    const clientSafeError = toClientSafeError(safeError);
-
-    return NextResponse.json(
-      {
-        success: false,
-        error: clientSafeError.message,
-        errorDetails: clientSafeError,
-      },
-      { status: toApiErrorStatus(safeError.code) },
-    );
+    return formatApiErrorResponse(error);
   }
 }

src/app/api/user/[username]/route.ts

@@ -1,51 +1,9 @@
 import { NextResponse } from "next/server";
-import { getUserProfile, UserFetchError } from "@/features/developer/services";
-import { normalizeSelectedLanguages } from "@/features/scoring";
-import { toSafeApiError } from "@/lib/github";
-import type { SafeApiError } from "@/types/api";
+import { getUserProfile } from "@/features/developer/services";
+import { formatApiErrorResponse, parseSelectedLanguagesFromSearchParams } from "@/lib/api";
 
 export const runtime = "nodejs";
 
-type ClientSafeError = Pick<SafeApiError, "code" | "message" | "targetUsernames">;
-
-function parseSelectedLanguagesFromSearchParams(searchParams: URLSearchParams): string[] {
-  const fromRepeated = searchParams.getAll("selectedLanguage");
-  const fromCsv = searchParams
-    .get("selectedLanguages")
-    ?.split(",")
-    .map((language) => language.trim())
-    .filter(Boolean);
-
-  return normalizeSelectedLanguages([...(fromRepeated ?? []), ...(fromCsv ?? [])]);
-}
-
-function toClientSafeError(error: SafeApiError): ClientSafeError {
-  return {
-    code: error.code,
-    message: error.message,
-    targetUsernames: error.targetUsernames,
-  };
-}
-
-function toApiErrorStatus(code: ReturnType<typeof toSafeApiError>["code"]): number {
-  switch (code) {
-    case "RATE_LIMITED":
-    case "TEMPORARY_THROTTLE":
-      return 429;
-    case "GITHUB_TIMEOUT":
-    case "GITHUB_RESOURCE_LIMIT":
-    case "GITHUB_AUTH":
-      return code === "GITHUB_AUTH" ? 401 : 503;
-    case "GITHUB_NOT_FOUND":
-      return 404;
-    case "NETWORK":
-      return 503;
-    case "UNKNOWN":
-    default:
-      return 500;
-  }
-}
-
 export async function GET(request: Request, { params }: { params: Promise<{ username: string }> }) {
   const { username } = await params;
   const trimmed = username?.trim();
@@ -65,40 +23,6 @@ export async function GET(request: Request, { params }: { params: Promise<{ user
     return NextResponse.json({ success: true, user, location });
   } catch (error: unknown) {
     console.error("User profile fetch error:", error);
-
-    let safeError: SafeApiError;
-
-    if (error instanceof UserFetchError) {
-      const mappedCause = toSafeApiError(error.causeError);
-      if (
-        mappedCause.code === "GITHUB_NOT_FOUND" ||
-        (error.causeError instanceof Error && error.causeError.message === "User not found")
-      ) {
-        safeError = {
-          code: "GITHUB_NOT_FOUND",
-          message: "GitHub user not found",
-          targetUsernames: [error.username],
-          rateLimit: mappedCause.rateLimit,
-        };
-      } else {
-        safeError = mappedCause;
-      }
-    } else {
-      safeError =
-        error instanceof Error && error.message === "User not found"
-          ? { code: "GITHUB_NOT_FOUND", message: "GitHub user not found" }
-          : toSafeApiError(error);
-    }
-
-    const clientSafeError = toClientSafeError(safeError);
-
-    return NextResponse.json(
-      {
-        success: false,
-        error: clientSafeError.message,
-        errorDetails: clientSafeError,
-      },
-      { status: toApiErrorStatus(safeError.code) },
-    );
+    return formatApiErrorResponse(error);
   }
 }

src/app/user/[username]/page.tsx

@@ -1,3 +1,4 @@
+import { cache } from "react";
 import type { Metadata } from "next";
 import { JsonLd } from "@/components/seo/json-ld";
 import { UserProfileClient, UserNotFoundCard } from "@/features/developer";
@@ -9,6 +10,10 @@ import { toAbsoluteUrl } from "@/lib/seo";
 import countriesData from "@/data/countries.json";
 import { detectCountry } from "@/lib/geo";
 
+const getCachedUserProfile = cache(async (username: string) => {
+  return getUserProfile(username);
+});
+
 type CountryInfo = {
   slug: string;
   title: string;
@@ -27,7 +32,7 @@ export async function generateMetadata({ params }: Props): Promise<Metadata> {
 
   let displayName = cleanUsername;
   try {
-    const { user } = await getUserProfile(cleanUsername);
+    const { user } = await getCachedUserProfile(cleanUsername);
     displayName = user.name?.trim() || cleanUsername;
   } catch {
     // Fallback if user cannot be fetched during metadata generation
@@ -96,7 +101,7 @@ export default async function UserProfilePage({ params, searchParams }: Props) {
   let fetchErrorMessage: string | null = null;
 
   try {
-    profileData = await getUserProfile(cleanUsername);
+    profileData = await getCachedUserProfile(cleanUsername);
   } catch (err: unknown) {
     fetchErrorMessage = err instanceof Error ? err.message : "Failed to load user profile";
   }