refactor(lib): split game.js into scoring and username modules

Extract username generation into a dedicated module, simplify game.js to
focus on round scoring logic, and update consumers accordingly.

src/app/components/LeaderboardList.js

@@ -3,7 +3,20 @@
 import { Medal } from 'lucide-react';
 import { Badge } from '@/components/ui/badge';
 import { Skeleton } from '@/components/ui/skeleton';
-import { formatDistance, getDistanceColor } from '../../lib/game';
+import { formatDistance, calculateScore } from '../../lib/game';
+
+// Keyed by the round score the distance would earn, so the tint tracks the
+// scoring ladder instead of re-typing its thresholds.
+const DISTANCE_COLORS = {
+  5: 'text-green-700 dark:text-green-300',
+  4: 'text-blue-700 dark:text-blue-300',
+  3: 'text-yellow-700 dark:text-yellow-300',
+  2: 'text-orange-700 dark:text-orange-300',
+};
+
+function getDistanceColor(distance) {
+  return DISTANCE_COLORS[calculateScore(distance)] ?? 'text-red-700 dark:text-red-300';
+}
 
 function getScoreColor(score) {
   if (score >= 50) return 'text-purple-700 dark:text-purple-300';

src/lib/game.js

@@ -17,14 +17,21 @@ export function calculateDistance(lat1, lon1, lat2, lon2) {
   }
 }
 
+// Distance ceiling in meters -> points. The single scoring ladder; anything
+// that bands a result (colors, labels, the scoring table on the home page)
+// should derive from calculateScore rather than re-typing these thresholds.
+export const SCORE_BANDS = [
+  { maxMeters: 50, points: 5 },
+  { maxMeters: 100, points: 4 },
+  { maxMeters: 200, points: 3 },
+  { maxMeters: 500, points: 2 },
+  { maxMeters: 1000, points: 1 },
+];
+
 // Calculate score based on distance (0-5 points scale)
 export function calculateScore(distance) {
-  if (distance <= 50) return 5;
-  if (distance <= 100) return 4;
-  if (distance <= 200) return 3;
-  if (distance <= 500) return 2;
-  if (distance <= 1000) return 1;
-  return 0;
+  const band = SCORE_BANDS.find((entry) => distance <= entry.maxMeters);
+  return band ? band.points : 0;
 }
 
 // Format distance for display
@@ -35,32 +42,3 @@ export function formatDistance(distance) {
     return `${(distance / 1000).toFixed(2)}km`;
   }
 }
-
-
-// Get or set username from localStorage
-export function getUsername() {
-  if (typeof window === 'undefined') return null;
-  return localStorage.getItem('vngeoguessr_username');
-}
-
-export function setUsername(username) {
-  if (typeof window === 'undefined') return;
-  localStorage.setItem('vngeoguessr_username', username);
-}
-
-// Get result message based on score
-export function getResultMessage(score, distance) {
-  if (score > 4) return "Excellent! Outstanding guess!";
-  if (score > 2) return "Good job! Nice work!";
-  if (score > 0) return "Not bad! Keep trying!";
-  return "Nice try! Better luck next time!";
-}
-
-// Get distance color for leaderboard display
-export function getDistanceColor(distance) {
-  if (distance <= 50) return 'text-green-700 dark:text-green-300';
-  if (distance <= 100) return 'text-blue-700 dark:text-blue-300';
-  if (distance <= 200) return 'text-yellow-700 dark:text-yellow-300';
-  if (distance <= 500) return 'text-orange-700 dark:text-orange-300';
-  return 'text-red-700 dark:text-red-300';
-}

src/lib/pano-index.js

@@ -6,7 +6,7 @@
 // replaces asking the Graph API what is near a random point, which fails
 // outright in dense districts and takes seconds where it works.
 //
-// SERVER-SIDE ONLY. These files are ~25MB of exact answers; importing them from
+// SERVER-SIDE ONLY. These files are ~28MB of exact answers; importing them from
 // anywhere the browser can reach hands every round's solution to the player.
 // src/lib/regions.js is the client-safe view of the same tree and deliberately
 // imports nothing from here -- tests/regions.test.js enforces that boundary.

src/lib/username.js

@@ -0,0 +1,15 @@
+// Player name in localStorage, mirroring theme.js: one module owns one
+// browser-storage concern, so server code importing lib/game.js for scoring
+// never touches window.
+
+export const USERNAME_STORAGE_KEY = 'vngeoguessr_username';
+
+export function getUsername() {
+  if (typeof window === 'undefined') return null;
+  return localStorage.getItem(USERNAME_STORAGE_KEY);
+}
+
+export function setUsername(username) {
+  if (typeof window === 'undefined') return;
+  localStorage.setItem(USERNAME_STORAGE_KEY, username);
+}