refactor(layout): extract ghost-city detection into a named isGhostCi… (JhaSourav07#2089)

## Description

Fixes JhaSourav07#293

## Changes made
- Extracted logic into a pure predicate function.
- Removed inline loop and accumulator.
- Added dedicated unit tests for `isGhostCity`.

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [ ] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

(closes JhaSourav07#293)

Author: JhaSourav07

lib/svg/layout.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { computeTowers, computeFaceOpacity, computeTowerHeight } from './layout';
+import { isGhostCity, computeTowers, computeFaceOpacity, computeTowerHeight } from './layout';
 import type { ContributionCalendar } from '../../types';
 import {
   GHOST_HEIGHT_PX,
@@ -313,3 +313,41 @@ describe('computeTowerHeight', () => {
     expect(computeTowerHeight(999999, 'log', false)).toBe(MAX_LOG_HEIGHT);
   });
 });
+
+describe('isGhostCity', () => {
+  it('should return true if there are zero contributions across all weeks', () => {
+    const emptyCalendarWeeks = [
+      {
+        contributionDays: [
+          { contributionCount: 0, locAdditions: 0, locDeletions: 0 },
+          { contributionCount: 0, locAdditions: 0, locDeletions: 0 },
+        ],
+      },
+    ];
+    expect(isGhostCity(emptyCalendarWeeks)).toBe(true);
+  });
+
+  it('should return false if at least one day has standard contributions', () => {
+    const activeCalendarWeeks = [
+      {
+        contributionDays: [
+          { contributionCount: 0, locAdditions: 0, locDeletions: 0 },
+          { contributionCount: 5, locAdditions: 0, locDeletions: 0 },
+        ],
+      },
+    ];
+    expect(isGhostCity(activeCalendarWeeks)).toBe(false);
+  });
+
+  it('should return false if at least one day has lines of code (LoC) modifications', () => {
+    const locOnlyCalendarWeeks = [
+      {
+        contributionDays: [
+          { contributionCount: 0, locAdditions: 120, locDeletions: 0 },
+          { contributionCount: 0, locAdditions: 0, locDeletions: 0 },
+        ],
+      },
+    ];
+    expect(isGhostCity(locOnlyCalendarWeeks)).toBe(false);
+  });
+});

lib/svg/layout.ts

@@ -36,6 +36,31 @@ export interface TowerData {
   intensityLevel: number; // Quartile level (0 for no commits, 1 to 4 based on contribution intensity)
 }
 
+interface MinimalDay {
+  contributionCount?: number;
+  locAdditions?: number;
+  locDeletions?: number;
+}
+
+interface MinimalWeek {
+  contributionDays: MinimalDay[];
+}
+
+/**
+ * Determines if the entire visible calendar monolith is empty (a "ghost city").
+ * It returns true only if there are absolutely zero contributions (commits or LoC)
+ * across all visible weeks.
+ */
+export function isGhostCity(weeks: MinimalWeek[]): boolean {
+  return !weeks.some((week) =>
+    week.contributionDays.some((day) => {
+      const commits = day.contributionCount || 0;
+      const loc = (day.locAdditions || 0) + (day.locDeletions || 0);
+      return commits > 0 || loc > 0;
+    })
+  );
+}
+
 export function computeTowerHeight(
   count: number,
   scale: 'linear' | 'log',
@@ -86,22 +111,22 @@ export function computeTowers(
   const weeks = calendar.weeks.slice(-14);
   const towers: TowerData[] = [];
 
+  const shouldShowGhostCity = isGhostCity(weeks);
+
   // Calculate if the entire monolith is empty and retrieve the maximum count (commits or LoC)
-  let totalVisibleContributions = 0;
+
   let maxCommits = 0;
   weeks.forEach((week) => {
     week.contributionDays.forEach((day) => {
       const count =
         mode === 'loc' ? (day.locAdditions || 0) + (day.locDeletions || 0) : day.contributionCount;
-      totalVisibleContributions += count;
+
       if (count > maxCommits) {
         maxCommits = count;
       }
     });
   });
 
-  const shouldShowGhostCity = totalVisibleContributions === 0;
-
   // Pre-check: is todayDate present in the visible 14-week window?
   const todayInWindow = weeks.some((w) => w.contributionDays.some((d) => d.date === todayDate));