fix: return null deltaPercentage when previous month has zero contributions

- Hardcoded +100% was misleading regardless of current month total
- deltaPercentage is now number | null in MonthlyStats type
- calculateMonthlyStats returns null when previousMonthTotal === 0
- generateMonthlySVG and generateAutoThemeMonthlySVG render 'N/A' for null
- Updated test to expect null instead of 100

Author: KaparthyReddy

lib/calculate.test.ts

@@ -348,7 +348,7 @@ describe('calculateMonthlyStats', () => {
 
     expect(result.previousMonthTotal).toBe(0);
     expect(result.currentMonthTotal).toBe(10);
-    expect(result.deltaPercentage).toBe(100);
+    expect(result.deltaPercentage).toBeNull();
   });
 
   it('handles zero current month contributions', () => {

lib/calculate.ts

@@ -207,16 +207,16 @@ export function calculateMonthlyStats(
   }).format(now);
 
   const deltaAbsolute = currentMonthTotal - previousMonthTotal;
-  let deltaPercentage = 0;
-
-  if (previousMonthTotal === 0) {
-    if (currentMonthTotal > 0) {
-      deltaPercentage = 100;
-    }
-  } else {
-    deltaPercentage = Math.round((deltaAbsolute / previousMonthTotal) * 100);
-    if (deltaPercentage === -0) deltaPercentage = 0;
-  }
+  // When there is no baseline (previous month = 0), the percentage change is
+  // mathematically undefined. Return null so the renderer can display 'N/A'
+  // instead of the misleading hardcoded +100%.
+  const deltaPercentage: number | null =
+    previousMonthTotal === 0
+      ? null
+      : (() => {
+          const pct = Math.round((deltaAbsolute / previousMonthTotal) * 100);
+          return pct === -0 ? 0 : pct;
+        })();
 
   return {
     currentMonthTotal,

lib/svg/generator.ts

@@ -434,18 +434,22 @@ export function generateMonthlySVG(stats: MonthlyStats, params: BadgeParams): st
           : `${stats.deltaAbsolute} commits`;
   } else if (params.delta_format === 'both') {
     deltaText =
-      stats.deltaPercentage > 0
-        ? `+${stats.deltaPercentage}% (+${stats.deltaAbsolute})`
-        : stats.deltaPercentage < 0
-          ? `${stats.deltaPercentage}% (${stats.deltaAbsolute})`
-          : `0% (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`;
+      stats.deltaPercentage === null
+        ? `N/A (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`
+        : stats.deltaPercentage > 0
+          ? `+${stats.deltaPercentage}% (+${stats.deltaAbsolute})`
+          : stats.deltaPercentage < 0
+            ? `${stats.deltaPercentage}% (${stats.deltaAbsolute})`
+            : `0% (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`;
   } else {
     deltaText =
-      stats.deltaPercentage > 0
-        ? `+${stats.deltaPercentage}%`
-        : stats.deltaPercentage < 0
-          ? `${stats.deltaPercentage}%`
-          : `0%`;
+      stats.deltaPercentage === null
+        ? 'N/A'
+        : stats.deltaPercentage > 0
+          ? `+${stats.deltaPercentage}%`
+          : stats.deltaPercentage < 0
+            ? `${stats.deltaPercentage}%`
+            : `0%`;
   }
   const deltaColor = stats.deltaAbsolute >= 0 ? accent : '#ff4444';
 
@@ -514,18 +518,22 @@ function generateAutoThemeMonthlySVG(stats: MonthlyStats, params: BadgeParams):
           : `${stats.deltaAbsolute} commits`;
   } else if (params.delta_format === 'both') {
     deltaText =
-      stats.deltaPercentage > 0
-        ? `+${stats.deltaPercentage}% (+${stats.deltaAbsolute})`
-        : stats.deltaPercentage < 0
-          ? `${stats.deltaPercentage}% (${stats.deltaAbsolute})`
-          : `0% (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`;
+      stats.deltaPercentage === null
+        ? `N/A (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`
+        : stats.deltaPercentage > 0
+          ? `+${stats.deltaPercentage}% (+${stats.deltaAbsolute})`
+          : stats.deltaPercentage < 0
+            ? `${stats.deltaPercentage}% (${stats.deltaAbsolute})`
+            : `0% (${stats.deltaAbsolute > 0 ? '+' : ''}${stats.deltaAbsolute})`;
   } else {
     deltaText =
-      stats.deltaPercentage > 0
-        ? `+${stats.deltaPercentage}%`
-        : stats.deltaPercentage < 0
-          ? `${stats.deltaPercentage}%`
-          : `0%`;
+      stats.deltaPercentage === null
+        ? 'N/A'
+        : stats.deltaPercentage > 0
+          ? `+${stats.deltaPercentage}%`
+          : stats.deltaPercentage < 0
+            ? `${stats.deltaPercentage}%`
+            : `0%`;
   }
 
   return `

types/index.ts

@@ -77,8 +77,8 @@ export interface MonthlyStats {
   /** Total number of contributions in the previous calendar month. */
   previousMonthTotal: number;
 
-  /** Percentage change in contributions compared to the previous month (can be negative). */
-  deltaPercentage: number;
+  /** Percentage change in contributions compared to the previous month (can be negative). Null when previous month has zero contributions (undefined baseline). */
+  deltaPercentage: number | null;
 
   /** Absolute change in contribution count compared to the previous month (can be negative). */
   deltaAbsolute: number;