feat(stacks-utils): formatCount support for negative values (#2153)

Author: giamir

.changeset/strong-stamps-occur.md

@@ -0,0 +1,5 @@
+---
+"@stackoverflow/stacks-utils": patch
+---
+
+formatCount support for negative values

packages/stacks-utils/README.md

@@ -27,6 +27,10 @@ formatCount(9999); // "9,999"
 formatCount(10000); // "10k"
 formatCount(12345); // "12.3k"
 formatCount(1234567); // "1.2m"
+
+// Negative numbers
+formatCount(-1234); // "-1,234"
+formatCount(-12345); // "-12.3k"
 ```
 
 You can also import from the class:

packages/stacks-utils/src/NumberFormatter.test.ts

@@ -45,6 +45,21 @@ describe("NumberFormatter.formatCount", () => {
         });
     });
 
+    describe("negative numbers", () => {
+        it("should format negative numbers in standard format", () => {
+            expect(NumberFormatter.formatCount(-42)).toBe("-42");
+            expect(NumberFormatter.formatCount(-999)).toBe("-999");
+            expect(NumberFormatter.formatCount(-1234)).toBe("-1,234");
+            expect(NumberFormatter.formatCount(-9999)).toBe("-9,999");
+        });
+
+        it("should format negative numbers in compact format", () => {
+            expect(NumberFormatter.formatCount(-10000)).toBe("-10k");
+            expect(NumberFormatter.formatCount(-12345)).toBe("-12.3k");
+            expect(NumberFormatter.formatCount(-1234567)).toBe("-1.2m");
+        });
+    });
+
     describe("convenience function export", () => {
         it("should work with the exported formatCount function", () => {
             expect(formatCount(1234)).toBe("1,234");

packages/stacks-utils/src/NumberFormatter.ts

@@ -18,18 +18,21 @@ export class NumberFormatter {
      * @param count - The number to format
      * @param compactThreshold - (Optional) The number at which to switch from standard to compact format
      * @returns A formatted string:
-     *   - Less than 10,000: standard format with commas (e.g., "1,234", "999")
-     *   - 10,000 or more: compact format with lowercase suffixes (e.g., "10k", "1.2m")
+     *   - Less than 10,000: standard format with commas (e.g., "1,234", "999", "-1,234")
+     *   - 10,000 or more: compact format with lowercase suffixes (e.g., "10k", "1.2m", "-10k")
      */
     public static formatCount(
         count: number,
         compactThreshold: number = 10000
     ): string {
+        const absoluteValue = Math.abs(count);
+        const sign = count < 0 ? "-" : "";
+
         for (const formatter of NumberFormatter.getFormatters(
             compactThreshold
         )) {
-            if (formatter.condition(count)) {
-                return formatter.format(count);
+            if (formatter.condition(absoluteValue)) {
+                return sign + formatter.format(absoluteValue);
             }
         }
         return count.toString(); // should never reach here