From 93691e725f704560ea4a85647e3dce71fca236c0 Mon Sep 17 00:00:00 2001
From: William Martin <contact@willmartian.com>
Date: Fri, 30 Jun 2023 10:25:54 -0400
Subject: [PATCH] add daysRemaining util function and unit tests

---
 libs/common/src/platform/misc/utils.spec.ts | 21 +++++++++++++++++++++
 libs/common/src/platform/misc/utils.ts      |  9 +++++++++
 2 files changed, 30 insertions(+)

diff --git a/libs/common/src/platform/misc/utils.spec.ts b/libs/common/src/platform/misc/utils.spec.ts
index 5f7d63fee2..ac21f28d72 100644
--- a/libs/common/src/platform/misc/utils.spec.ts
+++ b/libs/common/src/platform/misc/utils.spec.ts
@@ -358,4 +358,25 @@ describe("Utils Service", () => {
       expect(actual.protocol).toBe("http:");
     });
   });
+
+  describe("daysRemaining", () => {
+    const now = new Date(2023, 9, 2);
+    jest.spyOn(Date, "now").mockReturnValue(now.getTime());
+
+    it("should return 0 for equal dates", () => {
+      expect(Utils.daysRemaining(new Date(2023, 9, 2))).toBe(0);
+    });
+
+    it("should return 0 for dates in the past", () => {
+      expect(Utils.daysRemaining(new Date(2020, 5, 11))).toBe(0);
+      expect(Utils.daysRemaining(new Date(2023, 9, 1))).toBe(0);
+    });
+
+    it("should handle future dates", () => {
+      expect(Utils.daysRemaining(new Date(2023, 9, 3))).toBe(1);
+      expect(Utils.daysRemaining(new Date(2023, 10, 12))).toBe(41);
+      // leap year
+      expect(Utils.daysRemaining(new Date(2024, 9, 2))).toBe(366);
+    });
+  });
 });
diff --git a/libs/common/src/platform/misc/utils.ts b/libs/common/src/platform/misc/utils.ts
index 4c30822cc8..542c471bc8 100644
--- a/libs/common/src/platform/misc/utils.ts
+++ b/libs/common/src/platform/misc/utils.ts
@@ -538,6 +538,15 @@ export class Utils {
     return of(undefined).pipe(switchMap(() => generator()));
   }
 
+  /**
+   * Return the number of days remaining before a target date arrives.
+   * Returns 0 if the day has already passed.
+   */
+  static daysRemaining(targetDate: Date): number {
+    const diffTime = targetDate.getTime() - Date.now();
+    return Math.max(0, Math.round(diffTime / (1000 * 60 * 60 * 24)));
+  }
+
   private static isAppleMobile(win: Window) {
     return (
       win.navigator.userAgent.match(/iPhone/i) != null ||