From cd973b252a1304b207893b8f2327fc861d7492db Mon Sep 17 00:00:00 2001
From: かっこかり <67428053+kakkokari-gtyih@users.noreply.github.com>
Date: Thu, 8 Jan 2026 12:16:33 +0900
Subject: fix(frontend):
 2月29日を誕生日に設定している場合、平年は3月1日を誕生日として扱うように
 (#17072)
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* fix(frontend): 2月29日を誕生日に設定している場合、平年は3月1日を誕生日として扱うように

* Update Changelog

* add tests

* spdx
---
 packages/frontend/src/utility/is-birthday.ts | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 packages/frontend/src/utility/is-birthday.ts

(limited to 'packages/frontend/src/utility')

diff --git a/packages/frontend/src/utility/is-birthday.ts b/packages/frontend/src/utility/is-birthday.ts
new file mode 100644
index 0000000000..ff875281a2
--- /dev/null
+++ b/packages/frontend/src/utility/is-birthday.ts
@@ -0,0 +1,28 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import * as Misskey from 'misskey-js';
+
+export function isBirthday(user: Misskey.entities.UserDetailed, now = new Date()): boolean {
+	if (user.birthday == null) return false;
+
+	const [_, bm, bd] = user.birthday.split('-').map((v) => parseInt(v, 10));
+	if (isNaN(bm) || isNaN(bd)) return false;
+
+	const y = now.getFullYear();
+	const m = now.getMonth() + 1;
+	const d = now.getDate();
+
+	// 閏日生まれで平年の場合は3月1日を誕生日として扱う
+	if (bm === 2 && bd === 29 && m === 3 && d === 1 && !isLeapYear(y)) {
+		return true;
+	}
+
+	return m === bm && d === bd;
+}
+
+function isLeapYear(year: number): boolean {
+	return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
+}
-- 
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