1 files changed, 28 insertions, 0 deletions
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);
+}