From d582a144361e8d2bfa888e7ba7dc17beec86b3a4 Mon Sep 17 00:00:00 2001
From: coyaSONG <66289470+coyaSONG@users.noreply.github.com>
Date: Sat, 18 Jul 2026 01:38:55 +0900
Subject: [PATCH] Add DateTime.toEpochSeconds

---
 .changeset/add-datetime-epoch-seconds.md |  5 +++++
 packages/effect/src/DateTime.ts          |  8 ++++++++
 packages/effect/src/internal/dateTime.ts |  3 +++
 packages/effect/test/DateTime.test.ts    | 10 ++++++++++
 4 files changed, 26 insertions(+)
 create mode 100644 .changeset/add-datetime-epoch-seconds.md

diff --git a/.changeset/add-datetime-epoch-seconds.md b/.changeset/add-datetime-epoch-seconds.md
new file mode 100644
index 00000000000..1e9efbd633f
--- /dev/null
+++ b/.changeset/add-datetime-epoch-seconds.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Add `DateTime.toEpochSeconds` for whole Unix timestamps.
diff --git a/packages/effect/src/DateTime.ts b/packages/effect/src/DateTime.ts
index 5f11606c891..738e7188738 100644
--- a/packages/effect/src/DateTime.ts
+++ b/packages/effect/src/DateTime.ts
@@ -938,6 +938,14 @@ export const zonedOffsetIso: (self: Zoned) => string = Internal.zonedOffsetIso
  */
 export const toEpochMillis: (self: DateTime) => number = Internal.toEpochMillis
 
+/**
+ * Get the whole seconds since the Unix epoch of a `DateTime`.
+ *
+ * @since 3.22.0
+ * @category conversions
+ */
+export const toEpochSeconds: (self: DateTime) => number = Internal.toEpochSeconds
+
 /**
  * Remove the time aspect of a `DateTime`, first adjusting for the time
  * zone. It will return a `DateTime.Utc` only containing the date.
diff --git a/packages/effect/src/internal/dateTime.ts b/packages/effect/src/internal/dateTime.ts
index 544ecd86efa..a20b3942e1b 100644
--- a/packages/effect/src/internal/dateTime.ts
+++ b/packages/effect/src/internal/dateTime.ts
@@ -613,6 +613,9 @@ export const zonedOffsetIso = (self: DateTime.Zoned): string => offsetToString(z
 /** @internal */
 export const toEpochMillis = (self: DateTime.DateTime): number => self.epochMillis
 
+/** @internal */
+export const toEpochSeconds = (self: DateTime.DateTime): number => Math.floor(self.epochMillis / 1000)
+
 /** @internal */
 export const removeTime = (self: DateTime.DateTime): DateTime.Utc =>
   withDate(self, (date) => {
diff --git a/packages/effect/test/DateTime.test.ts b/packages/effect/test/DateTime.test.ts
index 6c9aa7ade46..fb692450fef 100644
--- a/packages/effect/test/DateTime.test.ts
+++ b/packages/effect/test/DateTime.test.ts
@@ -368,6 +368,16 @@ describe("DateTime", () => {
       ))
   })
 
+  describe("toEpochSeconds", () => {
+    it("converts milliseconds to whole seconds", () => {
+      strictEqual(DateTime.toEpochSeconds(DateTime.unsafeMake(1_999)), 1)
+    })
+
+    it("floors timestamps before the Unix epoch", () => {
+      strictEqual(DateTime.toEpochSeconds(DateTime.unsafeMake(-1)), -1)
+    })
+  })
+
   describe("removeTime", () => {
     it("removes time", () => {
       const dt = DateTime.unsafeMakeZoned("2024-01-01T01:00:00Z", {