From 4c41bf2c2d1ada5054eddbb18bdfa2819fe8f6b7 Mon Sep 17 00:00:00 2001
From: Joe Thel <joe.thel@deepgram.com>
Date: Tue, 15 Apr 2025 10:26:36 -0700
Subject: [PATCH] Fix miscalculation of quarter numbers

---
 src/DateFormat.elm |  2 +-
 tests/Fuzzers.elm  |  2 +-
 tests/Tests.elm    | 29 +++++++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/DateFormat.elm b/src/DateFormat.elm
index bcd63e9..b36895e 100644
--- a/src/DateFormat.elm
+++ b/src/DateFormat.elm
@@ -859,7 +859,7 @@ isLeapYear year_ =
 
 quarter : Zone -> Posix -> Int
 quarter zone posix =
-    monthNumber_ zone posix // 4
+    (monthNumber_ zone posix - 1) // 3
 
 
 
diff --git a/tests/Fuzzers.elm b/tests/Fuzzers.elm
index 994c799..ea3a50b 100644
--- a/tests/Fuzzers.elm
+++ b/tests/Fuzzers.elm
@@ -9,7 +9,7 @@ datetime =
     Fuzz.map Time.millisToPosix
         (Fuzz.intRange
             1529000000
-            1530000000
+            48699800000
         )
 
 
diff --git a/tests/Tests.elm b/tests/Tests.elm
index 9d6e824..7d2606c 100644
--- a/tests/Tests.elm
+++ b/tests/Tests.elm
@@ -254,6 +254,35 @@ suite =
             , describe "quarterNumber"
                 [ fuzz Fuzzers.datetime "Is between 1 and 4" <|
                     withinRange 1 4 DateFormat.quarterNumber
+                , fuzz Fuzzers.datetime "Assigns months to appropriate quarters" <|
+                    \date ->
+                        let
+                            quarterToMonths q =
+                                case q of
+                                    "1" ->
+                                        [ "1", "2", "3" ]
+
+                                    "2" ->
+                                        [ "4", "5", "6" ]
+
+                                    "3" ->
+                                        [ "7", "8", "9" ]
+
+                                    "4" ->
+                                        [ "10", "11", "12" ]
+
+                                    _ ->
+                                        []
+
+                            quarter =
+                                DateFormat.format [ DateFormat.quarterNumber ] utc date
+
+                            month =
+                                DateFormat.format [ DateFormat.monthNumber ] utc date
+                        in
+                        Expect.equal
+                            True
+                            (quarter |> quarterToMonths |> List.member month)
                 ]
             , describe "quarterSuffix"
                 [ fuzz Fuzzers.datetime "Is between 1 and 4" <|