datetime-diff function for H2 (#27064)

* Add datetime-diff for h2

* Set supports? to true

* Refactor h2 datetime-diff

* Formatting

src/metabase/driver/h2.clj

@@ -39,6 +39,7 @@
                               :percentile-aggregations false
                               :actions                 true
                               :actions/custom          true
+                              :datetime-diff           true
                               :now                     true}]
   (defmethod driver/database-supports? [:h2 feature]
     [_driver _feature _database]
@@ -255,6 +256,39 @@
   [driver [_ field]]
   (hsql/call :log10 (sql.qp/->honeysql driver field)))
 
+(defn- datediff
+  "Like H2's `datediff` function but accounts for timestamps with time zones."
+  [unit x y]
+  (hsql/call :datediff (hsql/raw (name unit)) (hx/->timestamp x) (hx/->timestamp y)))
+
+(defn- time-zoned-extract
+  "Like H2's extract but accounts for timestamps with time zones."
+  [unit x]
+  (extract unit (hx/->timestamp x)))
+
+(defmethod sql.qp/datetime-diff [:h2 :year]    [driver _unit x y] (hx// (sql.qp/datetime-diff driver :month x y) 12))
+(defmethod sql.qp/datetime-diff [:h2 :quarter] [driver _unit x y] (hx// (sql.qp/datetime-diff driver :month x y) 3))
+
+(defmethod sql.qp/datetime-diff [:h2 :month]
+  [_driver _unit x y]
+  (hx/+ (datediff :month x y)
+        ;; datediff counts month boundaries not whole months, so we need to adjust
+        ;; if x<y but x>y in the month calendar then subtract one month
+        ;; if x>y but x<y in the month calendar then add one month
+        (hsql/call
+         :case
+         (hsql/call :and (hsql/call :< x y) (hsql/call :> (time-zoned-extract :day x) (time-zoned-extract :day y)))
+         -1
+         (hsql/call :and (hsql/call :> x y) (hsql/call :< (time-zoned-extract :day x) (time-zoned-extract :day y)))
+         1
+         :else 0)))
+
+(defmethod sql.qp/datetime-diff [:h2 :week] [_driver _unit x y] (hx// (datediff :day x y) 7))
+(defmethod sql.qp/datetime-diff [:h2 :day]  [_driver _unit x y] (datediff :day x y))
+(defmethod sql.qp/datetime-diff [:h2 :hour] [_driver _unit x y] (hx// (datediff :millisecond x y) 3600000))
+(defmethod sql.qp/datetime-diff [:h2 :minute] [_driver _unit x y] (datediff :minute x y))
+(defmethod sql.qp/datetime-diff [:h2 :second] [_driver _unit x y] (datediff :second x y))
+
 
 ;;; +----------------------------------------------------------------------------------------------------------------+
 ;;; |                                         metabase.driver.sql-jdbc impls                                         |