From 9739d202339a65fc8073049a1f74acf1a03f02d0 Mon Sep 17 00:00:00 2001
From: Elijah Wright <git@elijahs.space>
Date: Fri, 30 May 2025 01:57:26 -0700
Subject: [PATCH] fix isTaxYearLeapYear

---
 .../src/main/resources/tax/constants.xml      | 62 +++++++++++++++----
 .../gov/irs/factgraph/compnodes/Modulo.scala  | 35 +++++++++++
 2 files changed, 85 insertions(+), 12 deletions(-)
 create mode 100644 direct-file/fact-graph-scala/shared/src/main/scala/gov/irs/factgraph/compnodes/Modulo.scala

diff --git a/direct-file/backend/src/main/resources/tax/constants.xml b/direct-file/backend/src/main/resources/tax/constants.xml
index d8887a2..f8008fc 100644
--- a/direct-file/backend/src/main/resources/tax/constants.xml
+++ b/direct-file/backend/src/main/resources/tax/constants.xml
@@ -50,24 +50,62 @@
           <!-- TODO: replace this with the calc to determine leap year (e.g. divisible by 4, but not 100 unless also divisible by 400) -->
           <Case>
             <When>
-              <Any>
+              <Equal>
+                <Left>
+                  <Modulo>
+                    <Left>
+                      <Dependency path="/taxYear" />
+                    </Left>
+                    <Right>
+                      <Int>100</Int>
+                    </Right>
+                  </Modulo>
+                </Left>
+                <Right>
+                  <Int>0</Int>
+                </Right>
+              </Equal>
+            </When>
+            <Then>
+              <When>
                 <Equal>
                   <Left>
-                    <Dependency path="/taxYear" />
+                    <Modulo>
+                      <Left>
+                        <Dependency path="/taxYear" />
+                      </Left>
+                      <Right>
+                        <Int>400</Int>
+                      </Right>
+                    </Modulo>
                   </Left>
                   <Right>
-                    <Int>2024</Int>
+                    <Int>0</Int>
                   </Right>
                 </Equal>
-                <Equal>
-                  <Left>
-                    <Dependency path="/taxYear" />
-                  </Left>
-                  <Right>
-                    <Int>2028</Int>
-                  </Right>
-                </Equal>
-              </Any>
+              </When>
+              <Then>
+                <True />
+              </When>
+            </Then>
+          </Case>
+          <Case>
+            <When>
+              <Equal>
+                <Left>
+                  <Modulo>
+                    <Left>
+                      <Dependency path="/taxYear" />
+                    </Left>
+                    <Right>
+                      <Int>4</Int>
+                    </Right>
+                  </Modulo>
+                </Left>
+                <Right>
+                  <Int>0</Int>
+                </Right>
+              </Equal>
             </When>
             <Then>
               <True />
diff --git a/direct-file/fact-graph-scala/shared/src/main/scala/gov/irs/factgraph/compnodes/Modulo.scala b/direct-file/fact-graph-scala/shared/src/main/scala/gov/irs/factgraph/compnodes/Modulo.scala
new file mode 100644
index 0000000..4ab7cbb
--- /dev/null
+++ b/direct-file/fact-graph-scala/shared/src/main/scala/gov/irs/factgraph/compnodes/Modulo.scala
@@ -0,0 +1,35 @@
+ package gov.irs.factgraph.compnodes
+
+import gov.irs.factgraph.{Expression, FactDictionary, Factual}
+import gov.irs.factgraph.definitions.fact.CompNodeConfigTrait
+import gov.irs.factgraph.operators.BinaryOperator
+
+object Modulo extends CompNodeFactory:
+  override val Key: String = "Modulo"
+
+  private val operator = ModuloOperator()
+
+  def apply(lhs: CompNode, rhs: CompNode): BooleanNode =
+    if (lhs.getClass != rhs.getClass)
+      throw new UnsupportedOperationException(
+        s"cannot modulate a ${lhs.getClass.getName} and a ${rhs.getClass.getName}",
+      )
+
+    BooleanNode(
+      Expression.Binary(
+        lhs.expr,
+        rhs.expr,
+        operator,
+      ),
+    )
+
+  override def fromDerivedConfig(e: CompNodeConfigTrait)(using Factual)(using
+      FactDictionary,
+  ): CompNode =
+    val lhs = CompNode.getConfigChildNode(e, "Left")
+    val rhs = CompNode.getConfigChildNode(e, "Right")
+
+    this(lhs, rhs)
+
+private final class ModuloOperator extends BinaryOperator[Boolean, Any, Any]:
+  override protected def operation(x: Any, y: Any): Boolean = x % y
\ No newline at end of file