From 4a6d0eed45a8c57b71c802e66b8ae32193232ce7 Mon Sep 17 00:00:00 2001
From: James Agnew <jamesagnew@gmail.com>
Date: Mon, 28 Jan 2019 17:08:39 -0500
Subject: [PATCH] First crack at this

---
 .../hl7/fhir/r4/model/BaseDateTimeType.java   | 40 +++++++++++++++++-
 .../org/hl7/fhir/r4/utils/FHIRPathEngine.java |  4 +-
 .../fhir/r4/model/BaseDateTimeTypeTest.java   | 42 +++++++++++++++++++
 3 files changed, 82 insertions(+), 4 deletions(-)
 create mode 100644 org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/model/BaseDateTimeTypeTest.java

diff --git a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/BaseDateTimeType.java b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/BaseDateTimeType.java
index d3e6b5807..f7d72bd71 100644
--- a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/BaseDateTimeType.java
+++ b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/BaseDateTimeType.java
@@ -855,6 +855,44 @@ public abstract class BaseDateTimeType extends PrimitiveType<Date> {
   public Date dateTimeValue() {
     return getValue();
   }
-  
+
+	/**
+	 * This method implements an equality check using the rules as defined by FHIRPath.
+	 *
+	 * This method returns:
+	 * <ul>
+	 *     <li>true if the given datetimes represent the exact same instant with the same precision (irrespective of the timezone)</li>
+	 *     <li>true if the given datetimes represent the exact same instant but one includes milliseconds of <code>.[0]+</code> while the other includes only SECONDS precision (irrespecitve of the timezone)</li>
+	 *     <li>true if the given datetimes represent the exact same year/year-month/year-month-date (if both operands have the same precision)</li>
+	 *     <li>false if the given datetimes have the same precision but do not represent the same instant (irrespective of timezone)</li>
+	 *     <li>null otherwise (since these datetimes are not comparable)</li>
+	 * </ul>
+	 */
+	public Boolean equalsUsingFhirPathRules(BaseDateTimeType theOther) {
+
+		// Same precision
+		if (getPrecision() == theOther.getPrecision()) {
+			return getValue().getTime() == theOther.getValue().getTime();
+		}
+
+		// Both represent 0 millis but the millis are optional
+		if (((Integer)0).equals(getMillis())) {
+			if (((Integer)0).equals(theOther.getMillis())) {
+				if (getPrecision().ordinal() >= TemporalPrecisionEnum.SECOND.ordinal()) {
+					if (theOther.getPrecision().ordinal() >= TemporalPrecisionEnum.SECOND.ordinal()) {
+						return getValue().getTime() == theOther.getValue().getTime();
+					}
+				}
+			}
+		}
+
+		if (getPrecision() != theOther.getPrecision()) {
+			return null;
+		}
+
+		return false;
+	}
+
+
 
 }
diff --git a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/utils/FHIRPathEngine.java b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/utils/FHIRPathEngine.java
index 069b6e55c..83d235f95 100644
--- a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/utils/FHIRPathEngine.java
+++ b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/utils/FHIRPathEngine.java
@@ -463,9 +463,7 @@ public class FHIRPathEngine {
     DateTimeType dateRight = new DateTimeType(dateRightString);
 
     if (theEquivalenceTest) {
-      TemporalPrecisionEnum lowestPrecision = dateLeft.getPrecision().ordinal() < dateRight.getPrecision().ordinal() ? dateLeft.getPrecision() : dateRight.getPrecision();
-      dateLeft.setPrecision(lowestPrecision);
-      dateRight.setPrecision(lowestPrecision);
+      return dateLeft.equalsUsingFhirPathRules(dateRight) == Boolean.TRUE ? 0 : 1;
     }
 
     if (dateLeft.getPrecision().ordinal() > TemporalPrecisionEnum.DAY.ordinal()) {
diff --git a/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/model/BaseDateTimeTypeTest.java b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/model/BaseDateTimeTypeTest.java
new file mode 100644
index 000000000..cb1fe5cd4
--- /dev/null
+++ b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/model/BaseDateTimeTypeTest.java
@@ -0,0 +1,42 @@
+package org.hl7.fhir.r4.model;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class BaseDateTimeTypeTest {
+
+    /**
+     * <ul>
+     *     <li>true if the given datetimes represent the exact same instant with the same precision (irrespective of the timezone)</li>
+     *     <li>true if the given datetimes represent the exact same instant but one includes milliseconds of <code>.[0]+</code> while the other includes only SECONDS precision (irrespecitve of the timezone)</li>
+     *     <li>true if the given datetimes represent the exact same year/year-month/year-month-date (if both operands have the same precision)</li>
+     *     <li>false if the given datetimes have the same precision but do not represent the same instant (irrespective of timezone)</li>
+     *     <li>null otherwise (since these datetimes are not comparable)</li>
+     * </ul>
+     */
+    @Test
+    public void equalsUsingFhirPathRules() {
+        // Exact same - Same timezone
+        assertTrue(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33.444Z"));
+        // Exact same - Different timezone
+        assertTrue(compareDateTimes("2001-01-02T11:22:33.444-03:00", "2001-01-02T10:22:33.444-04:00"));
+        // Exact same - Dates
+        assertTrue(compareDateTimes("2001", "2001"));
+        assertTrue(compareDateTimes("2001-01", "2001-01"));
+        assertTrue(compareDateTimes("2001-01-02", "2001-01-02"));
+        // Same precision but different values - Dates
+        assertFalse(compareDateTimes("2001", "2002"));
+        assertFalse(compareDateTimes("2001-01", "2001-02"));
+        assertFalse(compareDateTimes("2001-01-02", "2001-01-03"));
+        // Different instant - Same timezone
+        assertFalse(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33.445Z"));
+        // Different precision
+        assertNull(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33Z"));
+    }
+
+    private Boolean compareDateTimes(String theLeft, String theRight) {
+        return new DateTimeType(theLeft).equalsUsingFhirPathRules(new DateTimeType(theRight));
+    }
+
+}
\ No newline at end of file