NIAD-3304: Add CodeSystemUtil for mapping between code systems (#1126)

* NIAD-3304: Add CodeSystemUtil for mapping between code systems

* Add CodeSystemUtil to map from JSON FHIR codes (urls) to HL7 XML codes (OIDs).
* Add functionality to ensure that the JSON FHIR Code is preserved when the JSON FHIR Code is not a known code system.
* Add unit tests for the above functionality.

* NIAD-3304: Add CodeSystemUtil for mapping between code systems

Refactor test string to align with use case.

Author: MartinWheelerMT

service/src/main/java/uk/nhs/adaptors/gp2gp/ehr/utils/CodeSystemsUtil.java

@@ -0,0 +1,21 @@
+package uk.nhs.adaptors.gp2gp.ehr.utils;
+
+import lombok.AccessLevel;
+import lombok.NoArgsConstructor;
+
+import java.util.Map;
+
+@NoArgsConstructor(access = AccessLevel.PRIVATE)
+public final class CodeSystemsUtil {
+
+    private static final Map<String, String> SYSTEM_CODES = Map.of(
+        "http://snomed.info/sct", "2.16.840.1.113883.2.1.3.2.4.15",
+        "https://fhir.hl7.org.uk/Id/egton-codes", "2.16.840.1.113883.2.1.6.3",
+        "http://read.info/readv2", "2.16.840.1.113883.2.1.6.2",
+        "http://read.info/ctv3", "2.16.840.1.113883.2.1.3.2.4.14"
+    );
+
+    public static String getHl7code(String fhirCodeSystem) {
+        return SYSTEM_CODES.getOrDefault(fhirCodeSystem, fhirCodeSystem);
+    }
+}

service/src/test/java/uk/nhs/adaptors/gp2gp/utils/CodeSystemUtilTest.java

@@ -0,0 +1,38 @@
+package uk.nhs.adaptors.gp2gp.utils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import uk.nhs.adaptors.gp2gp.ehr.utils.CodeSystemsUtil;
+
+import java.util.stream.Stream;
+
+public class CodeSystemUtilTest {
+
+    private static Stream<Arguments> knownCodeSystems() {
+        return Stream.of(
+            Arguments.of("http://snomed.info/sct", "2.16.840.1.113883.2.1.3.2.4.15"),
+            Arguments.of("https://fhir.hl7.org.uk/Id/egton-codes", "2.16.840.1.113883.2.1.6.3"),
+            Arguments.of("http://read.info/readv2", "2.16.840.1.113883.2.1.6.2"),
+            Arguments.of("http://read.info/ctv3", "2.16.840.1.113883.2.1.3.2.4.14")
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("knownCodeSystems")
+    void When_FhirCodeSystemIsKnown_Expect_CorrectHl7Code(String fhirCodeSystem, String expectedHl7Code) {
+        var hl7Code = CodeSystemsUtil.getHl7code(fhirCodeSystem);
+
+        assertThat(hl7Code).isEqualTo(expectedHl7Code);
+    }
+
+    @Test
+    void When_FhirCodeSystemIsUnknown_Expect_FhirCodeSystemIsProvided() {
+        var hl7Code = CodeSystemsUtil.getHl7code("https://unknown.code/system");
+
+        assertThat(hl7Code).isEqualTo("https://unknown.code/system");
+    }
+}