Add substring-before() implementation

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/DefaultFunctionLibrary.java

@@ -165,6 +165,7 @@ public DefaultFunctionLibrary() { // NOPMD - intentional
     // P1: https://www.w3.org/TR/xpath-functions-31/#func-subsequence
     // P1: https://www.w3.org/TR/xpath-functions-31/#func-substring-after
     // P1: https://www.w3.org/TR/xpath-functions-31/#func-substring-before
+    registerFunction(FnSubstringBefore.SIGNATURE_TWO_ARG);
     // https://www.w3.org/TR/xpath-functions-31/#func-sum
     registerFunction(FnSum.SIGNATURE_ONE_ARG);
     registerFunction(FnSum.SIGNATURE_TWO_ARG);

core/src/main/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnSubstringBefore.java

@@ -0,0 +1,90 @@
+/*
+ * SPDX-FileCopyrightText: none
+ * SPDX-License-Identifier: CC0-1.0
+ */
+
+package gov.nist.secauto.metaschema.core.metapath.function.library;
+
+import gov.nist.secauto.metaschema.core.metapath.DynamicContext;
+import gov.nist.secauto.metaschema.core.metapath.ISequence;
+import gov.nist.secauto.metaschema.core.metapath.MetapathConstants;
+import gov.nist.secauto.metaschema.core.metapath.function.FunctionUtils;
+import gov.nist.secauto.metaschema.core.metapath.function.IArgument;
+import gov.nist.secauto.metaschema.core.metapath.function.IFunction;
+import gov.nist.secauto.metaschema.core.metapath.item.IItem;
+import gov.nist.secauto.metaschema.core.metapath.item.atomic.IDecimalItem;
+import gov.nist.secauto.metaschema.core.metapath.item.atomic.IStringItem;
+import gov.nist.secauto.metaschema.core.util.ObjectUtils;
+
+import java.util.List;
+
+import edu.umd.cs.findbugs.annotations.NonNull;
+
+import org.apache.commons.lang3.StringUtils;
+
+/**
+ * Implements <a href=
+ * "https://www.w3.org/TR/xpath-functions-31/#func-substring-before">fn:substring-before</a>.
+ */
+public final class FnSubstringBefore {
+  private static final String NAME = "substring-before";
+  @NonNull
+  static final IFunction SIGNATURE_TWO_ARG = IFunction.builder()
+      .name(NAME)
+      .namespace(MetapathConstants.NS_METAPATH_FUNCTIONS)
+      .deterministic()
+      .contextIndependent()
+      .focusIndependent()
+      .argument(IArgument.builder()
+          .name("arg1")
+          .type(IStringItem.class)
+          .zeroOrOne()
+          .build())
+      .argument(IArgument.builder()
+          .name("arg2")
+          .type(IStringItem.class)
+          .zeroOrOne()
+          .build())
+      .returnType(IStringItem.class)
+      .returnOne()
+      .functionHandler(FnSubstringBefore::executeTwoArg)
+      .build();
+
+  private FnSubstringBefore() {
+    // disable construction
+  }
+
+  @SuppressWarnings({ "unused", "PMD.OnlyOneReturn" })
+  @NonNull
+  private static ISequence<IStringItem> executeTwoArg(
+      @NonNull IFunction function,
+      @NonNull List<ISequence<?>> arguments,
+      @NonNull DynamicContext dynamicContext,
+      IItem focus) {
+
+    // From the XPath 3.1 specification:
+    // If the value of $arg1 or $arg2 is the empty sequence, or contains only
+    // ignorable collation units, it is interpreted as the zero-length string.
+    IStringItem arg1 = arguments.get(0).isEmpty() ? IStringItem.valueOf("") : FunctionUtils.asTypeOrNull(arguments.get(0).getFirstItem(true));
+    IStringItem arg2 = arguments.get(1).isEmpty() ? IStringItem.valueOf("") : FunctionUtils.asTypeOrNull(arguments.get(1).getFirstItem(true));
+
+    return ISequence.of(IStringItem.valueOf(fnSubstringBefore(arg1.asString(), arg2.asString())));
+  }
+
+  /**
+   * An implementation of XPath 3.1 <a href=
+   * "https://www.w3.org/TR/xpath-functions-31/#func-substring-before">fn:substring-before</a>.
+   *
+   * @param arg1
+   *          the source string to get a substring from
+   * @param arg2
+   *          the substring to match and find the substring to return before the match
+   * @return the substring
+   */
+  @NonNull
+  public static String fnSubstringBefore(
+      @NonNull String arg1,
+      @NonNull String arg2) {
+	  return StringUtils.substringBefore(arg1,arg2);
+  }
+}

core/src/test/java/gov/nist/secauto/metaschema/core/metapath/function/library/FnSubstringBeforeTest.java

@@ -0,0 +1,48 @@
+/*
+ * SPDX-FileCopyrightText: none
+ * SPDX-License-Identifier: CC0-1.0
+ */
+
+package gov.nist.secauto.metaschema.core.metapath.function.library;
+
+import static gov.nist.secauto.metaschema.core.metapath.TestUtils.string;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import gov.nist.secauto.metaschema.core.metapath.ExpressionTestBase;
+import gov.nist.secauto.metaschema.core.metapath.MetapathExpression;
+import gov.nist.secauto.metaschema.core.metapath.item.atomic.IStringItem;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
+
+import edu.umd.cs.findbugs.annotations.NonNull;
+
+class FnSubstringBeforeTest
+    extends ExpressionTestBase {
+  private static Stream<Arguments> provideValues() { // NOPMD - false positive
+    return Stream.of(
+        Arguments.of(
+            string("t"),
+            "substring-before('tattoo', 'attoo')"),
+        Arguments.of(
+                string(""),
+                "substring-before('tattoo', 'tatto')"),
+        Arguments.of(
+                string(""),
+                "substring-before((), ())")
+    );
+  }
+
+  @ParameterizedTest
+  @MethodSource("provideValues")
+  void testExpression(@NonNull IStringItem expected, @NonNull String metapath) {
+    assertEquals(
+        expected,
+        MetapathExpression.compile(metapath)
+            .evaluateAs(null, MetapathExpression.ResultType.ITEM, newDynamicContext()));
+  }
+
+}