[bug-58468] implement DAYS function

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1901361 13f79535-47bb-0310-9956-ffa450edef68

poi/src/main/java/org/apache/poi/ss/formula/atp/AnalysisToolPak.java

@@ -98,6 +98,7 @@ public final class AnalysisToolPak implements UDFFinder {
         r(m, "CUBEVALUE", null);
         r(m, "CUMIPMT", null);
         r(m, "CUMPRINC", null);
+        r(m, "DAYS", Days.instance);
         r(m, "DEC2BIN", Dec2Bin.instance);
         r(m, "DEC2HEX", Dec2Hex.instance);
         r(m, "DEC2OCT", null);

poi/src/main/java/org/apache/poi/ss/formula/functions/Days.java

@@ -0,0 +1,93 @@
+/* ====================================================================
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You under the Apache License, Version 2.0
+   (the "License"); you may not use this file except in compliance with
+   the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+==================================================================== */
+package org.apache.poi.ss.formula.functions;
+
+import java.time.LocalDate;
+import java.time.temporal.ChronoUnit;
+import java.util.Date;
+
+import org.apache.poi.ss.formula.OperationEvaluationContext;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.OperandResolver;
+import org.apache.poi.ss.formula.eval.ValueEval;
+import org.apache.poi.ss.usermodel.DateUtil;
+import org.apache.poi.ss.util.DateParser;
+import org.apache.poi.util.LocaleUtil;
+
+/**
+ * <p>Calculates the number of days between two dates based on a real year,
+ * which is used in some accounting calculations.</p>
+ *
+ * <p> 
+ * {@code DAYS(end_date,start_date)}
+ * 
+ * <ul>
+ * <li>Start_date, end_date (required):<br/>
+ * The two dates between which you want to know the number of days.<br/>
+ * If start_date occurs after end_date, the DAYS function returns a negative number.</li>
+ * 
+ * </ul>
+ * </p>
+ * 
+ * @see <a href="https://support.office.com/en-us/article/DAYS-function-57740535-D549-4395-8728-0F07BFF0B9DF">DAYS function - Microsoft Office</a>
+ */
+public class Days implements FreeRefFunction {
+
+    public static final Days instance = new Days();
+
+    private Days() {}
+
+    @Override
+    public ValueEval evaluate(ValueEval[] args, OperationEvaluationContext ec) {
+        return evaluate(ec.getRowIndex(), ec.getColumnIndex(), args[0], args[1]);
+    }
+
+    private ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1) {
+        double result;
+        try {
+            LocalDate d0 = getDate(arg0, srcRowIndex, srcColumnIndex);
+            LocalDate d1 = getDate(arg1, srcRowIndex, srcColumnIndex);
+            result = evaluate(d0, d1);
+        } catch (EvaluationException e) {
+            return e.getErrorEval();
+        }
+        return new NumberEval(result);
+    }
+
+    private static double evaluate(LocalDate endDate, LocalDate startDate) {
+        return ChronoUnit.DAYS.between(startDate, endDate);
+    }
+
+    private static LocalDate getDate(ValueEval eval, int srcRowIndex, int srcColumnIndex) throws EvaluationException {
+        ValueEval ve = OperandResolver.getSingleValue(eval, srcRowIndex, srcColumnIndex);
+        try {
+            double d0 = NumericFunction.singleOperandEvaluate(ve, srcRowIndex, srcColumnIndex);
+            return getDate(d0);
+        } catch (Exception e) {
+            String strText1 = OperandResolver.coerceValueToString(ve);
+            return DateParser.parseLocalDate(strText1);
+        }
+    }
+
+    private static LocalDate getDate(double date) {
+        Date d = DateUtil.getJavaDate(date, false);
+        return d.toInstant()
+                .atZone(LocaleUtil.getUserTimeZone().toZoneId())
+                .toLocalDate();
+    }
+}

poi/src/test/java/org/apache/poi/ss/formula/functions/TestDays.java

@@ -0,0 +1,69 @@
+
+/* ====================================================================
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You under the Apache License, Version 2.0
+   (the "License"); you may not use this file except in compliance with
+   the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+==================================================================== */
+package org.apache.poi.ss.formula.functions;
+
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.usermodel.DateUtil;
+import org.apache.poi.ss.usermodel.FormulaError;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.time.LocalDate;
+
+import static org.apache.poi.ss.util.Utils.addRow;
+import static org.apache.poi.ss.util.Utils.assertDouble;
+import static org.apache.poi.ss.util.Utils.assertError;
+
+/**
+ * Testcase for DAYS() functions
+ */
+public class TestDays {
+
+    //https://support.microsoft.com/en-us/office/days-function-57740535-d549-4395-8728-0f07bff0b9df
+    @Test
+    void testMicrosoftExample1() throws IOException {
+        try (HSSFWorkbook wb = initWorkbook1()) {
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            HSSFCell cell = wb.getSheetAt(0).getRow(0).createCell(12);
+            assertDouble(fe, cell, "DAYS(\"15-MAR-2021\",\"1-FEB-2021\")", 42, 0.00000000001);
+            assertDouble(fe, cell, "DAYS(A2,A3)", 364, 0.00000000001);
+        }
+    }
+
+    @Test
+    void testInvalid() throws IOException {
+        try (HSSFWorkbook wb = initWorkbook1()) {
+            HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+            HSSFCell cell = wb.getSheetAt(0).getRow(0).createCell(12);
+            assertError(fe, cell, "DAYS(\"15-XYZ\",\"1-FEB-2021\")", FormulaError.VALUE);
+            assertError(fe, cell, "DAYS(\"15-MAR-2021\",\"1-XYZ\")", FormulaError.VALUE);
+        }
+    }
+
+    private HSSFWorkbook initWorkbook1() {
+        HSSFWorkbook wb = new HSSFWorkbook();
+        HSSFSheet sheet = wb.createSheet();
+        addRow(sheet, 0, "Data");
+        addRow(sheet, 1, DateUtil.getExcelDate(LocalDate.parse("2021-12-31")));
+        addRow(sheet, 2, DateUtil.getExcelDate(LocalDate.parse("2021-01-01")));
+        return wb;
+    }
+}