POI Bug 58468 - Implement Days function

main/SS/Formula/Atp/AnalysisToolPak.cs

@@ -105,6 +105,7 @@ private static Dictionary<String, FreeRefFunction> CreateFunctionsMap()
             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);

main/SS/Formula/Functions/Days.cs

@@ -0,0 +1,69 @@
+using NPOI.SS.Formula.Atp;
+using NPOI.SS.Formula.Eval;
+using NPOI.SS.UserModel;
+using NPOI.Util;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace NPOI.SS.Formula.Functions
+{
+    public class Days : FreeRefFunction
+    {
+        public static Days Instance = new Days();
+
+        private Days() { }
+
+        public ValueEval Evaluate(ValueEval[] args, OperationEvaluationContext ec)
+        {
+            return Days.Evaluate(ec.RowIndex, ec.ColumnIndex, args[0], args[1]);
+        }
+        private static ValueEval Evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1)
+        {
+            double result;
+            try
+            {
+                var d0 = getDate(arg0, srcRowIndex, srcColumnIndex);
+                var d1 = getDate(arg1, srcRowIndex, srcColumnIndex);
+                result = Evaluate(d0, d1);
+            }
+            catch(EvaluationException e)
+            {
+                return e.GetErrorEval();
+            }
+            return new NumberEval(result);
+        }
+
+        private static double Evaluate(DateTime endDate, DateTime startDate)
+        {
+            return (endDate-startDate).Days;
+        }
+
+        private static DateTime getDate(ValueEval eval, int srcRowIndex, int srcColumnIndex)
+        {
+            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);
+                DateTime result = DateTime.MinValue;
+                if(DateTime.TryParse(strText1,out result))
+                    return result;
+
+                throw new EvaluationException(ErrorEval.VALUE_INVALID);
+            }
+        }
+
+        private static DateTime getDate(double date)
+        {
+            DateTime d = DateUtil.GetJavaDate(date, false);
+            return d.ToLocalTime();
+        }
+    }
+}

testcases/main/SS/Formula/Functions/TestDays.cs

@@ -0,0 +1,47 @@
+using NPOI.HSSF.UserModel;
+using NPOI.SS.UserModel;
+using NUnit.Framework;
+using NUnit.Framework.Internal;
+using System;
+
+namespace TestCases.SS.Formula.Functions
+{
+    [TestFixture]
+    public class TestDays
+    {
+        //https://support.microsoft.com/en-us/office/days-function-57740535-d549-4395-8728-0f07bff0b9df
+        [Test]
+        public void TestMicrosoftExample1()
+        {
+            using(HSSFWorkbook wb = initWorkbook1())
+            {
+                HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+                var cell = wb.GetSheetAt(0).GetRow(0).CreateCell(12);
+                SS.Util.Utils.AssertDouble(fe, cell, "DAYS(\"15-MAR-2021\",\"1-FEB-2021\")", 42, 0.00000000001);
+                SS.Util.Utils.AssertDouble(fe, cell, "DAYS(A2,A3)", 364, 0.00000000001);
+            }
+        }
+
+        [Test]
+        public void TestInvalid()
+        {
+            using(HSSFWorkbook wb = initWorkbook1())
+            {
+                HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+                var cell = wb.GetSheetAt(0).GetRow(0).CreateCell(12);
+                SS.Util.Utils.AssertError(fe, cell, "DAYS(\"15-XYZ\",\"1-FEB-2021\")", FormulaError.VALUE);
+                SS.Util.Utils.AssertError(fe, cell, "DAYS(\"15-MAR-2021\",\"1-XYZ\")", FormulaError.VALUE);
+            }
+        }
+
+        private HSSFWorkbook initWorkbook1()
+        {
+            HSSFWorkbook wb = new HSSFWorkbook();
+            var sheet = wb.CreateSheet();
+            SS.Util.Utils.AddRow(sheet, 0, "Data");
+            SS.Util.Utils.AddRow(sheet, 1, DateUtil.GetExcelDate(DateTime.Parse("2021-12-31")));
+            SS.Util.Utils.AddRow(sheet, 2, DateUtil.GetExcelDate(DateTime.Parse("2021-01-01")));
+            return wb;
+        }
+    }
+}