Add WORKDAY function for calculating working days excluding weekends and holidays

src/libraries/Microsoft.PowerFx.Core/Localization/Strings.cs

@@ -366,6 +366,10 @@ internal static class TexlStrings
         public static StringGetter AboutEOMonth = (b) => StringResources.Get("AboutEOMonth", b);
         public static StringGetter EOMonthArg1 = (b) => StringResources.Get("EOMonthArg1", b);
         public static StringGetter EOMonthArg2 = (b) => StringResources.Get("EOMonthArg2", b);
+        public static StringGetter AboutWorkday = (b) => StringResources.Get("AboutWorkday", b);
+        public static StringGetter WorkdayArg1 = (b) => StringResources.Get("WorkdayArg1", b);
+        public static StringGetter WorkdayArg2 = (b) => StringResources.Get("WorkdayArg2", b);
+        public static StringGetter WorkdayArg3 = (b) => StringResources.Get("WorkdayArg3", b);
 
         public static StringGetter AboutCalendar__MonthsLong = (b) => StringResources.Get("AboutCalendar__MonthsLong", b);
         public static StringGetter AboutCalendar__MonthsShort = (b) => StringResources.Get("AboutCalendar__MonthsShort", b);

src/libraries/Microsoft.PowerFx.Core/Texl/BuiltinFunctionsCore.cs

@@ -104,8 +104,9 @@ internal class BuiltinFunctionsCore
         public static readonly TexlFunction Degrees = _library.Add(new DegreesFunction());
         public static readonly TexlFunction DegreesT = _library.Add(new DegreesTableFunction());
         public static readonly TexlFunction DropColumns = _library.Add(new DropColumnsFunction());
-        public static readonly TexlFunction EDate = _library.Add(new EDateFunction());
-        public static readonly TexlFunction EOMonth = _library.Add(new EOMonthFunction());
+        public static readonly TexlFunction EDate = _library.Add(new EDateFunction());
+        public static readonly TexlFunction EOMonth = _library.Add(new EOMonthFunction());
+        public static readonly TexlFunction Workday = _library.Add(new WorkdayFunction());
         public static readonly TexlFunction EncodeHTML = _library.Add(new EncodeHTMLFunction());
         public static readonly TexlFunction EncodeUrl = _library.Add(new EncodeUrlFunction());
         public static readonly TexlFunction EndsWith = _library.Add(new EndsWithFunction());

src/libraries/Microsoft.PowerFx.Core/Texl/Builtins/DateTime.cs

@@ -371,7 +371,25 @@ public EOMonthFunction()
 
         public override IEnumerable<TexlStrings.StringGetter[]> GetSignatures()
         {
-            yield return new[] { TexlStrings.EOMonthArg1, TexlStrings.EOMonthArg2 };
+            yield return new[] { TexlStrings.EOMonthArg1, TexlStrings.EOMonthArg2 };
+        }
+    }
+
+    // Workday()
+    // Equivalent Excel function: WORKDAY
+    internal sealed class WorkdayFunction : BuiltinFunction
+    {
+        public override bool IsSelfContained => true;
+
+        public WorkdayFunction()
+            : base("Workday", TexlStrings.AboutWorkday, FunctionCategories.DateTime, DType.Date, 0, 2, 3, DType.DateTime, DType.Number, DType.EmptyTable)
+        {
+        }
+
+        public override IEnumerable<TexlStrings.StringGetter[]> GetSignatures()
+        {
+            yield return new[] { TexlStrings.WorkdayArg1, TexlStrings.WorkdayArg2 };
+            yield return new[] { TexlStrings.WorkdayArg1, TexlStrings.WorkdayArg2, TexlStrings.WorkdayArg3 };
         }
     }
 

src/libraries/Microsoft.PowerFx.Interpreter/Functions/Library.cs

@@ -653,6 +653,22 @@ static Library()
                     returnBehavior: ReturnBehavior.AlwaysEvaluateAndReturnResult,
                     targetFunction: EOMonth)
             },
+            {
+                BuiltinFunctionsCore.Workday,
+                StandardErrorHandling<FormulaValue>(
+                    BuiltinFunctionsCore.Workday.Name,
+                    expandArguments: NoArgExpansion,
+                    replaceBlankValues: ReplaceBlankWith(
+                        new DateTimeValue(IRContext.NotInSource(FormulaType.DateTime), _epoch),
+                        new NumberValue(IRContext.NotInSource(FormulaType.Number), 0)),
+                    checkRuntimeTypes: ExactSequence(
+                        DateOrDateTime,
+                        ExactValueType<NumberValue>,
+                        ExactValueTypeOrBlank<TableValue>),
+                    checkRuntimeValues: DeferRuntimeValueChecking,
+                    returnBehavior: ReturnBehavior.AlwaysEvaluateAndReturnResult,
+                    targetFunction: Workday)
+            },
             {
                 BuiltinFunctionsCore.EncodeHTML,
                 StandardErrorHandling<StringValue>(

src/libraries/Microsoft.PowerFx.Interpreter/Functions/LibraryDate.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics.Contracts;
 using System.Globalization;
 using System.Linq;
@@ -926,6 +927,90 @@ public static FormulaValue EOMonth(EvalVisitor runner, EvalVisitorContext contex
             }
         }
 
+        public static FormulaValue Workday(EvalVisitor runner, EvalVisitorContext context, IRContext irContext, FormulaValue[] args)
+        {
+            var timeZoneInfo = runner.TimeZoneInfo;
+
+            DateTime startDate = runner.GetNormalizedDateTime(args[0]);
+
+            if (args[1] is not NumberValue daysValue)
+            {
+                throw CommonExceptions.RuntimeMisMatch;
+            }
+
+            // Truncate toward zero for Excel compatibility
+            int days = (int)Math.Truncate(daysValue.Value);
+
+            // Collect holidays if provided
+            var holidays = new HashSet<DateTime>();
+            if (args.Length > 2 && args[2] is not BlankValue)
+            {
+                if (args[2] is TableValue holidayTable)
+                {
+                    foreach (var row in holidayTable.Rows)
+                    {
+                        if (row.IsValue)
+                        {
+                            var fields = row.Value.Fields.ToArray();
+                            if (fields.Length > 0)
+                            {
+                                var field = fields[0];
+                                if (field.Value is DateValue dateValue)
+                                {
+                                    holidays.Add(dateValue.GetConvertedValue(timeZoneInfo).Date);
+                                }
+                                else if (field.Value is DateTimeValue dateTimeValue)
+                                {
+                                    holidays.Add(dateTimeValue.GetConvertedValue(timeZoneInfo).Date);
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            try
+            {
+                DateTime currentDate = startDate.Date;
+
+                // Early return for zero days
+                if (days == 0)
+                {
+                    DateTime resultDate = MakeValidDateTime(runner, currentDate, timeZoneInfo);
+                    return new DateValue(irContext, resultDate);
+                }
+
+                int direction = days > 0 ? 1 : -1;
+                int remainingDays = Math.Abs(days);
+
+                while (remainingDays > 0)
+                {
+                    currentDate = currentDate.AddDays(direction);
+
+                    // Check if it's a weekend (Saturday or Sunday)
+                    if (currentDate.DayOfWeek == DayOfWeek.Saturday || currentDate.DayOfWeek == DayOfWeek.Sunday)
+                    {
+                        continue;
+                    }
+
+                    // Check if it's a holiday
+                    if (holidays.Contains(currentDate))
+                    {
+                        continue;
+                    }
+
+                    remainingDays--;
+                }
+
+                DateTime newDate = MakeValidDateTime(runner, currentDate, timeZoneInfo);
+                return new DateValue(irContext, newDate);
+            }
+            catch
+            {
+                return CommonErrors.ArgumentOutOfRange(irContext);
+            }
+        }
+
         private static double WeekStartDay(double startOfWeek)
         {
             if (startOfWeek == 1 || startOfWeek == 2)

src/strings/PowerFxResources.en-US.resx

@@ -1127,6 +1127,34 @@
     <value>Number of months by which to change the date. A positive value yields a future date, a negative value a past date, and zero will not change the month.</value>
     <comment>Description of the second argument to the 'EOMonth' function.</comment>
   </data>
+  <data name="AboutWorkday" xml:space="preserve">
+    <value>Returns a date that represents a specified number of working days before or after a starting date. Working days exclude weekends and any specified holidays.</value>
+    <comment>Description of 'Workday' function.</comment>
+  </data>
+  <data name="WorkdayArg1" xml:space="preserve">
+    <value>start_date</value>
+    <comment>function_parameter - First parameter for the Workday function - the starting date.</comment>
+  </data>
+  <data name="WorkdayArg2" xml:space="preserve">
+    <value>days</value>
+    <comment>function_parameter - Second parameter for the Workday function - the number of working days to add or subtract.</comment>
+  </data>
+  <data name="WorkdayArg3" xml:space="preserve">
+    <value>holidays</value>
+    <comment>function_parameter - Third parameter for the Workday function - optional table of holiday dates to exclude.</comment>
+  </data>
+  <data name="AboutWorkday_start_date" xml:space="preserve">
+    <value>A date value that represents the start date.</value>
+    <comment>Description of the first argument to the 'Workday' function.</comment>
+  </data>
+  <data name="AboutWorkday_days" xml:space="preserve">
+    <value>The number of nonweekend and nonholiday days before or after start_date. A positive value for days yields a future date; a negative value yields a past date.</value>
+    <comment>Description of the second argument to the 'Workday' function.</comment>
+  </data>
+  <data name="AboutWorkday_holidays" xml:space="preserve">
+    <value>An optional table of one or more dates to exclude from the working calendar, such as state and federal holidays and floating holidays.</value>
+    <comment>Description of the third argument to the 'Workday' function.</comment>
+  </data>
   <data name="AboutInt" xml:space="preserve">
     <value>Truncates 'number' by rounding toward negative infinity.</value>
     <comment>Description of 'Int' function.</comment>

src/tests/Microsoft.PowerFx.Core.Tests.Shared/ExpressionTestCases/Workday.txt

@@ -0,0 +1,116 @@
+
+// WORKDAY basic tests
+
+// Basic forward workday calculations
+>> Workday(Date(2024,8,24),30)
+Date(2024,10,4)
+
+// Basic backward workday calculations  
+>> Workday(Date(2024,8,24),-10)
+Date(2024,8,12)
+
+// Zero days should return the start date
+>> Workday(Date(2024,8,24),0)
+Date(2024,8,24)
+
+// Starting on a Saturday (weekend)
+>> Workday(Date(2024,8,24),1)
+Date(2024,8,26)
+
+// Starting on a Sunday (weekend)
+>> Workday(Date(2024,8,25),1)
+Date(2024,8,26)
+
+// Starting on a Friday
+>> Workday(Date(2024,8,23),1)
+Date(2024,8,26)
+
+// Starting on a Monday
+>> Workday(Date(2024,8,26),1)
+Date(2024,8,27)
+
+// Multiple weeks forward
+>> Workday(Date(2024,1,15),20)
+Date(2024,2,12)
+
+// Multiple weeks backward
+>> Workday(Date(2024,2,15),-20)
+Date(2024,1,18)
+
+// Crossing year boundary forward
+>> Workday(Date(2024,12,20),10)
+Date(2025,1,3)
+
+// Crossing year boundary backward
+>> Workday(Date(2025,1,10),-10)
+Date(2024,12,27)
+
+// Fractional days should be truncated
+>> Workday(Date(2024,8,24),5.9)
+Date(2024,8,30)
+
+// Negative fractional days should be truncated
+>> Workday(Date(2024,8,24),-5.9)
+Date(2024,8,19)
+
+// WORKDAY with holidays
+
+// Single holiday
+>> Workday(Date(2024,8,24),5,Table({Date:Date(2024,8,28)}))
+Date(2024,9,2)
+
+// Multiple holidays
+>> Workday(Date(2024,8,24),10,Table({Date:Date(2024,8,28)},{Date:Date(2024,9,2)}))
+Date(2024,9,6)
+
+// Holiday on weekend should not affect result
+>> Workday(Date(2024,8,24),5,Table({Date:Date(2024,8,25)}))
+Date(2024,8,30)
+
+// Backward with holidays
+>> Workday(Date(2024,8,30),-5,Table({Date:Date(2024,8,26)}))
+Date(2024,8,21)
+
+// Holiday that is the start date
+>> Workday(Date(2024,8,26),5,Table({Date:Date(2024,8,26)}))
+Date(2024,9,2)
+
+// Multiple holidays in range
+>> Workday(Date(2024,12,20),10,Table({Date:Date(2024,12,25)},{Date:Date(2025,1,1)}))
+Date(2025,1,7)
+
+// WORKDAY with DateTime inputs
+
+>> Workday(DateTime(2024,8,24,12,30,45),5)
+Date(2024,8,30)
+
+>> Workday(DateTime(2024,8,24,12,30,45),-5)
+Date(2024,8,19)
+
+// WORKDAY with Blank values
+
+>> Workday(Blank(),10)
+Date(1900,1,12)
+
+>> Workday(Date(2024,8,24),Blank())
+Date(2024,8,24)
+
+>> Workday(Blank(),Blank())
+Date(1899,12,30)
+
+// Edge cases
+
+// Large number of workdays forward
+>> Workday(Date(2024,1,1),250)
+Date(2024,12,16)
+
+// Large number of workdays backward
+>> Workday(Date(2024,12,31),-250)
+Date(2024,1,16)
+
+// Ensure date values are truncated and do not include time
+>> Text(Workday(DateTime(2024,8,24,12,34,56),5),"yyyy-mm-dd hh:mm:ss")
+"2024-08-30 00:00:00"
+
+>> Value(Workday(Date(2024,8,24),5))
+45535