feat(Duration): Added option for business days calculation at duration ctor

src/Todoist.Net/Extensions/DateTimeExtensions.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 
 namespace Todoist.Net.Extensions
 {
@@ -8,5 +8,37 @@ public static string ToFilterParameter(this DateTime dateTime)
         {
             return dateTime.ToString("s");
         }
+
+        public static DateTime AddBusinessDays(this DateTime date, int days)
+        {
+            if (days < 0)
+            {
+                throw new ArgumentException("days cannot be negative", "days");
+            }
+
+            if (days == 0) return date;
+
+            if (date.DayOfWeek == DayOfWeek.Friday)
+            {
+                date = date.AddDays(2);
+                days -= 1;
+            }
+            else if (date.DayOfWeek == DayOfWeek.Saturday)
+            {
+                date = date.AddDays(1);
+                days -= 1;
+            }
+
+            date = date.AddDays(days / 5 * 7);
+            int extraDays = days % 5;
+
+            if ((int)date.DayOfWeek + extraDays > 5)
+            {
+                extraDays += 2;
+            }
+
+            return date.AddDays(extraDays);
+
+        }
     }
 }

src/Todoist.Net/Models/Duration.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Text.Json.Serialization;
 
+using Todoist.Net.Extensions;
+
 namespace Todoist.Net.Models
 {
     /// <summary>
@@ -23,6 +25,16 @@ public Duration(int amount, DurationUnit unit)
             Unit = unit;
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Duration" /> class.
+        /// </summary>
+        /// <param name="businessDaysAmount">Business Days amount</param>
+        public Duration(int businessDaysAmount)
+        {
+            Unit = DurationUnit.Day;
+            Amount = (int)(DateTime.Now.Date.AddBusinessDays(businessDaysAmount) - DateTime.Now.Date).TotalDays;
+        }
+
         [JsonConstructor]
         internal Duration()
         {