Australia - Add Friday before AFL Grand Final (#684)

#565
#681

Author: tinohager

src/Nager.Date/HolidayProviders/AustraliaHolidayProvider.cs

@@ -190,6 +190,7 @@ protected override IEnumerable<HolidaySpecification> GetHolidaySpecifications(in
             holidaySpecifications.AddRangeIfNotNull(this.LabourDay(year));
             holidaySpecifications.AddRangeIfNotNull(this.MonarchBirthday(year));
             holidaySpecifications.AddIfNotNull(this.MourningForQueenElizabeth(year));
+            holidaySpecifications.AddIfNotNull(this.FridayBeforeTheAflGrandFinal(year));
 
             return holidaySpecifications;
         }
@@ -308,6 +309,68 @@ private HolidaySpecification[] MonarchBirthday(int year)
             return null;
         }
 
+        private HolidaySpecification? FridayBeforeTheAflGrandFinal(int year)
+        {
+            var holidayName = "Friday before AFL Grand Final";
+            var subdivisionCodes = new string[] { "AU-VIC" };
+
+            switch (year)
+            {
+                case 2016:
+                case 2017:
+                case 2018:
+                case 2019:
+                case 2021:
+                case 2023:
+                    {
+                        var lastFridayInSeptember = DateHelper.FindLastDay(year, Month.September, DayOfWeek.Friday);
+
+                        return new HolidaySpecification
+                        {
+                            Date = lastFridayInSeptember,
+                            EnglishName = holidayName,
+                            LocalName = holidayName,
+                            HolidayTypes = HolidayTypes.Public,
+                            SubdivisionCodes = subdivisionCodes
+                        };
+                    }
+                case 2020:
+                    return new HolidaySpecification
+                    {
+                        Date = new DateTime(year, 10 , 23),
+                        EnglishName = holidayName,
+                        LocalName = holidayName,
+                        HolidayTypes = HolidayTypes.Public,
+                        SubdivisionCodes = subdivisionCodes
+                    };
+                case 2022:
+                    return new HolidaySpecification
+                    {
+                        Date = new DateTime(year, 09, 23),
+                        EnglishName = holidayName,
+                        LocalName = holidayName,
+                        HolidayTypes = HolidayTypes.Public,
+                        SubdivisionCodes = subdivisionCodes
+                    };
+            }
+
+            if (year > DateTime.Today.Year)
+            {
+                var tentativeDate = DateHelper.FindLastDay(year, Month.September, DayOfWeek.Friday);
+
+                return new HolidaySpecification
+                {
+                    Date = tentativeDate,
+                    EnglishName = $"{holidayName} (Tentative Date)",
+                    LocalName = $"{holidayName} (Tentative Date)",
+                    HolidayTypes = HolidayTypes.Public,
+                    SubdivisionCodes = subdivisionCodes
+                };
+            }
+
+            return null;
+        }
+
         /// <inheritdoc/>
         public override IEnumerable<string> GetSources()
         {