Add competition/.net/filter.md

competition/.net/filter.md

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+## TaeKwonDo Competition Filer Function
+```
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public class PlayerDto
+{
+    public int Id { get; set; }
+    public string Name { get; set; }
+    public string Gender { get; set; }
+    public DateOnly DateOfBirth { get; set; }
+    public int ClubId { get; set; }
+    public double? Weight { get; set; }
+    public double? Height { get; set; }
+    public string? Picture { get; set; }
+    public string? Phone { get; set; }
+    public string? CPR { get; set; }
+    public string? Email { get; set; }
+}
+
+public class GroupedPlayers
+{
+    public string Gender { get; set; }
+    public string AgeCategory { get; set; }
+    public string WeightClass { get; set; }
+    public List<PlayerDto> Players { get; set; }
+}
+
+public static class TaekwondoPredrawHelper
+{
+    // Calculate age from DateOfBirth compared to current year
+    private static int CalculateAge(DateOnly dob)
+    {
+        var today = DateOnly.FromDateTime(DateTime.Now);
+        int age = today.Year - dob.Year;
+        if (dob > today.AddYears(-age)) age--;
+        return age;
+    }
+
+    // Official WT Age Categories (source: World Taekwondo rules)
+    private static string GetAgeCategory(int age)
+    {
+        if (age >= 4 && age <= 5) return "4-5 Years";
+        if (age >= 6 && age <= 7) return "6-7 Years";
+        if (age >= 8 && age <= 9) return "8-9 Years";
+        if (age >= 10 && age <= 11) return "10-11 Years (Child)";
+        if (age >= 12 && age <= 14) return "12-14 Years (Cadet)";
+        if (age >= 15 && age <= 17) return "15-17 Years (Junior)";
+        if (age >= 18 && age <= 32) return "18-32 Years (Senior)";
+        if (age >= 33 && age <= 40) return "33-40 Years (Ultra 1)";
+        if (age >= 41 && age <= 50) return "41-50 Years (Ultra 2)";
+        if (age >= 51 && age <= 60) return "51-60 Years (Ultra 3)";
+        if (age >= 61) return "61+ Years (Ultra 4)";
+        return "Unknown";
+    }
+
+    // WT Weight Classes example (adjust for event specifics)
+    private static string GetWeightClass(double? weight)
+    {
+        if (!weight.HasValue) return "Unknown";
+        if (weight < 46) return "Under 46kg";
+        if (weight < 54) return "Under 54kg";
+        if (weight < 58) return "Under 58kg";
+        if (weight < 63) return "Under 63kg";
+        if (weight < 68) return "Under 68kg";
+        if (weight < 74) return "Under 74kg";
+        if (weight < 80) return "Under 80kg";
+        if (weight < 87) return "Under 87kg";
+        return "Over 87kg";
+    }
+
+    public static List<GroupedPlayers> GroupPlayersForPredraw(List<PlayerDto> players)
+    {
+        var grouped = players.GroupBy(p =>
+            new
+            {
+                Gender = p.Gender,
+                AgeCategory = GetAgeCategory(CalculateAge(p.DateOfBirth)),
+                WeightClass = GetWeightClass(p.Weight)
+            })
+            .Select(g => new GroupedPlayers
+            {
+                Gender = g.Key.Gender,
+                AgeCategory = g.Key.AgeCategory,
+                WeightClass = g.Key.WeightClass,
+                Players = g.ToList()
+            })
+            .ToList();
+
+        return grouped;
+    }
+}
+
+```
+
+## How To Use The Filter
+
+```
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+class Program
+{
+    static void Main()
+    {
+        // 1. Participants registered for the competition
+        var participants = new List<PlayerDto>
+        {
+            new PlayerDto { Id = 101, Name = "Ali", Gender = "Male", DateOfBirth = new DateOnly(1998, 5, 10), Weight = 65 },
+            new PlayerDto { Id = 102, Name = "Sara", Gender = "Female", DateOfBirth = new DateOnly(2010, 8, 20), Weight = 54 },
+            new PlayerDto { Id = 103, Name = "John", Gender = "Male", DateOfBirth = new DateOnly(2007, 3, 15), Weight = 57 },
+            new PlayerDto { Id = 104, Name = "Maria", Gender = "Female", DateOfBirth = new DateOnly(1985, 12, 5), Weight = 73 },
+            new PlayerDto { Id = 105, Name = "Khaled", Gender = "Male", DateOfBirth = new DateOnly(1978, 7, 1), Weight = 82 }
+        };
+
+        // 2. Group participants using the WT predraw helper
+        var groupedParticipants = TaekwondoPredrawHelper.GroupPlayersForPredraw(participants);
+
+        // 3. Display grouped results for predraw
+        foreach (var group in groupedParticipants)
+        {
+            Console.WriteLine($"Group: Gender={group.Gender}, Age Category={group.AgeCategory}, Weight Class={group.WeightClass}");
+            foreach (var player in group.Players)
+            {
+                Console.WriteLine($"  - {player.Name} (DOB: {player.DateOfBirth}, Weight: {player.Weight}kg)");
+            }
+        }
+    }
+}
+```