Many changes. Will update merge request description with details

src/Nadeko.Econ/Gambling/Betdraw/BetdrawGame.cs

@@ -0,0 +1,83 @@
+namespace Nadeko.Econ.Gambling.Betdraw;
+
+public sealed class BetdrawGame
+{
+    private static readonly NadekoRandom _rng = new();
+
+    private const decimal SINGLE_GUESS_MULTI = 2.075M;
+    private const decimal DOUBLE_GUESS_MULTI = 4.15M;
+    
+    public BetdrawGame()
+    {
+        
+    }
+    
+    public BetdrawResult Draw(BetdrawValueGuess? val, BetdrawColorGuess? col, decimal amount)
+    {
+        if (val is null && col is null)
+            throw new ArgumentNullException(nameof(val));
+
+        var card = new Deck().CardPool[_rng.Next(0, 52)];
+
+        var realVal = card.Number < 7
+            ? BetdrawValueGuess.Low
+            : BetdrawValueGuess.High;
+
+        var realCol = card.Suit is Deck.CardSuit.Diamonds or Deck.CardSuit.Hearts
+            ? BetdrawColorGuess.Red
+            : BetdrawColorGuess.Black;
+        
+        // if card is 7, autoloss
+        if (card.Number == 7)
+        {
+            return new()
+            {
+                Won = 0M,
+                Multiplier = 0M,
+                ResultType = BetdrawResultType.Lose,
+                Card = card,
+            };
+        }
+
+        byte win = 0;
+        if (val is BetdrawValueGuess valGuess)
+        {
+            if (realVal != valGuess)
+                return new()
+                {
+                    Won = 0M,
+                    Multiplier = 0M,
+                    ResultType = BetdrawResultType.Lose,
+                    Card = card
+                };
+
+            ++win;
+        }
+        
+        if (col is BetdrawColorGuess colGuess)
+        {
+            if (realCol != colGuess)
+                return new()
+                {
+                    Won = 0M,
+                    Multiplier = 0M,
+                    ResultType = BetdrawResultType.Lose,
+                    Card = card
+                };
+
+            ++win;
+        }
+
+        var multi = win == 1
+            ? SINGLE_GUESS_MULTI
+            : DOUBLE_GUESS_MULTI;
+
+        return new()
+        {
+            Won = amount * multi,
+            Multiplier = multi,
+            ResultType = BetdrawResultType.Win,
+            Card = card
+        };
+    }
+}