Begin work on outlining dynamic side

PkmnLib.Dynamic/Models/Choices/TurnChoiceComparer.cs

@@ -0,0 +1,83 @@
+namespace PkmnLib.Dynamic.Models.Choices;
+
+/// <summary>
+/// Comparer for turnchoices, to determine the order in which they should be executed.
+/// </summary>
+public class TurnChoiceComparer : IComparer<ITurnChoice>
+{
+    private enum CompareValues
+    {
+        XEqualsY = 0,
+        XLessThanY = -1,
+        XGreaterThanY = 1
+    }
+
+    private CompareValues CompareForSameType(ITurnChoice x, ITurnChoice y)
+    {
+        // Higher speed goes first
+        var speedComparison = x.Speed.CompareTo(y.Speed);
+        if (speedComparison != 0)
+            return (CompareValues)speedComparison;
+        // If speed is equal, we use the random values we've given to each choice to tiebreak.
+        // This is to ensure that the order of choices is deterministic.
+        return (CompareValues)x.RandomValue.CompareTo(y.RandomValue);
+    }
+    
+    private CompareValues CompareImpl(ITurnChoice? x, ITurnChoice? y)
+    {
+        // Deal with possible null values
+        switch (x)
+        {
+            case null when y is null:
+                return CompareValues.XEqualsY;
+            case null:
+                return CompareValues.XLessThanY;
+        }
+        if (y is null)
+            return CompareValues.XGreaterThanY;
+
+        switch (x)
+        {
+            case IMoveChoice moveX:
+                // Move choices go first
+                if (y is IMoveChoice moveY)
+                {
+                    // Higher priority goes first
+                    var priorityComparison = moveX.Priority.CompareTo(moveY.Priority);
+                    if (priorityComparison != 0)
+                        return (CompareValues)priorityComparison;
+                    return CompareForSameType(moveX, moveY);
+                }
+                return CompareValues.XGreaterThanY;
+            case IItemChoice itemX:
+                // Item choices go second
+                return y switch
+                {
+                    IMoveChoice => CompareValues.XLessThanY,
+                    IItemChoice itemY => CompareForSameType(itemX, itemY),
+                    _ => CompareValues.XGreaterThanY
+                };
+            case ISwitchChoice switchX:
+                // Switch choices go third
+                return y switch
+                {
+                    IMoveChoice or IItemChoice => CompareValues.XLessThanY,
+                    ISwitchChoice switchY => CompareForSameType(switchX, switchY),
+                    _ => CompareValues.XGreaterThanY
+                };
+            case IPassChoice passX:
+                // Pass choices go last
+                return y switch
+                {
+                    IMoveChoice or IItemChoice or ISwitchChoice => CompareValues.XLessThanY,
+                    IPassChoice passY => CompareForSameType(passX, passY),
+                    _ => CompareValues.XGreaterThanY
+                };
+        }
+        
+        return CompareValues.XLessThanY;
+    }
+
+    /// <inheritdoc />
+    public int Compare(ITurnChoice? x, ITurnChoice? y) => (int) CompareImpl(x, y);
+}