Implements accuracy/evasion

PkmnLib.Dynamic/Libraries/BattleStatCalculator.cs

@@ -27,4 +27,9 @@ public interface IBattleStatCalculator
     /// Calculate a single boosted stat of a Pokemon, including stat boosts.
     /// </summary>
     uint CalculateBoostedStat(IPokemon pokemon, Statistic stat);
+    
+    /// <summary>
+    /// Calculates the accuracy for a move, taking into account any accuracy modifiers.
+    /// </summary>
+    byte CalculateModifiedAccuracy(IExecutingMove executingMove, IPokemon target, byte hitIndex, byte moveAccuracy);
 }

PkmnLib.Dynamic/Models/BattleFlow/MoveTurnExecutor.cs

@@ -140,10 +140,10 @@ internal static class MoveTurnExecutor
             // modifying it.
             if (accuracy != 255)
             {
-                executingMove.RunScriptHook(x => x.ChangeAccuracy(executingMove, target, hitIndex, ref accuracy));
+                accuracy = battle.Library.StatCalculator.CalculateModifiedAccuracy(executingMove, target,
+                    hitIndex, accuracy);
             }
             
-            // TODO: Deal with accuracy/evasion stats.
             if (accuracy < 100 && battle.Random.GetInt(100) >= accuracy)
             {
                 executingMove.RunScriptHook(x => x.OnMoveMiss(executingMove, target));

PkmnLib.Dynamic/ScriptHandling/Registry/ScriptRegistry.cs

@@ -43,9 +43,10 @@ public class ScriptRegistry
         if (type == null)
             throw new ArgumentNullException(nameof(type));
 
-        var constructor = type.GetConstructor(Type.EmptyTypes);
+        var constructor = type.GetConstructor(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
+            null, Type.EmptyTypes, null);
         if (constructor == null)
-            throw new ArgumentException("The type must have a parameterless constructor.");
+            throw new ArgumentException($"Type {type} does not have a parameterless constructor.");
 
         // We create a lambda that creates a new instance of the script type.
         // This is more performant than using Activator.CreateInstance.

PkmnLib.Dynamic/ScriptHandling/Script.cs

@@ -207,7 +207,7 @@ public abstract class Script
     /// This function allows a script to modify the accuracy of a move used. This value represents
     /// the percentage accuracy, so anything above 100% will make it always hit.
     /// </summary>
-    public virtual void ChangeAccuracy(IExecutingMove move, IPokemon target, byte hit, ref byte accuracy)
+    public virtual void ChangeAccuracyModifier(IExecutingMove move, IPokemon target, byte hit, ref float modifier)
     {
     }
 

PkmnLib.Static/StatisticSet.cs

@@ -248,7 +248,7 @@ public abstract record ClampedStatisticSet<T> : StatisticSet<T>
     {
     }
 
-    private static T Clamp(T value, T min, T max)
+    protected static T Clamp(T value, T min, T max)
     {
         if (value.CompareTo(min) < 0)
             return min;
@@ -307,6 +307,20 @@ public record StatBoostStatisticSet : ClampedStatisticSet<sbyte>
     /// <inheritdoc />
     protected override sbyte Max => 6;
 
+    private sbyte _evasion;
+    public sbyte Evasion
+    {
+        get => _evasion;
+        set => _evasion = Clamp(value, Min, Max);
+    }
+    
+    private sbyte _accuracy;
+    public sbyte Accuracy
+    {
+        get => _accuracy;
+        set => _accuracy = Clamp(value, Min, Max);
+    }
+
     /// <inheritdoc cref="StatBoostStatisticSet"/>
     public StatBoostStatisticSet() : base(0, 0, 0, 0, 0, 0)
     {

Plugins/PkmnLib.Plugin.Gen7/Libraries/Gen7BattleStatCalculator.cs

@@ -1,5 +1,7 @@
+using System;
 using PkmnLib.Dynamic.Libraries;
 using PkmnLib.Dynamic.Models;
+using PkmnLib.Dynamic.ScriptHandling;
 using PkmnLib.Static;
 
 namespace PkmnLib.Plugin.Gen7.Libraries;
@@ -48,6 +50,33 @@ public class Gen7BattleStatCalculator : IBattleStatCalculator
         return (uint)boostedStat;
     }
 
+    /// <inheritdoc />
+    public byte CalculateModifiedAccuracy(IExecutingMove executingMove, IPokemon target, byte hitIndex, byte moveAccuracy)
+    {
+        var accuracyModifier = 1.0f;
+        executingMove.RunScriptHook(x => x.ChangeAccuracyModifier(executingMove, target, hitIndex, ref accuracyModifier));
+        var modifiedAccuracy = (int)(moveAccuracy * accuracyModifier);
+        var targetEvasion = target.StatBoost.Evasion;
+        var userAccuracy = executingMove.User.StatBoost.Accuracy;
+        var difference = targetEvasion - userAccuracy;
+        var statModifier = difference switch
+        {
+            > 0 => 3.0f / (3.0f + difference),
+            < 0 => 3.0f + Math.Abs(difference) / 3.0f,
+            _ => 1.0f
+        };
+        modifiedAccuracy = (int)(modifiedAccuracy * statModifier);
+        modifiedAccuracy = modifiedAccuracy switch
+        {
+            > 255 => 255,
+            < 0 => 0,
+            _ => modifiedAccuracy
+        };
+        // NOTE: the main games also consider friendship here, but we don't yet have the concept of a "player Pokémon"
+        //       in the battle system, so for now we're just ignoring that.
+        return (byte)modifiedAccuracy;
+    }
+
     private static uint CalculateHealthStat(IPokemon pokemon)
     {
         var baseValue = (ulong)pokemon.Form.BaseStats.Hp;

Plugins/PkmnLib.Plugin.Gen7/Scripts/Side/AuroraVeilEffect.cs

@@ -28,6 +28,8 @@ public class AuroraVeilEffect : Script
 {
     public int NumberOfTurns { get; set; }
     
+    private AuroraVeilEffect(){}
+
     public AuroraVeilEffect(int numberOfTurns)
     {
         NumberOfTurns = numberOfTurns;