Implements terrain

Plugins/PkmnLib.Plugin.Gen7/Scripts/Terrain/PsychicTerrain.cs

@@ -3,5 +3,34 @@ namespace PkmnLib.Plugin.Gen7.Scripts.Terrain;
 [Script(ScriptCategory.Terrain, "psychic_terrain")]
 public class PsychicTerrain : Script
 {
-    // TODO: Implement Terrain
+    private static bool IsAffectedByTerrain(IPokemon pokemon) =>
+        !pokemon.IsFloating;
+
+    /// <inheritdoc />
+    public override void ChangeBasePower(IExecutingMove move, IPokemon target, byte hit, ref ushort basePower)
+    {
+        if (!IsAffectedByTerrain(move.User))
+            return;
+
+        // It boosts the power of Psychic-type moves used by affected Pokémon by 50% (regardless of whether the target of
+        // the move is affected by Psychic Terrain).
+        var type = move.GetHitData(target, hit).Type;
+        if (type?.Name == "psychic")
+        {
+            basePower = basePower.MultiplyOrMax(1.5f);
+        }
+    }
+
+    /// <inheritdoc />
+    public override void IsInvulnerableToMove(IExecutingMove move, IPokemon target, ref bool invulnerable)
+    {
+        if (!IsAffectedByTerrain(target))
+            return;
+
+        // Psychic Terrain prevents priority moves from affecting affected Pokémon.
+        if (move.MoveChoice.Priority > 0)
+        {
+            invulnerable = true;
+        }
+    }
 }