A little more cleanup to the magic system

src/main/java/com/minelittlepony/unicopia/ability/UnicornCastingAbility.java

@@ -111,14 +111,10 @@ public class UnicornCastingAbility implements Ability<Hit> {
             TypedActionResult<SpellType<?>> newSpell = getNewSpell(player);
 
             if (newSpell.getResult() != ActionResult.FAIL) {
-                @Nullable
                 SpellType<?> spell = newSpell.getValue();
-                if (!player.getSpellSlot().isPresent() && spell == null) {
-                    spell = SpellType.SHIELD;
-                }
 
-                player.subtractEnergyCost(spell == null ? 2 : 4);
-                player.setSpell(spell == null ? null : spell.create());
+                player.subtractEnergyCost(spell.isEmpty() ? 2 : 4);
+                spell.apply(player);
             }
         }
     }
@@ -139,12 +135,12 @@ public class UnicornCastingAbility implements Ability<Hit> {
     }
 
     private TypedActionResult<SpellType<?>> getNewSpell(Pony player) {
-        final SpellType<?> current = player.getSpellSlot().get(true).map(Spell::getType).orElse(null);
+        final SpellType<?> current = player.getSpellSlot().get(true).map(Spell::getType).orElse(SpellType.empty());
         return Streams.stream(player.getMaster().getItemsHand())
                 .filter(GemstoneItem::isEnchanted)
                 .map(stack -> GemstoneItem.consumeSpell(stack, player.getMaster(), current, SpellType::mayAttach))
                 .findFirst()
-                .orElse(TypedActionResult.<SpellType<?>>pass(null));
+                .orElse(TypedActionResult.<SpellType<?>>pass(current == SpellType.EMPTY_KEY ? SpellType.SHIELD : SpellType.EMPTY_KEY));
     }
 
     @Override

src/main/java/com/minelittlepony/unicopia/ability/magic/Spell.java

@@ -5,8 +5,6 @@ import java.util.UUID;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 import com.minelittlepony.unicopia.util.NbtSerialisable;
 
-import net.minecraft.entity.projectile.ProjectileEntity;
-
 /**
  * Interface for a magic spells
  */
@@ -38,25 +36,17 @@ public interface Spell extends NbtSerialisable, Affine {
     boolean isDirty();
 
     /**
-     * Marks this effect as dirty.
+     * Applies this spell to the supplied caster.
      */
-    void setDirty(boolean dirty);
+    boolean apply(Caster<?> caster);
 
     /**
-     * Called when first attached to a gem.
+     * Marks this effect as dirty.
      */
-    default void onPlaced(Caster<?> caster) {
-
-    }
+    void setDirty();
 
     /**
      * Called when a gem is destroyed.
      */
-    default void onDestroyed(Caster<?> caster) {
-        setDead();
-    }
-
-    default boolean handleProjectileImpact(ProjectileEntity projectile) {
-        return false;
-    }
+    void onDestroyed(Caster<?> caster);
 }

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/AbstractPlacedSpell.java

@@ -41,7 +41,7 @@ public abstract class AbstractPlacedSpell extends AbstractSpell implements Attac
 
             if (dimension == null) {
                 dimension = source.getWorld().getRegistryKey().getValue();
-                setDirty(true);
+                setDirty();
             } else if (!source.getWorld().getRegistryKey().getValue().equals(dimension)) {
                 return false;
             }
@@ -55,7 +55,7 @@ public abstract class AbstractPlacedSpell extends AbstractSpell implements Attac
                 entity.world.spawnEntity(entity);
 
                 castEntity.set(entity);
-                setDirty(true);
+                setDirty();
             }
         }
 

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/AbstractSpell.java

@@ -3,6 +3,7 @@ package com.minelittlepony.unicopia.ability.magic.spell;
 import java.util.UUID;
 
 import com.minelittlepony.unicopia.Affinity;
+import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.Spell;
 
 import net.minecraft.nbt.CompoundTag;
@@ -34,6 +35,7 @@ public abstract class AbstractSpell implements Spell {
     @Override
     public void setDead() {
         isDead = true;
+        setDirty();
     }
 
     @Override
@@ -47,8 +49,8 @@ public abstract class AbstractSpell implements Spell {
     }
 
     @Override
-    public void setDirty(boolean dirty) {
-        isDirty = dirty;
+    public void setDirty() {
+        isDirty = true;
     }
 
     @Override
@@ -56,6 +58,17 @@ public abstract class AbstractSpell implements Spell {
         return getType().getAffinity();
     }
 
+    @Override
+    public boolean apply(Caster<?> caster) {
+        caster.setSpell(this);
+        return true;
+    }
+
+    @Override
+    public void onDestroyed(Caster<?> caster) {
+        setDead();
+    }
+
     @Override
     public void toNBT(CompoundTag compound) {
         compound.putBoolean("dead", isDead);
@@ -64,7 +77,7 @@ public abstract class AbstractSpell implements Spell {
 
     @Override
     public void fromNBT(CompoundTag compound) {
-        setDirty(false);
+        isDirty = false;
         if (compound.contains("uuid")) {
             uuid = compound.getUuid("uuid");
         }

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/DisguiseSpell.java

@@ -16,6 +16,8 @@ import com.minelittlepony.unicopia.entity.player.Pony;
 import com.minelittlepony.unicopia.entity.player.PlayerDimensions;
 import com.minelittlepony.unicopia.particle.MagicParticleEffect;
 import com.minelittlepony.unicopia.particle.UParticles;
+import com.minelittlepony.unicopia.projectile.ProjectileImpactListener;
+
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.EntityDimensions;
 import net.minecraft.entity.LivingEntity;
@@ -25,7 +27,7 @@ import net.minecraft.entity.player.PlayerEntity;
 import net.minecraft.entity.projectile.ProjectileEntity;
 import net.minecraft.nbt.CompoundTag;
 
-public class DisguiseSpell extends AbstractSpell implements Attached, Suppressable, FlightType.Provider, PlayerDimensions.Provider {
+public class DisguiseSpell extends AbstractSpell implements Attached, Suppressable, FlightType.Provider, PlayerDimensions.Provider, ProjectileImpactListener {
 
     private final Disguise disguise = new Disguise();
 
@@ -49,7 +51,7 @@ public class DisguiseSpell extends AbstractSpell implements Attached, Suppressab
     @Override
     public void onSuppressed(Caster<?> otherSource) {
         suppressionCounter = 100;
-        setDirty(true);
+        setDirty();
     }
 
     @Override
@@ -67,12 +69,12 @@ public class DisguiseSpell extends AbstractSpell implements Attached, Suppressab
         }
 
         disguise.setAppearance(entity);
-        setDirty(true);
+        setDirty();
         return this;
     }
 
     @Override
-    public boolean handleProjectileImpact(ProjectileEntity projectile) {
+    public boolean onProjectileImpact(ProjectileEntity projectile) {
         return disguise.getAppearance() == projectile;
     }
 

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/RevealingSpell.java

@@ -22,11 +22,6 @@ public class RevealingSpell extends AbstractSpell implements Attached, Thrown {
         super(type);
     }
 
-    @Override
-    public void onPlaced(Caster<?> source) {
-        source.getLevel().set(1);
-    }
-
     @Override
     public boolean onThrownTick(MagicProjectileEntity projectile) {
         return onBodyTick(projectile);

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/ShieldSpell.java

@@ -90,7 +90,7 @@ public class ShieldSpell extends AbstractSpell implements Attached, Thrown {
             cost /= 2.725D;
 
             if (!source.subtractEnergyCost(cost)) {
-                onDestroyed(source);
+                setDead();
             }
         }
 

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/SiphoningSpell.java

@@ -86,14 +86,14 @@ public class SiphoningSpell extends AbstractPlacedSpell {
 
             if (ticksUpset > 0 || maxHealthGain <= 0) {
                 if (source.getWorld().random.nextInt(3000) == 0) {
-                    onDestroyed(source);
+                    setDead();
                 } else {
                     e.damage(damage, e.getHealth() / 4);
                 }
                 if (maxHealthGain <= 0) {
                     ticksUpset = 100;
                 }
-                setDirty(true);
+                setDirty();
             } else {
                 e.heal((float)Math.min(0.5F * (1 + source.getLevel().get()), maxHealthGain * 0.6));
                 ParticleUtils.spawnParticle(new FollowingParticleEffect(UParticles.HEALTH_DRAIN, e, 0.2F), e.world, e.getPos(), Vec3d.ZERO);

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/SpellType.java

@@ -10,6 +10,7 @@ import javax.annotation.Nullable;
 
 import com.minelittlepony.unicopia.Affinity;
 import com.minelittlepony.unicopia.ability.magic.Affine;
+import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.Spell;
 
 import net.minecraft.nbt.CompoundTag;
@@ -117,11 +118,24 @@ public final class SpellType<T extends Spell> implements Affine, SpellPredicate<
         return null;
     }
 
+    public boolean apply(Caster<?> caster) {
+        if (isEmpty()) {
+            caster.setSpell(null);
+            return false;
+        }
+
+        return create().apply(caster);
+    }
+
     @Override
     public boolean test(@Nullable Spell spell) {
         return spell != null && spell.getType() == this;
     }
 
+    public boolean isEmpty() {
+        return this == EMPTY_KEY;
+    }
+
     public static <T extends Spell> SpellType<T> register(Identifier id, Affinity affinity, int color, boolean obtainable, Factory<T> factory) {
         SpellType<T> type = new SpellType<>(id, affinity, color, obtainable, factory);
         byAffinity(affinity).add(type);
@@ -133,6 +147,11 @@ public final class SpellType<T extends Spell> implements Affine, SpellPredicate<
         return register(new Identifier("unicopia", name), affinity, color, obtainable, factory);
     }
 
+    @SuppressWarnings("unchecked")
+    public static <T extends Spell> SpellType<T> empty() {
+        return (SpellType<T>)EMPTY_KEY;
+    }
+
     @SuppressWarnings("unchecked")
     public static <T extends Spell> SpellType<T> getKey(Identifier id) {
         return (SpellType<T>)(EMPTY_ID.equals(id) ? EMPTY_KEY : REGISTRY.getOrDefault(id, EMPTY_KEY));

src/main/java/com/minelittlepony/unicopia/command/DisguiseCommand.java

@@ -2,6 +2,7 @@ package com.minelittlepony.unicopia.command;
 
 import java.util.function.Function;
 
+import com.minelittlepony.unicopia.ability.magic.Spell;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 import com.minelittlepony.unicopia.entity.player.Pony;
 import com.mojang.brigadier.CommandDispatcher;
@@ -79,9 +80,7 @@ public class DisguiseCommand {
 
     static int reveal(ServerCommandSource source, PlayerEntity player) {
         Pony iplayer = Pony.of(player);
-        iplayer.getSpellSlot().get(SpellType.DISGUISE, true).ifPresent(disguise -> {
-            disguise.onDestroyed(iplayer);
-        });
+        iplayer.getSpellSlot().get(SpellType.DISGUISE, true).ifPresent(Spell::setDead);
 
         if (player.getEntityWorld().getGameRules().getBoolean(GameRules.SEND_COMMAND_FEEDBACK)) {
             player.sendMessage(new TranslatableText("commands.disguise.removed"), false);

src/main/java/com/minelittlepony/unicopia/entity/Equine.java

@@ -5,6 +5,7 @@ import java.util.Optional;
 import javax.annotation.Nullable;
 
 import com.minelittlepony.unicopia.Race;
+import com.minelittlepony.unicopia.projectile.ProjectileImpactListener;
 import com.minelittlepony.unicopia.util.NbtSerialisable;
 
 import net.minecraft.entity.Entity;
@@ -12,7 +13,7 @@ import net.minecraft.entity.damage.DamageSource;
 import net.minecraft.entity.projectile.ProjectileEntity;
 import net.minecraft.util.Tickable;
 
-public interface Equine<T extends Entity> extends NbtSerialisable, Tickable {
+public interface Equine<T extends Entity> extends NbtSerialisable, Tickable, ProjectileImpactListener {
     Race getSpecies();
 
     Physics getPhysics();
@@ -44,6 +45,7 @@ public interface Equine<T extends Entity> extends NbtSerialisable, Tickable {
     /**
      * Event triggered when this entity is hit by a projectile.
      */
+    @Override
     default boolean onProjectileImpact(ProjectileEntity projectile) {
         return false;
     }

src/main/java/com/minelittlepony/unicopia/entity/Living.java

@@ -11,6 +11,7 @@ import com.minelittlepony.unicopia.ability.magic.spell.SpellPredicate;
 import com.minelittlepony.unicopia.ability.magic.spell.SpellType;
 import com.minelittlepony.unicopia.item.UItems;
 import com.minelittlepony.unicopia.network.EffectSync;
+import com.minelittlepony.unicopia.projectile.ProjectileImpactListener;
 
 import net.minecraft.entity.LivingEntity;
 import net.minecraft.entity.damage.DamageSource;
@@ -139,7 +140,9 @@ public abstract class Living<T extends LivingEntity> implements Equine<T>, Caste
     @Override
     public boolean onProjectileImpact(ProjectileEntity projectile) {
         return getSpellSlot().get(true)
-                .filter(effect -> !effect.isDead() && effect.handleProjectileImpact(projectile))
+                .filter(effect -> !effect.isDead()
+                        && effect instanceof ProjectileImpactListener
+                        && ((ProjectileImpactListener)effect).onProjectileImpact(projectile))
                 .isPresent();
     }
 

src/main/java/com/minelittlepony/unicopia/entity/behaviour/SheepBehaviour.java

@@ -66,7 +66,7 @@ public class SheepBehaviour extends EntityBehaviour<SheepEntity> {
                         }
                     } while (dropAmount-- > 0);
                 }
-                spell.setDirty(true);
+                spell.setDirty();
             }
         }
     }

src/main/java/com/minelittlepony/unicopia/network/EffectSync.java

@@ -89,6 +89,7 @@ public class EffectSync implements SpellContainer {
     private void updateReference(@Nullable Spell effect) {
         if (spell.isPresent() && spell.get() != effect) {
             spell.get().setDead();
+            spell.get().onDestroyed(owner);
         }
         spell = Optional.ofNullable(effect);
     }

src/main/java/com/minelittlepony/unicopia/projectile/MagicProjectileEntity.java

@@ -121,15 +121,6 @@ public class MagicProjectileEntity extends ThrownItemEntity implements Magical,
         return effectDelegate;
     }
 
-    @Override
-    public void setSpell(Spell effect) {
-        Caster.super.setSpell(effect);
-
-        if (effect != null) {
-            effect.onPlaced(this);
-        }
-    }
-
     public void setThrowDamage(float damage) {
         getDataTracker().set(DAMAGE, Math.max(0, damage));
     }

src/main/java/com/minelittlepony/unicopia/projectile/ProjectileImpactListener.java

@@ -0,0 +1,7 @@
+package com.minelittlepony.unicopia.projectile;
+
+import net.minecraft.entity.projectile.ProjectileEntity;
+
+public interface ProjectileImpactListener {
+    boolean onProjectileImpact(ProjectileEntity projectile);
+}