1 files changed, 98 insertions, 0 deletions
diff --git a/src/main/java/world/anhgelus/lifesteal/LifeStealer.java b/src/main/java/world/anhgelus/lifesteal/LifeStealer.java
new file mode 100644
index 0000000..86410de
--- /dev/null
+++ b/src/main/java/world/anhgelus/lifesteal/LifeStealer.java
@@ -0,0 +1,98 @@
+package world.anhgelus.lifesteal;
+
+import com.mojang.serialization.Codec;
+import com.mojang.serialization.codecs.RecordCodecBuilder;
+import net.minecraft.component.DataComponentTypes;
+import net.minecraft.component.type.NbtComponent;
+import net.minecraft.entity.attribute.EntityAttributeModifier;
+import net.minecraft.entity.attribute.EntityAttributes;
+import net.minecraft.item.ItemStack;
+import net.minecraft.item.Items;
+import net.minecraft.nbt.NbtCompound;
+import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.util.Identifier;
+import net.minecraft.util.math.MathHelper;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.UUID;
+
+public class LifeStealer {
+    public static final Identifier HEALTH_MODIFIER = Identifier.of(LifeSteal.MOD_ID, "health_modifier");
+    public static final String PLAYER_KEY = "player";
+
+    private ServerPlayerEntity player;
+    private final UUID uuid;
+    private float healthModifier;
+
+    public LifeStealer(ServerPlayerEntity player, Data data) {
+        this.player = player;
+        this.uuid = player.getUuid();
+        this.healthModifier = data.healthModifier();
+    }
+
+    private void updateHealth() {
+        healthModifier = MathHelper.clamp(healthModifier, -20, 20);
+        final var attr = player.getAttributeInstance(EntityAttributes.MAX_HEALTH);
+        if (attr == null) throw new IllegalStateException("No health attribute assigned to LifeStealer");
+        if (attr.hasModifier(HEALTH_MODIFIER)) attr.removeModifier(HEALTH_MODIFIER);
+        final var modifier = new EntityAttributeModifier(HEALTH_MODIFIER, healthModifier, EntityAttributeModifier.Operation.ADD_VALUE);
+        attr.addTemporaryModifier(modifier);
+    }
+
+    public ItemStack getHeart() {
+        final var nbt = new NbtCompound();
+        nbt.putString(PLAYER_KEY, player.getUuid().toString());
+        final var is = new ItemStack(Items.NETHER_STAR);
+        is.set(DataComponentTypes.CUSTOM_NAME, player.getName());
+        is.set(DataComponentTypes.CUSTOM_DATA, NbtComponent.of(nbt));
+        return is;
+    }
+
+    public void respawn(ServerPlayerEntity newPlayer) {
+        if (!newPlayer.getUuid().equals(uuid)) throw new IllegalArgumentException("Player does not have the same UUID");
+        this.player = newPlayer;
+        updateHealth();
+    }
+
+    public void kill() {
+        healthModifier = MathHelper.clamp(healthModifier + 2, -20, 20);
+        updateHealth();
+    }
+
+    public void killed() {
+        healthModifier = MathHelper.clamp(healthModifier - 2, -20, 20);
+        if (healthModifier <= 0) {
+            //TODO: ban player
+            return;
+        }
+        updateHealth();
+    }
+
+    public float getHealthModifier() {
+        return healthModifier;
+    }
+
+    public record Data(float healthModifier) {
+        public final static String HEALTH_MODIFIER_KEY = "health_modifier";
+        public static final Codec<Data> CODEC = RecordCodecBuilder.create(i -> i.group(
+                Codec.FLOAT.fieldOf(HEALTH_MODIFIER_KEY).forGetter(Data::healthModifier)
+        ).apply(i, Data::new));
+
+        public static Data DEFAULT = new Data(0.0F);
+    }
+
+    public static class Manager {
+        private static final Map<UUID, LifeStealer> players = new HashMap<>();
+
+        public static LifeStealer getLifeStealer(ServerPlayerEntity player) {
+            return players.computeIfAbsent(player.getUuid(), k -> new LifeStealer(player, Data.DEFAULT));
+        }
+
+        @Nullable
+        public static LifeStealer getLifeStealer(UUID uuid) {
+            return players.get(uuid);
+        }
+    }
+}