Add helper for working with entity attributes.

Author: Darkhax

Common/src/main/java/net/darkhax/bookshelf/api/util/AttributeHelper.java

@@ -0,0 +1,113 @@
+package net.darkhax.bookshelf.api.util;
+
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.ai.attributes.Attribute;
+import net.minecraft.world.entity.ai.attributes.AttributeModifier;
+import net.minecraft.world.entity.ai.attributes.Attributes;
+import net.minecraft.world.item.ItemStack;
+
+import java.util.Collection;
+
+/**
+ * This class contains static helper functions for working with entity attributes and calculating attribute values.
+ */
+public final class AttributeHelper {
+
+    /**
+     * Calculates the attack damage attribute value for a given ItemStack.
+     *
+     * @param stack The ItemStack to calculate values for.
+     * @return The attack damage value for the ItemStack.
+     */
+    public static double getAttackDamage(ItemStack stack) {
+
+        return calculateValue(stack, Attributes.ATTACK_DAMAGE, EquipmentSlot.MAINHAND);
+    }
+
+    /**
+     * Calculates the attack speed attribute value for a given ItemStack.
+     *
+     * @param stack The ItemStack to calculate values for.
+     * @return The attack speed value for the ItemStack.
+     */
+    public static double getAttackSpeed(ItemStack stack) {
+
+        return calculateValue(stack, Attributes.ATTACK_SPEED, EquipmentSlot.MAINHAND);
+    }
+
+    /**
+     * Calculates the attack knockback attribute value for a given ItemStack.
+     *
+     * @param stack The ItemStack to calculate values for.
+     * @return The attack knockback value for the ItemStack.
+     */
+    public static double getAttackKnockback(ItemStack stack) {
+
+        return calculateValue(stack, Attributes.ATTACK_KNOCKBACK, EquipmentSlot.MAINHAND);
+    }
+
+    /**
+     * Calculates an attribute value for an ItemStack when used in a given slot.
+     *
+     * @param stack     The ItemStack to calculate values for.
+     * @param attribute The attribute to calculate.
+     * @param slot      The equipment slot to calculate for.
+     * @return The calculated attribute value.
+     */
+    public static double calculateValue(ItemStack stack, Attribute attribute, EquipmentSlot slot) {
+
+        return calculateValue(attribute, stack.getAttributeModifiers(slot).get(attribute));
+    }
+
+    /**
+     * Calculates an attribute value using a collection of attribute modifiers.
+     *
+     * @param attribute The attribute to calculate a value for.
+     * @param modifiers A collection of modifiers to process.
+     * @return The calculated attribute value.
+     */
+    public static double calculateValue(Attribute attribute, Collection<AttributeModifier> modifiers) {
+
+        return attribute.sanitizeValue(calculateValue(modifiers, attribute.getDefaultValue()));
+    }
+
+    /**
+     * Calculates an attribute value using a collection of attribute modifiers.
+     *
+     * @param modifiers A collection of modifiers to process.
+     * @param baseValue The base value to use for the calculation.
+     * @return The calculated attribute value.
+     */
+    public static double calculateValue(Collection<AttributeModifier> modifiers, double baseValue) {
+
+        double baseTotal = baseValue;
+
+        for (AttributeModifier modifier : modifiers) {
+
+            if (modifier.getOperation() == AttributeModifier.Operation.ADDITION) {
+
+                baseTotal += modifier.getAmount();
+            }
+        }
+
+        double modifiedValue = baseTotal;
+
+        for (AttributeModifier modifier : modifiers) {
+
+            if (modifier.getOperation() == AttributeModifier.Operation.MULTIPLY_BASE) {
+
+                modifiedValue += baseTotal * modifier.getAmount();
+            }
+        }
+
+        for (AttributeModifier modifier : modifiers) {
+
+            if (modifier.getOperation() == AttributeModifier.Operation.MULTIPLY_TOTAL) {
+
+                modifiedValue *= 1 + modifier.getAmount();
+            }
+        }
+
+        return modifiedValue;
+    }
+}