Add functional interfaces (#21)

* Add functional interfaces

* Update functional interfaces to reflect latest changes

---------

Co-authored-by: theEvilReaper <theEvilReaper@users.noreply.github.com>

Author: theEvilReaper

src/main/java/net/onelitefeather/guira/functional/OptionalSetupGetter.java

@@ -0,0 +1,27 @@
+package net.onelitefeather.guira.functional;
+
+import net.onelitefeather.guira.data.SetupData;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Optional;
+import java.util.UUID;
+
+/**
+ * Functional interface for getting setup data associated with a specific {@link UUID}.
+ *
+ * @author theEvilReaper
+ * @version 0.1.0
+ * @since 0.3.0
+ */
+@FunctionalInterface
+public interface OptionalSetupGetter {
+
+    /**
+     * Gets the setup data for the given {@link UUID}.
+     *
+     * @param uuid the {@link UUID} of the player
+     * @return an Optional containing the setup data if it exists, or an empty Optional if it does not
+     */
+    @NotNull Optional<@Nullable SetupData> get(@NotNull UUID uuid);
+}

src/main/java/net/onelitefeather/guira/functional/SetupDataGetter.java

@@ -0,0 +1,26 @@
+package net.onelitefeather.guira.functional;
+
+import net.onelitefeather.guira.data.SetupData;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.UUID;
+
+/**
+ * Functional interface for getting setup data associated with a specific {@link UUID}.
+ *
+ * @author theEvilReaper
+ * @version 0.1.0
+ * @since 0.3.0
+ */
+@FunctionalInterface
+public interface SetupDataGetter {
+
+    /**
+     * Retrieves the setup data for the specified {@link UUID}.
+     *
+     * @param uuid the {@link UUID} of the player
+     * @return the setup data associated with the {@link UUID}, or null if no data exists
+     */
+    @Nullable SetupData getData(@NotNull UUID uuid);
+}