Added CurrencyHolder interface

Introduced `CurrencyHolder` to centralize currency management logic. Applied the interface to `EconomyController`, `BankController`, and related classes to unify and enhance functionality. Deprecated older currency formatting methods in favor of `Currency` methods.

Author: NonSwag

plugin/src/main/java/net/thenextlvl/service/wrapper/service/model/WrappedAccount.java

@@ -13,18 +13,25 @@
 
 @NullMarked
 public class WrappedAccount implements Account {
+    private final EconomyController controller;
     private final @Nullable World world;
     private final Economy economy;
     private final OfflinePlayer holder;
 
-    public WrappedAccount(@Nullable World world, Economy economy, OfflinePlayer holder) {
+    public WrappedAccount(EconomyController controller, @Nullable World world, Economy economy, OfflinePlayer holder) {
+        this.controller = controller;
         this.world = world;
         this.economy = economy;
         this.holder = holder;
     }
 
     @Override
     public BigDecimal deposit(Number amount) {
+    public CurrencyHolder getController() {
+        return controller;
+    }
+
+    @Override
         var response = economy.depositPlayer(holder, world != null ? world.getName() : null, amount.doubleValue());
         return new BigDecimal(response.balance);
     }

src/main/java/net/thenextlvl/service/api/economy/Account.java

@@ -1,5 +1,6 @@
 package net.thenextlvl.service.api.economy;
 
+import net.thenextlvl.service.api.economy.currency.CurrencyHolder;
 import org.bukkit.World;
 import org.jspecify.annotations.NullMarked;
 
@@ -12,6 +13,13 @@
  */
 @NullMarked
 public interface Account extends Comparable<Account> {
+    /**
+     * Retrieves the associated {@code CurrencyHolder} for the account.
+     *
+     * @return the {@code CurrencyHolder} capable of managing currencies for the account
+     */
+    CurrencyHolder getController();
+
     /**
      * Deposits the specified amount into the account balance.
      *

src/main/java/net/thenextlvl/service/api/economy/EconomyController.java

@@ -1,6 +1,7 @@
 package net.thenextlvl.service.api.economy;
 
 import net.thenextlvl.service.api.Controller;
+import net.thenextlvl.service.api.economy.currency.CurrencyHolder;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.World;
 import org.jetbrains.annotations.Unmodifiable;
@@ -16,22 +17,7 @@
  * The AccountController interface provides methods to create, retrieve and delete accounts.
  */
 @NullMarked
-public interface EconomyController extends Controller {
-    /**
-     * Formats the specified amount as a string.
-     *
-     * @param amount the number amount to be formatted
-     * @return the formatted amount as a string
-     */
-    String format(Number amount);
-
-    /**
-     * Retrieves the number of fractional digits used for formatting currency amounts.
-     *
-     * @return the number of fractional digits used for formatting currency amounts
-     */
-    int fractionalDigits();
-
+public interface EconomyController extends Controller, CurrencyHolder {
     /**
      * Retrieves the plural form of the currency name based on the provided locale.
      *

src/main/java/net/thenextlvl/service/api/economy/bank/BankController.java

@@ -1,6 +1,7 @@
 package net.thenextlvl.service.api.economy.bank;
 
 import net.thenextlvl.service.api.Controller;
+import net.thenextlvl.service.api.economy.currency.CurrencyHolder;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.World;
 import org.jetbrains.annotations.Unmodifiable;
@@ -12,22 +13,7 @@
 import java.util.concurrent.CompletableFuture;
 
 @NullMarked
-public interface BankController extends Controller {
-    /**
-     * Formats the specified amount as a string.
-     *
-     * @param amount the number amount to be formatted
-     * @return the formatted amount as a string
-     */
-    String format(Number amount);
-
-    /**
-     * Retrieves the number of fractional digits used for formatting currency amounts.
-     *
-     * @return the number of fractional digits used for formatting currency amounts
-     */
-    int fractionalDigits();
-
+public interface BankController extends Controller, CurrencyHolder {
     /**
      * Creates a bank for the specified player with the given name.
      * <p>

src/main/java/net/thenextlvl/service/api/economy/currency/CurrencyHolder.java

@@ -0,0 +1,118 @@
+package net.thenextlvl.service.api.economy.currency;
+
+import net.kyori.adventure.text.serializer.plain.PlainTextComponentSerializer;
+import org.jetbrains.annotations.Unmodifiable;
+
+import java.util.Locale;
+import java.util.Optional;
+import java.util.Set;
+import java.util.function.Consumer;
+
+/**
+ * Represents an entity capable of handling currencies in an economy system.
+ * This interface provides methods for formatting, retrieving, creating,
+ * and deleting currencies, as well as determining support for multiple currencies.
+ */
+public interface CurrencyHolder {
+    /**
+     * Formats the specified amount as a string.
+     *
+     * @param amount the number amount to be formatted
+     * @return the formatted amount as a string
+     * @deprecated use {@link Currency#format(Number, Locale)}
+     */
+    @Deprecated(forRemoval = true, since = "2.4.0")
+    default String format(Number amount) {
+        return PlainTextComponentSerializer.plainText().serialize(getDefaultCurrency().format(amount, Locale.US));
+    }
+
+    /**
+     * Retrieves the number of fractional digits used for formatting currency amounts.
+     *
+     * @return the number of fractional digits used for formatting currency amounts
+     * @deprecated use {@link Currency#getFractionalDigits()}
+     */
+    @Deprecated(forRemoval = true, since = "2.4.0")
+    default int fractionalDigits() {
+        return getDefaultCurrency().getFractionalDigits();
+    }
+
+    /**
+     * Retrieves all currencies managed by the currency holder.
+     *
+     * @return an unmodifiable set of currencies
+     * @throws UnsupportedOperationException if {@link #hasMultiCurrencySupport()} is {@code false}
+     */
+    default @Unmodifiable Set<Currency> getCurrencies() {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+    /**
+     * Retrieves a currency by its name.
+     *
+     * @param name the name of the currency to retrieve
+     * @return an {@code Optional} containing the currency, or empty
+     * @throws UnsupportedOperationException if {@link #hasMultiCurrencySupport()} is {@code false}
+     */
+    default Optional<Currency> getCurrency(String name) {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+    /**
+     * Checks if a currency with the specified name exists.
+     *
+     * @param name the name of the currency to check for existence
+     * @return {@code true} if the currency exists, otherwise {@code false}
+     * @throws UnsupportedOperationException if {@link #hasMultiCurrencySupport()} is {@code false}
+     */
+    default boolean hasCurrency(String name) {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+    /**
+     * Creates a new currency by configuring a {@link Currency.Builder}.
+     * <p>
+     * If a currency with the same name already exists, this method returns empty.
+     *
+     * @param name    the name of the new currency
+     * @param builder a consumer to configure the {@link Currency.Builder} for currency creation
+     * @return an optional containing the created {@link Currency}, or empty
+     * @throws UnsupportedOperationException if {@link #hasMultiCurrencySupport()} is {@code false}
+     */
+    default Optional<Currency> createCurrency(String name, Consumer<Currency.Builder> builder) {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+    /**
+     * Deletes a currency with the specified name.
+     *
+     * @param name the name of the currency to delete
+     * @return {@code true} if the currency was successfully deleted, otherwise {@code false}
+     * @throws UnsupportedOperationException if {@link #hasMultiCurrencySupport()} is {@code false}
+     */
+    default boolean deleteCurrency(String name) {
+        throw new UnsupportedOperationException("Not implemented yet");
+    }
+
+    /**
+     * Retrieves the default currency for this economy controller.
+     *
+     * @return the default currency
+     */
+    Currency getDefaultCurrency();
+
+    /**
+     * Determines whether the economy controller supports multiple currencies.
+     *
+     * @return {@code true} if multi-currency is supported, otherwise {@code false}
+     * @implSpec If multiple currencies are supported, all respective methods have to be implemented.
+     * @see #createCurrency(String, Consumer)
+     * @see #deleteCurrency(String)
+     * @see #getCurrencies()
+     * @see #getCurrency(String)
+     * @see #hasCurrency(String)
+     */
+    default boolean hasMultiCurrencySupport() {
+        return false;
+    }
+}