rough prototype

src/main/java/me/clip/placeholderapi/PlaceholderAPI.java

@@ -65,8 +65,8 @@ public final class PlaceholderAPI {
     @NotNull
     public static String setPlaceholders(final OfflinePlayer player,
                                          @NotNull final String text) {
-        return REPLACER_PERCENT.apply(text, player,
-                PlaceholderAPIPlugin.getInstance().getLocalExpansionManager()::getExpansion);
+        final LocalExpansionManager manager = PlaceholderAPIPlugin.getInstance().getLocalExpansionManager();
+        return REPLACER_PERCENT.apply(text, player, manager::getExpansion, manager::resolvePlaceholderValue);
     }
 
     /**
@@ -124,8 +124,8 @@ public final class PlaceholderAPI {
     @NotNull
     public static String setBracketPlaceholders(final OfflinePlayer player,
                                                 @NotNull final String text) {
-        return REPLACER_BRACKET.apply(text, player,
-                PlaceholderAPIPlugin.getInstance().getLocalExpansionManager()::getExpansion);
+        final LocalExpansionManager manager = PlaceholderAPIPlugin.getInstance().getLocalExpansionManager();
+        return REPLACER_BRACKET.apply(text, player, manager::getExpansion, manager::resolvePlaceholderValue);
     }
 
     /**

src/main/java/me/clip/placeholderapi/PlaceholderHook.java

@@ -35,8 +35,40 @@ public abstract class PlaceholderHook {
         return onPlaceholderRequest(null, params);
     }
 
+    /**
+     * Override this method when a placeholder should return a non-string value for type handling.
+     * <br>The default delegates to {@link #onPlaceholderTypeHandledRequest(Player, String)} with an online
+     * {@link Player}, matching the behavior of {@link #onRequest(OfflinePlayer, String)}.
+     *
+     * @param player Player to parse the placeholder against
+     * @param params Placeholder parameters
+     * @return Object to resolve through type handlers, or null to leave the placeholder unchanged
+     */
+    @Nullable
+    public Object onTypeHandledRequest(final OfflinePlayer player, @NotNull final String params) {
+        if (player != null && player.isOnline()) {
+            return onPlaceholderTypeHandledRequest(player.getPlayer(), params);
+        }
+
+        return onPlaceholderTypeHandledRequest(null, params);
+    }
+
     @Nullable
     public String onPlaceholderRequest(final Player player, @NotNull final String params) {
         return null;
     }
+
+    /**
+     * Override this method when a player placeholder should return a non-string value for type handling.
+     * <br>The default returns null so legacy string placeholders are only resolved through
+     * {@link #onRequest(OfflinePlayer, String)}.
+     *
+     * @param player Online player to parse the placeholder against
+     * @param params Placeholder parameters
+     * @return Object to resolve through type handlers, or null to leave the placeholder unchanged
+     */
+    @Nullable
+    public Object onPlaceholderTypeHandledRequest(final Player player, @NotNull final String params) {
+        return null;
+    }
 }

src/main/java/me/clip/placeholderapi/expansion/PlaceholderContext.java

@@ -0,0 +1,33 @@
+package me.clip.placeholderapi.expansion;
+
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public final class PlaceholderContext<T> {
+    @Nullable private final Player player;
+    @NotNull private final T type;
+    @NotNull private final String args;
+
+    public PlaceholderContext(@Nullable final Player player, @NotNull final T type,
+                              @NotNull final String args) {
+        this.player = player;
+        this.type = type;
+        this.args = args;
+    }
+
+    @Nullable
+    public Player player() {
+        return player;
+    }
+
+    @NotNull
+    public T type() {
+        return type;
+    }
+
+    @NotNull
+    public String args() {
+        return args;
+    }
+}

src/main/java/me/clip/placeholderapi/expansion/PlaceholderExpansion.java

@@ -20,6 +20,7 @@
 
 package me.clip.placeholderapi.expansion;
 
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.logging.Level;
@@ -140,6 +141,10 @@ public abstract class PlaceholderExpansion extends PlaceholderHook {
                 || Bukkit.getPluginManager().getPlugin(getRequiredPlugin()) != null;
     }
 
+    public Collection<TypeHandler<?>> provideTypeHandlers() {
+        return Collections.emptyList();
+    }
+
     /**
      * Attempt to register this PlaceholderExpansion
      *

src/main/java/me/clip/placeholderapi/expansion/TypeHandler.java

@@ -0,0 +1,15 @@
+package me.clip.placeholderapi.expansion;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public interface TypeHandler<T> {
+    Class<T> typeClass();
+
+    default boolean includeDerivatives() {
+        return true;
+    }
+
+    @Nullable
+    String onRequest(@NotNull final PlaceholderContext<T> context);
+}

src/main/java/me/clip/placeholderapi/expansion/manager/LocalExpansionManager.java

@@ -44,19 +44,16 @@ import me.clip.placeholderapi.PlaceholderAPIPlugin;
 import me.clip.placeholderapi.events.ExpansionRegisterEvent;
 import me.clip.placeholderapi.events.ExpansionUnregisterEvent;
 import me.clip.placeholderapi.events.ExpansionsLoadedEvent;
-import me.clip.placeholderapi.expansion.Cacheable;
-import me.clip.placeholderapi.expansion.Cleanable;
-import me.clip.placeholderapi.expansion.Configurable;
-import me.clip.placeholderapi.expansion.PlaceholderExpansion;
-import me.clip.placeholderapi.expansion.Taskable;
-import me.clip.placeholderapi.expansion.VersionSpecific;
+import me.clip.placeholderapi.expansion.*;
 import me.clip.placeholderapi.expansion.cloud.CloudExpansion;
 import me.clip.placeholderapi.util.FileUtil;
 import me.clip.placeholderapi.util.Futures;
 import me.clip.placeholderapi.util.Msg;
 import org.bukkit.Bukkit;
+import org.bukkit.OfflinePlayer;
 import org.bukkit.command.CommandSender;
 import org.bukkit.configuration.file.FileConfiguration;
+import org.bukkit.entity.Player;
 import org.bukkit.event.EventHandler;
 import org.bukkit.event.EventPriority;
 import org.bukkit.event.HandlerList;
@@ -86,6 +83,7 @@ public final class LocalExpansionManager implements Listener {
 
     @NotNull
     private final Map<String, PlaceholderExpansion> expansions = new ConcurrentHashMap<>();
+    private final Map<Class<?>, TypeHandler> typeHandlers = new ConcurrentHashMap<>();
     private final ReentrantLock expansionsLock = new ReentrantLock();
 
 
@@ -208,6 +206,64 @@ public final class LocalExpansionManager implements Listener {
         return Optional.empty();
     }
 
+    @Nullable
+    public String resolvePlaceholderValue(@NotNull final PlaceholderExpansion expansion, @Nullable final OfflinePlayer player,
+                                          @NotNull final String args) {
+        Object value = expansion.onRequest(player, args);
+
+        if (value != null) {
+            return (String) value;
+        }
+
+        value = expansion.onTypeHandledRequest(player, args);
+
+        if (value instanceof String) {
+            return (String) value;
+        }
+
+        if (value != null) {
+            return resolveTypeHandler(value, player, args);
+        }
+
+        return null;
+    }
+
+    @Nullable
+    public String resolveTypeHandler(@NotNull final Object value, @Nullable final OfflinePlayer player,
+                                     @NotNull final String args) {
+        TypeHandler handler = null;
+
+        for (final TypeHandler<?> typeHandler : typeHandlers.values()) {
+            if (typeHandler.typeClass() == value.getClass()) {
+                handler = typeHandler;
+            }
+        }
+
+        if (handler == null) {
+            for (final TypeHandler<?> typeHandler : typeHandlers.values()) {
+                if (typeHandler.includeDerivatives() && typeHandler.typeClass().isAssignableFrom(value.getClass())) {
+                    handler = typeHandler;
+                }
+            }
+        }
+
+        if (handler == null) {
+            Msg.warn("Failed to resolve type handler for placeholder %s and type %s", args, value.getClass().getSimpleName());
+            return null;
+        }
+
+        return handler.onRequest(new PlaceholderContext<>(player(player), value, args));
+    }
+
+    @Nullable
+    private Player player(@Nullable final OfflinePlayer player) {
+        if (player == null || !player.isOnline()) {
+            return null;
+        }
+
+        return player.getPlayer();
+    }
+
     /**
      * Attempt to register a {@link PlaceholderExpansion}
      *
@@ -228,6 +284,16 @@ public final class LocalExpansionManager implements Listener {
             return false;
         }
 
+        for (final TypeHandler<?> typeHandler : expansion.provideTypeHandlers()) {
+            if (typeHandler.typeClass().isAssignableFrom(String.class)) {
+                Msg.warn("Failed to load type handler %s from expansion %s as there is already a type handler for this type.",
+                        expansion.getIdentifier(), typeHandler.typeClass().getSimpleName());
+                continue;
+            }
+
+            typeHandlers.putIfAbsent(typeHandler.typeClass(), typeHandler);
+        }
+
         if (expansion instanceof Configurable) {
             Map<String, Object> defaults = ((Configurable) expansion).getDefaults();
             String pre = "expansions." + identifier + ".";

src/main/java/me/clip/placeholderapi/replacer/CharsReplacer.java

@@ -49,13 +49,15 @@ public final class CharsReplacer implements Replacer {
      * May be {@code null} if no player context is available.
      * @param lookup A function that maps a lowercase identifier string to a registered
      * {@link PlaceholderExpansion}.
+     * @param resolver Resolves a registered {@link PlaceholderExpansion} to its replacement value.
      * @return A string with all valid placeholders replaced by their respective values.
      * Returns the original text if no placeholders are found.
      */
     @NotNull
     @Override
     public String apply(@NotNull final String text, @Nullable final OfflinePlayer player,
-                        @NotNull final Function<String, @Nullable PlaceholderExpansion> lookup) {
+                        @NotNull final Function<String, @Nullable PlaceholderExpansion> lookup,
+                        @NotNull final PlaceholderResolver resolver) {
         final char head = closure.head;
         int startPlaceholder = text.indexOf(head);
 
@@ -124,7 +126,7 @@ public final class CharsReplacer implements Replacer {
             String replacement = null;
 
             if (expansion != null) {
-                replacement = expansion.onRequest(player, parameters);
+                replacement = resolver.resolve(expansion, player, parameters);
             }
 
             if (replacement != null) {

src/main/java/me/clip/placeholderapi/replacer/Replacer.java

@@ -30,9 +30,25 @@ import org.jetbrains.annotations.Nullable;
 public interface Replacer {
 
     @NotNull
-    String apply(@NotNull final String text, @Nullable final OfflinePlayer player,
-                 @NotNull final Function<String, @Nullable PlaceholderExpansion> lookup);
+    default String apply(@NotNull final String text, @Nullable final OfflinePlayer player,
+                         @NotNull final Function<String, @Nullable PlaceholderExpansion> lookup) {
+        return apply(text, player, lookup, PlaceholderExpansion::onRequest);
+    }
 
+    @NotNull
+    String apply(@NotNull final String text, @Nullable final OfflinePlayer player,
+                 @NotNull final Function<String, @Nullable PlaceholderExpansion> lookup,
+                 @NotNull final PlaceholderResolver resolver);
+
+    @FunctionalInterface
+    interface PlaceholderResolver {
+
+        @Nullable
+        String resolve(@NotNull final PlaceholderExpansion expansion,
+                       @Nullable final OfflinePlayer player,
+                       @NotNull final String params);
+
+    }
 
     enum Closure {
         BRACKET('{', '}'),