Fix event

src/main/java/emu/grasscutter/Grasscutter.java

@@ -8,6 +8,7 @@ import emu.grasscutter.auth.DefaultAuthentication;
 import emu.grasscutter.command.CommandMap;
 import emu.grasscutter.command.DefaultPermissionHandler;
 import emu.grasscutter.command.PermissionHandler;
+import emu.grasscutter.game.dungeons.challenge.DungeonChallenge;
 import emu.grasscutter.game.managers.energy.EnergyManager;
 import emu.grasscutter.game.managers.stamina.StaminaManager;
 import emu.grasscutter.plugin.PluginManager;
@@ -113,6 +114,7 @@ public final class Grasscutter {
 		ResourceLoader.loadAll();
 		ScriptLoader.init();
 		EnergyManager.initialize();
+		DungeonChallenge.initialize();
 	
 		// Initialize database.
 		DatabaseManager.initialize();

src/main/java/emu/grasscutter/game/dungeons/DungeonDrop.java

@@ -0,0 +1,22 @@
+package emu.grasscutter.game.dungeons;
+
+import java.util.List;
+
+public class DungeonDrop {
+	private int dungeonId;
+	private List<DungeonDropEntry> drops;
+
+	public int getDungeonId() {
+		return dungeonId;
+	}
+	public void setDungeonId(int dungeonId) {
+		this.dungeonId = dungeonId;
+	}
+	
+	public List<DungeonDropEntry> getDrops() {
+		return drops;
+	}
+	public void setDrops(List<DungeonDropEntry> drops) {
+		this.drops = drops;
+	}
+}

src/main/java/emu/grasscutter/game/dungeons/DungeonDropEntry.java

@@ -0,0 +1,46 @@
+package emu.grasscutter.game.dungeons;
+
+import java.util.List;
+
+public class DungeonDropEntry {
+	private List<Integer> counts;
+	private List<Integer> items;
+	private List<Integer> probabilities;
+	private List<Integer> itemProbabilities;
+	private boolean mpDouble;
+
+	public List<Integer> getCounts() {
+		return counts;
+	}
+	public void setCounts(List<Integer> counts) {
+		this.counts = counts;
+	}
+	
+	public List<Integer> getItems() {
+		return items;
+	}
+	public void setItems(List<Integer> items) {
+		this.items = items;
+	}
+
+	public List<Integer> getProbabilities() {
+		return probabilities;
+	}
+	public void setProbabilities(List<Integer> probabilities) {
+		this.probabilities = probabilities;
+	}
+
+	public List<Integer> getItemProbabilities() {
+		return itemProbabilities;
+	}
+	public void setItemProbabilities(List<Integer> itemProbabilities) {
+		this.itemProbabilities = itemProbabilities;
+	}
+
+	public boolean isMpDouble() {
+		return mpDouble;
+	}
+	public void setMpDouble(boolean mpDouble) {
+		this.mpDouble = mpDouble;
+	}
+}

src/main/java/emu/grasscutter/game/dungeons/challenge/DungeonChallenge.java

@@ -1,21 +1,37 @@
 package emu.grasscutter.game.dungeons.challenge;
 
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.data.DataLoader;
 import emu.grasscutter.data.common.ItemParamData;
 import emu.grasscutter.data.excels.DungeonData;
+import emu.grasscutter.game.dungeons.DungeonDrop;
+import emu.grasscutter.game.dungeons.DungeonDropEntry;
 import emu.grasscutter.game.dungeons.challenge.trigger.ChallengeTrigger;
 import emu.grasscutter.game.inventory.GameItem;
+import emu.grasscutter.game.inventory.ItemType;
 import emu.grasscutter.game.player.Player;
 import emu.grasscutter.game.props.ActionReason;
 import emu.grasscutter.game.world.Scene;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.scripts.constants.EventType;
 import emu.grasscutter.scripts.data.SceneGroup;
 import emu.grasscutter.scripts.data.ScriptArgs;
 import emu.grasscutter.server.packet.send.PacketGadgetAutoPickDropInfoNotify;
+import emu.grasscutter.utils.Utils;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
 import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
 import it.unimi.dsi.fastutil.ints.IntSet;
 
+import java.io.InputStreamReader;
+import java.io.Reader;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import com.google.gson.reflect.TypeToken;
 
 public class DungeonChallenge extends WorldChallenge {
 
@@ -25,6 +41,24 @@ public class DungeonChallenge extends WorldChallenge {
 	private boolean stage;
 	private IntSet rewardedPlayers;
 
+	private final static Int2ObjectMap<List<DungeonDropEntry>> dungeonDropData = new Int2ObjectOpenHashMap<>();
+
+	public static void initialize() {
+		// Read the data we need for dungeon rewards drops.
+		try (Reader fileReader = new InputStreamReader(DataLoader.load("DungeonDrop.json"))) {
+			List<DungeonDrop> dungeonDropList = Grasscutter.getGsonFactory().fromJson(fileReader, TypeToken.getParameterized(Collection.class, DungeonDrop.class).getType());
+
+			for (DungeonDrop entry : dungeonDropList) {
+				dungeonDropData.put(entry.getDungeonId(), entry.getDrops());
+			}
+
+			Grasscutter.getLogger().info("Loaded {} dungeon drop data entries.", dungeonDropData.size());
+		}
+		catch (Exception ex) {
+			Grasscutter.getLogger().error("Unable to load dungeon drop data.", ex);
+		}
+	}
+
 	public DungeonChallenge(Scene scene, SceneGroup group,
 							int challengeId, int challengeIndex,
 							List<Integer> paramList,
@@ -67,8 +101,64 @@ public class DungeonChallenge extends WorldChallenge {
 		}
 	}
 	
-	public void getStatueDrops(Player player) {
+	private List<GameItem> rollRewards(boolean useCondensed) {
+		List<GameItem> rewards = new ArrayList<>();
+		int dungeonId = this.getScene().getDungeonData().getId();
+		// If we have specific drop data for this dungeon, we use it.
+		if (dungeonDropData.containsKey(dungeonId)) {
+			List<DungeonDropEntry> dropEntries = dungeonDropData.get(dungeonId);
+
+			// Roll for each drop group.
+			for (var entry : dropEntries) {
+				// Determine the number of drops we get for this entry.
+				int start = entry.getCounts().get(0);
+				int end = entry.getCounts().get(entry.getCounts().size() - 1);
+				var candidateAmounts = IntStream.range(start, end + 1).boxed().collect(Collectors.toList());
+
+				int amount = Utils.drawRandomListElement(candidateAmounts, entry.getProbabilities());
+
+				if (useCondensed) {
+					amount += Utils.drawRandomListElement(candidateAmounts, entry.getProbabilities());
+				}
+
+				// Double rewards in multiplay mode, if specified.
+				if (entry.isMpDouble() && this.getScene().getPlayerCount() > 1) {
+					amount *= 2;
+				}
+
+				// Roll items for this group.
+				// Here, we have to handle stacking, or the client will not display results correctly.
+				// For now, we use the following logic: If the possible drop item are a list of multiple items,
+				// we roll them separately. If not, we stack them. This should work out in practice, at least
+				// for the currently existing set of dungeons.
+				if (entry.getItems().size() == 1) {
+					rewards.add(new GameItem(entry.getItems().get(0), amount));
+				}
+				else {
+					for (int i = 0; i < amount; i++) {
+						// int itemIndex = ThreadLocalRandom.current().nextInt(0, entry.getItems().size());
+						// int itemId = entry.getItems().get(itemIndex);
+						int itemId = Utils.drawRandomListElement(entry.getItems(), entry.getItemProbabilities());
+						rewards.add(new GameItem(itemId, 1));
+					}
+				}
+			}
+		}
+		// Otherwise, we fall back to the preview data.
+		else {
+			Grasscutter.getLogger().info("No drop data found or dungeon {}, falling back to preview data ...", dungeonId);
+			for (ItemParamData param : getScene().getDungeonData().getRewardPreview().getPreviewItems()) {
+				rewards.add(new GameItem(param.getId(), Math.max(param.getCount(), 1)));
+			}
+		}	
+
+		return rewards;
+	}
+
+	public void getStatueDrops(Player player, GadgetInteractReq request) {
 		DungeonData dungeonData = getScene().getDungeonData();
+		int resinCost = dungeonData.getStatueCostCount() != 0 ? dungeonData.getStatueCostCount() : 20;
+
 		if (!isSuccess() || dungeonData == null || dungeonData.getRewardPreview() == null || dungeonData.getRewardPreview().getPreviewItems().length == 0) {
 			return;
 		}
@@ -78,11 +168,42 @@ public class DungeonChallenge extends WorldChallenge {
 			return;
 		}
 		
+		// Get rewards.
 		List<GameItem> rewards = new ArrayList<>();
-		for (ItemParamData param : getScene().getDungeonData().getRewardPreview().getPreviewItems()) {
-			rewards.add(new GameItem(param.getId(), Math.max(param.getCount(), 1)));
+
+		if (request.getIsUseCondenseResin()) {
+			// Check if condensed resin is usable here.
+			// For this, we use the following logic for now:
+			// The normal resin cost of the dungeon has to be 20.
+			if (resinCost != 20) {
+				return;
 			}
 
+			// Make sure the player has condensed resin.
+			GameItem condensedResin = player.getInventory().getInventoryTab(ItemType.ITEM_MATERIAL).getItemById(220007);
+			if (condensedResin == null || condensedResin.getCount() <= 0) {
+				return;
+			}
+
+			// Deduct.
+			player.getInventory().removeItem(condensedResin, 1);
+
+			// Roll rewards.
+			rewards.addAll(this.rollRewards(true));
+		}
+		else {
+			// If the player used regular resin, try to deduct.
+			// Stop if insufficient resin.
+			boolean success = player.getResinManager().useResin(resinCost);
+			if (!success) {
+				return;
+			}
+
+			// Roll rewards.
+			rewards.addAll(this.rollRewards(false));
+		}
+		
+		// Add rewards to player and send notification.
 		player.getInventory().addItems(rewards, ActionReason.DungeonStatueDrop);
 		player.sendPacket(new PacketGadgetAutoPickDropInfoNotify(rewards));
 		

src/main/java/emu/grasscutter/game/entity/gadget/GadgetChest.java

@@ -4,7 +4,7 @@ import emu.grasscutter.Grasscutter;
 import emu.grasscutter.game.entity.EntityGadget;
 import emu.grasscutter.game.player.Player;
 import emu.grasscutter.net.proto.BossChestInfoOuterClass.BossChestInfo;
-import emu.grasscutter.net.proto.InterOpTypeOuterClass;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.net.proto.InterOpTypeOuterClass.InterOpType;
 import emu.grasscutter.net.proto.InteractTypeOuterClass;
 import emu.grasscutter.net.proto.InteractTypeOuterClass.InteractType;
@@ -18,7 +18,7 @@ public class GadgetChest extends GadgetContent {
 		super(gadget);
 	}
 
-	public boolean onInteract(Player player, InterOpType opType) {
+	public boolean onInteract(Player player, GadgetInteractReq req) {
 		var chestInteractHandlerMap = getGadget().getScene().getWorld().getServer().getWorldDataManager().getChestInteractHandlerMap();
 		var handler = chestInteractHandlerMap.get(getGadget().getGadgetData().getJsonName());
 		if(handler == null){
@@ -26,7 +26,7 @@ public class GadgetChest extends GadgetContent {
 			return false;
 		}
 
-		if(opType == InterOpType.INTER_OP_TYPE_START && handler.isTwoStep()){
+		if(req.getOpType() == InterOpType.INTER_OP_TYPE_START && handler.isTwoStep()){
 			player.sendPacket(new PacketGadgetInteractRsp(getGadget(), InteractType.INTERACT_TYPE_OPEN_CHEST, InterOpType.INTER_OP_TYPE_START));
 			return false;
 		}else{

src/main/java/emu/grasscutter/game/entity/gadget/GadgetContent.java

@@ -3,6 +3,7 @@ package emu.grasscutter.game.entity.gadget;
 import emu.grasscutter.game.entity.EntityGadget;
 import emu.grasscutter.game.player.Player;
 import emu.grasscutter.net.proto.InterOpTypeOuterClass;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.net.proto.SceneGadgetInfoOuterClass.SceneGadgetInfo;
 
 public abstract class GadgetContent {
@@ -16,7 +17,7 @@ public abstract class GadgetContent {
 		return gadget;
 	}
 	
-	public abstract boolean onInteract(Player player, InterOpTypeOuterClass.InterOpType opType);
+	public abstract boolean onInteract(Player player, GadgetInteractReq req);
 	
 	public abstract void onBuildProto(SceneGadgetInfo.Builder gadgetInfo);
 }

src/main/java/emu/grasscutter/game/entity/gadget/GadgetGatherPoint.java

@@ -7,7 +7,7 @@ import emu.grasscutter.game.inventory.GameItem;
 import emu.grasscutter.game.player.Player;
 import emu.grasscutter.game.props.ActionReason;
 import emu.grasscutter.net.proto.GatherGadgetInfoOuterClass.GatherGadgetInfo;
-import emu.grasscutter.net.proto.InterOpTypeOuterClass;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.net.proto.SceneGadgetInfoOuterClass.SceneGadgetInfo;
 
 public class GadgetGatherPoint extends GadgetContent {
@@ -26,7 +26,7 @@ public class GadgetGatherPoint extends GadgetContent {
 		return getGatherData().getItemId();
 	}
 
-	public boolean onInteract(Player player, InterOpTypeOuterClass.InterOpType opType) {
+	public boolean onInteract(Player player, GadgetInteractReq req) {
 		GameItem item = new GameItem(gatherData.getItemId(), 1);
 		
 		player.getInventory().addItem(item, ActionReason.Gather);

src/main/java/emu/grasscutter/game/entity/gadget/GadgetRewardStatue.java

@@ -3,7 +3,7 @@ package emu.grasscutter.game.entity.gadget;
 import emu.grasscutter.game.dungeons.challenge.DungeonChallenge;
 import emu.grasscutter.game.entity.EntityGadget;
 import emu.grasscutter.game.player.Player;
-import emu.grasscutter.net.proto.InterOpTypeOuterClass;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.net.proto.InteractTypeOuterClass.InteractType;
 import emu.grasscutter.net.proto.SceneGadgetInfoOuterClass.SceneGadgetInfo;
 import emu.grasscutter.server.packet.send.PacketGadgetInteractRsp;
@@ -14,9 +14,9 @@ public class GadgetRewardStatue extends GadgetContent {
 		super(gadget);
 	}
 
-	public boolean onInteract(Player player, InterOpTypeOuterClass.InterOpType opType) {
+	public boolean onInteract(Player player, GadgetInteractReq req) {
 		if (player.getScene().getChallenge() != null && player.getScene().getChallenge() instanceof DungeonChallenge dungeonChallenge) {
-			dungeonChallenge.getStatueDrops(player);
+			dungeonChallenge.getStatueDrops(player, req);
 		}
 		
 		player.sendPacket(new PacketGadgetInteractRsp(getGadget(), InteractType.INTERACT_TYPE_OPEN_STATUE));

src/main/java/emu/grasscutter/game/entity/gadget/GadgetWorktop.java

@@ -4,7 +4,7 @@ import java.util.Arrays;
 
 import emu.grasscutter.game.entity.EntityGadget;
 import emu.grasscutter.game.player.Player;
-import emu.grasscutter.net.proto.InterOpTypeOuterClass;
+import emu.grasscutter.net.proto.GadgetInteractReqOuterClass.GadgetInteractReq;
 import emu.grasscutter.net.proto.SceneGadgetInfoOuterClass.SceneGadgetInfo;
 import emu.grasscutter.net.proto.WorktopInfoOuterClass.WorktopInfo;
 import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
@@ -35,7 +35,7 @@ public class GadgetWorktop extends GadgetContent {
 		this.worktopOptions.remove(option);
 	}
 
-	public boolean onInteract(Player player, InterOpTypeOuterClass.InterOpType opType) {
+	public boolean onInteract(Player player, GadgetInteractReq req) {
 		return false;
 	}
 

src/main/java/emu/grasscutter/game/player/Player.java

@@ -990,7 +990,7 @@ public class Player {
 	}
 	
 
-	public void interactWith(int gadgetEntityId, InterOpTypeOuterClass.InterOpType opType) {
+	public void interactWith(int gadgetEntityId, GadgetInteractReq req) {
 		GameEntity entity = getScene().getEntityById(gadgetEntityId);
 		if (entity == null) {
 			return;
@@ -1023,7 +1023,7 @@ public class Player {
 				return;
 			}
 			
-			boolean shouldDelete = gadget.getContent().onInteract(this, opType);
+			boolean shouldDelete = gadget.getContent().onInteract(this, req);
 			
 			if (shouldDelete) {
 				entity.getScene().removeEntity(entity);

src/main/java/emu/grasscutter/server/event/game/ServerTickEvent.java

@@ -1,9 +1,23 @@
 package emu.grasscutter.server.event.game;
 
 import emu.grasscutter.server.event.types.ServerEvent;
+import java.time.Instant;
 
 public final class ServerTickEvent extends ServerEvent {
-    public ServerTickEvent() {
+    private final Instant start, end;
+
+    public ServerTickEvent(Instant start, Instant end) {
         super(Type.GAME);
+
+        this.start = start;
+        this.end = end;
+    }
+
+    public Instant getTickStart() {
+        return this.start;
+    }
+
+    public Instant getTickEnd() {
+        return this.end;
     }
 }

src/main/java/emu/grasscutter/server/game/GameServer.java

@@ -26,11 +26,14 @@ import emu.grasscutter.server.event.types.ServerEvent;
 import emu.grasscutter.server.event.game.ServerTickEvent;
 import emu.grasscutter.server.event.internal.ServerStartEvent;
 import emu.grasscutter.server.event.internal.ServerStopEvent;
+import emu.grasscutter.server.scheduler.ServerTaskScheduler;
 import emu.grasscutter.task.TaskMap;
 import kcp.highway.ChannelConfig;
 import kcp.highway.KcpServer;
+import lombok.Getter;
 
 import java.net.InetSocketAddress;
+import java.time.Instant;
 import java.time.OffsetDateTime;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
@@ -42,6 +45,7 @@ public final class GameServer extends KcpServer {
 	private final InetSocketAddress address;
 	private final GameServerPacketHandler packetHandler;
 	private final ServerQuestHandler questHandler;
+    @Getter private final ServerTaskScheduler scheduler;
 
 	private final Map<Integer, Player> players;
 	private final Set<World> worlds;
@@ -80,6 +84,7 @@ public final class GameServer extends KcpServer {
 		this.address = address;
 		this.packetHandler = new GameServerPacketHandler(PacketHandler.class);
 		this.questHandler = new ServerQuestHandler();
+        this.scheduler = new ServerTaskScheduler();
 		this.players = new ConcurrentHashMap<>();
 		this.worlds = Collections.synchronizedSet(new HashSet<>());
 
@@ -238,7 +243,10 @@ public final class GameServer extends KcpServer {
 		return DatabaseHelper.getAccountByName(username);
 	}
 
-	public synchronized void onTick(){
+    public synchronized void onTick() {
+        var tickStart = Instant.now();
+
+        // Tick worlds.
         Iterator<World> it = this.getWorlds().iterator();
         while (it.hasNext()) {
             World world = it.next();
@@ -250,11 +258,17 @@ public final class GameServer extends KcpServer {
             world.onTick();
         }
 
+        // Tick players.
         for (Player player : this.getPlayers().values()) {
             player.onTick();
         }
 
-		ServerTickEvent event = new ServerTickEvent(); event.call();
+        // Tick scheduler.
+        this.getScheduler().runTasks();
+
+        // Call server tick event.
+        ServerTickEvent event = new ServerTickEvent(tickStart, Instant.now());
+        event.call();
     }
 
 	public void registerWorld(World world) {

src/main/java/emu/grasscutter/server/packet/recv/HandlerGadgetInteractReq.java

@@ -13,7 +13,7 @@ public class HandlerGadgetInteractReq extends PacketHandler {
 	public void handle(GameSession session, byte[] header, byte[] payload) throws Exception {
 		GadgetInteractReq req = GadgetInteractReq.parseFrom(payload);
 		
-		session.getPlayer().interactWith(req.getGadgetEntityId(), req.getOpType());
+		session.getPlayer().interactWith(req.getGadgetEntityId(), req);
 	}
 
 }

src/main/java/emu/grasscutter/server/scheduler/AsyncServerTask.java

@@ -0,0 +1,98 @@
+package emu.grasscutter.server.scheduler;
+
+import lombok.Getter;
+
+import javax.annotation.Nullable;
+
+/**
+ * A server task that should be run asynchronously.
+ */
+public final class AsyncServerTask implements Runnable {
+    /* The runnable to run. */
+    private final Runnable task;
+    /* This ID is assigned by the scheduler. */
+    @Getter private final int taskId;
+    /* The result callback to run. */
+    @Nullable private final Runnable callback;
+
+    /* Has the task already been started? */
+    private boolean started = false;
+    /* Has the task finished execution? */
+    private boolean finished = false;
+    /* The result produced in the async task. */
+    @Nullable private Object result = null;
+
+    /**
+     * For tasks without a callback.
+     * @param task The task to run.
+     */
+    public AsyncServerTask(Runnable task, int taskId) {
+        this(task, null, taskId);
+    }
+
+    /**
+     * For tasks with a callback.
+     * @param task The task to run.
+     * @param callback The task to run after the task is complete.
+     */
+    public AsyncServerTask(Runnable task, @Nullable Runnable callback, int taskId) {
+        this.task = task;
+        this.callback = callback;
+        this.taskId = taskId;
+    }
+
+    /**
+     * Returns the state of the task.
+     * @return True if the task has been started, false otherwise.
+     */
+    public boolean hasStarted() {
+        return this.started;
+    }
+
+    /**
+     * Returns the state of the task.
+     * @return True if the task has finished execution, false otherwise.
+     */
+    public boolean isFinished() {
+        return this.finished;
+    }
+
+    /**
+     * Runs the task.
+     */
+    @Override public void run() {
+        // Declare the task as started.
+        this.started = true;
+
+        // Run the runnable.
+        this.task.run();
+
+        // Declare the task as finished.
+        this.finished = true;
+    }
+
+    /**
+     * Runs the callback.
+     */
+    public void complete() {
+        // Run the callback.
+        if(this.callback != null)
+            this.callback.run();
+    }
+
+    /**
+     * Sets the result of the async task.
+     * @param result The result of the async task.
+     */
+    public void setResult(@Nullable Object result) {
+        this.result = result;
+    }
+
+    /**
+     * Returns the set result of the async task.
+     * @return The result, or null if it has not been set.
+     */
+    @Nullable public Object getResult() {
+        return this.result;
+    }
+}

src/main/java/emu/grasscutter/server/scheduler/ServerTask.java

@@ -0,0 +1,67 @@
+package emu.grasscutter.server.scheduler;
+
+import emu.grasscutter.Grasscutter;
+import lombok.*;
+
+/**
+ * This class works the same as a runnable, except with more information.
+ */
+public final class ServerTask implements Runnable {
+    /* The runnable to run. */
+    private final Runnable runnable;
+    /* This ID is assigned by the scheduler. */
+    @Getter private final int taskId;
+    /* The period at which the task should be run. */
+    /* The delay between the first execute. */
+    private final int period, delay;
+
+    public ServerTask(Runnable runnable, int taskId, int period, int delay) {
+        this.runnable = runnable;
+        this.taskId = taskId;
+        this.period = period;
+        this.delay = delay;
+    }
+
+    /* The amount of times the task has been run. */
+    @Getter private int ticks = 0;
+    /* Should the check consider delay? */
+    private boolean considerDelay = true;
+
+    /**
+     * Cancels the task from running the next time.
+     */
+    public void cancel() {
+        Grasscutter.getGameServer().getScheduler().cancelTask(this.taskId);
+    }
+
+    /**
+     * Checks if the task should run at the current tick.
+     * @return True if the task should run, false otherwise.
+     */
+    public boolean shouldRun() {
+        if(this.delay != -1 && this.considerDelay) {
+            this.considerDelay = false;
+            return this.ticks == this.delay;
+        } else if(this.period != -1)
+            return this.ticks % this.period == 0;
+        else return true;
+    }
+
+    /**
+     * Checks if the task should be canceled.
+     * @return True if the task should be canceled, false otherwise.
+     */
+    public boolean shouldCancel() {
+        return this.period == -1;
+    }
+
+    /**
+     * Runs the task.
+     */
+    @Override public void run() {
+        // Run the runnable.
+        this.runnable.run();
+        // Increase tick count.
+        this.ticks++;
+    }
+}

src/main/java/emu/grasscutter/server/scheduler/ServerTaskScheduler.java

@@ -0,0 +1,148 @@
+package emu.grasscutter.server.scheduler;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A class to manage all time-based tasks scheduled on the server.
+ * This handles both synchronous and asynchronous tasks.
+ *
+ * Developers note: A server tick is ONE REAL-TIME SECOND.
+ */
+public final class ServerTaskScheduler {
+    /* A map to contain all running tasks. */
+    private final ConcurrentHashMap<Integer, ServerTask> tasks
+        = new ConcurrentHashMap<>();
+    /* A map to contain all async tasks. */
+    private final ConcurrentHashMap<Integer, AsyncServerTask> asyncTasks
+        = new ConcurrentHashMap<>();
+
+    /* The ID assigned to the next runnable. */
+    private int nextTaskId = 0;
+
+    /**
+     * Ran every server tick.
+     * Attempts to run all scheduled tasks.
+     * This method is synchronous and will block until all tasks are complete.
+     */
+    public void runTasks() {
+        // Skip if there are no tasks.
+        if(this.tasks.size() == 0)
+            return;
+
+        // Run all tasks.
+        for(ServerTask task : this.tasks.values()) {
+            // Check if the task should run.
+            if (task.shouldRun()) {
+                // Run the task.
+                task.run();
+            }
+
+            // Check if the task should be canceled.
+            if (task.shouldCancel()) {
+                // Cancel the task.
+                this.cancelTask(task.getTaskId());
+            }
+        }
+
+        // Run all async tasks.
+        for(AsyncServerTask task : this.asyncTasks.values()) {
+            if(!task.hasStarted()) {
+                // Create a thread for the task.
+                Thread thread = new Thread(task);
+                // Start the thread.
+                thread.start();
+            } else if(task.isFinished()) {
+                // Cancel the task.
+                this.asyncTasks.remove(task.getTaskId());
+                // Run the task's callback.
+                task.complete();
+            }
+        }
+    }
+
+    /**
+     * Gets a task from the scheduler.
+     * @param taskId The ID of the task to get.
+     * @return The task, or null if it does not exist.
+     */
+    public ServerTask getTask(int taskId) {
+        return this.tasks.get(taskId);
+    }
+
+    /**
+     * Gets an async task from the scheduler.
+     * @param taskId The ID of the task to get.
+     * @return The task, or null if it does not exist.
+     */
+    public AsyncServerTask getAsyncTask(int taskId) {
+        return this.asyncTasks.get(taskId);
+    }
+
+    /**
+     * Removes a task from the scheduler.
+     * @param taskId The ID of the task to remove.
+     */
+    public void cancelTask(int taskId) {
+        this.tasks.remove(taskId);
+    }
+
+    /**
+     * Schedules a task to be run on a separate thread.
+     * The task runs on the next server tick.
+     * @param runnable The runnable to run.
+     * @return The ID of the task.
+     */
+    public int scheduleAsyncTask(Runnable runnable) {
+        // Get the next task ID.
+        var taskId = this.nextTaskId++;
+        // Create a new task.
+        this.asyncTasks.put(taskId, new AsyncServerTask(runnable, taskId));
+        // Return the task ID.
+        return taskId;
+    }
+
+    /**
+     * Schedules a task to be run on the next server tick.
+     * @param runnable The runnable to run.
+     * @return The ID of the task.
+     */
+    public int scheduleTask(Runnable runnable) {
+        return this.scheduleDelayedRepeatingTask(runnable, -1, -1);
+    }
+
+    /**
+     * Schedules a task to be run after the amount of ticks has passed.
+     * @param runnable The runnable to run.
+     * @param delay The amount of ticks to wait before running.
+     * @return The ID of the task.
+     */
+    public int scheduleDelayedTask(Runnable runnable, int delay) {
+        return this.scheduleDelayedRepeatingTask(runnable, -1, delay);
+    }
+
+    /**
+     * Schedules a task to be run every amount of ticks.
+     * @param runnable The runnable to run.
+     * @param period The amount of ticks to wait before running again.
+     * @return The ID of the task.
+     */
+    public int scheduleRepeatingTask(Runnable runnable, int period) {
+        return this.scheduleDelayedRepeatingTask(runnable, period, 0);
+    }
+
+    /**
+     * Schedules a task to be run after the amount of ticks has passed.
+     * @param runnable The runnable to run.
+     * @param period The amount of ticks to wait before running again.
+     * @param delay The amount of ticks to wait before running the first time.
+     * @return The ID of the task.
+     */
+    public int scheduleDelayedRepeatingTask(Runnable runnable, int period, int delay) {
+        // Get the next task ID.
+        var taskId = this.nextTaskId++;
+        // Create a new task.
+        this.tasks.put(taskId, new ServerTask(runnable, taskId, period, delay));
+        // Return the task ID.
+        return taskId;
+    }
+}

src/main/java/emu/grasscutter/utils/Utils.java

@@ -7,6 +7,7 @@ import java.nio.file.StandardCopyOption;
 import java.time.*;
 import java.time.temporal.TemporalAdjusters;
 import java.util.*;
+import java.util.concurrent.ThreadLocalRandom;
 
 import emu.grasscutter.Grasscutter;
 import emu.grasscutter.data.DataLoader;
@@ -377,4 +378,35 @@ public final class Utils {
 			return null;
 		}
 	}
+
+	/***
+	 * Draws a random element from the given list, following the given probability distribution, if given.
+	 * @param list The list from which to draw the element.
+	 * @param probabilities The probability distribution. This is given as a list of probabilities of the same length it `list`.
+	 * @return A randomly drawn element from the given list.
+	 */
+	public static <T> T drawRandomListElement(List<T> list, List<Integer> probabilities) {
+		// If we don't have a probability distribution, or the size of the distribution does not match
+		// the size of the list, we assume uniform distribution.
+		if (probabilities == null || probabilities.size() <= 1 || probabilities.size() != list.size()) {
+			int index = ThreadLocalRandom.current().nextInt(0, list.size());
+			return list.get(index);
+		}
+
+		// Otherwise, we roll with the given distribution.
+		int totalProbabilityMass = probabilities.stream().reduce(Integer::sum).get();
+		int roll = ThreadLocalRandom.current().nextInt(1, totalProbabilityMass + 1);
+
+		int currentTotalChance = 0;
+		for (int i = 0; i < list.size(); i++) {
+			currentTotalChance += probabilities.get(i);
+
+			if (roll <= currentTotalChance) {
+				return list.get(i);
+			}
+		}
+
+		// Should never happen.
+		return list.get(0);
+	}
 }