Add Folia support via reflections to support older versions.

src/main/java/eu/decentsoftware/holograms/api/DecentHolograms.java

@@ -9,6 +9,9 @@
 import eu.decentsoftware.holograms.api.listeners.WorldListener;
 import eu.decentsoftware.holograms.api.nms.NMS;
 import eu.decentsoftware.holograms.api.nms.PacketListener;
+import eu.decentsoftware.holograms.api.utils.scheduler.SchedulerAdapter;
+import eu.decentsoftware.holograms.api.utils.scheduler.adapters.BukkitSchedulerAdapter;
+import eu.decentsoftware.holograms.api.utils.scheduler.adapters.FoliaSchedulerAdapter;
 import eu.decentsoftware.holograms.api.utils.BungeeUtils;
 import eu.decentsoftware.holograms.api.utils.Common;
 import eu.decentsoftware.holograms.api.utils.DExecutor;
@@ -42,6 +45,7 @@
 public final class DecentHolograms {
 
     private final JavaPlugin plugin;
+    private final SchedulerAdapter scheduler;
     private HologramManager hologramManager;
     private CommandManager commandManager;
     private FeatureManager featureManager;
@@ -56,6 +60,7 @@ public final class DecentHolograms {
 
     DecentHolograms(@NonNull JavaPlugin plugin) {
         this.plugin = plugin;
+        this.scheduler = FoliaSchedulerAdapter.isSupported() ? new FoliaSchedulerAdapter(plugin) : new BukkitSchedulerAdapter(plugin);
     }
 
     /*

src/main/java/eu/decentsoftware/holograms/api/actions/ActionType.java

@@ -66,7 +66,7 @@ public boolean execute(Player player, String... args) {
             Validate.notNull(player);
 
             String string = String.join(" ", args);
-            Bukkit.getScheduler().runTask(DECENT_HOLOGRAMS.getPlugin(), () -> {
+            DECENT_HOLOGRAMS.getScheduler().executeAtEntity(player, () -> {
                 //
                 player.chat(PAPI.setPlaceholders(player, string.replace("{player}", player.getName())));
             });
@@ -80,7 +80,7 @@ public boolean execute(Player player, String... args) {
             Validate.notNull(player);
 
             String string = String.join(" ", args);
-            Bukkit.getScheduler().runTask(DECENT_HOLOGRAMS.getPlugin(), () -> {
+            DECENT_HOLOGRAMS.getScheduler().executeAtEntity(player, () -> {
                 //
                 Bukkit.dispatchCommand(Bukkit.getConsoleSender(), PAPI.setPlaceholders(player, string.replace("{player}", player.getName())));
             });
@@ -113,7 +113,7 @@ public boolean execute(Player player, String... args) {
             if (location == null) {
                 return false;
             }
-            Bukkit.getScheduler().runTask(DECENT_HOLOGRAMS.getPlugin(), () -> player.teleport(location));
+            DECENT_HOLOGRAMS.getScheduler().executeAtEntity(player, () -> player.teleport(location));
             return true;
         }
     };

src/main/java/eu/decentsoftware/holograms/api/holograms/Hologram.java

@@ -642,7 +642,7 @@ public boolean show(@NonNull Player player, int pageIndex) {
                 } else {
                     // We need to run the task later on older versions as, if we don't, it causes issues with some holograms *randomly* becoming invisible.
                     // I *think* this is from despawning and spawning the entities (with the same ID) in the same tick.
-                    S.sync(() -> showPageTo(player, page, pageIndex), 0L);
+                    S.sync(player, () -> showPageTo(player, page, pageIndex), 0L);
                 }
                 return true;
             }

src/main/java/eu/decentsoftware/holograms/api/utils/UpdateChecker.java

@@ -1,7 +1,7 @@
 package eu.decentsoftware.holograms.api.utils;
 
+import eu.decentsoftware.holograms.api.DecentHologramsAPI;
 import org.apache.commons.lang.Validate;
-import org.bukkit.Bukkit;
 import org.bukkit.plugin.java.JavaPlugin;
 
 import java.io.IOException;
@@ -23,7 +23,7 @@ public UpdateChecker(JavaPlugin plugin, int resourceId) {
     }
 
     public void getVersion(Consumer<String> consumer) {
-        Bukkit.getScheduler().runTaskAsynchronously(plugin, () -> {
+        DecentHologramsAPI.get().getScheduler().runAsync(() -> {
             try (InputStream inputStream = new URL("https://api.spigotmc.org/legacy/update.php?resource=" + resourceId).openStream();
                  Scanner scanner = new Scanner(inputStream)) {
                 if (scanner.hasNext() && consumer != null) {

src/main/java/eu/decentsoftware/holograms/api/utils/scheduler/S.java

@@ -3,52 +3,39 @@
 import eu.decentsoftware.holograms.api.DecentHolograms;
 import eu.decentsoftware.holograms.api.DecentHologramsAPI;
 import eu.decentsoftware.holograms.api.utils.DExecutor;
-import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
 import org.bukkit.plugin.IllegalPluginAccessException;
 import org.bukkit.scheduler.BukkitTask;
 
+import java.util.concurrent.TimeUnit;
+
 public class S {
 
     private static final DecentHolograms DECENT_HOLOGRAMS = DecentHologramsAPI.get();
 
-    public static void stopTask(int id) {
-        Bukkit.getScheduler().cancelTask(id);
-    }
-
-    public static void sync(Runnable runnable) {
-        Bukkit.getScheduler().runTask(DECENT_HOLOGRAMS.getPlugin(), runnable);
-    }
-
-    public static BukkitTask sync(Runnable runnable, long delay) {
-        return Bukkit.getScheduler().runTaskLater(DECENT_HOLOGRAMS.getPlugin(), runnable, delay);
+    public static void sync(Entity entity, Runnable runnable, long delay) {
+        DECENT_HOLOGRAMS.getScheduler().runAtEntityDelayed(entity, runnable, delay);
     }
 
-    public static BukkitTask syncTask(Runnable runnable, long interval) {
-        return Bukkit.getScheduler().runTaskTimer(DECENT_HOLOGRAMS.getPlugin(), runnable, 0, interval);
-    }
 
     public static void async(Runnable runnable) {
         try {
-            Bukkit.getScheduler().runTaskAsynchronously(DECENT_HOLOGRAMS.getPlugin(), runnable);
+            DECENT_HOLOGRAMS.getScheduler().runAsync(runnable);
         } catch (IllegalPluginAccessException e) {
             DExecutor.execute(runnable);
         }
     }
 
     public static void async(Runnable runnable, long delay) {
         try {
-            Bukkit.getScheduler().runTaskLaterAsynchronously(DECENT_HOLOGRAMS.getPlugin(), runnable, delay);
+            DECENT_HOLOGRAMS.getScheduler().runAsyncDelayed(runnable, delay * 50, TimeUnit.MILLISECONDS);
         } catch (IllegalPluginAccessException e) {
             DExecutor.execute(runnable);
         }
     }
 
-    public static BukkitTask asyncTask(Runnable runnable, long interval) {
-        return Bukkit.getScheduler().runTaskTimerAsynchronously(DECENT_HOLOGRAMS.getPlugin(), runnable, 0, interval);
-    }
-
     public static BukkitTask asyncTask(Runnable runnable, long interval, long delay) {
-        return Bukkit.getScheduler().runTaskTimerAsynchronously(DECENT_HOLOGRAMS.getPlugin(), runnable, delay, interval);
+        return DECENT_HOLOGRAMS.getScheduler().runAsyncRate(runnable, 0, interval * 50, TimeUnit.MILLISECONDS);
     }
 
 }

src/main/java/eu/decentsoftware/holograms/api/utils/scheduler/SchedulerAdapter.java

@@ -0,0 +1,70 @@
+package eu.decentsoftware.holograms.api.utils.scheduler;
+
+import org.bukkit.entity.Entity;
+import org.bukkit.scheduler.BukkitTask;
+
+import java.util.concurrent.TimeUnit;
+
+public interface SchedulerAdapter {
+
+    /**
+     * Schedules the specified task to be executed asynchronously immediately.
+     *
+     * @param runnable The task to execute.
+     */
+    void runAsync(Runnable runnable);
+
+    /**
+     * Schedules the specified task to be executed asynchronously after the time delay has passed.
+     *
+     * @param runnable The task to execute.
+     * @param delay    The time delay to pass before the task should be executed.
+     * @param unit     The time unit for the initial delay and period.
+     */
+    void runAsyncDelayed(Runnable runnable, long delay, TimeUnit unit);
+
+    /**
+     * Schedules the specified task to be executed asynchronously after the delay has passed,
+     * and then periodically executed with the specified period.
+     *
+     * @param runnable The task to execute.
+     * @param delay    The time delay to pass before the task should be executed.
+     * @param period   The time between task executions after the first execution of the task.
+     * @param unit     The time unit for the initial delay and period.
+     * @return The BukkitTask that represents the scheduled task.
+     */
+    BukkitTask runAsyncRate(Runnable runnable, long delay, long period, TimeUnit unit);
+
+    /**
+     * Schedules a task. If the task failed to schedule because the scheduler is retired (entity removed),
+     * then returns {@code false}. Otherwise, either the run callback will be invoked after the specified delay,
+     * or the retired callback will be invoked if the scheduler is retired.
+     * Note that the retired callback is invoked in critical code, so it should not attempt to remove the entity,
+     * remove other entities, load chunks, load worlds, modify ticket levels, etc.
+     *
+     * <p>
+     * It is guaranteed that the task and retired callback are invoked on the region which owns the entity.
+     * </p>
+     *
+     * @param entity   The entity relative to which the scheduler is obtained.
+     * @param runnable The task to execute.
+     */
+    void executeAtEntity(Entity entity, Runnable runnable);
+
+    /**
+     * Schedules a task with the given delay. If the task failed to schedule because the scheduler is retired (entity removed),
+     * then returns {@code false}. Otherwise, either the run callback will be invoked after the specified delay,
+     * or the retired callback will be invoked if the scheduler is retired.
+     * Note that the retired callback is invoked in critical code, so it should not attempt to remove the entity,
+     * remove other entities, load chunks, load worlds, modify ticket levels, etc.
+     *
+     * <p>
+     * It is guaranteed that the task and retired callback are invoked on the region which owns the entity.
+     * </p>
+     *
+     * @param entity   The entity relative to which the scheduler is obtained.
+     * @param runnable The task to execute.
+     * @param delay    The time delay to pass before the task should be executed, in ticks.
+     */
+    void runAtEntityDelayed(Entity entity, Runnable runnable, long delay);
+}

src/main/java/eu/decentsoftware/holograms/api/utils/scheduler/adapters/BukkitSchedulerAdapter.java

@@ -0,0 +1,42 @@
+package eu.decentsoftware.holograms.api.utils.scheduler.adapters;
+
+import eu.decentsoftware.holograms.api.utils.scheduler.SchedulerAdapter;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Entity;
+import org.bukkit.plugin.Plugin;
+import org.bukkit.scheduler.BukkitTask;
+
+import java.util.concurrent.TimeUnit;
+
+@RequiredArgsConstructor
+public class BukkitSchedulerAdapter implements SchedulerAdapter {
+
+    private @NonNull Plugin plugin;
+
+    @Override
+    public void runAsync(Runnable runnable) {
+        Bukkit.getScheduler().runTaskAsynchronously(plugin, runnable);
+    }
+
+    @Override
+    public void runAsyncDelayed(Runnable runnable, long delay, TimeUnit unit) {
+        Bukkit.getScheduler().runTaskLaterAsynchronously(plugin, runnable, unit.toMillis(delay) / 50);
+    }
+
+    @Override
+    public BukkitTask runAsyncRate(Runnable runnable, long delay, long period, TimeUnit unit) {
+        return Bukkit.getScheduler().runTaskTimerAsynchronously(plugin, runnable, unit.toMillis(delay) / 50, unit.toMillis(period) / 50);
+    }
+
+    @Override
+    public void executeAtEntity(Entity entity, Runnable runnable) {
+        Bukkit.getScheduler().runTask(plugin, runnable);
+    }
+
+    @Override
+    public void runAtEntityDelayed(Entity entity, Runnable runnable, long delay) {
+        Bukkit.getScheduler().runTaskLater(plugin, runnable, delay);
+    }
+}