Implement /magnet command

src/dev/w1zzrd/invtweaks/InvTweaksPlugin.java

@@ -1,5 +1,6 @@
 package dev.w1zzrd.invtweaks;
 
+import dev.w1zzrd.invtweaks.command.MagnetCommandExecutor;
 import dev.w1zzrd.invtweaks.command.SortCommandExecutor;
 import dev.w1zzrd.invtweaks.listener.SortListener;
 import dev.w1zzrd.invtweaks.listener.StackReplaceListener;
@@ -21,8 +22,16 @@ public final class InvTweaksPlugin extends JavaPlugin {
      */
     public static final String LOG_PLUGIN_NAME = "[InventoryTweaks]";
 
+    // TODO: Magic values: make a config
+    private static final double MAGNET_DISTANCE = 8.0;
+    private static final long MAGNET_INTERVAL = 5;
+    private static final int MAGNET_SUBDIVIDE = 2;
+
     private final Logger logger = Bukkit.getLogger();
 
+    // Command executor references in case I need them or something idk
+    private SortCommandExecutor sortCommandExecutor;
+    private MagnetCommandExecutor magnetCommandExecutor;
 
     @Override
     public void onEnable() {
@@ -36,8 +45,8 @@ public final class InvTweaksPlugin extends JavaPlugin {
     public void onDisable() {
         logger.fine(LOG_PLUGIN_NAME + " Plugin disabled");
 
-        // Un-register all listeners
-        HandlerList.unregisterAll(this);
+        disableEvents();
+        disableCommands();
     }
 
 
@@ -45,7 +54,12 @@ public final class InvTweaksPlugin extends JavaPlugin {
      * Initialize commands registered by this plugin
      */
     private void initCommands() {
-        Objects.requireNonNull(getCommand("sort")).setExecutor(new SortCommandExecutor());
+        sortCommandExecutor = new SortCommandExecutor();
+        magnetCommandExecutor = new MagnetCommandExecutor(this, MAGNET_DISTANCE, MAGNET_INTERVAL, MAGNET_SUBDIVIDE);
+
+        // TODO: Bind command by annotation
+        Objects.requireNonNull(getCommand("sort")).setExecutor(sortCommandExecutor);
+        Objects.requireNonNull(getCommand("magnet")).setExecutor(magnetCommandExecutor);
     }
 
     /**
@@ -54,7 +68,24 @@ public final class InvTweaksPlugin extends JavaPlugin {
     private void initEvents() {
         final PluginManager pluginManager = getServer().getPluginManager();
 
+        // TODO: Register listeners by annotation
         pluginManager.registerEvents(new StackReplaceListener(), this);
         pluginManager.registerEvents(new SortListener(), this);
     }
+
+    /**
+     * Do whatever is necessary to disable commands and their execution
+     */
+    private void disableCommands() {
+        sortCommandExecutor = null;
+        magnetCommandExecutor = null;
+    }
+
+    /**
+     * Do whatever is necessary to disable event listeners
+     */
+    private void disableEvents() {
+        // Un-register all listeners
+        HandlerList.unregisterAll(this);
+    }
 }

src/dev/w1zzrd/invtweaks/command/MagnetCommandExecutor.java

@@ -0,0 +1,229 @@
+package dev.w1zzrd.invtweaks.command;
+
+import org.bukkit.Bukkit;
+import org.bukkit.Location;
+import org.bukkit.World;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandExecutor;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Item;
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.Plugin;
+import org.bukkit.scheduler.BukkitTask;
+
+import java.util.*;
+
+public class MagnetCommandExecutor implements CommandExecutor {
+
+    /**
+     * List of players with magnet mode active
+     */
+    private final List<UUID> activeMagnets = new ArrayList<>();
+    private final List<UUID> activeMagnetsView = Collections.unmodifiableList(activeMagnets);
+
+    private final Plugin plugin;
+    private final long interval;
+    private final int subdivide;
+
+    private final double sqRadius;
+
+
+    private int divIndex = 0;
+
+    private BukkitTask refreshTask = null;
+
+    /**
+     * Initialize the magnet executor and manger
+     * @param plugin Owner plugin for this executor
+     * @param sqRadius Radius of the cube to search for items in (half side length)
+     * @param interval Interval (in ticks) between magnetism checks for active magnets
+     * @param subdivide What fraction of the list of active magnets should be iterated over during a magnetism check.
+     *                  Set to 1 to check the whole list each iteration
+     */
+    public MagnetCommandExecutor(final Plugin plugin, final double sqRadius, final long interval, final int subdivide) {
+        this.plugin = plugin;
+        this.sqRadius = sqRadius;
+        this.interval = interval;
+        this.subdivide = subdivide;
+    }
+
+
+    @Override
+    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
+        if (!(sender instanceof Player))
+            return false;
+
+        toggleMagnet((Player) sender);
+
+        return true;
+    }
+
+    /**
+     * Toggle magnet state for the given player
+     * @param player Player to toggle state for
+     * @return True if, after this method call, the UUID is part of the list of active magnets, else false.
+     */
+    public boolean toggleMagnet(final Player player) {
+        return toggleMagnet(player.getUniqueId());
+    }
+
+    /**
+     * Toggle magnet state for the given UUID
+     * @param uuid UUID to toggle state for
+     * @return True if, after this method call, the UUID is part of the list of active magnets, else false.
+     */
+    public boolean toggleMagnet(final UUID uuid) {
+        try {
+            final int index = Collections.binarySearch(activeMagnets, uuid);
+
+            // See JavaDoc: Collections.binarySearch
+            if (index < 0) {
+                activeMagnets.add(-(index + 1), uuid);
+                return true;
+            } else {
+                activeMagnets.remove(index);
+                return false;
+            }
+        } finally {
+            updateMagnetismTask();
+        }
+    }
+
+
+    /**
+     * Get an list of the currently active magnets
+     * @return Unmodifiable list view of the active magnets
+     */
+    public List<UUID> getActiveMagnets() {
+        return activeMagnetsView;
+    }
+
+    /**
+     * Remove a player from the list of active magnets
+     * @param player Player to remove from active magnets
+     * @return True if a call to this method changed the list of active magnets
+     */
+    public boolean removeMagnet(final Player player) {
+        return removeMagnet(player.getUniqueId());
+    }
+
+    /**
+     * Remove a UUID from the list of active magnets
+     * @param uuid UUID to remove from active magnets
+     * @return True if a call to this method changed the list of active magnets
+     */
+    public boolean removeMagnet(final UUID uuid) {
+        try {
+            final int index = Collections.binarySearch(activeMagnets, uuid);
+            if (index < 0)
+                return false;
+
+            activeMagnets.remove(index);
+            return true;
+        } finally {
+            updateMagnetismTask();
+        }
+    }
+
+    /**
+     * Add a player to the list of active magnets
+     * @param player Player to mark as a magnet
+     * @return True if a call to this method changed the list of active magnets
+     */
+    public boolean addMagnet(final Player player) {
+        return addMagnet(player.getUniqueId());
+    }
+
+    /**
+     * Add a UUID to the list of active magnets
+     * @param uuid UUID to mark as a magnet
+     * @return True if a call to this method changed the list of active magnets
+     */
+    public boolean addMagnet(final UUID uuid) {
+        try {
+            final int index = Collections.binarySearch(activeMagnets, uuid);
+
+            if (index < 0) {
+                activeMagnets.add(-(index + 1), uuid);
+                return true;
+            }
+
+            return false;
+        } finally {
+            updateMagnetismTask();
+        }
+    }
+
+    /**
+     * Check if a given player is a magnet
+     * @param player Player to check magnet state for
+     * @return True if the given player is marked as a magnet
+     */
+    public boolean isMagnet(final Player player) {
+        return isMagnet(player.getUniqueId());
+    }
+
+    /**
+     * Check if a given UUID is registered as a magnet
+     * @param uuid UUID of a player to check
+     * @return True if the given UUID is marked as a magnet
+     */
+    public boolean isMagnet(final UUID uuid) {
+        return Collections.binarySearch(activeMagnets, uuid) >= 0;
+    }
+
+    /**
+     * Check if a magnet refresh task needs to be registered for magnet players<br><br>
+     *
+     * A refresh is created if there are active magnet players, there it no active refresh task and the plugin is
+     * enabled. The refresh task is cancelled and state reset if there are no active magnet players, or the plugin is
+     * disabled.
+     */
+    private void updateMagnetismTask() {
+        if (refreshTask == null && activeMagnets.size() > 0 && plugin.isEnabled())
+            refreshTask = Bukkit.getScheduler().runTaskTimer(plugin, this::taskApplyMagnetism, 0, interval);
+        else if (refreshTask != null && (activeMagnets.size() == 0 || !plugin.isEnabled())) {
+            Bukkit.getScheduler().cancelTask(refreshTask.getTaskId());
+            refreshTask = null;
+            activeMagnets.clear();
+            divIndex = 0;
+        }
+    }
+
+    /**
+     * Task for teleporting items to magnet players
+     *
+     * @see MagnetCommandExecutor#updateMagnetismTask()
+     */
+    private void taskApplyMagnetism() {
+        final int size = activeMagnets.size();
+
+        final List<UUID> toRemove = new ArrayList<>();
+
+        // Iterate over a subdivision of the active magnets
+        for (int index = divIndex; index < size; index += subdivide) {
+            final UUID uuid = activeMagnets.get(index);
+            final Player player = Bukkit.getPlayer(uuid);
+
+            // If the given magnet has logged out, remove the player after the loop
+            if (player == null) toRemove.add(uuid);
+            else {
+                final Location playerLocation = player.getLocation();
+
+                // Get all items near the player that can don't have a pickup delay and teleport them to the player
+                player.getWorld()
+                        .getNearbyEntities(playerLocation, sqRadius, sqRadius, sqRadius)
+                        .stream()
+                        .filter(it -> it instanceof Item)
+                        .filter(it -> ((Item) it).getPickupDelay() <= 0)
+                        .forEach(it -> it.teleport(playerLocation));
+            }
+        }
+
+        // Remove logged-out players
+        toRemove.forEach(this::removeMagnet);
+
+        // Update subdivision to check next iteration
+        divIndex = (divIndex + 1) % subdivide;
+    }
+}

src/plugin.yml

@@ -7,4 +7,8 @@ commands:
   sort:
     description: Sort chest you are looking at
     usage: /<command>
-    permission: invtweaks.sort
+    permission: invtweaks.sort
+  magnet:
+    description: Toggle item magnet mode for player
+    usage: /<command>
+    permission: invtweaks.magnet