Add default Clear command. Partially fixes BUKKIT-2671

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/command/SimpleCommandMap.java

@@ -56,6 +56,7 @@ public class SimpleCommandMap implements CommandMap {
         fallbackCommands.add(new DifficultyCommand());
         fallbackCommands.add(new WeatherCommand());
         fallbackCommands.add(new SpawnpointCommand());
+        fallbackCommands.add(new ClearCommand());
     }
 
     public SimpleCommandMap(final Server server) {

paper-api/src/main/java/org/bukkit/command/defaults/ClearCommand.java

@@ -0,0 +1,116 @@
+package org.bukkit.command.defaults;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.commons.lang.Validate;
+import org.bukkit.Bukkit;
+import org.bukkit.ChatColor;
+import org.bukkit.Material;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.entity.Player;
+import org.bukkit.util.StringUtil;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class ClearCommand extends VanillaCommand {
+    private static List<String> materials;
+    static {
+        ArrayList<String> materialList = new ArrayList<String>();
+        for (Material material : Material.values()) {
+            materialList.add(material.name());
+        }
+        Collections.sort(materialList);
+        materials = ImmutableList.copyOf(materialList);
+    }
+
+    public ClearCommand() {
+        super("clear");
+        this.description = "Clears the player's inventory. Can specify item and data filters too.";
+        this.usageMessage = "/clear <player> [item] [data]";
+        this.setPermission("bukkit.command.clear");
+    }
+
+    @Override
+    public boolean execute(CommandSender sender, String currentAlias, String[] args) {
+        if (!testPermission(sender)) return true;
+
+        Player player = null;
+        if (args.length > 0) {
+            player = Bukkit.getPlayer(args[0]);
+        } else if (sender instanceof Player) {
+            player = (Player) sender;
+        }
+
+        if (player != null) {
+            int id;
+
+            if (args.length > 1 && !(args[1].equals("-1"))) {
+                Material material = Material.matchMaterial(args[1]);
+                if (material == null) {
+                    sender.sendMessage(ChatColor.RED + "There's no item called " + args[1]);
+                    return false;
+                }
+
+                id = material.getId();
+            } else {
+                id = -1;
+            }
+
+            int data = args.length >= 3 ? getInteger(sender, args[2], 0) : -1;
+            int count = player.getInventory().clear(id, data);
+            Command.broadcastCommandMessage(sender, "Cleared the inventory of " + player.getDisplayName() + ", removing " + count + " items");
+        } else {
+            sender.sendMessage(ChatColor.RED + "Can't find user " + args[0]);
+        }
+
+        return true;
+    }
+
+    @Override
+    public boolean matches(String input) {
+        return input.equalsIgnoreCase("clear");
+    }
+
+    @Override
+    public List<String> tabComplete(CommandSender sender, String alias, String[] args) throws IllegalArgumentException {
+        Validate.notNull(sender, "Sender cannot be null");
+        Validate.notNull(args, "Arguments cannot be null");
+        Validate.notNull(alias, "Alias cannot be null");
+
+        if (args.length == 1) {
+            return super.tabComplete(sender, alias, args);
+        }
+        if (args.length == 2) {
+            final String arg = args[1];
+            final List<String> materials = ClearCommand.materials;
+            List<String> completion = null;
+
+            final int size = materials.size();
+            int i = Collections.binarySearch(materials, arg, String.CASE_INSENSITIVE_ORDER);
+
+            if (i < 0) {
+                // Insertion (start) index
+                i = -1 - i;
+            }
+
+            for ( ; i < size; i++) {
+                String material = materials.get(i);
+                if (StringUtil.startsWithIgnoreCase(material, arg)) {
+                    if (completion == null) {
+                        completion = new ArrayList<String>();
+                    }
+                    completion.add(material);
+                } else {
+                    break;
+                }
+            }
+
+            if (completion != null) {
+                return completion;
+            }
+        }
+        return ImmutableList.of();
+    }
+}