Add a tab completion API for chat messages. Adds BUKKIT-2607

This implementation provides access to a (mutable) list and the base
message. Also provided is a convenience method for getting the last
'token' in the provided string.

By: Wesley Wolfe <weswolf@aol.com>

paper-api/src/main/java/org/bukkit/event/player/PlayerChatTabCompleteEvent.java

@@ -0,0 +1,68 @@
+package org.bukkit.event.player;
+
+import java.util.Collection;
+
+import org.apache.commons.lang.Validate;
+import org.bukkit.entity.Player;
+import org.bukkit.event.HandlerList;
+
+/**
+ * Called when a player attempts to tab-complete a chat message.
+ */
+public class PlayerChatTabCompleteEvent extends PlayerEvent {
+    private static final HandlerList handlers = new HandlerList();
+    private final String message;
+    private final String lastToken;
+    private final Collection<String> completions;
+
+    public PlayerChatTabCompleteEvent(final Player who, final String message, final Collection<String> completions) {
+        super(who);
+        Validate.notNull(message, "Message cannot be null");
+        Validate.notNull(completions, "Completions cannot be null");
+        this.message = message;
+        int i = message.lastIndexOf(' ');
+        if (i < 0) {
+            this.lastToken = message;
+        } else {
+            this.lastToken = message.substring(i + 1);
+        }
+        this.completions = completions;
+    }
+
+    /**
+     * Gets the chat message being tab-completed.
+     *
+     * @return the chat message
+     */
+    public String getChatMessage() {
+        return message;
+    }
+
+    /**
+     * Gets the last 'token' of the message being tab-completed.
+     * The token is the substring starting with the character after the last space in the message.
+     *
+     * @return The last token for the chat message
+     */
+    public String getLastToken() {
+        return lastToken;
+    }
+
+    /**
+     * This is the collection of completions for this event.
+     *
+     * @return the current completions
+     */
+    public Collection<String> getTabCompletions() {
+        return completions;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+}

paper-api/src/test/java/org/bukkit/event/PlayerChatTabCompleteEventTest.java

@@ -0,0 +1,28 @@
+package org.bukkit.event;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import org.bukkit.event.player.PlayerChatTabCompleteEvent;
+import org.bukkit.plugin.messaging.TestPlayer;
+import org.junit.Test;
+
+import com.google.common.collect.ImmutableList;
+
+public class PlayerChatTabCompleteEventTest {
+
+    @Test
+    public void testGetLastToken() {
+        assertThat(getToken("Hello everyone!"), is("everyone!"));
+        assertThat(getToken(" welcome to the show..."), is("show..."));
+        assertThat(getToken("The whitespace is here "), is(""));
+        assertThat(getToken("Too much whitespace is here  "), is(""));
+        assertThat(getToken("The_whitespace_is_missing"), is("The_whitespace_is_missing"));
+        assertThat(getToken(""), is(""));
+        assertThat(getToken(" "), is(""));
+    }
+
+    private String getToken(String message) {
+        return new PlayerChatTabCompleteEvent(TestPlayer.getInstance(), message, ImmutableList.<String>of()).getLastToken();
+    }
+}