Add BossBar API (#213)

api/src/main/java/com/velocitypowered/api/proxy/ProxyServer.java

@@ -10,11 +10,15 @@ import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.proxy.server.ServerInfo;
 import com.velocitypowered.api.scheduler.Scheduler;
 import com.velocitypowered.api.util.ProxyVersion;
+import com.velocitypowered.api.util.bossbar.BossBar;
+import com.velocitypowered.api.util.bossbar.BossBarColor;
+import com.velocitypowered.api.util.bossbar.BossBarOverlay;
 import java.net.InetSocketAddress;
 import java.util.Collection;
 import java.util.Optional;
 import java.util.UUID;
 import net.kyori.text.Component;
+import org.checkerframework.checker.nullness.qual.NonNull;
 
 /**
  * Provides an interface to a Minecraft server proxy.
@@ -173,4 +177,17 @@ public interface ProxyServer {
    * @return the proxy version
    */
   ProxyVersion getVersion();
+
+  /**
+   * Creates a new {@link BossBar}.
+   *
+   * @param title boss bar title
+   * @param color boss bar color
+   * @param overlay boss bar overlay
+   * @param progress boss bar progress
+   * @return a completely new and fresh boss bar
+   */
+  @NonNull
+  BossBar createBossBar(@NonNull Component title, @NonNull BossBarColor color,
+      @NonNull BossBarOverlay overlay, float progress);
 }

api/src/main/java/com/velocitypowered/api/util/bossbar/BossBar.java

@@ -0,0 +1,163 @@
+package com.velocitypowered.api.util.bossbar;
+
+import com.velocitypowered.api.proxy.Player;
+import java.util.Collection;
+import net.kyori.text.Component;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * Represents a boss bar, which can be send to a (group of) player(s).
+ * <b>Boss bars only work on 1.9 and above.</b>
+ */
+public interface BossBar {
+
+  /**
+   * Adds all specified players to this boss bar.
+   *
+   * @param players players
+   * @see #addPlayer(Player)
+   */
+  void addPlayers(Iterable<Player> players);
+
+  /**
+   * Adds player to this boss bar. This adds the player to the {@link #getPlayers()} and makes him
+   * see the boss bar.
+   *
+   * @param player the player you wish to add
+   */
+  void addPlayer(@NonNull Player player);
+
+  /**
+   * Removes player from this boss bar. This removes the player from {@link #getPlayers()} and makes
+   * him not see the boss bar.
+   *
+   * @param player the player you wish to remove
+   */
+  void removePlayer(@NonNull Player player);
+
+  /**
+   * Removes all specified players from this boss bar.
+   *
+   * @param players players
+   * @see #removePlayer(Player)
+   */
+  void removePlayers(Iterable<Player> players);
+
+  /**
+   * Removes all players, that see this boss bar.
+   *
+   * @see #removePlayer(Player)
+   */
+  void removeAllPlayers();
+
+  /**
+   * Gets the title of this boss bar.
+   *
+   * @return title
+   */
+  @NonNull
+  Component getTitle();
+
+  /**
+   * Sets a new title of the boss bar.
+   *
+   * @param title new title
+   */
+  void setTitle(@NonNull Component title);
+
+  /**
+   * Gets the boss bar's progress. In Minecraft, this is called 'health' of the boss bar.
+   *
+   * @return progress
+   */
+  float getProgress();
+
+  /**
+   * Sets a new progress of the boss bar. In Minecraft, this is called 'health' of the boss bar.
+   *
+   * @param progress a float between 0 and 1, representing boss bar's progress
+   * @throws IllegalArgumentException if the new progress is not between 0 and 1
+   */
+  void setProgress(float progress);
+
+  /**
+   * Returns a copy of the {@link Collection} of all {@link Player} added to the boss bar.
+   * <i>Can be empty.</i>
+   *
+   * @return players
+   */
+  Collection<Player> getPlayers();
+
+  /**
+   * Gets the color of the boss bar.
+   *
+   * @return boss bar color
+   */
+  @NonNull
+  BossBarColor getColor();
+
+  /**
+   * Sets a new color of the boss bar.
+   *
+   * @param color the color you wish the boss bar be displayed with
+   */
+  void setColor(@NonNull BossBarColor color);
+
+  /**
+   * Gets the overlay of the boss bar.
+   *
+   * @return boss bar overlay
+   */
+  @NonNull
+  BossBarOverlay getOverlay();
+
+  /**
+   * Sets a new overlay of the boss bar.
+   *
+   * @param overlay the overlay you wish the boss bar be displayed with
+   */
+  void setOverlay(@NonNull BossBarOverlay overlay);
+
+  /**
+   * Returns whenever this boss bar is visible to all added {@link #getPlayers()}. By default, it
+   * returns <code>true</code>.
+   *
+   * @return <code>true</code> if visible, otherwise <code>false</code>
+   */
+  boolean isVisible();
+
+  /**
+   * Sets a new visibility to the boss bar.
+   *
+   * @param visible boss bar visibility value
+   */
+  void setVisible(boolean visible);
+
+  /**
+   * Returns a copy of of the {@link Collection} of all {@link BossBarFlag}s added to the boss bar.
+   *
+   * @return flags
+   */
+  Collection<BossBarFlag> getFlags();
+
+  /**
+   * Adds new flags to the boss bar.
+   *
+   * @param flags the flags you wish to add
+   */
+  void addFlags(BossBarFlag... flags);
+
+  /**
+   * Removes flag from the boss bar.
+   *
+   * @param flag the flag you wish to remove
+   */
+  void removeFlag(BossBarFlag flag);
+
+  /**
+   * Removes flags from the boss bar.
+   *
+   * @param flags the flags you wish to remove
+   */
+  void removeFlags(BossBarFlag... flags);
+}

api/src/main/java/com/velocitypowered/api/util/bossbar/BossBarColor.java

@@ -0,0 +1,14 @@
+package com.velocitypowered.api.util.bossbar;
+
+/**
+ * Represents a color of a {@link BossBar}.
+ */
+public enum BossBarColor {
+  PINK,
+  BLUE,
+  RED,
+  GREEN,
+  YELLOW,
+  PURPLE,
+  WHITE;
+}

api/src/main/java/com/velocitypowered/api/util/bossbar/BossBarFlag.java

@@ -0,0 +1,10 @@
+package com.velocitypowered.api.util.bossbar;
+
+/**
+ * Represents any {@link BossBar}'s flags.
+ */
+public enum BossBarFlag {
+  DARKEN_SKY,
+  DRAGON_BAR,
+  CREATE_FOG
+}

api/src/main/java/com/velocitypowered/api/util/bossbar/BossBarOverlay.java

@@ -0,0 +1,12 @@
+package com.velocitypowered.api.util.bossbar;
+
+/**
+ * Represents a overlay of a {@link BossBar}.
+ */
+public enum BossBarOverlay {
+  SOLID,
+  SEGMENTED_6,
+  SEGMENTED_10,
+  SEGMENTED_12,
+  SEGMENTED_20
+}