Make DisconnectEvent more sane

This is a step towards fixing #289 and removing some less-than-optimal behavior in plugins I maintain internally.

api/src/main/java/com/velocitypowered/api/event/connection/DisconnectEvent.java

@@ -1,5 +1,8 @@
 package com.velocitypowered.api.event.connection;
 
+import static com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus.CANCELLED_BY_PROXY;
+import static com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus.SUCCESSFUL_LOGIN;
+
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.proxy.Player;
 
@@ -10,31 +13,50 @@ import com.velocitypowered.api.proxy.Player;
 public final class DisconnectEvent {
 
   private final Player player;
-  private final boolean disconnectedDuringLogin;
+  private final LoginStatus loginStatus;
 
+  @Deprecated
   public DisconnectEvent(Player player) {
     this(player, false);
   }
 
+  @Deprecated
   public DisconnectEvent(Player player,
       boolean disconnectedDuringLogin) {
+    this(player, disconnectedDuringLogin ? CANCELLED_BY_PROXY : SUCCESSFUL_LOGIN);
+  }
+
+  public DisconnectEvent(Player player, LoginStatus loginStatus) {
     this.player = Preconditions.checkNotNull(player, "player");
-    this.disconnectedDuringLogin = disconnectedDuringLogin;
+    this.loginStatus = Preconditions.checkNotNull(loginStatus, "loginStatus");
   }
 
   public Player getPlayer() {
     return player;
   }
 
+  @Deprecated
   public boolean disconnectedDuringLogin() {
-    return this.disconnectedDuringLogin;
+    return this.loginStatus == CANCELLED_BY_PROXY;
+  }
+
+  public LoginStatus getLoginStatus() {
+    return loginStatus;
   }
 
   @Override
   public String toString() {
     return "DisconnectEvent{"
         + "player=" + player + ", "
-        + "disconnectedDuringLogin=" + disconnectedDuringLogin
+        + "loginStatus=" + loginStatus
         + '}';
   }
+
+  public enum LoginStatus {
+
+    SUCCESSFUL_LOGIN,
+    CONFLICTING_LOGIN,
+    CANCELLED_BY_USER,
+    CANCELLED_BY_PROXY
+  }
 }