Set server max players to number of total members (#25)

src/main/java/pro/cloudnode/smp/smpcore/Member.java

@@ -242,6 +242,21 @@ public boolean delete() {
         return members;
     }
 
+    public static int count() {
+        try (
+                final @NotNull Connection conn = SMPCore.getInstance().db()
+                        .getConnection(); final @NotNull PreparedStatement stmt = conn.prepareStatement("SELECT COUNT(*) as `n` FROM `members`")
+        ) {
+            final @NotNull ResultSet rs = stmt.executeQuery();
+            rs.next();
+            return rs.getInt("n");
+        }
+        catch (final @NotNull SQLException e) {
+            SMPCore.getInstance().getLogger().log(Level.SEVERE, "could not count members", e);
+            return 0;
+        }
+    }
+
     public static @NotNull Set<@NotNull String> getNames() {
         return get().stream().map(m -> m.player().getName()).filter(Objects::nonNull).collect(Collectors.toSet());
     }

src/main/java/pro/cloudnode/smp/smpcore/SMPCore.java

@@ -15,6 +15,7 @@
 import pro.cloudnode.smp.smpcore.command.TimeCommand;
 import pro.cloudnode.smp.smpcore.command.UnbanCommand;
 import pro.cloudnode.smp.smpcore.listener.NationTeamUpdaterListener;
+import pro.cloudnode.smp.smpcore.listener.PlayerSlotsListener;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -69,6 +70,7 @@ public void onEnable() {
         initDatabase();
 
         getServer().getPluginManager().registerEvents(new NationTeamUpdaterListener(), this);
+        getServer().getPluginManager().registerEvents(new PlayerSlotsListener(), this);
 
         final @NotNull HashMap<@NotNull String, @NotNull Command> commands = new HashMap<>() {{
             put("smpcore", new MainCommand());

src/main/java/pro/cloudnode/smp/smpcore/listener/PlayerSlotsListener.java

@@ -0,0 +1,31 @@
+package pro.cloudnode.smp.smpcore.listener;
+
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerLoginEvent;
+import org.bukkit.event.server.ServerListPingEvent;
+import org.jetbrains.annotations.NotNull;
+import pro.cloudnode.smp.smpcore.Member;
+
+import java.util.Optional;
+
+public final class PlayerSlotsListener implements Listener {
+    /**
+     * Change the max players number in server list ping
+     */
+    @EventHandler
+    public void onServerListPing(final @NotNull ServerListPingEvent event) {
+        event.setMaxPlayers(Member.count());
+    }
+
+    /**
+     * If the player is a member, but the server thinks it's full, allow them to join
+     */
+    @EventHandler
+    public void onPlayerLogin(final @NotNull PlayerLoginEvent event) {
+        if (event.getResult() == PlayerLoginEvent.Result.KICK_FULL) {
+            final @NotNull Optional<@NotNull Member> member = Member.get(event.getPlayer());
+            if (member.isPresent()) event.allow();
+        }
+    }
+}