Statemachine for installation wizard (WIP)

EssentialsUpdate/src/com/earth2me/essentials/update/states/StateMachine.java

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+package com.earth2me.essentials.update.states;
+
+import com.earth2me.essentials.update.WorkListener;
+import com.earth2me.essentials.update.VersionInfo;
+import java.util.ArrayList;
+import java.util.List;
+import org.bukkit.Bukkit;
+import org.bukkit.entity.Player;
+import org.bukkit.plugin.Plugin;
+
+
+public class StateMachine extends WorkListener
+{
+	public enum MachineResult
+	{
+		ABORT, WAIT, DONE
+	}
+	private final transient List<AbstractState> states = new ArrayList<AbstractState>();
+	private transient AbstractState current;
+	private final transient Player player;
+
+	public StateMachine(final Plugin plugin, final Player player, final VersionInfo newVersionInfo)
+	{
+		super(plugin, newVersionInfo);
+		this.player = player;
+		states.clear();
+		final AbstractState state = new EssentialsChat(null);
+		states.add(state);
+		current = state;
+	}
+
+	public MachineResult askQuestion()
+	{
+		while (current.guessAnswer())
+		{
+			current = current.getNextState();
+			if (current == null)
+			{
+				return MachineResult.DONE;
+			}
+		}
+		current.askQuestion(player);
+		return MachineResult.WAIT;
+	}
+
+	public MachineResult reactOnMessage(final String message)
+	{
+		final AbstractState next = current.reactOnAnswer(player, message);
+		if (next == null)
+		{
+			if (current.isAbortion())
+			{
+				return MachineResult.ABORT;
+			}
+			else
+			{
+				return MachineResult.DONE;
+			}
+		}
+		current = next;
+		return askQuestion();
+	}
+	private int position = 0;
+
+	public void startWork()
+	{
+		callStateWork();
+	}
+
+	private void callStateWork()
+	{
+		if (position > states.size())
+		{
+			if (player.isOnline())
+			{
+				player.sendMessage("Installation done.");
+			}
+			return;
+		}
+		final AbstractState state = states.get(position);
+		state.doWork(this);
+	}
+
+	@Override
+	public void onWorkAbort(final String message)
+	{
+		position = 0;
+		Bukkit.getScheduler().scheduleSyncDelayedTask(getPlugin(), new Runnable()
+		{
+			@Override
+			public void run()
+			{
+				if (message != null && !message.isEmpty() && StateMachine.this.player.isOnline())
+				{
+					StateMachine.this.player.sendMessage(message);
+				}
+			}
+		});
+	}
+
+	@Override
+	public void onWorkDone(final String message)
+	{
+		position++;
+		Bukkit.getScheduler().scheduleSyncDelayedTask(getPlugin(), new Runnable()
+		{
+			@Override
+			public void run()
+			{
+				if (message != null && !message.isEmpty() && StateMachine.this.player.isOnline())
+				{
+					StateMachine.this.player.sendMessage(message);
+				}
+				StateMachine.this.callStateWork();
+			}
+		});
+	}
+}