using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using Munga.Net;

namespace VPod;

/// <summary>
/// Emulates a game client's ApplicationState machine over the Munga control
/// channel, driving it from the messages the console sends. This is the brain of
/// vPOD: it answers state queries, reassembles the streamed egg, and walks the
/// pod through the load/run/stop lifecycle the console's game window expects.
///
/// The console (RPGame/BTGame NetworkScan) gates purely on the reported
/// ApplicationState:
///   WaitingForEgg  -- ready; console streams the egg here
///   (egg complete) -> LoadingMission -> WaitingForLaunch  (console's "Loaded")
///   RunMission     -> LaunchingMission -> RunningMission   (console's "Running")
///   StopMission    -> EndingMission   -> WaitingForEgg     (mission over/reset)
///   AbortMission   -> AbortingMission -> WaitingForEgg
/// Intermediate states are shown for realism; the console only waits on the gate
/// states, so a short delay between them is harmless.
/// </summary>
internal sealed class PodSimulator
{
	private const int NetworkManagerFromHost = 0;

	private readonly MungaPodServer mServer;
	private readonly object mLock = new object();

	private ApplicationState mState = ApplicationState.InitializingState;
	private ApplicationID mApplicationId;
	private int mHostId;
	private int mTransitionDelayMs = 400;

	// Egg reassembly
	private byte[] mEggBuffer;
	private int mEggTotal;
	private int mEggReceived;
	private readonly HashSet<int> mEggChunks = new HashSet<int>();
	private string mEggText;

	// Cancels a pending delayed transition when a newer one supersedes it.
	private int mTransitionToken;
	private Timer mTransitionTimer;

	public event Action<ApplicationState> StateChanged;
	public event Action<string> EggReceived;   // full egg text (NUL-normalized)
	public event Action EggProgress;           // a chunk arrived (mid-transfer)
	public event Action<string> Log;

	public PodSimulator(MungaPodServer server, ApplicationID applicationId, int hostId)
	{
		mServer = server;
		mApplicationId = applicationId;
		mHostId = hostId;
	}

	public ApplicationState State { get { lock (mLock) { return mState; } } }

	public ApplicationID ApplicationId
	{
		get { lock (mLock) { return mApplicationId; } }
		set
		{
			lock (mLock) { mApplicationId = value; }
			Log?.Invoke("Reported application changed to " + value + ".");
		}
	}

	public int HostId { get { lock (mLock) { return mHostId; } } }

	public int TransitionDelayMs
	{
		get { lock (mLock) { return mTransitionDelayMs; } }
		set { lock (mLock) { mTransitionDelayMs = Math.Max(0, value); } }
	}

	public string EggText { get { lock (mLock) { return mEggText; } } }

	public int EggPercent
	{
		get
		{
			lock (mLock)
			{
				if (mEggTotal <= 0) return 0;
				return (int)(100L * mEggReceived / mEggTotal);
			}
		}
	}

	/// <summary>Bring the pod online: Initializing -> WaitingForEgg.</summary>
	public void PowerOn()
	{
		SetState(ApplicationState.InitializingState);
		ScheduleTransition(ApplicationState.WaitingForEgg, ResetEggOnArrive: true);
	}

	/// <summary>Operator reset: drop any mission and return to WaitingForEgg immediately.</summary>
	public void Reset()
	{
		lock (mLock)
		{
			ClearEggLocked();
			CancelPendingLocked();
		}
		SetState(ApplicationState.WaitingForEgg);
		Log?.Invoke("Reset to WaitingForEgg.");
	}

	public void HandleMessage(MungaPodServer.Incoming incoming)
	{
		MungaMessage msg = incoming?.Message;
		if (msg == null)
		{
			return;
		}

		switch (msg)
		{
		case StateQueryMessage _:
			RespondState();
			break;

		case EggFileMessage egg:
			HandleEggChunk(egg);
			break;

		case RunMissionMessage _:
			Log?.Invoke("<- RunMissionMessage");
			if (State == ApplicationState.WaitingForLaunch)
			{
				SetState(ApplicationState.LaunchingMission);
				mServer.Send(new ReadyToRunMessage(HostId), 0, HostId);
				ScheduleTransition(ApplicationState.RunningMission);
			}
			break;

		case StopMissionMessage _:
			Log?.Invoke("<- StopMissionMessage");
			if (State == ApplicationState.RunningMission || State == ApplicationState.SuspendingMission)
			{
				SetState(ApplicationState.EndingMission);
				ScheduleTransition(ApplicationState.WaitingForEgg, ResetEggOnArrive: true);
			}
			break;

		case AbortMissionMessage _:
			Log?.Invoke("<- AbortMissionMessage");
			SetState(ApplicationState.AbortingMission);
			mServer.Send(new AbortMissionResponseMessage(HostId), 0, HostId);
			ScheduleTransition(ApplicationState.WaitingForEgg, ResetEggOnArrive: true);
			break;

		case SuspendMissionMessage _:
			Log?.Invoke("<- SuspendMissionMessage");
			if (State == ApplicationState.RunningMission)
			{
				SetState(ApplicationState.SuspendingMission);
			}
			break;

		case ResumeMissionMessage _:
			Log?.Invoke("<- ResumeMissionMessage");
			if (State == ApplicationState.SuspendingMission)
			{
				SetState(ApplicationState.ResumingMission);
				ScheduleTransition(ApplicationState.RunningMission);
			}
			break;

		case LoadMissionMessage _:
			Log?.Invoke("<- LoadMissionMessage");
			if (State == ApplicationState.WaitingForEgg)
			{
				SetState(ApplicationState.LoadingMission);
				ScheduleTransition(ApplicationState.WaitingForLaunch);
			}
			break;

		case CheckLoadMessage _:
			Log?.Invoke("<- CheckLoadMessage");
			break;

		case LightsOutMissionMessage _:
			Log?.Invoke("<- LightsOutMissionMessage");
			break;
		}
	}

	private void RespondState()
	{
		ApplicationState state;
		ApplicationID app;
		int host;
		lock (mLock)
		{
			state = mState;
			app = mApplicationId;
			host = mHostId;
		}
		mServer.Send(new StateResponseMessage(host, state, app), 0, host);
	}

	private void HandleEggChunk(EggFileMessage egg)
	{
		bool complete = false;
		string text = null;
		lock (mLock)
		{
			if (mEggBuffer == null || mEggTotal != egg.NotationFileLength)
			{
				mEggTotal = egg.NotationFileLength;
				mEggBuffer = new byte[mEggTotal];
				mEggReceived = 0;
				mEggChunks.Clear();
			}
			int offset = egg.SequenceNumber * 1000;
			int len = egg.ThisMessageLength;
			if (offset >= 0 && offset + len <= mEggBuffer.Length && mEggChunks.Add(egg.SequenceNumber))
			{
				Buffer.BlockCopy(egg.NotationData, 0, mEggBuffer, offset, len);
				mEggReceived += len;
			}
			if (mEggReceived >= mEggTotal && mEggTotal > 0)
			{
				// On the wire the egg is NUL-delimited ASCII; show it line-per-field.
				text = Encoding.ASCII.GetString(mEggBuffer).Replace('\0', '\n');
				mEggText = text;
				complete = true;
			}
		}

		EggProgress?.Invoke();

		if (complete)
		{
			Log?.Invoke($"Egg received ({mEggTotal} bytes, {mEggChunks.Count} chunks). Acknowledging.");
			mServer.Send(new AcknowledgeEggFileMessage(), NetworkManagerFromHost, HostId);
			EggReceived?.Invoke(text);
			// WaitingForEgg -> LoadingMission -> WaitingForLaunch
			SetState(ApplicationState.LoadingMission);
			ScheduleTransition(ApplicationState.WaitingForLaunch);
		}
	}

	private void SetState(ApplicationState state)
	{
		bool changed;
		lock (mLock)
		{
			changed = mState != state;
			mState = state;
		}
		if (changed)
		{
			Log?.Invoke("State -> " + state);
			StateChanged?.Invoke(state);
		}
	}

	private void ScheduleTransition(ApplicationState target, bool ResetEggOnArrive = false)
	{
		int token;
		int delay;
		lock (mLock)
		{
			token = ++mTransitionToken;
			delay = mTransitionDelayMs;
			mTransitionTimer?.Dispose();
			mTransitionTimer = new Timer(delegate
			{
				bool proceed;
				lock (mLock)
				{
					proceed = token == mTransitionToken;
					if (proceed && ResetEggOnArrive)
					{
						ClearEggLocked();
					}
				}
				if (proceed)
				{
					SetState(target);
				}
			}, null, delay, Timeout.Infinite);
		}
	}

	private void CancelPendingLocked()
	{
		mTransitionToken++;
		mTransitionTimer?.Dispose();
		mTransitionTimer = null;
	}

	private void ClearEggLocked()
	{
		mEggBuffer = null;
		mEggTotal = 0;
		mEggReceived = 0;
		mEggChunks.Clear();
		mEggText = null;
	}
}