using Cysharp.Threading.Tasks.Triggers;
using JetBrains.Annotations;
using System;
using System.Drawing;
using System.Text;
using UdonSharp;
using UnityEngine;
using VRC.SDK3.UdonNetworkCalling;
using VRC.SDKBase;
using VRC.Udon.ClientBindings.Interfaces;
using VRC.Udon.Common;

namespace Marro.PacManUdon
{
    public enum NetworkEventType
    {
        FullSync = 0,
        PacManTurn = 1,
    }
    public class NetworkManager : UdonSharpBehaviour
    {
        // The network manager works by serializing event and state data into a byte array, including a timestamp for each event.
        // If user is owner, this data is created and stored in a buffer which is cleared upon transmission.
        // If user is not owner, this data is read into the same buffer and replayed based on the included timestamp.
        // Data replay is delayed with an offset on the timestamp to hide inconsistency in latency.

        // The timestamp is transferred in ms as a 32 bit uint, which gives a maximum time of about 49 days.
        // The maximum allowed age of a VRChat instance is 7 days, so this should not cause issues.

        // A byte array is used as a DataList or DataDictionary can only be transmitted as JSON which is much less efficient.
        // As Udon does not support instantiating objects, I have not created classes to represent the data being sent.
        // Correct parsing is dependend upon everything being read out identially to how it was created.

        // An event has the following structure:
        // [0-1]: (ushort) Size of event.
        // [2-5]: (uint) Time in seconds at which event occured.
        // [6]: (byte) Type of event. 0 = Full Sync, which is used to sync up from an undefinted state.
        // [7+]: Event-specific data

        #region Constants
        /// <summary>
        /// The maximum size of the buffer in bytes.
        /// </summary>
        private const int BufferMaxSizeBytes = 10000;
        /// <summary>
        /// How many bytes to increase the buffer size by if the current one is not enough.
        /// </summary>
        private const int BufferIncrementSizeBytes = 1000;

        /// <summary>
        /// The index in an event where the event size is stored.
        /// </summary>
        private const ushort HeaderEventSizeIndex = 0;
        /// <summary>
        /// The index in an event where the timestamp is stored.
        /// </summary>
        private const ushort HeaderTimestampIndex = 2;
        /// <summary>
        /// The index in an event where the event type is stored.
        /// </summary>
        private const ushort HeaderEventTypeIndex = 6;
        /// <summary>
        /// The total length of the header of an event, in bytes.
        /// </summary>
        private const ushort HeaderLength = 7;

        /// <summary>
        /// The multiplier from Unity time to a timestamp.
        /// </summary>
        private const int TimestampMultiplier = 1000;
        /// <summary>
        /// The zero value of a timestamp. Anything below this value is negative.
        /// </summary>
        private const uint TimestampZeroValue = 1000;
        /// <summary>
        /// The delay at which the receiving side replays events.
        /// </summary>
        private const float Delay = 0.250f;
        #endregion

        #region Private attributes
        /// <summary>
        /// Objects which are controlled by this <see cref="NetworkManager"/>.
        /// </summary>
        [SerializeField] private SyncedObject[] syncedObjects;

        /// <summary>
        /// An animator which visualizes whether the current perspective is the owner.
        /// </summary>
        [SerializeField] private Animator DebugImageToIndicateOwner;

        /// <summary>
        /// Whether the current perspective is the transmitting side.
        /// </summary>
        private bool isOwner;
        /// <summary>
        /// Whether the current perspective is synced with the owner. (Always true if current perspective is owner.)
        /// </summary>
        private bool isSynced;


        /// <summary>
        /// Offset from system time to network time, including delay.
        /// </summary>
        private float offsetTime;
        /// <summary>
        /// Time since last full sync, captured when this FixedUpdate started, with network delay applied.
        /// </summary>
        private float internalTime;

        /// <summary>
        /// Time at which next received event occured.
        /// </summary>
        private float nextEventTime;

        /// <summary>
        /// Amounot of retries in a row without a successful sync.
        /// </summary>
        private int retriesWithoutSuccess;

        /// <summary>
        /// Main buffer of data to be transmitted or processed
        /// </summary>
        private byte[] buffer;
        /// <summary>
        /// Index of <see cref="buffer"/>.
        /// </summary>
        private int bufferIndex;

        /// <summary>
        /// Data which is currently available on the network.
        /// </summary>
        [UdonSynced] private byte[] networkedData = new byte[0];
        #endregion

        #region Public fields
        /// <summary>
        /// Whether this <see cref="NetworkManager"/> is ready to transmit or receive data.
        /// If false, networking is disabled and this <see cref="NetworkManager"/> acts as a pass-through.
        /// </summary>
        public bool Ready { get; private set; } = false;

        /// <summary>
        /// The time since last full sync which is currently being simulated.
        /// </summary>
        public float SyncedTime { get; private set; }

        /// <summary>
        /// Time since the last simulation, in seconds.
        /// </summary>
        public float Dt { get; private set; }

        /// <summary>
        /// Is the current simulation to prepare for applying a network event?
        /// True = Yes, This update is preparing for a network update.
        /// False = No, this update is after the network update or there was no 
        /// </summary>
        public bool IsEventUpdate { get; private set; }

        /// <summary>
        /// Is the local user owner?
        /// </summary>
        public bool IsOwner => isOwner;
        #endregion

        #region General
        public void Awake()
        {
            offsetTime = Time.fixedTime;
        }

        public void Initialize()
        {
            if (Ready)
            {
                Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Already initialized, rejecting repeat call to {nameof(Initialize)}");
                return;
            }

            if (!BitConverter.IsLittleEndian)
            {
                Debug.LogError($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Fatal: NetworkManager only supports little endian! Network sync will not be possible.");
                var zero = 0;
                Debug.Log(1 / zero); // Intentionally crash
                return;
            }

            SetOwner(Networking.IsOwner(gameObject));

            buffer = new byte[BufferIncrementSizeBytes];
            bufferIndex = 0;
            isSynced = isOwner; // Owner is always synced
            retriesWithoutSuccess = 0;

            offsetTime = Time.fixedTime;
            internalTime = 0;
            SyncedTime = 0;
            Dt = Time.fixedDeltaTime;

            Ready = true;

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Initialized, time offset: {offsetTime}");
        }

        public void FixedUpdate()
        {
            UpdateInternalTime();

            if (!isOwner)
            {
                ProgressEventTime();
            }

            PerformFixedSyncedUpdate();
        }

        public void UpdateInternalTime()
        {
            internalTime = Time.fixedTime - offsetTime;
        }

        private void PerformFixedSyncedUpdate()
        {
            IsEventUpdate = false;
            ProgressSyncedTime(internalTime);

            foreach (var obj in syncedObjects)
            {
                obj.SyncedUpdate();
            }
        }

        private void HandleError()
        {
            retriesWithoutSuccess++;

            if (retriesWithoutSuccess > 3)
            {
                Debug.LogError($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Fatal: Retried 3 times without success.");
                var zero = 0;
                Debug.Log(1 / zero); // Intentionally crash
                return;
            }

            Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Encountered data error, attempting to recover via full sync.");

            ClearBuffer();

            if (!isOwner)
            {
                RequestEvent(NetworkEventType.FullSync);
            }
            else
            {
                SendEvent(NetworkEventType.FullSync);
            }
        }

        private void SetOwner(bool isOwner)
        {
            this.isOwner = isOwner;

            if (DebugImageToIndicateOwner != null)
            {
                DebugImageToIndicateOwner.SetFloat("Color", isOwner ? 1 : 0);
            }
        }
        #endregion

        #region Sender
        public void SendEvent(NetworkEventType eventType)
        {
            if (!isOwner)
            {
                Debug.LogError($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Attempted {nameof(SendEvent)} while not the owner!");
                return;
            }

            var eventTime = TimeToTimestamp(SyncedTime);

            InitializeEvent(eventType, eventTime, BufferMaxSizeBytes, out byte[][] data, out var index);

            foreach (var obj in syncedObjects)
            {
                obj.AppendSyncedData(data, ref index, eventType);
            }

            // Get event size, skipping over the event size which is not yet included
            ushort eventSize = 0;
            for (int i = 0; i < index; i++)
            {
                eventSize += (ushort)data[i].Length;
            }

            if (!EnsureSpaceToStoreEvent(eventSize))
            {
                return;
            }

            data[0] = BitConverter.GetBytes(eventSize);

            var oldIndex = this.bufferIndex;

            FlattenAndCopy(data, index, buffer, ref this.bufferIndex);

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Prepared event with {eventSize} bytes and timestamp {eventTime} for serialization, index went from {oldIndex} to {this.bufferIndex}");

            RequestSerialization();

            retriesWithoutSuccess = 0; // We had success!
        }

        private static void InitializeEvent(NetworkEventType eventType, uint eventTime, int maxSize, out byte[][] data, out int index)
        {
            data = new byte[maxSize][];
            index = 3;

            data[0] = new byte[2]; // Placeholder for event size 
            data[1] = BitConverter.GetBytes(eventTime);
            data[2] = new byte[] { GameManager.Int32ToByte((int)eventType) };
        }
        #endregion

        #region Receiver
        public void RequestEvent(NetworkEventType eventType)
        {
            if (isOwner)
            {
                Debug.LogError($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Attempted {nameof(RequestEvent)} while we are the owner!");
                return;
            }

            SendCustomNetworkEvent(VRC.Udon.Common.Interfaces.NetworkEventTarget.Owner, "RequestEventReceived", eventType);
        }

        private void ProcessIncomingData()
        {
            if (networkedData.Length == 0)
            {
                return; // Nothing to process
            }

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Received {networkedData.Length} bytes!\nBytes received:\n{BytesToString(networkedData)}");

            var length = networkedData.Length;
            int index = 0;
            while (index < length)
            {
                if (length - index < HeaderLength)
                {
                    Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) {nameof(ProcessIncomingData)}: Remaining data in networkedData is not long enough to form a complete event!");
                    HandleError();
                    return;
                }

                var eventSize = networkedData[index + HeaderEventSizeIndex];
                var eventType = (NetworkEventType)networkedData[index + HeaderEventTypeIndex];

                if (eventType == NetworkEventType.FullSync)
                {
                    ProcessIncomingFullSync(index, eventSize); // Immediately process full sync
                    index += eventSize;
                    continue;
                }

                if (!isSynced)
                {
                    Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Received event of type {eventType} while we are not yet synced to the remote time, ignoring event.");
                    index += eventSize;
                    continue;
                }

                AppendEventToBuffer(index, eventSize);
                index += eventSize;
            }
        }

        private void ProcessIncomingFullSync(int index, int size)
        {
            // Intentionally not doing a buffer size check here, since this is not appending to the buffer
            // (and there is no good way to continue if event is too large)

            // Clear buffer and copy the full sync into it
            buffer = new byte[size];
            Array.Copy(networkedData, index, buffer, 0, size);
            this.bufferIndex = size;

            // Sync up to the time in the full sync
            var timestamp = BitConverter.ToUInt32(networkedData, index + HeaderTimestampIndex);
            SyncToTimestamp(timestamp);

            // Immediately apply the full sync
            UpdateNextEventTime();
            isSynced = true;
        }

        private void ProgressEventTime()
        {
            IsEventUpdate = true;

            while (bufferIndex != 0 && nextEventTime <= internalTime)
            {
                ProcessIncomingEvent();
                UpdateNextEventTime();
            }
        }

        private void ProcessIncomingEvent()
        {
            var eventTime = TimestampToTime(BitConverter.ToUInt32(buffer, HeaderTimestampIndex));
            var eventType = (NetworkEventType)buffer[HeaderEventTypeIndex];
            var index = (int)HeaderLength; // Skip header

            ProgressSyncedTime(eventTime);

            foreach (var obj in syncedObjects)
            {
                obj.SyncedUpdate();
            }

            foreach (var obj in syncedObjects)
            {
                var success = obj.SetSyncedData(buffer, ref index, eventType);

                if (!success)
                {
                    Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Malformed data reported by {obj.name} during event type {eventType}!");
                    HandleError();
                    return;
                }

                if (index > this.bufferIndex)
                {
                    Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Buffer overflow during {nameof(SyncedObject.SetSyncedData)} for {obj.name} in event type {eventType}!");
                    HandleError();
                    return;
                }
            }

            var eventSize = BitConverter.ToUInt16(buffer, HeaderEventSizeIndex);
            if (index != eventSize)
            {
                Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Amount of data read does not match event size! Expected {eventSize}, read {index}.");
                HandleError();
                return;
            }

            RemoveProcessedDataFromBuffer(index);

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Processed incoming event! Total {index} bytes.");

            retriesWithoutSuccess = 0; // We had success!
        }
        #endregion

        #region Buffer
        private void ClearBuffer()
        {
            buffer = new byte[BufferMaxSizeBytes];
            bufferIndex = 0;
        }

        private void RemoveProcessedDataFromBuffer(int amountProcessed)
        {
            var oldBuffer = buffer;
            bufferIndex -= amountProcessed;
            buffer = new byte[BufferMaxSizeBytes];
            Array.Copy(oldBuffer, amountProcessed, buffer, 0, bufferIndex);
        }

        private bool IncreaseBufferSize(int newSize)
        {
            if (newSize < buffer.Length)
            {
                Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Cannot decrease the size of the buffer!");
                return false;
            }

            if (newSize > BufferMaxSizeBytes)
            {
                return false;
            }

            var oldBuffer = buffer;
            buffer = new byte[newSize];
            oldBuffer.CopyTo(buffer, 0);
            return true;
        }

        private bool EnsureSpaceToStoreEvent(int eventSize)
        {
            if (bufferIndex + eventSize <= buffer.Length)
            {
                return true; // Enough space!
            }

            var newBufferSize = ((bufferIndex + eventSize) / BufferIncrementSizeBytes + 1) * BufferIncrementSizeBytes;

            var success = IncreaseBufferSize(newBufferSize);
            if (success)
            {
                return true;
            }

            if (bufferIndex == 0)
            {
                Debug.LogError($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Buffer is not large enough to store event!");
            }
            else
            {
                Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Too much data in buffer to store event!");
            }

            HandleError(); // We can store event now that we cleared the buffer.
            return false;
        }

        private void AppendEventToBuffer(int index, int size)
        {
            if (!EnsureSpaceToStoreEvent(size))
            {
                return;
            }

            Array.Copy(networkedData, index, buffer, this.bufferIndex, size);
            this.bufferIndex += size;

            UpdateNextEventTime();
        }
        #endregion

        #region Time
        private void ProgressSyncedTime(float newTime)
        {
            //Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) updating SyncedTime from {SyncedTime} to {newTime}");
            Dt = newTime - SyncedTime;
            SyncedTime = newTime;
        }

        private void SyncToTimestamp(uint timestamp)
        {
            var oldOffset = offsetTime;
            var timeToSyncTo = timestamp / (float)TimestampMultiplier - Delay;
            offsetTime = Time.fixedTime - timeToSyncTo;

            var delta = offsetTime - oldOffset;
            internalTime = internalTime - delta;
            SyncedTime = SyncedTime - delta;

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Synced to timestamp {timestamp}, current time is {Time.fixedTime}, timeToSyncTo is {timeToSyncTo}, offsetTime is now {offsetTime}, internalTime is now {internalTime}, SyncedTime is now {SyncedTime}");
        }

        private void UpdateNextEventTime()
        {
            if (bufferIndex == 0)
            {
                return;
            }

            var nextEventTime = TimestampToTime(BitConverter.ToUInt32(buffer, HeaderTimestampIndex));
            if (nextEventTime >= this.nextEventTime)
            {
                this.nextEventTime = nextEventTime;
            }
            else
            {
                Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) New event is earlier than previous event!");
                HandleError();
                return;
            }
        }

        public static uint TimeToTimestamp(float time)
        {
            return (uint)((time * TimestampMultiplier) + TimestampZeroValue);
        }

        public static float TimestampToTime(uint timeStamp)
        {
            return (timeStamp - (long)TimestampZeroValue) / (float)TimestampMultiplier; // Use a long here to prevent an underflow
        }
        #endregion

        #region VRC events
        public override void OnOwnershipTransferred(VRCPlayerApi newOwner)
        {
            SetOwner(newOwner == Networking.LocalPlayer);

            if(isOwner)
            {
                HandleError();
            }
        }

        public override void OnPreSerialization()
        {
            if (isOwner)
            {
                networkedData = new byte[bufferIndex];
                Array.Copy(buffer, networkedData, bufferIndex);
            }
            else
            {
                networkedData = new byte[0]; // Prevent exception loop in VRChat SDK
            }
        }

        public override void OnPostSerialization(SerializationResult result)
        {
            if (!result.success)
            {
                Debug.LogWarning($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Serialization failed! Tried to send {result.byteCount} bytes.");
                return;
            }

            if (!isOwner || networkedData.Length == 0)
            {
                return;
            }

            Debug.Log($"({nameof(PacManUdon)} {nameof(NetworkManager)}) Serialized with {networkedData.Length} bytes!\nBytes sent:\n{BytesToString(networkedData)}");

            // Remove all transferred data from the buffer, leaving data that came in after serialization
            RemoveProcessedDataFromBuffer(networkedData.Length);
            networkedData = null;
        }

        public override void OnDeserialization()
        {
            if (!isOwner)
            {
                ProcessIncomingData();
            }
        }
        #endregion

        #region Utils
        public string BytesToString(byte[] bytes)
        {
            var sb = new StringBuilder("new byte[] { ");
            foreach (var b in bytes)
            {
                sb.Append(b + ", ");
            }
            sb.Append("}");
            return sb.ToString();
        }

        private static void FlattenAndCopy(byte[][] data, int length, byte[] target, ref int index)
        {
            for (int i = 0; i < length; i++)
            {
                var values = data[i];
                Array.Copy(values, 0, target, index, values.Length);
                index += values.Length;
            }
        }
        #endregion

        #region Debug
        public void SimulateSyncToTimestamp(uint timestamp)
        {
            SyncToTimestamp(timestamp);
        }
        #endregion
    }
}