// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

using Microsoft.MixedReality.Toolkit.Input;
using Microsoft.MixedReality.Toolkit.Utilities;
using Unity.Profiling;
using UnityEngine;
using UnityEngine.EventSystems;

namespace Microsoft.MixedReality.Toolkit.Teleport
{
    /// <summary>
    /// The Mixed Reality Toolkit's implementation of the <see cref="Microsoft.MixedReality.Toolkit.Teleport.IMixedRealityTeleportSystem"/>.
    /// </summary>
    public class MixedRealityTeleportSystem : BaseCoreSystem, IMixedRealityTeleportSystem
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="registrar">The <see cref="IMixedRealityServiceRegistrar"/> instance that loaded the service.</param>
        [System.Obsolete("This constructor is obsolete (registrar parameter is no longer required) and will be removed in a future version of the Microsoft Mixed Reality Toolkit.")]
        public MixedRealityTeleportSystem(
            IMixedRealityServiceRegistrar registrar) : base(registrar, null) // Teleport system does not use a profile
        {
            Registrar = registrar;
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        public MixedRealityTeleportSystem() : base(null) { } // Teleport system does not use a profile

        private TeleportEventData teleportEventData;

        private bool isTeleporting = false;
        private bool isProcessingTeleportRequest = false;

        private Vector3 targetPosition = Vector3.zero;
        private Vector3 targetRotation = Vector3.zero;

        /// <summary>
        /// Used to clean up event system when shutting down, if this system created one.
        /// </summary>
        private GameObject eventSystemReference = null;

        #region IMixedRealityService Implementation

        /// <inheritdoc/>
        public override string Name { get; protected set; } = "Mixed Reality Teleport System";

        /// <inheritdoc />
        public override void Initialize()
        {
            base.Initialize();
            InitializeInternal();
        }

        private void InitializeInternal()
        {
#if UNITY_EDITOR
            if (!UnityEditor.EditorApplication.isPlaying)
            {
                var eventSystems = Object.FindObjectsOfType<EventSystem>();

                if (eventSystems.Length == 0)
                {
                    if (!IsInputSystemEnabled)
                    {
                        eventSystemReference = new GameObject("Event System");
                        eventSystemReference.AddComponent<EventSystem>();
                    }
                    else
                    {
                        Debug.Log("The input system didn't properly add an event system to your scene. Please make sure the input system's priority is set higher than the teleport system.");
                    }
                }
                else if (eventSystems.Length > 1)
                {
                    Debug.Log("Too many event systems in the scene. The Teleport System requires only one.");
                }
            }
#endif // UNITY_EDITOR

            teleportEventData = new TeleportEventData(EventSystem.current);
        }

        /// <inheritdoc />
        public override void Destroy()
        {
            base.Destroy();

            if (eventSystemReference != null)
            {
                if (!Application.isPlaying)
                {
                    Object.DestroyImmediate(eventSystemReference);
                }
                else
                {
                    Object.Destroy(eventSystemReference);
                }
            }
        }

        #endregion IMixedRealityService Implementation

        #region IEventSystemManager Implementation

        private static readonly ProfilerMarker HandleEventPerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.HandleEvent");

        /// <inheritdoc />
        public override void HandleEvent<T>(BaseEventData eventData, ExecuteEvents.EventFunction<T> eventHandler)
        {
            using (HandleEventPerfMarker.Auto())
            {
                Debug.Assert(eventData != null);
                var teleportData = ExecuteEvents.ValidateEventData<TeleportEventData>(eventData);
                Debug.Assert(teleportData != null);
                Debug.Assert(!teleportData.used);

                // Process all the event listeners
                base.HandleEvent(teleportData, eventHandler);
            }
        }

        /// <summary>
        /// Register a <see href="https://docs.unity3d.com/ScriptReference/GameObject.html">GameObject</see> to listen to teleport events.
        /// </summary>
        public override void Register(GameObject listener) => base.Register(listener);

        /// <summary>
        /// Unregister a <see href="https://docs.unity3d.com/ScriptReference/GameObject.html">GameObject</see> from listening to teleport events.
        /// </summary>
        public override void Unregister(GameObject listener) => base.Unregister(listener);

        #endregion IEventSystemManager Implementation

        #region IMixedRealityTeleportSystem Implementation

        /// <summary>
        /// Is an input system registered?
        /// </summary>
        private bool IsInputSystemEnabled => CoreServices.InputSystem != null;

        private float teleportDuration = 0.25f;

        /// <inheritdoc />
        public float TeleportDuration
        {
            get => teleportDuration;
            set
            {
                if (isProcessingTeleportRequest)
                {
                    Debug.LogWarning("Couldn't change teleport duration. Teleport in progress.");
                    return;
                }

                teleportDuration = value;
            }
        }

        private static readonly ExecuteEvents.EventFunction<IMixedRealityTeleportHandler> OnTeleportRequestHandler =
            delegate (IMixedRealityTeleportHandler handler, BaseEventData eventData)
            {
                var casted = ExecuteEvents.ValidateEventData<TeleportEventData>(eventData);
                handler.OnTeleportRequest(casted);
            };

        private static readonly ProfilerMarker RaiseTeleportRequestPerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.RaiseTeleportRequest");

        /// <inheritdoc />
        public void RaiseTeleportRequest(IMixedRealityPointer pointer, IMixedRealityTeleportHotspot hotSpot)
        {
            using (RaiseTeleportRequestPerfMarker.Auto())
            {
                // initialize event
                teleportEventData.Initialize(pointer, hotSpot);

                // Pass handler
                HandleEvent(teleportEventData, OnTeleportRequestHandler);
            }
        }

        private static readonly ExecuteEvents.EventFunction<IMixedRealityTeleportHandler> OnTeleportStartedHandler =
            delegate (IMixedRealityTeleportHandler handler, BaseEventData eventData)
            {
                var casted = ExecuteEvents.ValidateEventData<TeleportEventData>(eventData);
                handler.OnTeleportStarted(casted);
            };

        private static readonly ProfilerMarker RaiseTeleportStartedPerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.RaiseTeleportStarted");

        /// <inheritdoc />
        public void RaiseTeleportStarted(IMixedRealityPointer pointer, IMixedRealityTeleportHotspot hotSpot)
        {
            if (isTeleporting)
            {
                Debug.LogError("Teleportation already in progress");
                return;
            }

            using (RaiseTeleportStartedPerfMarker.Auto())
            {
                isTeleporting = true;

                // initialize event
                teleportEventData.Initialize(pointer, hotSpot);

                // Pass handler
                HandleEvent(teleportEventData, OnTeleportStartedHandler);

                ProcessTeleportationRequest(teleportEventData);
            }
        }

        private static readonly ExecuteEvents.EventFunction<IMixedRealityTeleportHandler> OnTeleportCompletedHandler =
            delegate (IMixedRealityTeleportHandler handler, BaseEventData eventData)
            {
                var casted = ExecuteEvents.ValidateEventData<TeleportEventData>(eventData);
                handler.OnTeleportCompleted(casted);
            };

        private static readonly ProfilerMarker RaiseTeleportCompletePerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.RaiseTeleportComplete");

        /// <summary>
        /// Raise a teleportation completed event.
        /// </summary>
        /// <param name="pointer">The pointer that raised the event.</param>
        /// <param name="hotSpot">The teleport target</param>
        private void RaiseTeleportComplete(IMixedRealityPointer pointer, IMixedRealityTeleportHotspot hotSpot)
        {
            if (!isTeleporting)
            {
                Debug.LogError("No Active Teleportation in progress.");
                return;
            }

            using (RaiseTeleportCompletePerfMarker.Auto())
            {
                // initialize event
                teleportEventData.Initialize(pointer, hotSpot);

                // Pass handler
                HandleEvent(teleportEventData, OnTeleportCompletedHandler);

                isTeleporting = false;
            }
        }

        private static readonly ExecuteEvents.EventFunction<IMixedRealityTeleportHandler> OnTeleportCanceledHandler =
            delegate (IMixedRealityTeleportHandler handler, BaseEventData eventData)
            {
                var casted = ExecuteEvents.ValidateEventData<TeleportEventData>(eventData);
                handler.OnTeleportCanceled(casted);
            };

        private static readonly ProfilerMarker RaiseTeleportCanceledPerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.RaiseTeleportHandled");

        /// <inheritdoc />
        public void RaiseTeleportCanceled(IMixedRealityPointer pointer, IMixedRealityTeleportHotspot hotSpot)
        {
            using (RaiseTeleportCanceledPerfMarker.Auto())
            {
                // initialize event
                teleportEventData.Initialize(pointer, hotSpot);

                // Pass handler
                HandleEvent(teleportEventData, OnTeleportCanceledHandler);
            }
        }

        #endregion IMixedRealityTeleportSystem Implementation

        private static readonly ProfilerMarker ProcessTeleportationRequestPerfMarker = new ProfilerMarker("[MRTK] MixedRealityTeleportSystem.ProcessTeleportationRequest");

        private void ProcessTeleportationRequest(TeleportEventData eventData)
        {
            using (ProcessTeleportationRequestPerfMarker.Auto())
            {
                isProcessingTeleportRequest = true;

                targetRotation = Vector3.zero;
                if (eventData.Pointer is IMixedRealityTeleportPointer teleportPointer && !teleportPointer.IsNull())
                {
                    targetRotation.y = teleportPointer.PointerOrientation;
                }
                targetPosition = eventData.Pointer.Result.Details.Point;

                if (eventData.Hotspot != null)
                {
                    targetPosition = eventData.Hotspot.Position;

                    if (eventData.Hotspot.OverrideOrientation)
                    {
                        targetRotation.y = eventData.Hotspot.TargetRotation;
                    }
                }

                float height = targetPosition.y;
                targetPosition -= CameraCache.Main.transform.position - MixedRealityPlayspace.Position;
                targetPosition.y = height;

                MixedRealityPlayspace.Position = targetPosition;
                MixedRealityPlayspace.RotateAround(
                            CameraCache.Main.transform.position,
                            Vector3.up,
                            targetRotation.y - CameraCache.Main.transform.eulerAngles.y);

                isProcessingTeleportRequest = false;

                // Raise complete event using the pointer and hot spot provided.
                RaiseTeleportComplete(eventData.Pointer, eventData.Hotspot);
            }
        }
    }
}