using UnityEngine;
using UnityEngine.InputSystem;
using UnityEngine.UI;
using Unheimlich.Core;
using Unheimlich.Features.DetectiveBoard;
using Unheimlich.Features.Player;
using Unheimlich.World.CameraSystem;
using System.Collections.Generic;
using UnityEngine.EventSystems;

namespace Unheimlich.Features.DetectiveBoard.UI
{
    /// <summary>
    /// Handles mouse interaction for the detective board World Space canvas.
    /// Manages hover, selection, dragging, and click forwarding for Post-It nodes.
    /// Interactions are only active when the board is in inspection mode.
    /// </summary>
    public class DetectiveBoardInteraction : Singleton<DetectiveBoardInteraction>
    {
        [Header("Settings")]
        [SerializeField] private LayerMask _boardLayer;
        [SerializeField] private float _minInteractionDistance = 0.1f;
        [SerializeField] private float _maxInteractionDistance = 10f;
        
        private Camera _camera;
        private Canvas _boardCanvas;
        private RectTransform _boardArea;
        private DetectiveBoardController _boardController;
        private DetectiveBoardCanvas _canvasManager;
        private PostItNode _hoveredNode;
        private PostItNode _selectedNode;
        private ConnectionLine _hoveredLine;
        private bool _isDragging;
        private Plane _canvasPlane;
        private Vector3 _dragOffset;
        
        protected override void OnAwake() { }

        private void Start()
        {
            _boardCanvas = GetComponent<Canvas>();
            _canvasManager = GetComponent<DetectiveBoardCanvas>();
            _boardController = DetectiveBoardController.Instance;
            
            if (_canvasManager != null && _canvasManager.BoardArea != null)
                _boardArea = _canvasManager.BoardArea;
            
            if (PlayerController.Instance != null)
                _camera = PlayerController.Instance.PlayerCamera;
            
            if (_camera == null)
                _camera = Camera.main;
            
            UpdateCanvasPlane();
        }
        
        private void Update()
        {
            if (!IsInBoardInteractionMode())
            {
                ClearInteractionState();
                return;
            }
            
            UpdateCameraReference();
            UpdateCanvasPlane();
            
            if (_isDragging)
            {
                HandleDrag();
            }
            else
            {
                HandleHover();
                HandleLineHover();
            }
            
            HandleClick();
        }
        
        private void UpdateCameraReference()
        {
            if (DetectiveBoardVirtualCamera.Instance != null && DetectiveBoardVirtualCamera.Instance.IsActive)
            {
                _camera = DetectiveBoardVirtualCamera.Instance.VirtualCamera;
            }
            else if (PlayerController.Instance != null)
            {
                _camera = PlayerController.Instance.PlayerCamera;
            }
            else if (_camera == null)
            {
                _camera = Camera.main;
            }
        }
        
        private bool IsInBoardInteractionMode()
        {
            bool isActive = _boardController != null && _boardController.IsBoardActive;
            
            return isActive;
        }
        
        private void ClearInteractionState()
        {
            if (_hoveredNode != null)
            {
                _hoveredNode.SetHovered(false);
                _hoveredNode = null;
            }
            
            if (_hoveredLine != null && _canvasManager != null)
            {
                _canvasManager.SetHoveredLine(null);
                _hoveredLine = null;
            }
            
            if (_selectedNode != null && _isDragging)
            {
                _selectedNode.SetSelected(false);
                _selectedNode = null;
                _isDragging = false;
            }
        }
        
        private void UpdateCanvasPlane()
        {
            if (_boardCanvas != null)
            {
                Vector3 planeNormal = -_boardCanvas.transform.forward;
                Vector3 planePosition = _boardCanvas.transform.position;
                _canvasPlane = new Plane(planeNormal, planePosition);
            }
        }
        
        private void HandleHover()
        {
            PostItNode hitNode = RaycastForNode();
            
            if (hitNode != _hoveredNode)
            {
                if (_hoveredNode != null)
                {
                    _hoveredNode.SetHovered(false);
                }
                
                _hoveredNode = hitNode;
                
                if (_hoveredNode != null)
                {
                    _hoveredNode.SetHovered(true);
                }
            }
        }
        
        private void HandleLineHover()
        {
            if (_canvasManager == null || Mouse.current == null)
                return;
            
            if (_hoveredNode != null)
            {
                if (_hoveredLine != null)
                {
                    _canvasManager.SetHoveredLine(null);
                    _hoveredLine = null;
                }
                return;
            }
            
            ConnectionLine hitLine = RaycastForLine();
            
            if (hitLine != _hoveredLine)
            {
                _canvasManager.SetHoveredLine(hitLine);
                _hoveredLine = hitLine;
            }
        }
        
        private ConnectionLine RaycastForLine()
        {
            if (_camera == null || Mouse.current == null)
                return null;
            
            Vector2 mousePos = Mouse.current.position.ReadValue();
            
            GraphicRaycaster raycaster = _boardCanvas?.GetComponent<GraphicRaycaster>();
            if (raycaster != null && EventSystem.current != null)
            {
                var pointerEventData = new PointerEventData(EventSystem.current)
                {
                    position = mousePos
                };
                
                var results = new List<RaycastResult>();
                raycaster.Raycast(pointerEventData, results);
                
                foreach (var result in results)
                {
                    ConnectionLine line = result.gameObject.GetComponentInParent<ConnectionLine>();
                    if (line != null)
                        return line;
                }
            }
            
            return null;
        }
        
        private void HandleClick()
        {
            if (Mouse.current == null)
                return;
            
            PostItNode hitNode = RaycastForNode();
            
            if (Mouse.current.leftButton.wasPressedThisFrame)
            {
                if (hitNode != null)
                {
                    HandleLeftClick(hitNode);
                }
                else
                {
                    ConnectionLine hitLine = RaycastForLine();
                    if (hitLine != null && _canvasManager != null)
                    {
                        _canvasManager.OnLineClicked(hitLine);
                    }
                }
            }
            else if (Mouse.current.rightButton.wasPressedThisFrame && hitNode != null && _canvasManager != null)
            {
                _canvasManager.OnNodeRightClicked(hitNode);
            }
        }
        
        private void HandleLeftClick(PostItNode hitNode)
        {
            if (_canvasManager != null && _canvasManager.IsConnectMode)
            {
                if (hitNode != null)
                {
                    _canvasManager.OnNodeClicked(hitNode);
                }
                return;
            }
            
            if (_isDragging)
            {
                _isDragging = false;
                
                if (_selectedNode != null && hitNode == _selectedNode)
                {
                    return;
                }
                
                if (_selectedNode != null)
                {
                    _selectedNode.SetSelected(false);
                }
                
                if (hitNode != null)
                {
                    _selectedNode = hitNode;
                    _selectedNode.SetSelected(true);
                    _isDragging = true;
                    CalculateDragOffset();
                }
                else
                {
                    _selectedNode = null;
                }
            }
            else
            {
                if (hitNode != null)
                {
                    if (_selectedNode != null && _selectedNode != hitNode)
                    {
                        _selectedNode.SetSelected(false);
                    }
                    
                    _selectedNode = hitNode;
                    _selectedNode.SetSelected(true);
                    _isDragging = true;
                    CalculateDragOffset();
                }
                else
                {
                    if (_selectedNode != null)
                    {
                        _selectedNode.SetSelected(false);
                        _selectedNode = null;
                    }
                }
            }
        }
        
        private void HandleDrag()
        {
            if (_selectedNode == null || _camera == null)
                return;
            
            Vector2 mousePos = Mouse.current.position.ReadValue();
            Ray ray = _camera.ScreenPointToRay(new Vector3(mousePos.x, mousePos.y, 0));
            
            if (_canvasPlane.Raycast(ray, out float enter))
            {
                Vector3 worldHitPoint = ray.GetPoint(enter);
                Vector3 newWorldPos = worldHitPoint + _dragOffset;
                
                Vector3 localPos = _boardCanvas.transform.InverseTransformPoint(newWorldPos);
                Vector2 clampedPos = ClampPositionToBoard(new Vector2(localPos.x, localPos.y));
                
                _selectedNode.SetPosition(clampedPos);
                
                if (_canvasManager != null)
                {
                    _canvasManager.UpdateConnectionsForNode(_selectedNode);
                }
            }
        }
        
        private Vector2 ClampPositionToBoard(Vector2 position)
        {
            if (_boardArea == null)
                return position;
            
            Rect boardRect = _boardArea.rect;
            float halfWidth = boardRect.width * 0.5f;
            float halfHeight = boardRect.height * 0.5f;
            
            float clampedX = Mathf.Clamp(position.x, -halfWidth, halfWidth);
            float clampedY = Mathf.Clamp(position.y, -halfHeight, halfHeight);
            
            return new Vector2(clampedX, clampedY);
        }
        
        private void CalculateDragOffset()
        {
            if (_selectedNode == null || _camera == null)
                return;
            
            Vector2 mousePos = Mouse.current.position.ReadValue();
            Ray ray = _camera.ScreenPointToRay(new Vector3(mousePos.x, mousePos.y, 0));
            
            if (_canvasPlane.Raycast(ray, out float enter))
            {
                Vector3 worldHitPoint = ray.GetPoint(enter);
                Vector3 currentWorldPos = _selectedNode.transform.position;
                _dragOffset = currentWorldPos - worldHitPoint;
            }
        }
        
        /// <summary>
        /// Positions a freshly-created board node under the current mouse cursor
        /// and immediately enters drag mode on it, so the player can place it freely.
        /// Called by ClueHandUI after AddClueNode.
        /// </summary>
        public void SpawnNodeUnderMouseAndDrag(PostItNode node)
        {
            if (node == null || _camera == null)
                return;

            UpdateCanvasPlane();

            Vector2 mousePos = Mouse.current != null
                ? Mouse.current.position.ReadValue()
                : new Vector2(Screen.width * 0.5f, Screen.height * 0.5f);

            Ray ray = _camera.ScreenPointToRay(new Vector3(mousePos.x, mousePos.y, 0f));

            if (_canvasPlane.Raycast(ray, out float enter))
            {
                Vector3 worldHitPoint = ray.GetPoint(enter);
                Vector3 localPos = _boardCanvas.transform.InverseTransformPoint(worldHitPoint);
                node.SetPosition(new Vector2(localPos.x, localPos.y));
            }

            // Begin drag with zero offset so the node centre tracks the mouse exactly
            if (_selectedNode != null)
                _selectedNode.SetSelected(false);

            _selectedNode = node;
            _selectedNode.SetSelected(true);
            _isDragging = true;
            _dragOffset = Vector3.zero;
        }

        private PostItNode RaycastForNode()
        {
            if (_camera == null || Mouse.current == null)
                return null;
            
            Vector2 mousePos = Mouse.current.position.ReadValue();
            
            GraphicRaycaster raycaster = _boardCanvas?.GetComponent<GraphicRaycaster>();
            if (raycaster != null && EventSystem.current != null)
            {
                var pointerEventData = new PointerEventData(EventSystem.current)
                {
                    position = mousePos
                };
                
                var results = new List<RaycastResult>();
                raycaster.Raycast(pointerEventData, results);
                
                foreach (var result in results)
                {
                    PostItNode node = result.gameObject.GetComponentInParent<PostItNode>();
                    if (node != null)
                        return node;
                }
            }
            
            Ray ray = _camera.ScreenPointToRay(new Vector3(mousePos.x, mousePos.y, 0));
            
            if (Physics.Raycast(ray, out RaycastHit hit, _maxInteractionDistance, _boardLayer))
            {
                float distance = hit.distance;
                if (distance >= _minInteractionDistance)
                {
                    return hit.collider.GetComponentInParent<PostItNode>();
                }
            }
            
            return null;
        }
    }
}