#if INPUTSYSTEM_SUPPORT
using System.Collections.Generic;
using AlicizaX;
using AlicizaX.UI.Runtime;
using UnityEngine.EventSystems;

namespace UnityEngine.UI
{
    internal sealed class UXNavigationRuntime : MonoBehaviour
    {
        private static UXNavigationRuntime _instance;

        private const float DiscoveryInterval = 0.5f;
        private readonly HashSet<UXNavigationScope> _scopeSet = new();
        private readonly List<UXNavigationScope> _scopes = new(32);
        private readonly HashSet<Transform> _interactiveLayerRoots = new();

        private Transform _uiCanvasRoot;
        private UXNavigationScope _topScope;
        private GameObject _lastObservedSelection;
        private float _nextDiscoveryTime;
        private bool _discoveryDirty = true;
        private ulong _activationSerial;
        private bool _missingEventSystemLogged;

        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterSceneLoad)]
        private static void Bootstrap()
        {
            EnsureInstance();
            UXInputModeService.EnsureInstance();
        }

        internal static UXNavigationRuntime EnsureInstance()
        {
            if (_instance != null)
            {
                return _instance;
            }

            var go = new GameObject("[UXNavigationRuntime]");
            go.hideFlags = HideFlags.HideAndDontSave;
            DontDestroyOnLoad(go);
            _instance = go.AddComponent<UXNavigationRuntime>();
            return _instance;
        }

        internal static bool TryGetInstance(out UXNavigationRuntime runtime)
        {
            runtime = _instance;
            return runtime != null;
        }

        internal static bool IsHolderWithinTopScope(UIHolderObjectBase holder)
        {
            if (_instance == null || _instance._topScope == null || holder == null)
            {
                return true;
            }

            return _instance.IsHolderOwnedByScope(holder, _instance._topScope);
        }

        private void Awake()
        {
            if (_instance != null && _instance != this)
            {
                Destroy(gameObject);
                return;
            }

            _instance = this;
            DontDestroyOnLoad(gameObject);
            hideFlags = HideFlags.HideAndDontSave;
        }

        private void OnEnable()
        {
            UXInputModeService.OnModeChanged += OnInputModeChanged;
        }

        private void OnDisable()
        {
            UXInputModeService.OnModeChanged -= OnInputModeChanged;
        }

        private void OnDestroy()
        {
            UXInputModeService.OnModeChanged -= OnInputModeChanged;
            if (_instance == this)
            {
                _instance = null;
            }
        }

        internal void RegisterScope(UXNavigationScope scope)
        {
            if (scope == null || !_scopeSet.Add(scope))
            {
                return;
            }

            _scopes.Add(scope);
            MarkDiscoveryDirty();
        }

        internal void UnregisterScope(UXNavigationScope scope)
        {
            if (scope == null || !_scopeSet.Remove(scope))
            {
                return;
            }

            if (_topScope == scope)
            {
                _topScope = null;
            }

            scope.SetNavigationSuppressed(false);
            _scopes.Remove(scope);
            MarkDiscoveryDirty();
        }

        internal void MarkDiscoveryDirty()
        {
            _discoveryDirty = true;
        }

        private void Update()
        {
            TryBindUIRoot();
            if (_uiCanvasRoot == null)
            {
                return;
            }

            if (_discoveryDirty || Time.unscaledTime >= _nextDiscoveryTime)
            {
                DiscoverScopes();
            }

            UXNavigationScope newTopScope = FindTopScope();
            if (!ReferenceEquals(_topScope, newTopScope))
            {
                _topScope = newTopScope;
            }

            ApplyScopeSuppression();

            if (UXInputModeService.CurrentMode == UXInputMode.Gamepad)
            {
                EnsureGamepadSelection();
                if (_topScope != null)
                {
                    Cursor.visible = false;
                }
            }

            TrackSelection();
        }

        private void TryBindUIRoot()
        {
            if (_uiCanvasRoot != null)
            {
                return;
            }

            IUIModule uiModule = ModuleSystem.GetModule<IUIModule>();
            if (uiModule?.UICanvasRoot == null)
            {
                return;
            }

            _uiCanvasRoot = uiModule.UICanvasRoot;
            CacheInteractiveLayers();
            DiscoverScopes();
        }

        private void CacheInteractiveLayers()
        {
            _interactiveLayerRoots.Clear();
            if (_uiCanvasRoot == null)
            {
                return;
            }

            string cacheLayerName = $"Layer{(int)UILayer.All}-{UILayer.All}";
            for (int i = 0; i < _uiCanvasRoot.childCount; i++)
            {
                Transform child = _uiCanvasRoot.GetChild(i);
                if (child == null || child.name == cacheLayerName)
                {
                    continue;
                }

                _interactiveLayerRoots.Add(child);
                if (child.GetComponent<UXNavigationLayerWatcher>() == null)
                {
                    var watcher = child.gameObject.AddComponent<UXNavigationLayerWatcher>();
                    watcher.Initialize(this);
                }
            }
        }

        private void DiscoverScopes()
        {
            _discoveryDirty = false;
            _nextDiscoveryTime = Time.unscaledTime + DiscoveryInterval;
            CacheInteractiveLayers();
            bool addedScope = false;

            foreach (Transform layerRoot in _interactiveLayerRoots)
            {
                if (layerRoot == null || IsNavigationSkipped(layerRoot))
                {
                    continue;
                }

                UIHolderObjectBase[] holders = layerRoot.GetComponentsInChildren<UIHolderObjectBase>(true);
                for (int i = 0; i < holders.Length; i++)
                {
                    UIHolderObjectBase holder = holders[i];
                    if (holder == null
                        || holder.GetComponent<UXNavigationScope>() != null
                        || IsNavigationSkipped(holder.transform))
                    {
                        continue;
                    }

                    holder.gameObject.AddComponent<UXNavigationScope>();
                    addedScope = true;
                }
            }

            if (addedScope)
            {
                for (int i = 0; i < _scopes.Count; i++)
                {
                    _scopes[i]?.InvalidateSelectableCache();
                }
            }
        }

        private UXNavigationScope FindTopScope()
        {
            UXNavigationScope bestScope = null;
            for (int i = 0; i < _scopes.Count; i++)
            {
                UXNavigationScope scope = _scopes[i];
                if (scope == null)
                {
                    continue;
                }

                bool available = IsScopeAvailable(scope);
                if (scope.WasAvailable != available)
                {
                    scope.WasAvailable = available;
                    if (available)
                    {
                        scope.ActivationSerial = ++_activationSerial;
                    }
                }

                if (!available)
                {
                    continue;
                }

                if (bestScope == null || CompareScopePriority(scope, bestScope) < 0)
                {
                    bestScope = scope;
                }
            }

            return bestScope;
        }

        private bool IsScopeAvailable(UXNavigationScope scope)
        {
            if (scope == null || !scope.isActiveAndEnabled || !scope.gameObject.activeInHierarchy)
            {
                return false;
            }

            Canvas canvas = scope.Canvas;
            if (canvas == null || canvas.gameObject.layer != UIComponent.UIShowLayer)
            {
                return false;
            }

            return !IsNavigationSkipped(scope.transform)
                   && scope.HasAvailableSelectable()
                   && TryGetInteractiveLayerRoot(scope.transform, out _);
        }

        private static bool IsNavigationSkipped(Transform current)
        {
            return current != null && current.GetComponentInParent<UXNavigationSkip>(true) != null;
        }

        private bool TryGetInteractiveLayerRoot(Transform current, out Transform layerRoot)
        {
            layerRoot = null;
            if (current == null || _uiCanvasRoot == null)
            {
                return false;
            }

            while (current != null)
            {
                if (current.parent == _uiCanvasRoot)
                {
                    layerRoot = current;
                    return _interactiveLayerRoots.Contains(current);
                }

                current = current.parent;
            }

            return false;
        }

        private bool IsHolderOwnedByScope(UIHolderObjectBase holder, UXNavigationScope scope)
        {
            if (holder == null || scope == null)
            {
                return false;
            }

            UXNavigationScope nearestScope = holder.GetComponent<UXNavigationScope>();
            if (nearestScope == null)
            {
                nearestScope = holder.GetComponentInParent<UXNavigationScope>(true);
            }

            return nearestScope == scope;
        }

        private void ApplyScopeSuppression()
        {
            for (int i = 0; i < _scopes.Count; i++)
            {
                UXNavigationScope scope = _scopes[i];
                if (scope == null)
                {
                    continue;
                }

                bool suppress = IsScopeAvailable(scope)
                    && _topScope != null
                    && !ReferenceEquals(scope, _topScope)
                    && _topScope.BlockLowerScopes
                    && CompareScopePriority(_topScope, scope) < 0;
                scope.SetNavigationSuppressed(suppress);
            }
        }

        private void EnsureGamepadSelection()
        {
            EventSystem eventSystem = EventSystem.current;
            if (eventSystem == null)
            {
                if (!_missingEventSystemLogged)
                {
                    Debug.LogWarning("UXNavigationRuntime requires an active EventSystem for gamepad navigation.");
                    _missingEventSystemLogged = true;
                }

                return;
            }

            _missingEventSystemLogged = false;

            if (_topScope == null || !_topScope.RequireSelectionWhenGamepad)
            {
                return;
            }

            GameObject currentSelected = eventSystem.currentSelectedGameObject;
            if (_topScope.IsSelectableOwnedAndValid(currentSelected))
            {
                _topScope.RecordSelection(currentSelected);
                return;
            }

            Selectable preferred = _topScope.GetPreferredSelectable();
            eventSystem.SetSelectedGameObject(preferred != null ? preferred.gameObject : null);
            _lastObservedSelection = eventSystem.currentSelectedGameObject;
            if (_lastObservedSelection != null)
            {
                _topScope.RecordSelection(_lastObservedSelection);
            }
        }

        private void TrackSelection()
        {
            EventSystem eventSystem = EventSystem.current;
            if (eventSystem == null)
            {
                _lastObservedSelection = null;
                return;
            }

            GameObject currentSelected = eventSystem.currentSelectedGameObject;
            if (ReferenceEquals(_lastObservedSelection, currentSelected))
            {
                return;
            }

            _lastObservedSelection = currentSelected;
            if (_topScope != null && _topScope.IsSelectableOwnedAndValid(currentSelected))
            {
                _topScope.RecordSelection(currentSelected);
            }
        }

        private void OnInputModeChanged(UXInputMode mode)
        {
            EventSystem eventSystem = EventSystem.current;
            if (mode == UXInputMode.Pointer)
            {
                if (_topScope != null)
                {
                    Cursor.visible = true;
                    if (eventSystem != null)
                    {
                        eventSystem.SetSelectedGameObject(null);
                    }
                }

                _lastObservedSelection = null;
                return;
            }

            if (_topScope != null)
            {
                Cursor.visible = false;
            }

            EnsureGamepadSelection();
        }

        private static int CompareScopePriority(UXNavigationScope left, UXNavigationScope right)
        {
            int leftOrder = left.Canvas != null ? left.Canvas.sortingOrder : int.MinValue;
            int rightOrder = right.Canvas != null ? right.Canvas.sortingOrder : int.MinValue;
            int orderCompare = rightOrder.CompareTo(leftOrder);
            if (orderCompare != 0)
            {
                return orderCompare;
            }

            int hierarchyCompare = right.GetHierarchyDepth().CompareTo(left.GetHierarchyDepth());
            if (hierarchyCompare != 0)
            {
                return hierarchyCompare;
            }

            return right.ActivationSerial.CompareTo(left.ActivationSerial);
        }
    }
}
#endif