#if INPUTSYSTEM_SUPPORT && UX_NAVIGATION
using AlicizaX;
using AlicizaX.UI.Runtime;
using UnityEngine.EventSystems;

namespace UnityEngine.UI
{
    public interface IUXNavigationCursorPolicy
    {
        void OnInputModeChanged(UXInputMode mode, UXNavigationScope topScope);
    }

    public sealed class UXNavigationRuntime : MonoBehaviour
    {
        private const int InitialScopeCapacity = 64;
        private const int InvalidIndex = -1;

        private static UXNavigationRuntime _instance;
        private static IUXNavigationCursorPolicy _cursorPolicy;

        private UXNavigationScope[] _scopes = new UXNavigationScope[InitialScopeCapacity];
        private int[] _freeIndices = new int[InitialScopeCapacity];
        private int _freeCount;
        private int _scopeCount;
        private int _scopeCapacityHighWater;

        private UXNavigationScope _topScope;
        private ulong _activationSerial;
        private bool _stateDirty = true;
        private bool _suppressionDirty = true;

        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterSceneLoad)]
        private static void Bootstrap()
        {
            if (!AppServices.TryGetApp<IUIService>(out var uiService) || uiService == null)
            {
                return;
            }

            EnsureInstance();
            UXInputModeService.EnsureInstance();
        }

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

            GameObject 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;
        }

        public static void SetCursorPolicy(IUXNavigationCursorPolicy cursorPolicy)
        {
            _cursorPolicy = cursorPolicy;
        }

        public static void NotifySelection(GameObject selectedObject)
        {
            if (_instance != null)
            {
                _instance.RecordSelection(selectedObject);
            }
        }

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

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

            return scope == _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 || scope.RuntimeIndex != InvalidIndex)
            {
                return;
            }

            int index;
            if (_freeCount > 0)
            {
                index = _freeIndices[--_freeCount];
            }
            else
            {
                if (_scopeCapacityHighWater >= _scopes.Length)
                {
                    ReportCapacityExceeded("UXNavigationRuntime scope capacity exceeded.");
                    return;
                }

                index = _scopeCapacityHighWater++;
            }

            _scopes[index] = scope;
            scope.RuntimeIndex = index;
            _scopeCount++;
            MarkStateDirty();
        }

        internal void UnregisterScope(UXNavigationScope scope)
        {
            if (scope == null)
            {
                return;
            }

            int index = scope.RuntimeIndex;
            if (index < 0 || index >= _scopes.Length || _scopes[index] != scope)
            {
                return;
            }

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

            scope.IsAvailable = false;
            scope.WasAvailable = false;
            scope.SetNavigationSuppressed(false);
            scope.RuntimeIndex = InvalidIndex;
            _scopes[index] = null;
            _freeIndices[_freeCount++] = index;
            _scopeCount--;
            MarkStateDirty();
        }

        internal void MarkStateDirty()
        {
            _stateDirty = true;
            _suppressionDirty = true;
        }

        internal void MarkSuppressionDirty()
        {
            _suppressionDirty = true;
        }

        internal void InvalidateSkipCaches()
        {
            for (int i = 0; i < _scopeCapacityHighWater; i++)
            {
                UXNavigationScope scope = _scopes[i];
                if (scope != null)
                {
                    scope.InvalidateSkipCacheOnly();
                }
            }

            MarkStateDirty();
        }

        private void FlushStateIfDirty()
        {
            if (_stateDirty)
            {
                UXNavigationScope newTopScope = FindTopScope();
                _stateDirty = false;
                if (!ReferenceEquals(_topScope, newTopScope))
                {
                    _topScope = newTopScope;
                    _suppressionDirty = true;
                }
            }

            if (_suppressionDirty)
            {
                ApplyScopeSuppression();
                _suppressionDirty = false;
            }

            if (UXInputModeService.CurrentMode == UXInputMode.Gamepad || UXInputModeService.CurrentMode == UXInputMode.Keyboard)
            {
                EnsureNavigationSelection();
            }
        }

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

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

                    _suppressionDirty = true;
                }

                if (available && (bestScope == null || IsHigherPriority(scope, bestScope)))
                {
                    bestScope = scope;
                }
            }

            return bestScope;
        }

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

            Canvas canvas = scope.Canvas;
            return canvas != null
                   && canvas.gameObject.layer == UIComponent.UIShowLayer
                   && !scope.IsNavigationSkipped
                   && scope.HasAvailableSelectable();
        }

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

                bool suppress = scope.IsAvailable
                                && _topScope != null
                                && scope != _topScope
                                && _topScope.BlockLowerScopes
                                && IsHigherPriority(_topScope, scope);
                scope.SetNavigationSuppressed(suppress);
            }
        }

        private void EnsureNavigationSelection()
        {
            EventSystem eventSystem = EventSystem.current;
            if (eventSystem == null || _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);
            GameObject selectedObject = eventSystem.currentSelectedGameObject;
            if (selectedObject != null)
            {
                _topScope.RecordSelection(selectedObject);
            }
        }

        private void RecordSelection(GameObject selectedObject)
        {
            if (_stateDirty || _suppressionDirty)
            {
                FlushStateIfDirty();
            }

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

        private void OnInputModeChanged(UXInputMode mode)
        {
            _cursorPolicy?.OnInputModeChanged(mode, _topScope);
            if (mode == UXInputMode.Gamepad || mode == UXInputMode.Keyboard)
            {
                FlushStateIfDirty();
                EnsureNavigationSelection();
            }
        }

        private static bool IsHigherPriority(UXNavigationScope left, UXNavigationScope right)
        {
            int leftOrder = left.Canvas != null ? left.Canvas.sortingOrder : int.MinValue;
            int rightOrder = right.Canvas != null ? right.Canvas.sortingOrder : int.MinValue;
            if (leftOrder != rightOrder)
            {
                return leftOrder > rightOrder;
            }

            int leftDepth = left.GetHierarchyDepth();
            int rightDepth = right.GetHierarchyDepth();
            if (leftDepth != rightDepth)
            {
                return leftDepth > rightDepth;
            }

            return left.ActivationSerial > right.ActivationSerial;
        }

        private static void ReportCapacityExceeded(string message)
        {
#if UNITY_EDITOR || DEVELOPMENT_BUILD
            Debug.LogError(message);
#endif
        }
    }
}
#endif