using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using AppleHills.Core.Settings;
using Core.Lifecycle;
using Core.SaveLoad;
using UI;
using UnityEngine;
using UnityEngine.SceneManagement;

namespace Core
{
    /// <summary>
    /// Singleton service for loading and unloading Unity scenes asynchronously, with events for progress and completion.
    /// </summary>
    public class SceneManagerService : ManagedBehaviour
    {
        private LoadingScreenController _loadingScreen;
        private static SceneManagerService _instance;
        
        /// <summary>
        /// Singleton instance of the SceneManagerService. No longer creates an instance if one doesn't exist.
        /// </summary>
        public static SceneManagerService Instance => _instance;

        // Events for scene lifecycle
        // NOTE: Most components should use lifecycle hooks (OnSceneReady, OnSceneUnloading)
        // instead of subscribing to these events. Events are primarily for orchestration.
        
        /// <summary>
        /// Fired when a scene starts loading. Used by loading screen orchestration.
        /// </summary>
        public event Action<string> SceneLoadStarted;
        
        /// <summary>
        /// Fired when a scene finishes loading.
        /// Used by loading screen orchestration and cross-scene components (e.g., PauseMenu).
        /// For component initialization, use OnSceneReady() lifecycle hook instead.
        /// </summary>
        public event Action<string> SceneLoadCompleted;

        private readonly Dictionary<string, AsyncOperation> _activeLoads = new();
        private readonly Dictionary<string, AsyncOperation> _activeUnloads = new();
        private LogVerbosity _logVerbosity = LogVerbosity.Debug;
        private const string BootstrapSceneName = "BootstrapScene";

        // ManagedBehaviour configuration
        public override int ManagedAwakePriority => 15; // Core infrastructure, after GameManager

        private new void Awake()
        {
            base.Awake(); // CRITICAL: Register with LifecycleManager!
            
            // Set instance immediately so it's available before OnManagedAwake() is called
            _instance = this;
            
            // Initialize current scene tracking - critical for scene management
            InitializeCurrentSceneTracking();
            
            // Ensure BootstrapScene is loaded at startup
            var bootstrap = SceneManager.GetSceneByName(BootstrapSceneName);
            if (!bootstrap.isLoaded)
            {
                SceneManager.LoadScene(BootstrapSceneName, LoadSceneMode.Additive);
            }
        }

        protected override void OnManagedAwake()
        {
            // Set up loading screen reference and events
            // This must happen in ManagedAwake because LoadingScreenController instance needs to be set first
            _loadingScreen = LoadingScreenController.Instance;
            SetupLoadingScreenEvents();
            
            // Load verbosity settings
            _logVerbosity = DeveloperSettingsProvider.Instance.GetSettings<DebugSettings>().sceneLogVerbosity;
            
            LogDebugMessage($"SceneManagerService initialized, current scene is: {CurrentGameplayScene}");
        }

        /// <summary>
        /// Initialize current scene tracking immediately in Awake
        /// This ensures scene management works correctly regardless of boot timing
        /// </summary>
        private void InitializeCurrentSceneTracking()
        {
            // Get the active scene and use it as the current gameplay scene
            Scene activeScene = SceneManager.GetActiveScene();
            
            if (activeScene.IsValid())
            {
                // If this is the MainMenu or another gameplay scene, track it
                if (activeScene.name != BootstrapSceneName)
                {
                    CurrentGameplayScene = activeScene.name;
                    LogDebugMessage($"Initialized with current scene: {CurrentGameplayScene}");
                }
                // Otherwise default to MainMenu
                else
                {
                    CurrentGameplayScene = "AppleHillsOverworld";
                    LogDebugMessage($"Initialized with default scene: {CurrentGameplayScene}");
                }
            }
            else
            {
                CurrentGameplayScene = "AppleHillsOverworld";
                LogDebugMessage($"No valid active scene, defaulting to: {CurrentGameplayScene}");
            }
        }
    
        private void SetupLoadingScreenEvents()
        {
            if (_loadingScreen == null) return;
    
            SceneLoadStarted += _ => _loadingScreen.ShowLoadingScreen(() => GetAggregateLoadProgress());
            SceneLoadCompleted += _ => _loadingScreen.HideLoadingScreen();
        }

        /// <summary>
        /// Load a single scene asynchronously (additive).
        /// </summary>
        /// <param name="sceneName">Name of the scene to load.</param>
        /// <param name="progress">Optional progress reporter.</param>
        public async Task LoadSceneAsync(string sceneName, IProgress<float> progress = null)
        {
            SceneLoadStarted?.Invoke(sceneName);
            var op = SceneManager.LoadSceneAsync(sceneName, LoadSceneMode.Additive);
            _activeLoads[sceneName] = op;
            while (!op.isDone)
            {
                progress?.Report(op.progress);
                await Task.Yield();
            }
            _activeLoads.Remove(sceneName);
            SceneLoadCompleted?.Invoke(sceneName);
        }

        /// <summary>
        /// Unload a single scene asynchronously.
        /// </summary>
        /// <param name="sceneName">Name of the scene to unload.</param>
        /// <param name="progress">Optional progress reporter.</param>
        public async Task UnloadSceneAsync(string sceneName, IProgress<float> progress = null)
        {
            var scene = SceneManager.GetSceneByName(sceneName);
            if (!scene.isLoaded)
            {
                Logging.Warning($"[SceneManagerService] Attempted to unload scene '{sceneName}', but it is not loaded.");
                return;
            }
            
            var op = SceneManager.UnloadSceneAsync(sceneName);
            _activeUnloads[sceneName] = op;
            while (!op.isDone)
            {
                progress?.Report(op.progress);
                await Task.Yield();
            }
            _activeUnloads.Remove(sceneName);
        }

        /// <summary>
        /// Load multiple scenes asynchronously.
        /// </summary>
        /// <param name="sceneNames">Enumerable of scene names to load.</param>
        /// <param name="progress">Optional progress reporter.</param>
        public async Task LoadScenesAsync(IEnumerable<string> sceneNames, IProgress<float> progress = null)
        {
            // Show loading screen at the start of multiple scene loading
            if (_loadingScreen != null)
            {
                _loadingScreen.ShowLoadingScreen();
            }
        
            int total = 0;
            int done = 0;
            var ops = new List<AsyncOperation>();
            foreach (var name in sceneNames)
            {
                total++;
                var op = SceneManager.LoadSceneAsync(name, LoadSceneMode.Additive);
                _activeLoads[name] = op;
                ops.Add(op);
                SceneLoadStarted?.Invoke(name);
            }
        
            while (done < total)
            {
                done = 0;
                float aggregate = 0f;
                foreach (var op in ops)
                {
                    if (op.isDone) done++;
                    aggregate += op.progress;
                }
                float avgProgress = aggregate / total;
                progress?.Report(avgProgress);
            
                await Task.Yield();
            }
        
            foreach (var name in sceneNames)
            {
                _activeLoads.Remove(name);
                SceneLoadCompleted?.Invoke(name);
            }
        
            // Hide loading screen after all scenes are loaded
            if (_loadingScreen != null)
            {
                _loadingScreen.HideLoadingScreen();
            }
        }

        /// <summary>
        /// Unload multiple scenes asynchronously.
        /// </summary>
        /// <param name="sceneNames">Enumerable of scene names to unload.</param>
        /// <param name="progress">Optional progress reporter.</param>
        public async Task UnloadScenesAsync(IEnumerable<string> sceneNames, IProgress<float> progress = null)
        {
            // Show loading screen at the start of multiple scene unloading
            if (_loadingScreen != null)
            {
                _loadingScreen.ShowLoadingScreen();
            }
        
            int total = 0;
            int done = 0;
            var ops = new List<AsyncOperation>();
            foreach (var name in sceneNames)
            {
                total++;
                var op = SceneManager.UnloadSceneAsync(name);
                _activeUnloads[name] = op;
                ops.Add(op);
            }
        
            while (done < total)
            {
                done = 0;
                float aggregate = 0f;
                foreach (var op in ops)
                {
                    aggregate += op.progress;
                    if (op.isDone) done++;
                }
                float avg = aggregate / total;
                progress?.Report(avg);
            
                await Task.Yield();
            }
        
            foreach (var name in sceneNames)
            {
                _activeUnloads.Remove(name);
            }
        
            // Hide loading screen after all scenes are unloaded
            if (_loadingScreen != null)
            {
                _loadingScreen.HideLoadingScreen();
            }
        }

        // Optionally: expose current progress for all active operations
        public float GetAggregateLoadProgress()
        {
            if (_activeLoads.Count == 0) return 1f;
            float sum = 0f;
            foreach (var op in _activeLoads.Values) sum += op.progress;
            return sum / _activeLoads.Count;
        }
        public float GetAggregateUnloadProgress()
        {
            if (_activeUnloads.Count == 0) return 1f;
            float sum = 0f;
            foreach (var op in _activeUnloads.Values) sum += op.progress;
            return sum / _activeUnloads.Count;
        }

        // Tracks the currently loaded gameplay scene (not persistent/bootstrapper)
        public string CurrentGameplayScene { get; set; } = "AppleHillsOverworld";

        public async Task ReloadCurrentScene(IProgress<float> progress = null, bool autoHideLoadingScreen = true, bool skipSave = false)
        {
            await SwitchSceneAsync(CurrentGameplayScene, progress, autoHideLoadingScreen, skipSave);
        }

        /// <summary>
        /// Switches from current gameplay scene to a new one
        /// </summary>
        /// <param name="newSceneName">Name of the scene to load</param>
        /// <param name="progress">Optional progress reporter</param>
        /// <param name="autoHideLoadingScreen">Whether to automatically hide the loading screen when complete. If false, caller must hide it manually.</param>
        /// <param name="skipSave">If true, skips saving scene data during transition. Useful for level restart to prevent re-saving cleared data.</param>
        public async Task SwitchSceneAsync(string newSceneName, IProgress<float> progress = null, bool autoHideLoadingScreen = true, bool skipSave = false)
        {
            string oldSceneName = CurrentGameplayScene;
            
            // PHASE 1: Show loading screen at the start
            // Use explicit progress provider to combine unload + load progress
            if (_loadingScreen != null)
            {
                _loadingScreen.ShowLoadingScreen(() => GetAggregateLoadProgress());
            }

            // PHASE 2: Broadcast scene unloading - notify components to cleanup
            LogDebugMessage($"Broadcasting OnSceneUnloading for: {oldSceneName}");
            LifecycleManager.Instance?.BroadcastSceneUnloading(oldSceneName);
            
            // PHASE 3: Save scene-specific data via SaveLoadManager (unless skipSave is true)
            if (!skipSave && SaveLoadManager.Instance != null)
            {
                var debugSettings = DeveloperSettingsProvider.Instance.GetSettings<DebugSettings>();
                if (debugSettings.useSaveLoadSystem)
                {
                    LogDebugMessage($"Saving scene data for: {oldSceneName}");
                    SaveLoadManager.Instance.SaveSceneData();
                }
            }
            else if (skipSave)
            {
                LogDebugMessage($"Skipping save for: {oldSceneName} (skipSave=true)");
            }
            
            // PHASE 4: Clear PuzzleManager state before scene transition
            if (PuzzleS.PuzzleManager.Instance != null)
            {
                LogDebugMessage($"Clearing puzzle state before scene transition");
                PuzzleS.PuzzleManager.Instance.ClearPuzzleState();
            }

            // PHASE 5: Remove all AstarPath (A* Pathfinder) singletons before loading the new scene
            var astarPaths = FindObjectsByType<AstarPath>(FindObjectsSortMode.None);
            foreach (var astar in astarPaths)
            {
                if (Application.isPlaying)
                    Destroy(astar.gameObject);
                else
                    DestroyImmediate(astar.gameObject);
            }
            
            // PHASE 6: Unload previous gameplay scene (Unity will call OnDestroy → OnManagedDestroy)
            if (!string.IsNullOrEmpty(oldSceneName) && oldSceneName != BootstrapSceneName)
            {
                var prevScene = SceneManager.GetSceneByName(oldSceneName);
                if (prevScene.isLoaded)
                {
                    await UnloadSceneAsync(oldSceneName);
                }
                else
                {
                    Logging.Warning($"[SceneManagerService] Previous scene '{oldSceneName}' is not loaded, skipping unload.");
                }
            }
            
            // PHASE 7: Ensure BootstrapScene is loaded before loading new scene
            var bootstrap = SceneManager.GetSceneByName(BootstrapSceneName);
            if (!bootstrap.isLoaded)
            {
                SceneManager.LoadScene(BootstrapSceneName, LoadSceneMode.Additive);
            }
            
            // PHASE 8: Begin scene loading mode - enables priority-ordered component initialization
            LogDebugMessage($"Beginning scene load for: {newSceneName}");
            LifecycleManager.Instance?.BeginSceneLoad(newSceneName);
            
            // PHASE 9: Load new gameplay scene
            await LoadSceneAsync(newSceneName, progress);
            CurrentGameplayScene = newSceneName;
            
            // PHASE 10: Broadcast scene ready - processes batched components in priority order, then calls OnSceneReady
            LogDebugMessage($"Broadcasting OnSceneReady for: {newSceneName}");
            LifecycleManager.Instance?.BroadcastSceneReady(newSceneName);
            
            // PHASE 11: Restore scene-specific data via SaveLoadManager
            if (!skipSave && SaveLoadManager.Instance != null)
            {
                var debugSettings = DeveloperSettingsProvider.Instance.GetSettings<DebugSettings>();
                if (debugSettings.useSaveLoadSystem)
                {
                    LogDebugMessage($"Restoring scene data for: {newSceneName}");
                    SaveLoadManager.Instance.RestoreSceneData();
                }
            }
            else if (skipSave)
            {
                LogDebugMessage($"Skipping restore for: {newSceneName} (skipSave=true)");
            }
            
            // PHASE 12: Only hide the loading screen if autoHideLoadingScreen is true
            if (autoHideLoadingScreen && _loadingScreen != null)
            {
                _loadingScreen.HideLoadingScreen();
            }
        }
        
        private void LogDebugMessage(string message)
        {
            if (_logVerbosity <= LogVerbosity.Debug)
            {
                Logging.Debug($"[SceneManagerService] {message}");
            }
        }
    }
}