#nullable enable

using System;
using System.Collections.Generic;
using System.Linq;
using Cysharp.Threading.Tasks;
using ShrinkEventBus;
using UnityEngine;

namespace ShrinkApp
{
    public sealed class ShrinkAppHost : MonoBehaviour
    {
        private readonly List<string> _startedModules = new();
        private ShrinkAppContext? _context;
        private bool _unityStarted;
        private bool _publishedStartedEvent;

        public bool IsRunning { get; private set; }
        public bool HasFailed { get; private set; }
        public string LastError { get; private set; } = string.Empty;
        public IReadOnlyList<string> StartedModules => _startedModules;

        internal void Configure(ShrinkAppContext context)
        {
            _context = context ?? throw new ArgumentNullException(nameof(context));
        }

        internal async UniTask StartAppAsync()
        {
            if (IsRunning || HasFailed)
                return;
            if (_context == null)
                throw new InvalidOperationException("ShrinkAppHost is not configured.");

            var installers = CreateInstallerInstances();
            var orderedInstallers = SortInstallers(installers, _context.Settings);

            try
            {
                foreach (var installer in orderedInstallers)
                    installer.RegisterServices(_context);

                foreach (var installer in orderedInstallers)
                {
                    await installer.InitializeAsync(_context);
                    _startedModules.Add(installer.ModuleId);
                }

                IsRunning = true;
                PublishStartedEventIfReady();
            }
            catch (Exception ex)
            {
                HasFailed = true;
                LastError = ex.Message;
                EventBus.TriggerEvent(new ShrinkAppStartFailedEvent
                {
                    ErrorMessage = ex.Message,
                    FailedModuleId = _startedModules.LastOrDefault() ?? string.Empty
                });
                throw;
            }
        }

        private void Start()
        {
            _unityStarted = true;
            PublishStartedEventIfReady();
        }

        private void PublishStartedEventIfReady()
        {
            if (_publishedStartedEvent || !_unityStarted || !IsRunning)
                return;

            _publishedStartedEvent = true;
            EventBus.TriggerEvent(new ShrinkAppStartedEvent
            {
                ModuleIds = _startedModules.ToArray()
            });
        }

        private static IReadOnlyList<IShrinkAppModuleInstaller> CreateInstallerInstances()
        {
            var installers = new List<IShrinkAppModuleInstaller>();
            foreach (var installerType in ShrinkAppGeneratedRegistry.GetInstallerTypes())
            {
                if (installerType == null)
                    continue;
                if (!typeof(IShrinkAppModuleInstaller).IsAssignableFrom(installerType))
                    throw new InvalidOperationException($"Installer type does not implement IShrinkAppModuleInstaller: {installerType.FullName}");
                if (installerType.IsAbstract)
                    throw new InvalidOperationException($"Installer type cannot be abstract: {installerType.FullName}");

                if (Activator.CreateInstance(installerType) is not IShrinkAppModuleInstaller installer)
                    throw new InvalidOperationException($"Failed to create installer: {installerType.FullName}");

                installers.Add(installer);
            }

            return installers;
        }

        private static IReadOnlyList<IShrinkAppModuleInstaller> SortInstallers(
            IReadOnlyList<IShrinkAppModuleInstaller> installers,
            ShrinkAppSettings settings)
        {
            var disabled = new HashSet<string>(
                settings.disabledModuleIds?.Where(id => !string.IsNullOrWhiteSpace(id)).Select(id => id.Trim()) ??
                Enumerable.Empty<string>(),
                StringComparer.OrdinalIgnoreCase);

            var enabledInstallers = installers
                .Where(installer => !disabled.Contains(installer.ModuleId))
                .ToArray();

            var byId = new Dictionary<string, IShrinkAppModuleInstaller>(StringComparer.OrdinalIgnoreCase);
            foreach (var installer in enabledInstallers)
            {
                if (string.IsNullOrWhiteSpace(installer.ModuleId))
                    throw new InvalidOperationException($"Installer {installer.GetType().FullName} has an empty ModuleId.");
                if (!byId.TryAdd(installer.ModuleId.Trim(), installer))
                    throw new InvalidOperationException($"Duplicate installer ModuleId: {installer.ModuleId}");
            }

            var visitState = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
            var ordered = new List<IShrinkAppModuleInstaller>();
            foreach (var installer in enabledInstallers.OrderBy(item => item.Order).ThenBy(item => item.ModuleId, StringComparer.OrdinalIgnoreCase))
            {
                Visit(installer, byId, visitState, ordered);
            }

            return ordered;
        }

        private static void Visit(
            IShrinkAppModuleInstaller installer,
            IReadOnlyDictionary<string, IShrinkAppModuleInstaller> byId,
            IDictionary<string, int> visitState,
            IList<IShrinkAppModuleInstaller> ordered)
        {
            var state = visitState.TryGetValue(installer.ModuleId, out var existingState) ? existingState : 0;
            if (state == 2)
                return;
            if (state == 1)
                throw new InvalidOperationException($"Circular installer dependency detected at module: {installer.ModuleId}");

            visitState[installer.ModuleId] = 1;
            foreach (var dependencyId in installer.DependsOn ?? Array.Empty<string>())
            {
                if (string.IsNullOrWhiteSpace(dependencyId))
                    continue;

                if (!byId.TryGetValue(dependencyId.Trim(), out var dependency))
                    throw new InvalidOperationException(
                        $"Installer dependency missing. Module={installer.ModuleId}, DependsOn={dependencyId}");

                Visit(dependency, byId, visitState, ordered);
            }

            visitState[installer.ModuleId] = 2;
            if (!ordered.Contains(installer))
                ordered.Add(installer);
        }
    }
}