using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace TeamAAS.Vision
{
    /// <summary>
    /// 视觉引擎管理器(懒汉单例,Lazy 线程安全)。
    ///
    /// 职责:
    /// 1. 引擎探测(Discover):通过通用模块扫描器(AssemblyScanner)收集
    ///    IVisualEngine 实现——插件 DLL 由 PluginLoader 在启动时加载进 AppDomain
    ///    (Runtime\Plugins 目录),无需硬编码已知引擎程序集列表;
    /// 2. 引擎切换(SetCurrent):按配置的 EngineName 一键切换;
    /// 3. 引擎取用(GetOrLoad):按名称取引擎,找不到回退第一个。
    ///
    /// 引擎实现位于各引擎插件类库(如 Plugins.Vpp),本管理器只依赖抽象接口,
    /// 引擎 SDK 的加载与解析由插件体系完成 —— 引擎可整体替换,宿主零改动。
    /// </summary>
    public sealed class VisualEngineManager
    {
        /// <summary>懒汉单例:首次访问 Instance 时才创建(Lazy 默认 ExecutionAndPublication 线程安全)</summary>
        private static readonly Lazy<VisualEngineManager> _lazy =
            new Lazy<VisualEngineManager>(() => new VisualEngineManager(), LazyThreadSafetyMode.ExecutionAndPublication);

        /// <summary>全局单例入口</summary>
        public static VisualEngineManager Instance => _lazy.Value;

        private readonly List<IVisualEngine> _engines = new List<IVisualEngine>();
        private bool _discovered;

        private VisualEngineManager() { }

        /// <summary>
        /// 反射创建 AppDomain 内全部 IVisualEngine 实现实例(无参构造;构造失败跳过)。
        /// 自包含实现,不依赖外部扫描器(原 Global 的 AssemblyScanner)——引擎插件 DLL
        /// 由 PluginLoader 在启动时先行加载进 AppDomain,故此处直接扫描已加载程序集即可。
        /// </summary>
        private static IEnumerable<IVisualEngine> CreateEngineInstances()
        {
            foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
            {
                Type[] types;
                try { types = asm.GetTypes(); }
                catch (System.Reflection.ReflectionTypeLoadException ex)
                {
                    types = ex.Types?.Where(t => t != null).ToArray() ?? Type.EmptyTypes;
                }
                catch { continue; }

                foreach (var t in types)
                {
                    if (t == null || t.IsAbstract || t.IsInterface || t.IsGenericTypeDefinition) continue;
                    if (!typeof(IVisualEngine).IsAssignableFrom(t)) continue;
                    IVisualEngine inst;
                    try { inst = Activator.CreateInstance(t) as IVisualEngine; }
                    catch (Exception ex)
                    {
                        // 引擎 SDK 运行库缺失等 → 跳过该实现;Debug 输出便于诊断“引擎没起来/主页画面空白”
                        System.Diagnostics.Debug.WriteLine($"[VisualEngine] 引擎 {t.FullName} 实例化失败,已跳过: {ex.Message}");
                        continue;
                    }
                    if (inst != null) yield return inst;
                }
            }
        }

        /// <summary>探测到的全部可用引擎</summary>
        public IReadOnlyList<IVisualEngine> Engines => _engines;

        /// <summary>当前生效引擎(配置里的 EngineName;未配置/未找到时为第一个)</summary>
        public IVisualEngine Current { get; private set; }

        /// <summary>引擎是否已探测完成(避免宿主过早取用)</summary>
        public bool Discovered => _discovered;

        /// <summary>引擎清单变化通知</summary>
        public event Action EnginesChanged;

        /// <summary>执行探测(幂等,可重复调用)</summary>
        public void Discover()
        {
            if (_discovered) return;
            _discovered = true;

            // 通用模块扫描:收集全部 IVisualEngine 实现(EngineName 去重由本管理器负责)
            foreach (var engine in CreateEngineInstances())
            {
                if (_engines.Any(e => e.EngineName == engine.EngineName)) continue;
                _engines.Add(engine);
            }

            EnginesChanged?.Invoke();
        }

        /// <summary>按名称取引擎;找不到时回退第一个,完全没有引擎返回 null。</summary>
        public IVisualEngine GetOrLoad(string engineName)
        {
            if (_engines.Count == 0) return null;
            var match = _engines.FirstOrDefault(e =>
                string.Equals(e.EngineName, engineName, StringComparison.OrdinalIgnoreCase));
            return match ?? _engines[0];
        }

        /// <summary>切换当前引擎(一键切换);名称不存在返回 false。</summary>
        public bool SetCurrent(string engineName)
        {
            var engine = _engines.FirstOrDefault(e =>
                string.Equals(e.EngineName, engineName, StringComparison.OrdinalIgnoreCase));
            if (engine == null) return false;
            Current = engine;
            return true;
        }
    }
}