using System.Collections.Generic;

namespace BaseGames.AI
{
    /// <summary>
    /// 每敌人实例一份的轻量执行器。持有当前状态、状态计时器、trace。
    /// 共享的 AiGraph 不持有任何实例态。
    /// </summary>
    public sealed class AiRuntime
    {
        readonly AiGraph _graph;
        readonly IAiContext _ctx;
        AiState _current;
        float _timeInState;

        readonly Queue<AiSignal> _pending = new Queue<AiSignal>();
        readonly List<TransitionRecord> _trace = new List<TransitionRecord>();
        const int TraceCap = 16;

        public AiRuntime(AiGraph graph, IAiContext ctx)
        {
            _graph = graph;
            _ctx = ctx;
            EnterInitial();
        }

        public string CurrentStateName => _current.Name;
        public bool IsSuspended { get; private set; }
        public IReadOnlyList<TransitionRecord> Trace => _trace;
        public float TimeInStateValue => _timeInState;

        void EnterInitial()
        {
            _byContext.Remove(_ctx);   // 幂等：避免同一 ctx 重复键异常
            _byContext.Add(_ctx, this);
            _current = _graph.GetState(_graph.EntryState);
            _timeInState = 0f;
            _current.OnEnter?.Invoke(_ctx);
        }

        /// <summary>供 BrainBuilder.After() 通过 context 读取当前 runtime 的状态计时器。</summary>
        static readonly System.Runtime.CompilerServices.ConditionalWeakTable<IAiContext, AiRuntime> _byContext
            = new System.Runtime.CompilerServices.ConditionalWeakTable<IAiContext, AiRuntime>();
        internal static float TimeInState(IAiContext ctx)
            => _byContext.TryGetValue(ctx, out var rt) ? rt._timeInState : 0f;

        /// <summary>推送一个信号，用于事件驱动转换（push）。</summary>
        public void Send(AiSignal signal) => _pending.Enqueue(signal);

        public void Tick(float dt)
        {
            // 1) 事件转换：push，最高优先，且不受 IsControllable 门限制
            while (_pending.Count > 0)
            {
                var sig = _pending.Dequeue();
                if (TryEventTransition(sig))
                {
                    IsSuspended = false; // 已推进转换，非挂起
                    return;
                }
            }

            // 2) IsControllable 让位门：受击/硬直/击飞时挂起，不推进决策也不跑 Tick。
            if (!_ctx.Vitals.IsControllable)
            {
                IsSuspended = true;
                return;
            }
            IsSuspended = false;

            // 3) 条件转换
            _timeInState += dt;

            if (TryTransition())
                return; // 本帧发生转换，新状态下一帧再 Tick

            _current.OnTick?.Invoke(_ctx, dt);
        }

        bool TryTransition()
        {
            // 全局/父层转换优先（只评估条件型；事件型由 TryEventTransition 处理）
            var globals = _graph.GlobalTransitions;
            for (int i = 0; i < globals.Count; i++)
            {
                var t = globals[i];
                if (!t.IsEvent && t.Condition(_ctx))
                    { if (Switch(t)) return true; }
            }

            var locals = _current.Transitions;
            for (int i = 0; i < locals.Count; i++)
            {
                var t = locals[i];
                if (!t.IsEvent && t.Condition(_ctx))
                    { if (Switch(t)) return true; }
            }

            return false;
        }

        bool TryEventTransition(AiSignal sig)
        {
            var globals = _graph.GlobalTransitions;
            for (int i = 0; i < globals.Count; i++)
            {
                var t = globals[i];
                if (t.IsEvent && t.Event.Value == sig)
                    { if (Switch(t)) return true; }
            }

            var locals = _current.Transitions;
            for (int i = 0; i < locals.Count; i++)
            {
                var t = locals[i];
                if (t.IsEvent && t.Event.Value == sig)
                    { if (Switch(t)) return true; }
            }
            return false;
        }

        bool Switch(Transition t)
        {
            if (t.Target == _current.Name) return false; // 自转换：no-op，不重跑 Exit/Enter
            var from = _current.Name;
            _current.OnExit?.Invoke(_ctx);
            _current = _graph.GetState(t.Target);
            _timeInState = 0f;
            RecordTrace(new TransitionRecord(from, t.Target, t.Label));
            _current.OnEnter?.Invoke(_ctx);
            return true;
        }

        void RecordTrace(TransitionRecord r)
        {
            _trace.Add(r);
            if (_trace.Count > TraceCap) _trace.RemoveAt(0);
        }

        /// <summary>对象池复用时重置到初始态，清空所有实例态。</summary>
        public void Reset()
        {
            _pending.Clear();
            _trace.Clear();
            _ctx.Blackboard.Clear();
            IsSuspended = false;
            EnterInitial();
        }
    }
}