using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Threading;

namespace AlicizaX.Fsm
{
    internal interface IFsmRunner : IDisposable, IMemory
    {
        int Id { get; }
        string DisplayName { get; }
        UnityEngine.Object Owner { get; }
        void Tick(float deltaTime);
    }


    public delegate void StateEnter<T>(T bb) where T : class, IMemory;

    public delegate int StateUpdate<T>(T bb) where T : class, IMemory; // -1 = stay

    public delegate void StateExit<T>(T bb) where T : class, IMemory;

    public delegate bool Condition<T>(T bb) where T : class, IMemory;

    // ===================== StateFunc =====================
    public sealed class StateFunc<T> where T : class, IMemory
    {
        public StateEnter<T> OnEnter;
        public StateUpdate<T> OnUpdate;
        public StateExit<T> OnExit;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static StateFunc<T> Make(StateEnter<T> enter = null, StateUpdate<T> update = null, StateExit<T> exit = null)
        {
            return new StateFunc<T>
            {
                OnEnter = enter ?? EmptyEnter,
                OnUpdate = update ?? Stay,
                OnExit = exit ?? EmptyExit,
            };
        }

        private static void EmptyEnter(T bb)
        {
        }

        private static int Stay(T bb) => -1;

        private static void EmptyExit(T bb)
        {
        }
    }

    // ===================== Transition =====================
    public struct Transition<T> where T : class, IMemory
    {
        public int From;
        public int To;
        public Condition<T> Cond; // may be null
        public int Priority; // smaller first
        public float Timeout; // >0 enables timeout

        public Transition(int from, int to, Condition<T> cond, int priority = 0, float timeout = 0f)
        {
            From = from;
            To = to;
            Cond = cond;
            Priority = priority;
            Timeout = timeout;
        }
    }

    internal struct TransitionIndex
    {
        public int Start; // start index in _trans
        public int Length; // number of entries
    }

    public readonly struct FsmConfig<T> where T : class, IMemory
    {
        public readonly StateFunc<T>[] Funcs; // [state] -> funcs
        public readonly Transition<T>[] Transitions; // flat transitions list
        public readonly int StateCount; // >0
        public readonly int DefaultState; // initial state

        public FsmConfig(StateFunc<T>[] func, Transition<T>[] transition, int defaultState = -1)
        {
            Funcs = func;
            Transitions = transition;
            StateCount = Funcs.Length;
            DefaultState = defaultState;
            if (Funcs == null || Funcs.Length == 0)
                throw new ArgumentException("Funcs must not be null/empty");
            if (StateCount <= 0) StateCount = Funcs.Length;
            if ((uint)DefaultState >= (uint)StateCount)
                throw new ArgumentOutOfRangeException(nameof(DefaultState));
        }
    }

    public sealed class Fsm<T> : IFsmRunner where T : class, IMemory
    {
        private static int _nextId;

        public static Fsm<T> Rent(FsmConfig<T> cfg, T blackboard, UnityEngine.Object owner = null, Func<int, string> stateNameGetter = null)
        {
            Fsm<T> fsm = MemoryPool.Acquire<Fsm<T>>();
            fsm.Init(cfg, blackboard, owner, stateNameGetter);
            return fsm;
        }

        public static void Return(Fsm<T> fsm)
        {
            if (fsm == null) return;
            MemoryPool.Release(fsm);
        }

        // ---- Instance ----
        private StateFunc<T>[] _funcs;
        private Transition<T>[] _trans;
        private TransitionIndex[] _index;
        private int _stateCount;

        private T _bb;
        private bool _disposed;

        public int Id { get; private set; }
        public string DisplayName { get; private set; }
        public int Current { get; private set; }
        public float TimeInState { get; private set; }
        public bool Initialized { get; private set; }
        public UnityEngine.Object Owner { get; private set; }
        private Func<int, string> _stateNameGetter;

        public T Blackboard
        {
            get => _bb;
        }

        public Fsm()
        {
        }

        private void Init(FsmConfig<T> cfg, T blackboard, UnityEngine.Object owner, Func<int, string> stateNameGetter)
        {
            Id = Interlocked.Increment(ref _nextId);
            DisplayName = typeof(T).Name;
            _funcs = cfg.Funcs;
            _trans = cfg.Transitions ?? Array.Empty<Transition<T>>();
            _index = BuildIndex(_trans, cfg.StateCount);
            _stateCount = cfg.StateCount;

            _bb = blackboard;
            Owner = owner;
            _stateNameGetter = stateNameGetter;

            Current = cfg.DefaultState;
            TimeInState = 0f;
            Initialized = false;
            _disposed = false;

#if UNITY_EDITOR
            FSMDebugger.Register(this, typeof(T));
            FSMDebugger.BindProvider(Id, owner, BlackboardSnapshot, _stateNameGetter);
#endif
        }

        private object BlackboardSnapshot() => _bb;

        private static TransitionIndex[] BuildIndex(Transition<T>[] t, int stateCount)
        {
            if (t.Length > 1)
            {
                Array.Sort(t, (a, b) =>
                {
                    int f = a.From.CompareTo(b.From);
                    return (f != 0) ? f : a.Priority.CompareTo(b.Priority);
                });
            }

            var idx = new TransitionIndex[stateCount];
            int cur = 0;
            while (cur < t.Length)
            {
                int from = t[cur].From;
                int end = cur + 1;
                while (end < t.Length && t[end].From == from) end++;
                if ((uint)from < (uint)stateCount)
                {
                    idx[from].Start = cur;
                    idx[from].Length = end - cur;
                }

                cur = end;
            }

            return idx;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Reset(int state)
        {
            if (_disposed) return;
            if ((uint)state >= (uint)_stateCount) return;

            if (Initialized) _funcs[Current].OnExit(_bb);
            Current = state;
            TimeInState = 0f;
            _funcs[Current].OnEnter(_bb);
            Initialized = true;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Tick(float deltaTime)
        {
            if (_disposed) return;

            bool flag = false;
            if (!Initialized)
            {
                Reset(Current);
                flag = true;
            }

            if (!flag)
            {
                TimeInState += deltaTime;

                // 1) state internal update (may suggest next state)
                int suggested = _funcs[Current].OnUpdate(_bb);
                if (suggested >= 0 && suggested != Current)
                {
                    ChangeState(suggested);
                }
                else
                {
                    // 2) transitions (timeout first, then condition)
                    ref readonly TransitionIndex ti = ref _index[Current];
                    for (int i = 0; i < ti.Length; i++)
                    {
                        ref readonly var tr = ref _trans[ti.Start + i];
                        bool timeoutOk = (tr.Timeout > 0f && TimeInState >= tr.Timeout);
                        bool condOk = (!timeoutOk && tr.Cond != null && tr.Cond(_bb));
                        if (timeoutOk || condOk)
                        {
                            ChangeState(tr.To);
                            break;
                        }
                    }
                }
            }


#if UNITY_EDITOR
            if (FSMDebugger.Enabled)
                FSMDebugger.Track(this);
#endif
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void ChangeState(int next)
        {
            if ((uint)next >= (uint)_stateCount || next == Current) return;
            _funcs[Current].OnExit(_bb);
            Current = next;
            TimeInState = 0f;
            _funcs[Current].OnEnter(_bb);
        }

        public void Dispose()
        {
            if (_disposed) return;
            _disposed = true;
#if UNITY_EDITOR
            FSMDebugger.Unregister(Id);
#endif
        }


        public void Clear()
        {
            _funcs = null;
            _trans = null;
            _index = null;
            _stateCount = 0;
            _stateNameGetter = null;
            Owner = null;
            Initialized = false;
            TimeInState = 0f;
            DisplayName = null;
            MemoryPool.Release(_bb);
            _bb = null;
        }
    }

#if UNITY_EDITOR
    // ===================== FSMDebugger (Editor Only) =====================
    public static class FSMDebugger
    {
        public sealed class Entry
        {
            public int Id;
            public string Name; // Blackboard type name
            public int StateIndex;
            public double LastSeenEditorTime;
            public float TimeInState;
            public FieldInfo[] Fields; // cached fields of blackboard
            public WeakReference<UnityEngine.Object> Owner; // may be null
            public Func<object> BlackboardGetter; // snapshot getter (only queried when painting)
            public Func<int, string> StateNameGetter; // may be null
        }

        private static readonly Dictionary<int, Entry> _entries = new Dictionary<int, Entry>(256);

        private const double PRUNE_INTERVAL_SEC = 3.0;
        private const double STALE_SEC = 10.0;
        private static double _lastPruneCheck;
        public static bool Enabled { get; private set; } = true;

        static FSMDebugger()
        {
            UnityEditor.EditorApplication.update += PruneLoop;
        }

        public static void SetEnabled(bool enabled) => Enabled = enabled;

        private static void PruneLoop()
        {
            double now = UnityEditor.EditorApplication.timeSinceStartup;
            if (now - _lastPruneCheck < PRUNE_INTERVAL_SEC) return;
            _lastPruneCheck = now;

            var toRemove = ListPool<int>.Get();
            foreach (var kv in _entries)
            {
                var e = kv.Value;
                bool deadOwner = false;
                if (e.Owner != null && e.Owner.TryGetTarget(out var target))
                {
                    deadOwner = target == null;
                }
                else if (e.Owner != null)
                {
                    deadOwner = true;
                }

                bool stale = (now - e.LastSeenEditorTime) > STALE_SEC;
                if (deadOwner || stale)
                    toRemove.Add(kv.Key);
            }

            for (int i = 0; i < toRemove.Count; i++)
                _entries.Remove(toRemove[i]);

            ListPool<int>.Release(toRemove);
        }

        internal static void Register<T>(in Fsm<T> fsm, Type blackboardType) where T : class, IMemory
        {
            var id = fsm.Id;
            if (_entries.ContainsKey(id)) return;

            var fields = blackboardType.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

            _entries[id] = new Entry
            {
                Id = id,
                Name = blackboardType.Name,
                StateIndex = -1,
                LastSeenEditorTime = UnityEditor.EditorApplication.timeSinceStartup,
                TimeInState = 0f,
                Fields = fields,
                Owner = null,
                BlackboardGetter = null,
                StateNameGetter = null
            };
        }

        internal static void BindProvider(int id, UnityEngine.Object owner, Func<object> bbGetter, Func<int, string> stateNameGetter)
        {
            if (!_entries.TryGetValue(id, out var e))
                return;
            e.Owner = owner != null ? new WeakReference<UnityEngine.Object>(owner) : null;
            e.BlackboardGetter = bbGetter;
            e.StateNameGetter = stateNameGetter;
        }

        internal static void Track<T>(in Fsm<T> fsm) where T : class, IMemory
        {
            if (!_entries.TryGetValue(fsm.Id, out var e))
                return;
            e.StateIndex = fsm.Current;
            e.TimeInState = fsm.TimeInState;
            e.LastSeenEditorTime = UnityEditor.EditorApplication.timeSinceStartup;
        }

        public static void Unregister(int id) => _entries.Remove(id);
        public static IReadOnlyDictionary<int, Entry> Entries => _entries;

        // --- tiny List pool ---
        private static class ListPool<TItem>
        {
            private static readonly Stack<List<TItem>> _pool = new Stack<List<TItem>>(8);
            public static List<TItem> Get() => _pool.Count > 0 ? _pool.Pop() : new List<TItem>(16);

            public static void Release(List<TItem> list)
            {
                list.Clear();
                _pool.Push(list);
            }
        }
    }
#endif
}