using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using UnityEngine;

namespace AlicizaX.ObjectPool
{
    internal sealed partial class ObjectPoolService
    {
        private sealed class ObjectPool<T> : ObjectPoolBase, IObjectPool<T> where T : ObjectBase
        {
            private struct ObjectSlot
            {
                public T Obj;
                public int SpawnCount;
                public float LastUseTime;
                public int PrevByName;
                public int NextByName;
                public int PrevAvailableByName;
                public int NextAvailableByName;
                public int PrevUnused;
                public int NextUnused;
                public byte Flags;

                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                public bool IsAlive() => (Flags & 1) != 0;

                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                public void SetAlive(bool alive)
                {
                    if (alive) Flags |= 1;
                    else Flags = 0;
                }
            }

            private ObjectSlot[] m_Slots;
            private int m_SlotCount;
            private int[] m_FreeStack;
            private int m_FreeTop;

            private readonly Dictionary<object, int> m_TargetMap;
            private readonly Dictionary<string, int> m_AllNameHeadMap;
            private readonly Dictionary<string, int> m_AvailableNameHeadMap;
            private readonly Dictionary<string, int> m_AvailableNameTailMap;

            private readonly bool m_AllowMultiSpawn;
            private float m_AutoReleaseInterval;
            private int m_Capacity;
            private float m_ExpireTime;
            private int m_Priority;
            private float m_AutoReleaseTime;

            private int m_PendingReleaseCount;
            private int m_ReleasePerFrameBudget;
            private int m_UnusedHead;
            private int m_UnusedTail;
            private int m_LastBudgetScanStart;
            private bool m_IsShuttingDown;

            private const int DefaultReleasePerFrame = 8;
            private const int InitSlotCapacity = 16;

            public ObjectPool(string name, bool allowMultiSpawn,
                float autoReleaseInterval, int capacity, float expireTime, int priority)
                : base(name)
            {
                int initCap = Math.Min(Math.Max(capacity, 1), InitSlotCapacity);
                m_Slots = new ObjectSlot[initCap];
                m_FreeStack = new int[initCap];
                m_TargetMap = new Dictionary<object, int>(initCap, AlicizaX.ReferenceComparer<object>.Instance);
                m_AllNameHeadMap = new Dictionary<string, int>(initCap, StringComparer.Ordinal);
                m_AvailableNameHeadMap = new Dictionary<string, int>(initCap, StringComparer.Ordinal);
                m_AvailableNameTailMap = new Dictionary<string, int>(initCap, StringComparer.Ordinal);
                m_AllowMultiSpawn = allowMultiSpawn;
                m_AutoReleaseInterval = autoReleaseInterval;
                m_Capacity = capacity;
                m_ExpireTime = expireTime;
                m_Priority = priority;
                m_AutoReleaseTime = 0f;
                m_PendingReleaseCount = 0;
                m_ReleasePerFrameBudget = DefaultReleasePerFrame;
                m_UnusedHead = -1;
                m_UnusedTail = -1;
                m_LastBudgetScanStart = -1;
                m_IsShuttingDown = false;
            }

            public override Type ObjectType => typeof(T);
            public override int Count => m_TargetMap.Count;
            public override bool AllowMultiSpawn => m_AllowMultiSpawn;

            public override float AutoReleaseInterval
            {
                get => m_AutoReleaseInterval;
                set
                {
                    if (value < 0f) throw new GameFrameworkException("AutoReleaseInterval is invalid.");
                    m_AutoReleaseInterval = value;
                }
            }

            public override int Capacity
            {
                get => m_Capacity;
                set
                {
                    if (value < 0) throw new GameFrameworkException("Capacity is invalid.");
                    m_Capacity = value;
                    if (Count > m_Capacity) MarkRelease(Count - m_Capacity);
                }
            }

            public override float ExpireTime
            {
                get => m_ExpireTime;
                set
                {
                    if (value < 0f) throw new GameFrameworkException("ExpireTime is invalid.");
                    m_ExpireTime = value;
                }
            }

            public override int Priority
            {
                get => m_Priority;
                set => m_Priority = value;
            }

            public override int ReleasePerFrameBudget
            {
                get => m_ReleasePerFrameBudget;
                set => m_ReleasePerFrameBudget = Math.Max(1, value);
            }

            public void Register(T obj, bool spawned)
            {
                if (obj == null) throw new GameFrameworkException("Object is invalid.");
                if (obj.Target == null) throw new GameFrameworkException("Object target is invalid.");
                if (m_TargetMap.TryGetValue(obj.Target, out int existingIdx) && m_Slots[existingIdx].IsAlive())
                    throw new GameFrameworkException(
                        $"Target '{obj.Target.GetType().FullName}' is already registered in pool '{FullName}'.");

                int idx = AllocSlot();
                ref var slot = ref m_Slots[idx];
                slot.Obj = obj;
                slot.SpawnCount = spawned ? 1 : 0;
                slot.LastUseTime = Time.realtimeSinceStartup;
                slot.PrevByName = -1;
                slot.NextByName = -1;
                slot.PrevAvailableByName = -1;
                slot.NextAvailableByName = -1;
                slot.PrevUnused = -1;
                slot.NextUnused = -1;
                slot.SetAlive(true);

                m_TargetMap[obj.Target] = idx;

                string objectName = obj.Name ?? string.Empty;
                if (m_AllNameHeadMap.TryGetValue(objectName, out int existingHead))
                {
                    m_Slots[existingHead].PrevByName = idx;
                    slot.NextByName = existingHead;
                }
                m_AllNameHeadMap[objectName] = idx;

                obj.LastUseTime = slot.LastUseTime;
                if (spawned)
                    obj.OnSpawn();
                else
                    MarkSlotAvailable(idx);

                if (Count > m_Capacity) MarkRelease(Count - m_Capacity);
                ValidateState();
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public T Spawn() => Spawn(string.Empty);

            public T Spawn(string name)
            {
                if (name == null) throw new GameFrameworkException("Name is invalid.");
                if (m_AllowMultiSpawn)
                    return SpawnAny(name);

                if (!m_AvailableNameHeadMap.TryGetValue(name, out int head)) return null;
                ref var slot = ref m_Slots[head];
                if (!slot.IsAlive() || slot.SpawnCount != 0 || !string.Equals(slot.Obj.Name, name, StringComparison.Ordinal))
                    throw new GameFrameworkException($"Object pool '{FullName}' available-name head is inconsistent.");

                float now = Time.realtimeSinceStartup;
                SpawnSlot(head, now);
                ValidateState();
                return slot.Obj;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            public bool CanSpawn() => CanSpawn(string.Empty);

            public bool CanSpawn(string name)
            {
                if (name == null) throw new GameFrameworkException("Name is invalid.");
                if (m_AllowMultiSpawn)
                    return m_AllNameHeadMap.ContainsKey(name);

                return m_AvailableNameHeadMap.ContainsKey(name);
            }

            public void Unspawn(T obj)
            {
                if (obj == null) throw new GameFrameworkException("Object is invalid.");
                Unspawn(obj.Target);
            }

            public void Unspawn(object target)
            {
                if (target == null) throw new GameFrameworkException("Target is invalid.");
                if (!m_TargetMap.TryGetValue(target, out int idx))
                {
                    if (m_IsShuttingDown) return;
                    throw new GameFrameworkException(
                        $"Cannot find target in pool '{Name}', type='{target.GetType().FullName}'");
                }

                UnspawnSlot(idx);
                ValidateState();
            }

            public override void Release()
            {
                MarkRelease(Count - m_Capacity);
            }

            public override void Release(int toReleaseCount)
            {
                MarkRelease(toReleaseCount);
            }

            public override void ReleaseAllUnused()
            {
                int released = 0;
                int current = m_UnusedHead;
                while (current >= 0)
                {
                    int next = m_Slots[current].NextUnused;
                    ref var slot = ref m_Slots[current];
                    if (CanReleaseSlot(ref slot))
                    {
                        ReleaseSlot(current);
                        released++;
                    }
                    current = next;
                }

                if (released > 0)
                {
                    m_PendingReleaseCount = Math.Max(0, m_PendingReleaseCount - released);
                    ShrinkStorageIfEmpty();
                    ValidateState();
                }
            }

            internal override void Update(float elapseSeconds, float realElapseSeconds)
            {
                m_AutoReleaseTime += realElapseSeconds;
                if (m_AutoReleaseTime >= m_AutoReleaseInterval)
                {
                    m_AutoReleaseTime = 0f;
                    MarkRelease(Count - m_Capacity);
                }

                bool checkExpire = m_ExpireTime < float.MaxValue;
                if (m_PendingReleaseCount <= 0 && !checkExpire) return;

                float now = Time.realtimeSinceStartup;
                float expireThreshold = checkExpire ? now - m_ExpireTime : float.MinValue;
                if (m_PendingReleaseCount > 0)
                {
                    int releaseBudget = Math.Min(m_ReleasePerFrameBudget, m_PendingReleaseCount);
                    int releasedByBudget = ReleaseUnused(releaseBudget, false, float.MinValue);
                    m_PendingReleaseCount = Math.Max(0, m_PendingReleaseCount - releasedByBudget);
                }
                else if (checkExpire)
                {
                    ReleaseExpired(m_ReleasePerFrameBudget, expireThreshold);
                }
            }

            internal override void Shutdown()
            {
                m_IsShuttingDown = true;
                for (int i = 0; i < m_SlotCount; i++)
                {
                    ref var slot = ref m_Slots[i];
                    if (!slot.IsAlive()) continue;
                    slot.Obj.Release(true);
                    MemoryPool.Release(slot.Obj);
                    slot.Obj = null;
                    slot.SetAlive(false);
                }

                m_TargetMap.Clear();
                m_AllNameHeadMap.Clear();
                m_AvailableNameHeadMap.Clear();
                m_AvailableNameTailMap.Clear();
                m_SlotCount = 0;
                m_FreeTop = 0;
                m_PendingReleaseCount = 0;
                m_UnusedHead = -1;
                m_UnusedTail = -1;
                m_LastBudgetScanStart = -1;
                m_IsShuttingDown = false;
                ValidateState();
            }

            public override int GetAllObjectInfos(ObjectInfo[] results)
            {
                if (results == null) throw new GameFrameworkException("Results is invalid.");

                int write = 0;
                int capacity = results.Length;
                for (int i = 0; i < m_SlotCount; i++)
                {
                    ref var slot = ref m_Slots[i];
                    if (!slot.IsAlive()) continue;

                    if (write < capacity)
                    {
                        results[write] = new ObjectInfo(slot.Obj.Name, slot.Obj.Locked,
                            slot.Obj.CustomCanReleaseFlag,
                            slot.Obj.LastUseTime, slot.SpawnCount);
                    }

                    write++;
                }

                return write;
            }

            internal override void OnLowMemory()
            {
                ReleaseAllUnused();
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private void SpawnSlot(int idx, float now)
            {
                ref var slot = ref m_Slots[idx];
                if (slot.SpawnCount == 0)
                    MarkSlotUnavailable(idx);

                slot.SpawnCount++;
                slot.LastUseTime = now;
                slot.Obj.LastUseTime = now;
                slot.Obj.OnSpawn();
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private void UnspawnSlot(int idx)
            {
                ref var slot = ref m_Slots[idx];
                float now = Time.realtimeSinceStartup;
                slot.LastUseTime = now;
                slot.Obj.LastUseTime = now;
                slot.Obj.OnUnspawn();
                slot.SpawnCount--;
                if (slot.SpawnCount < 0)
                    throw new GameFrameworkException($"Object '{slot.Obj.Name}' spawn count < 0.");
                if (slot.SpawnCount == 0)
                    MarkSlotAvailable(idx);
                if (Count > m_Capacity && slot.SpawnCount == 0)
                    MarkRelease(Count - m_Capacity);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private void MarkRelease(int count)
            {
                if (count > 0)
                    m_PendingReleaseCount = Math.Max(m_PendingReleaseCount, count);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private int AllocSlot()
            {
                if (m_FreeTop > 0)
                    return m_FreeStack[--m_FreeTop];

                if (m_SlotCount >= m_Slots.Length)
                    GrowSlots();

                return m_SlotCount++;
            }

            private void GrowSlots()
            {
                int newCap = Math.Max(m_Slots.Length * 2, InitSlotCapacity);
                Array.Resize(ref m_Slots, newCap);
                Array.Resize(ref m_FreeStack, newCap);
            }

            private void ReleaseSlot(int idx)
            {
                ref var slot = ref m_Slots[idx];
                if (!slot.IsAlive()) return;

                T obj = slot.Obj;
                if (slot.SpawnCount == 0)
                    MarkSlotUnavailable(idx);

                RemoveFromAllNameChain(idx);
                m_TargetMap.Remove(obj.Target);

                obj.Release(false);
                MemoryPool.Release(obj);

                slot.Obj = null;
                slot.SetAlive(false);
                slot.SpawnCount = 0;
                slot.PrevByName = -1;
                slot.NextByName = -1;
                slot.PrevAvailableByName = -1;
                slot.NextAvailableByName = -1;
                slot.PrevUnused = -1;
                slot.NextUnused = -1;

                if (m_FreeTop >= m_FreeStack.Length)
                    Array.Resize(ref m_FreeStack, m_FreeStack.Length * 2);
                m_FreeStack[m_FreeTop++] = idx;

                ShrinkStorageIfEmpty();
            }

            private void RemoveFromAllNameChain(int idx)
            {
                ref var slot = ref m_Slots[idx];
                string objectName = slot.Obj.Name ?? string.Empty;
                if (!m_AllNameHeadMap.TryGetValue(objectName, out int head))
                    return;

                int prev = slot.PrevByName;
                int next = slot.NextByName;
                if (prev >= 0)
                {
                    m_Slots[prev].NextByName = next;
                }
                else
                {
                    if (head != idx)
                        throw new GameFrameworkException($"Object pool '{FullName}' all-name chain is inconsistent.");

                    if (next >= 0)
                        m_AllNameHeadMap[objectName] = next;
                    else
                        m_AllNameHeadMap.Remove(objectName);
                }

                if (next >= 0)
                    m_Slots[next].PrevByName = prev;

                slot.PrevByName = -1;
                slot.NextByName = -1;
            }

            private int ReleaseUnused(int maxReleaseCount, bool requireExpired, float expireThreshold)
            {
                int released = 0;
                int current = requireExpired ? m_UnusedHead : GetBudgetScanStart();

                while (current >= 0 && released < maxReleaseCount)
                {
                    ref var slot = ref m_Slots[current];
                    int next = slot.NextUnused;

                    if (requireExpired && slot.LastUseTime > expireThreshold)
                    {
                        break;
                    }

                    if (CanReleaseSlot(ref slot))
                    {
                        ReleaseSlot(current);
                        released++;
                    }

                    current = next;
                }

                if (!requireExpired)
                {
                    m_LastBudgetScanStart = current >= 0 ? current : m_UnusedHead;
                }

                return released;
            }

            private void ReleaseExpired(int maxReleaseCount, float expireThreshold)
            {
                ReleaseUnused(maxReleaseCount, true, expireThreshold);
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private int GetBudgetScanStart()
            {
                if (m_LastBudgetScanStart >= 0)
                {
                    ref var slot = ref m_Slots[m_LastBudgetScanStart];
                    if (slot.IsAlive() && slot.SpawnCount == 0)
                    {
                        return m_LastBudgetScanStart;
                    }
                }

                return m_UnusedHead;
            }

            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            private static bool CanReleaseSlot(ref ObjectSlot slot)
            {
                return slot.IsAlive()
                       && slot.SpawnCount == 0
                       && !slot.Obj.Locked
                       && slot.Obj.CustomCanReleaseFlag;
            }

            private void ShrinkStorageIfEmpty()
            {
                if (m_TargetMap.Count > 0 || m_Slots.Length <= InitSlotCapacity)
                    return;

                m_Slots = new ObjectSlot[InitSlotCapacity];
                m_FreeStack = new int[InitSlotCapacity];
                m_AllNameHeadMap.Clear();
                m_AvailableNameHeadMap.Clear();
                m_AvailableNameTailMap.Clear();
                m_SlotCount = 0;
                m_FreeTop = 0;
                m_UnusedHead = -1;
                m_UnusedTail = -1;
                m_LastBudgetScanStart = -1;
            }

            [Conditional("UNITY_EDITOR"), Conditional("DEVELOPMENT_BUILD")]
            private void ValidateState()
            {
                int aliveCount = 0;
                int unusedCount = 0;
                for (int i = 0; i < m_SlotCount; i++)
                {
                    ref var slot = ref m_Slots[i];
                    if (!slot.IsAlive())
                        continue;

                    aliveCount++;

                    object target = slot.Obj.Target;
                    if (!m_TargetMap.TryGetValue(target, out int mappedIdx) || mappedIdx != i)
                        throw new GameFrameworkException($"Object pool '{FullName}' target index map is inconsistent.");

                    string objectName = slot.Obj.Name ?? string.Empty;
                    if (!m_AllNameHeadMap.TryGetValue(objectName, out int head))
                        throw new GameFrameworkException($"Object pool '{FullName}' all-name head is missing.");

                    if (slot.PrevByName < 0 && head != i)
                        throw new GameFrameworkException($"Object pool '{FullName}' all-name chain head is inconsistent.");

                    if (slot.NextByName >= 0 && m_Slots[slot.NextByName].PrevByName != i)
                        throw new GameFrameworkException($"Object pool '{FullName}' all-name chain link is inconsistent.");

                    bool inUnusedList = m_UnusedHead == i || slot.PrevUnused >= 0 || slot.NextUnused >= 0;
                    bool inAvailableList = false;

                    if (slot.SpawnCount == 0)
                    {
                        unusedCount++;
                        if (!inUnusedList)
                            throw new GameFrameworkException($"Object pool '{FullName}' unused list is inconsistent.");

                        if (!m_AvailableNameHeadMap.TryGetValue(objectName, out int availableHead))
                            throw new GameFrameworkException($"Object pool '{FullName}' available-name head is missing.");

                        inAvailableList = availableHead == i || slot.PrevAvailableByName >= 0 || slot.NextAvailableByName >= 0;
                        if (!inAvailableList)
                            throw new GameFrameworkException($"Object pool '{FullName}' available-name chain is inconsistent.");

                        if (slot.NextAvailableByName >= 0 && m_Slots[slot.NextAvailableByName].PrevAvailableByName != i)
                            throw new GameFrameworkException($"Object pool '{FullName}' available-name link is inconsistent.");
                    }
                    else
                    {
                        if (inUnusedList)
                            throw new GameFrameworkException($"Object pool '{FullName}' spawned object exists in unused list.");

                        if (slot.PrevAvailableByName >= 0 || slot.NextAvailableByName >= 0)
                            throw new GameFrameworkException($"Object pool '{FullName}' spawned object exists in available chain.");
                    }
                }

                if (aliveCount != m_TargetMap.Count)
                    throw new GameFrameworkException($"Object pool '{FullName}' alive count is inconsistent.");

                int walkUnusedCount = 0;
                int current = m_UnusedHead;
                int prevUnused = -1;
                while (current >= 0)
                {
                    ref var slot = ref m_Slots[current];
                    if (!slot.IsAlive() || slot.SpawnCount != 0)
                        throw new GameFrameworkException($"Object pool '{FullName}' unused chain contains invalid slot.");
                    if (slot.PrevUnused != prevUnused)
                        throw new GameFrameworkException($"Object pool '{FullName}' unused chain linkage is inconsistent.");

                    walkUnusedCount++;
                    prevUnused = current;
                    current = slot.NextUnused;
                }

                if (walkUnusedCount != unusedCount)
                    throw new GameFrameworkException($"Object pool '{FullName}' unused chain count is inconsistent.");
            }

            private void MarkSlotAvailable(int idx)
            {
                AddToUnusedListTail(idx);
                AddToAvailableNameChain(idx);
            }

            private void MarkSlotUnavailable(int idx)
            {
                RemoveFromUnusedList(idx);
                RemoveFromAvailableNameChain(idx);
            }

            private void AddToUnusedListTail(int idx)
            {
                ref var slot = ref m_Slots[idx];
                if (m_UnusedHead == idx || slot.PrevUnused >= 0 || slot.NextUnused >= 0)
                    return;

                slot.PrevUnused = m_UnusedTail;
                slot.NextUnused = -1;

                if (m_UnusedTail >= 0)
                    m_Slots[m_UnusedTail].NextUnused = idx;
                else
                    m_UnusedHead = idx;

                m_UnusedTail = idx;
            }

            private void RemoveFromUnusedList(int idx)
            {
                ref var slot = ref m_Slots[idx];
                if (m_UnusedHead != idx && slot.PrevUnused < 0 && slot.NextUnused < 0)
                    return;

                int prev = slot.PrevUnused;
                int next = slot.NextUnused;

                if (prev >= 0)
                    m_Slots[prev].NextUnused = next;
                else
                    m_UnusedHead = next;

                if (next >= 0)
                    m_Slots[next].PrevUnused = prev;
                else
                    m_UnusedTail = prev;

                slot.PrevUnused = -1;
                slot.NextUnused = -1;

                if (m_LastBudgetScanStart == idx)
                    m_LastBudgetScanStart = next >= 0 ? next : m_UnusedHead;
            }

            private void AddToAvailableNameChain(int idx)
            {
                ref var slot = ref m_Slots[idx];
                if (slot.PrevAvailableByName >= 0 || slot.NextAvailableByName >= 0)
                    throw new GameFrameworkException($"Object pool '{FullName}' available-name chain is inconsistent.");

                string objectName = slot.Obj.Name ?? string.Empty;
                if (m_AvailableNameTailMap.TryGetValue(objectName, out int tail))
                {
                    m_Slots[tail].NextAvailableByName = idx;
                    slot.PrevAvailableByName = tail;
                    slot.NextAvailableByName = -1;
                    m_AvailableNameTailMap[objectName] = idx;
                }
                else
                {
                    slot.PrevAvailableByName = -1;
                    slot.NextAvailableByName = -1;
                    m_AvailableNameHeadMap[objectName] = idx;
                    m_AvailableNameTailMap[objectName] = idx;
                }
            }

            private void RemoveFromAvailableNameChain(int idx)
            {
                ref var slot = ref m_Slots[idx];
                string objectName = slot.Obj.Name ?? string.Empty;
                if (slot.PrevAvailableByName < 0
                    && slot.NextAvailableByName < 0
                    && (!m_AvailableNameHeadMap.TryGetValue(objectName, out int head) || head != idx))
                {
                    return;
                }

                int prev = slot.PrevAvailableByName;
                int next = slot.NextAvailableByName;

                if (prev >= 0)
                    m_Slots[prev].NextAvailableByName = next;
                else if (next >= 0)
                    m_AvailableNameHeadMap[objectName] = next;
                else
                    m_AvailableNameHeadMap.Remove(objectName);

                if (next >= 0)
                    m_Slots[next].PrevAvailableByName = prev;
                else if (prev >= 0)
                    m_AvailableNameTailMap[objectName] = prev;
                else
                    m_AvailableNameTailMap.Remove(objectName);

                slot.PrevAvailableByName = -1;
                slot.NextAvailableByName = -1;
            }

            private T SpawnAny(string name)
            {
                if (!m_AllNameHeadMap.TryGetValue(name, out int head))
                    return null;

                float now = Time.realtimeSinceStartup;
                ref var slot = ref m_Slots[head];
                if (!slot.IsAlive() || !string.Equals(slot.Obj.Name, name, StringComparison.Ordinal))
                    return null;

                SpawnSlot(head, now);
                ValidateState();
                return slot.Obj;
            }
        }
    }
}