using System;
using System.Collections.Generic;
using System.Diagnostics;
using Godot;

/// <summary>
/// 校园学生角色控制器
/// </summary>
public partial class CampusStudent : CharacterBody2D
{
    /// <summary>
    /// 饰品精灵
    /// </summary>
    private Sprite2D _accessory;
    /// <summary>
    /// 动画播放器
    /// </summary>
    private AnimationPlayer _animationPlayer;

    /// <summary>
    /// 身体精灵
    /// </summary>
    private Sprite2D _body;
    /// <summary>
    /// 眼睛精灵
    /// </summary>
    private Sprite2D _eye;
    /// <summary>
    /// 发型精灵
    /// </summary>
    private Sprite2D _hairstyle;
    /// <summary>
    /// 上一帧的时间间隔
    /// </summary>
    private double _lastDelta;
    
    /// <summary>
    /// 面朝方向
    /// </summary>
    private enum FacingDirection
    {
        Up,
        Down,
        Left,
        Right
    }
    
    /// <summary>
    /// 上一次的面朝方向
    /// </summary>
    private FacingDirection _lastFacing = FacingDirection.Down;
    /// <summary>
    /// 上一次的位置
    /// </summary>
    private Vector2 _lastPosition;

    /// <summary>
    /// 服装精灵
    /// </summary>
    private Sprite2D _outfit;
    /// <summary>
    /// 是否已配置巡逻
    /// </summary>
    private bool _patrolConfigured;
    /// <summary>
    /// 当前巡逻点索引
    /// </summary>
    private int _patrolIndex;
    /// <summary>
    /// 巡逻点列表
    /// </summary>
    private List<Vector2> _patrolPoints = new();
    /// <summary>
    /// 手机精灵
    /// </summary>
    private Sprite2D _smartphone;
    /// <summary>
    /// 卡住计时器
    /// </summary>
    private float _stuckTimer;
    /// <summary>
    /// 当前目标点
    /// </summary>
    private Vector2 _currentTarget = Vector2.Zero;
    /// <summary>
    /// 是否有目标
    /// </summary>
    private bool _hasTarget;
    /// <summary>
    /// 是否启用行为控制
    /// </summary>
    private bool _behaviorControlEnabled;
    /// <summary>
    /// 行为目标点
    /// </summary>
    private Vector2 _behaviorTarget = Vector2.Zero;
    /// <summary>
    /// 是否有行为目标
    /// </summary>
    private bool _behaviorHasTarget;
    /// <summary>
    /// 手机闲置动画是否激活
    /// </summary>
    private bool _phoneIdleActive;
    /// <summary>
    /// 手机退出动作锁定
    /// </summary>
    private bool _phoneExitLocked;
    /// <summary>
    /// 是否使用物理移动
    /// </summary>
    private bool _usePhysicsMovement = true;
    /// <summary>
    /// 网格路径列表
    /// </summary>
    private readonly List<Vector2> _gridPath = new();
    /// <summary>
    /// 当前网格路径索引
    /// </summary>
    private int _gridPathIndex;
    /// <summary>
    /// 网格路径是否激活
    /// </summary>
    private bool _gridPathActive;
    /// <summary>
    /// 网格路径是否挂起
    /// </summary>
    private bool _gridPathPending;
    /// <summary>
    /// 网格重新寻路重试计时器
    /// </summary>
    private float _gridPathRetryTimer;
    /// <summary>
    /// 校园控制器
    /// </summary>
    private CampusController _campusController;
    
    /// <summary>
    /// 移动速度
    /// </summary>
    [Export] public float MoveSpeed { get; set; } = 60.0f;
    /// <summary>
    /// 目标到达判定距离
    /// </summary>
    [Export] public float TargetReachDistance { get; set; } = 6.0f;
    /// <summary>
    /// 是否使用16x16精灵
    /// </summary>
    [Export] public bool Use16X16Sprites { get; set; } = true;
    /// <summary>
    /// 卡住重新寻路时间
    /// </summary>
    [Export] public float StuckRepathSeconds { get; set; } = 0.6f;
    /// <summary>
    /// 卡住距离阈值
    /// </summary>
    [Export] public float StuckDistanceEpsilon { get; set; } = 2.0f;
    /// <summary>
    /// 网格重新寻路间隔
    /// </summary>
    [Export] public float GridRepathInterval { get; set; } = 0.25f;
    /// <summary>
    /// 调试绘制路径
    /// </summary>
    [Export] public bool DebugDrawPath { get; set; }
    /// <summary>
    /// 环境碰撞掩码
    /// </summary>
    [Export] public uint EnvironmentCollisionMask { get; set; } = 1u;
    /// <summary>
    /// 学生碰撞层
    /// </summary>
    [Export] public uint StudentCollisionLayer { get; set; } = 1u << 1;

    /// <summary>
    /// 准备就绪时调用
    /// </summary>
    public override void _Ready()
    {
        _animationPlayer = GetNodeOrNull<AnimationPlayer>("AnimationPlayer");
        _campusController = GetTree()?.CurrentScene as CampusController;
        CacheSprites();
        ConfigureCollision();

        if (_animationPlayer != null)
        {
            _animationPlayer.AnimationFinished += OnAnimationFinished;
        }

        if (_patrolConfigured) AdvanceTarget();

        PlayIdleAnimation();
        _lastPosition = GlobalPosition;
    }

    /// <summary>
    /// 物理处理
    /// </summary>
    /// <param name="delta">时间间隔</param>
    public override void _PhysicsProcess(double delta)
    {
        _lastDelta = delta;
        if (DebugDrawPath)
        {
            QueueRedraw();
        }
        if (_gridPathRetryTimer > 0.0f)
        {
            _gridPathRetryTimer = Mathf.Max(0.0f, _gridPathRetryTimer - (float)delta);
        }
        if (_phoneExitLocked)
        {
            Velocity = Vector2.Zero;
            if (_usePhysicsMovement)
            {
                MoveAndSlide();
            }
            return;
        }

        var hasPatrolTarget = !_behaviorControlEnabled && _patrolPoints.Count > 0;
        if (_behaviorControlEnabled && _behaviorHasTarget)
        {
            TryBuildPendingGridPath();
        }
        else if (hasPatrolTarget)
        {
            if (!_hasTarget || (!_gridPathPending && !_gridPathActive))
            {
                AdvanceTarget();
            }
            TryBuildPendingGridPath();
        }
        else
        {
            if (!_phoneIdleActive && !_phoneExitLocked)
            {
                PlayIdleAnimation();
            }
            return;
        }

        if (_gridPathActive)
        {
            if (ProcessGridPathMovement(delta))
            {
                if (hasPatrolTarget && !_gridPathActive)
                {
                    AdvanceTarget();
                }
                return;
            }
        }

        if (_gridPathPending)
        {
            Velocity = Vector2.Zero;
            if (_usePhysicsMovement)
            {
                MoveAndSlide();
            }

            if (!_phoneIdleActive && !_phoneExitLocked)
            {
                PlayIdleAnimation();
            }
            UpdateStuckTimer(delta);
            return;
        }

        if (!_phoneIdleActive && !_phoneExitLocked)
        {
            PlayIdleAnimation();
        }
    }

    /// <summary>
    /// 绘制调试信息
    /// </summary>
    public override void _Draw()
    {
        if (!DebugDrawPath) return;

        if (_gridPath.Count > 0 && _gridPathIndex < _gridPath.Count)
        {
            var pathColor = new Color(0.2f, 0.7f, 1.0f, 0.9f);
            var current = ToLocal(GlobalPosition);
            for (var i = _gridPathIndex; i < _gridPath.Count; i++)
            {
                var next = ToLocal(_gridPath[i]);
                DrawLine(current, next, pathColor, 2.0f);
                DrawCircle(next, 2.5f, pathColor);
                current = next;
            }
        }
    }

    /// <summary>
    /// 配置巡逻
    /// </summary>
    /// <param name="points">巡逻点列表</param>
    /// <param name="startIndex">起始索引</param>
    public void ConfigurePatrol(List<Vector2> points, int startIndex)
    {
        _patrolPoints = points ?? new List<Vector2>();
        if (_patrolPoints.Count == 0) return;

        _patrolIndex = (startIndex % _patrolPoints.Count + _patrolPoints.Count) % _patrolPoints.Count;
        _patrolConfigured = true;
        ApplyRandomTheme();

        AdvanceTarget();
    }

    /// <summary>
    /// 启用行为控制
    /// </summary>
    public void EnableBehaviorControl()
    {
        _behaviorControlEnabled = true;
        _behaviorHasTarget = false;
        _patrolConfigured = false;
        _patrolPoints.Clear();
    }

    /// <summary>
    /// 设置行为目标
    /// </summary>
    /// <param name="target">目标位置</param>
    public void SetBehaviorTarget(Vector2 target)
    {
        _behaviorControlEnabled = true;
        _behaviorTarget = target;
        _behaviorHasTarget = true;
        BeginGridTarget(target);
    }

    /// <summary>
    /// 清除行为目标
    /// </summary>
    public void ClearBehaviorTarget()
    {
        _behaviorHasTarget = false;
        _hasTarget = false;
        _currentTarget = Vector2.Zero;
        _stuckTimer = 0.0f;
        _gridPathActive = false;
        _gridPathPending = false;
        _gridPathIndex = 0;
        _gridPathRetryTimer = 0.0f;
        _gridPath.Clear();
    }

    /// <summary>
    /// 设置网格寻路目标
    /// </summary>
    /// <param name="target">目标位置</param>
    private void BeginGridTarget(Vector2 target)
    {
        _currentTarget = target;
        _hasTarget = true;
        _stuckTimer = 0.0f;
        _gridPathActive = false;
        _gridPathPending = true;
        _gridPathIndex = 0;
        _gridPathRetryTimer = 0.0f;
        _gridPath.Clear();
        TryBuildPendingGridPath();
    }

    /// <summary>
    /// 是否已到达行为目标
    /// </summary>
    /// <returns>到达返回true</returns>
    public bool HasReachedBehaviorTarget()
    {
        if (!_behaviorHasTarget) return true;
        if (_gridPathActive)
        {
            return _gridPathIndex >= _gridPath.Count;
        }
        if (_gridPathPending)
        {
            return false;
        }
        return true;
    }

    /// <summary>
    /// 开始玩手机
    /// </summary>
    public void StartPhoneIdle()
    {
        if (_animationPlayer == null || !_animationPlayer.HasAnimation("phone_up")) return;
        if (_phoneIdleActive) return;

        _phoneExitLocked = false;
        _phoneIdleActive = true;
        _animationPlayer.Play("phone_up");
    }

    /// <summary>
    /// 停止玩手机
    /// </summary>
    /// <param name="lockMovement">是否锁定移动</param>
    public void StopPhoneIdle(bool lockMovement = false)
    {
        if (_animationPlayer == null)
        {
            _phoneIdleActive = false;
            _phoneExitLocked = false;
            return;
        }

        if (_phoneExitLocked && !lockMovement)
        {
            return;
        }

        if (!_phoneIdleActive && !_phoneExitLocked)
        {
            return;
        }

        _phoneIdleActive = false;
        if (_animationPlayer.HasAnimation("phone_down"))
        {
            _phoneExitLocked = lockMovement;
            _animationPlayer.Play("phone_down");
        }
        else
        {
            _phoneExitLocked = false;
            PlayIdleAnimation();
        }
    }

    /// <summary>
    /// 应用随机主题
    /// </summary>
    public void ApplyRandomTheme()
    {
        // 随机替换身体与配件贴图，形成不同主题外观
        if (_body == null) CacheSprites();

        Debug.Assert(_body != null, nameof(_body) + " != null");
        _body.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Body, Use16X16Sprites));
        _hairstyle.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Hair, Use16X16Sprites));
        _outfit.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Outfit, Use16X16Sprites));
        _eye.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Eye, Use16X16Sprites));
        _accessory.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Accessory, Use16X16Sprites));
        _smartphone.Texture = ResourceLoader.Load<Texture2D>(Res.GetRandom(Res.Type.Phone, Use16X16Sprites));
    }

    /// <summary>
    /// 缓存精灵节点
    /// </summary>
    private void CacheSprites()
    {
        // 缓存子节点引用，避免每帧查找
        _body = GetNode<Sprite2D>("parts/body");
        _hairstyle = GetNode<Sprite2D>("parts/hairstyle");
        _outfit = GetNode<Sprite2D>("parts/outfit");
        _eye = GetNode<Sprite2D>("parts/eye");
        _accessory = GetNode<Sprite2D>("parts/accessory");
        _smartphone = GetNode<Sprite2D>("parts/smartphone");
    }

    /// <summary>
    /// 配置碰撞
    /// </summary>
    private void ConfigureCollision()
    {
        // 学生只与环境碰撞，不与其它学生碰撞
        CollisionLayer = StudentCollisionLayer;
        CollisionMask = EnvironmentCollisionMask;
        _usePhysicsMovement = true;
    }

    /// <summary>
    /// 推进到下一个目标
    /// </summary>
    private void AdvanceTarget()
    {
        if (_patrolPoints.Count == 0) return;
        if (_behaviorControlEnabled) return;

        // 避免当前点过近导致原地抖动，最多尝试一轮
        for (var i = 0; i < _patrolPoints.Count; i++)
        {
            var target = _patrolPoints[_patrolIndex];
            _patrolIndex = (_patrolIndex + 1) % _patrolPoints.Count;
            if (GlobalPosition.DistanceTo(target) > TargetReachDistance * 1.5f)
            {
                BeginGridTarget(target);
                return;
            }
        }

        BeginGridTarget(_patrolPoints[_patrolIndex]);
    }

    /// <summary>
    /// 更新卡住计时器
    /// </summary>
    /// <param name="delta">时间间隔</param>
    private void UpdateStuckTimer(double delta)
    {
        if (StuckRepathSeconds <= 0.0f || !_hasTarget)
        {
            _lastPosition = GlobalPosition;
            return;
        }

        // 若短时间内几乎没有位移，则重新请求路径来脱困
        if (GlobalPosition.DistanceTo(_lastPosition) <= StuckDistanceEpsilon)
            _stuckTimer += (float)delta;
        else
            _stuckTimer = 0.0f;

        _lastPosition = GlobalPosition;

        if (_stuckTimer >= StuckRepathSeconds)
        {
            _stuckTimer = 0.0f;
            RepathToCurrentTarget();
        }
    }

    /// <summary>
    /// 重新规划路径到当前目标
    /// </summary>
    private void RepathToCurrentTarget()
    {
        if (!_hasTarget) return;

        _gridPathActive = false;
        _gridPathPending = true;
        _gridPathIndex = 0;
        _gridPath.Clear();
        TryBuildPendingGridPath();
    }

    /// <summary>
    /// 尝试构建挂起的网格路径
    /// </summary>
    private void TryBuildPendingGridPath()
    {
        if (!_gridPathPending) return;
        if (_gridPathRetryTimer > 0.0f) return;

        var path = BuildGridPath(GlobalPosition, _currentTarget);
        if (path == null || path.Count == 0)
        {
            _gridPathRetryTimer = Mathf.Max(0.1f, GridRepathInterval);
            return;
        }

        _gridPath.Clear();
        _gridPath.AddRange(path);
        _gridPathIndex = 0;
        _gridPathActive = true;
        _gridPathPending = false;
        if (DebugDrawPath)
        {
            QueueRedraw();
        }
    }

    /// <summary>
    /// 应用移动
    /// </summary>
    /// <param name="delta">时间间隔</param>
    private void ApplyMovement(double delta)
    {
        if (_usePhysicsMovement)
        {
            MoveAndSlide();
            return;
        }

        // 关闭碰撞时直接平移，避免 CharacterBody2D 在无碰撞层时不移动
        GlobalPosition += Velocity * (float)delta;
    }

    /// <summary>
    /// 更新面朝向动画
    /// </summary>
    /// <param name="velocity">当前速度</param>
    private void UpdateFacingAnimation(Vector2 velocity)
    {
        if (_phoneIdleActive || _phoneExitLocked)
        {
            return;
        }

        if (velocity.LengthSquared() < 0.01f)
        {
            PlayIdleAnimation();
            return;
        }

        if (Mathf.Abs(velocity.X) >= Mathf.Abs(velocity.Y))
            _lastFacing = velocity.X >= 0 ? FacingDirection.Right : FacingDirection.Left;
        else
            _lastFacing = velocity.Y >= 0 ? FacingDirection.Down : FacingDirection.Up;

        switch (_lastFacing)
        {
            case FacingDirection.Left:
                PlayAnimation("walk_left");
                break;
            case FacingDirection.Right:
                PlayAnimation("walk_right");
                break;
            case FacingDirection.Up:
                PlayAnimation("walk_up");
                break;
            case FacingDirection.Down:
                PlayAnimation("walk_down");
                break;
        }
    }

    /// <summary>
    /// 播放闲置动画
    /// </summary>
    private void PlayIdleAnimation()
    {
        if (_phoneIdleActive || _phoneExitLocked)
        {
            return;
        }

        switch (_lastFacing)
        {
            case FacingDirection.Left:
                PlayAnimation("idle_left");
                break;
            case FacingDirection.Right:
                PlayAnimation("idle_right");
                break;
            case FacingDirection.Up:
                PlayAnimation("idle_back");
                break;
            case FacingDirection.Down:
                PlayAnimation("idle_front");
                break;
        }
    }

    /// <summary>
    /// 播放指定动画
    /// </summary>
    /// <param name="animationName">动画名称</param>
    private void PlayAnimation(string animationName)
    {
        if (_animationPlayer == null) return;

        if (_animationPlayer.CurrentAnimation != animationName) _animationPlayer.Play(animationName);
    }

    /// <summary>
    /// 动画结束回调
    /// </summary>
    /// <param name="animationName">动画名称</param>
    private void OnAnimationFinished(StringName animationName)
    {
        if (_animationPlayer == null) return;

        if (animationName == "phone_up" && _phoneIdleActive)
        {
            if (_animationPlayer.HasAnimation("phone_loop"))
            {
                _animationPlayer.Play("phone_loop");
            }
            return;
        }

        if (animationName == "phone_down" && !_phoneIdleActive)
        {
            _phoneExitLocked = false;
            PlayIdleAnimation();
        }
    }

    /// <summary>
    /// 处理网格路径移动
    /// </summary>
    /// <param name="delta">时间间隔</param>
    /// <returns>如果正在移动返回true</returns>
    private bool ProcessGridPathMovement(double delta)
    {
        if (_gridPathIndex >= _gridPath.Count)
        {
            Velocity = Vector2.Zero;
            if (_usePhysicsMovement)
            {
                MoveAndSlide();
            }

            if (!_phoneIdleActive && !_phoneExitLocked)
            {
                PlayIdleAnimation();
            }
            UpdateStuckTimer(delta);
            _gridPathActive = false;
            return true;
        }

        var target = _gridPath[_gridPathIndex];
        var toNext = target - GlobalPosition;
        if (toNext.LengthSquared() <= TargetReachDistance * TargetReachDistance)
        {
            _gridPathIndex += 1;
            return true;
        }

        if (delta <= 0.0)
        {
            return true;
        }

        var axisVelocity = ToAxisVelocity(toNext);
        var step = axisVelocity * MoveSpeed * (float)delta;

        Velocity = step / (float)delta;
        ApplyMovement(delta);
        UpdateFacingAnimation(Velocity);
        UpdateStuckTimer(delta);
        return true;
    }

    /// <summary>
    /// 转换为轴向速度
    /// </summary>
    /// <param name="delta">位移</param>
    /// <returns>轴向速度</returns>
    private Vector2 ToAxisVelocity(Vector2 delta)
    {
        if (Mathf.Abs(delta.X) >= Mathf.Abs(delta.Y))
        {
            return new Vector2(Mathf.Sign(delta.X), 0);
        }

        return new Vector2(0, Mathf.Sign(delta.Y));
    }

    /// <summary>
    /// 构建网格路径
    /// </summary>
    /// <param name="start">起点</param>
    /// <param name="target">终点</param>
    /// <returns>路径点列表</returns>
    private List<Vector2> BuildGridPath(Vector2 start, Vector2 target)
    {
        if (_campusController == null)
        {
            _campusController = GetTree()?.CurrentScene as CampusController;
        }

        var path = _campusController?.RequestGridPath(start, target);
        if (path == null || path.Count == 0)
        {
            return null;
        }

        RemoveImmediateBacktracks(path);
        return SimplifyGridPath(path);
    }

    /// <summary>
    /// 移除直接回头的路径点
    /// </summary>
    /// <param name="path">路径</param>
    private void RemoveImmediateBacktracks(List<Vector2> path)
    {
        if (path == null || path.Count < 3) return;

        var index = 2;
        while (index < path.Count)
        {
            if (path[index].DistanceTo(path[index - 2]) <= 0.01f)
            {
                path.RemoveAt(index - 1);
                index = Math.Max(2, index - 1);
                continue;
            }
            index += 1;
        }
    }

    /// <summary>
    /// 简化网格路径（移除共线点）
    /// </summary>
    /// <param name="path">路径</param>
    /// <returns>简化后的路径</returns>
    private List<Vector2> SimplifyGridPath(List<Vector2> path)
    {
        if (path == null || path.Count < 3) return path;

        var simplified = new List<Vector2> { path[0] };
        var lastDir = Vector2.Zero;

        for (var i = 1; i < path.Count; i++)
        {
            var delta = path[i] - path[i - 1];
            if (delta.LengthSquared() < 0.01f)
            {
                continue;
            }

            var axisDir = ToAxisVelocity(delta);
            if (simplified.Count == 1)
            {
                simplified.Add(path[i]);
                lastDir = axisDir;
                continue;
            }

            if (axisDir == lastDir)
            {
                simplified[simplified.Count - 1] = path[i];
            }
            else
            {
                simplified.Add(path[i]);
                lastDir = axisDir;
            }
        }

        return simplified;
    }

}