using UnityEngine;
using BaseGames.Enemies;

namespace BaseGames.Enemies.Navigation
{
    /// <summary>
    /// 地面单位导航：朝目标 X 直接行走，由 <see cref="EnemyMovement"/> 的墙/悬崖夹紧决定可达性。
    ///
    /// <para><b>不做任何地形扫描</b>：走得过去就是可达，被夹停的地方就是边界。
    /// 因此不存在"脱离导航图"这类状态——敌人无论被击退/冲锋到哪里，都能正常继续行走。</para>
    ///
    /// <para>只驱动水平方向；垂直交给刚体重力。移动经 <see cref="EnemyMoveInput"/> 下发，
    /// 速度为 0 时退化为移动层配置的步速。</para>
    /// </summary>
    [RequireComponent(typeof(EnemyMovement))]
    public sealed class GroundNavigator : MonoBehaviour, IEnemyNavigator
    {
        [Header("到达判定")]
        [Tooltip("身体中心 X 与目标 X 的距离小于此值即视为到达(m)")]
        [SerializeField] [Min(0.01f)] private float _stoppingDistance = 0.2f;

        [Header("游走取点（Wander 用）")]
        [Tooltip("单次游走的最近距离(m)")]
        [SerializeField] [Min(0f)] private float _wanderMinRange = 1.5f;
        [Tooltip("单次游走的最远距离(m)。走不到会被地形夹停，自然结束本次游走。")]
        [SerializeField] [Min(0f)] private float _wanderMaxRange = 5f;

        [Header("推进停滞检测")]
        [Tooltip("窗口时长(s)：此时长内净位移不足即判受阻")]
        [SerializeField] [Min(0.05f)] private float _stallWindowSeconds = 0.4f;
        [Tooltip("窗口内所需最小净位移(m)")]
        [SerializeField] [Min(0f)] private float _stallMinProgress = 0.05f;

        private EnemyBase     _enemy;
        private EnemyMovement _movement;
        private StallDetector _stall;

        private Vector2 _target;
        private bool    _hasTarget;
        private float   _speed;       // 0 = 用移动层配置步速
        private bool    _arrived;
        private bool    _blocked;

        public bool IsMoving   => _hasTarget && !_arrived && !_blocked;
        public bool HasArrived => _arrived;
        public bool IsBlocked  => _blocked;

        private void Awake()
        {
            _enemy    = GetComponent<EnemyBase>();
            _movement = GetComponent<EnemyMovement>();
            _stall    = new StallDetector(_stallWindowSeconds, _stallMinProgress);
            if (_enemy == null)
                Debug.LogError($"[GroundNavigator] {name} 找不到 EnemyBase，无法读取身体几何。", this);
        }

        // ── IEnemyNavigator ────────────────────────────────────────────
        public void MoveTowards(Vector2 target)
        {
            // 幂等：同一目标重复调用不重置状态，避免每帧调用时永远清掉到达/受阻标志
            if (_hasTarget && (target - _target).sqrMagnitude < 1e-6f) return;
            _target    = target;
            _hasTarget = true;
            _arrived   = false;
            _blocked   = false;
            _stall.Reset(BodyX);
        }

        public void Stop()
        {
            _hasTarget = false;
            _arrived   = false;
            _blocked   = false;
            HaltMovement();
        }

        /// <summary>
        /// 停下水平移动。
        /// <para>⚠ 必须直接写移动层输入，**不可**回调 <see cref="EnemyBase.StopMovement"/>——
        /// 后者会调用 <c>Nav.Stop()</c>，与本导航器互相调用造成无限递归（栈溢出）。
        /// 分层方向只允许 导航器 → 移动层，不允许反向回调。</para>
        /// </summary>
        private void HaltMovement()
        {
            if (_movement == null) return;
            _movement.PendingInput.MoveDir   = 0f;
            _movement.PendingInput.MoveSpeed = 0f;
            _movement.PendingInput.WantStop  = true;
        }

        public void SetSpeed(float speed) => _speed = Mathf.Max(0f, speed);

        public bool TryPickWanderPoint(out Vector2 point)
        {
            float sign = Random.value < 0.5f ? -1f : 1f;
            float x = WanderX(BodyX, _wanderMinRange, _wanderMaxRange, sign, Random.value);
            point = new Vector2(x, transform.position.y);
            return true;   // 地面单位总能尝试；走不到会被夹停并置 IsBlocked
        }

        // ── 驱动 ───────────────────────────────────────────────────────
        private float BodyX => _enemy != null ? _enemy.Body.Center.x : transform.position.x;

        private void FixedUpdate()
        {
            if (!_hasTarget || _arrived || _blocked || _movement == null) return;

            float bodyX = BodyX;
            if (Arrived(bodyX, _target.x, _stoppingDistance))
            {
                _arrived = true;
                HaltMovement();
                return;
            }

            float dir = Mathf.Sign(_target.x - bodyX);

            // 地形夹紧即为"不可达边界"：着地时前方是墙或悬崖 → 本次移动到此为止
            if (_movement.IsGrounded && _movement.WouldBlockAhead(dir))
            {
                _blocked = true;
                HaltMovement();
                return;
            }

            _movement.PendingInput.MoveDir   = dir;
            _movement.PendingInput.MoveSpeed = _speed;   // 0 → MoveHorizontal 用配置步速
            _movement.PendingInput.WantStop  = false;

            // 兜底：命令了移动却推不动（撞上未纳入检测层的碰撞体等）
            if (_stall.Tick(bodyX, Time.fixedDeltaTime))
            {
                _blocked = true;
                HaltMovement();
            }
        }

        // ── 纯函数（便于无场景单测）──────────────────────────────────────
        /// <summary>身体中心 X 是否已进入目标 X 的停止距离内。</summary>
        public static bool Arrived(float currentX, float targetX, float stopDistance)
            => Mathf.Abs(targetX - currentX) <= stopDistance;

        /// <summary>
        /// 游走目标 X：自当前位置朝 <paramref name="sign"/> 方向，
        /// 在 [minRange, maxRange] 区间内按插值系数 <paramref name="t"/>(0..1) 取点。
        /// </summary>
        public static float WanderX(float currentX, float minRange, float maxRange, float sign, float t)
            => currentX + sign * Mathf.Lerp(minRange, Mathf.Max(minRange, maxRange), Mathf.Clamp01(t));
    }
}