/// ---------------------------------------------
/// Movement Pack for Behavior Designer Pro
/// Copyright (c) Opsive. All Rights Reserved.
/// https://www.opsive.com
/// ---------------------------------------------

using Opsive.BehaviorDesigner.AddOns.Shared.Runtime.Pathfinding;

namespace Opsive.BehaviorDesigner.AddOns.MovementPack.Runtime.Tasks
{
    using Opsive.BehaviorDesigner.Runtime.Tasks;
    using Opsive.GraphDesigner.Runtime;
    using Opsive.GraphDesigner.Runtime.Variables;
    using UnityEngine;

    [Opsive.Shared.Utility.Description("Pursues the specified target with precise stopping. Manually controls agent speed based on distance to stop smoothly without overshooting.")]
    [NodeIcon("079b135d5d495e14abd9ad2cb0dfaf9e", "c0515b66e6314734ba5a8f2ec7d6f451")]
    public class PrecisePursue : MovementBase // 依然继承自 MovementBase
    {
        // --- 原有的 Pursue 变量 ---
        [Tooltip("The GameObject that the agent is seeking.")]
        [SerializeField] protected SharedVariable<GameObject> m_Target;
        [Tooltip("Specifies how far to predict the distance ahead of the target. Lower values indicate that less distance should be predicated.")]
        [SerializeField] protected SharedVariable<float> m_DistancePrediction = 20;
        [Tooltip("Specifies the multiplier for predicting the look ahead distance.")]
        [SerializeField] protected SharedVariable<float> m_DistancePredictionMultiplier = 20;

        // --- 新增的“方案一”变量 ---
        [Header("Precise Stopping")]
        [Tooltip("【新】开始减速的距离 (例如 6m)")]
        [SerializeField] protected SharedVariable<float> m_SlowDownDistance = 6f;
        [Tooltip("【新】减速到最慢时的速度 (防止完全停止)")]
        [SerializeField] protected SharedVariable<float> m_MinSpeed = 0.5f;

        // --- 私有变量 ---
        private Vector3 m_TargetPosition;
        private float m_OriginalMaxSpeed; // 用于存储 Agent 的原始最大速度
        private NavMeshAgentPathfinder m_Pathfinder => base.m_Pathfinder as NavMeshAgentPathfinder;

        /// <summary>
        /// The task has started.
        /// </summary>
        public override void OnStart()
        {
            base.OnStart();

            if (m_Target == null) {
                Debug.LogError("Error: A target must be set on the PrecisePursue ability.");
                return;
            }

            // --- 关键设置 ---
            // 1. 存储原始最大速度
            m_OriginalMaxSpeed = m_Pathfinder.Speed; 
            
            // 2. 关闭 NavMeshAgent 的自动刹车，因为我们要手动控制
            m_Pathfinder.m_NavMeshAgent.autoBraking = false;
            // ---------------

            m_TargetPosition = m_Target.Value.transform.position;
            SetDestination(GetTargetDestination());
        }

        /// <summary>
        /// (原 Pursue 脚本逻辑，保持不变)
        /// Returns the target destination.
        /// </summary>
        /// <returns>The target destination.</returns>
        private Vector3 GetTargetDestination()
        {
            // Calculate the current distance to the target and the current speed.
            var distance = (m_Target.Value.transform.position - transform.position).magnitude;
            var velocityMagnitude = m_Pathfinder.Velocity.magnitude;

            var futurePrediction = 0f;
            // Set the future prediction to the max prediction if the speed is too small to give an accurate prediction.
            if (velocityMagnitude <= distance / m_DistancePrediction.Value) {
                futurePrediction = m_DistancePrediction.Value;
            } else {
                futurePrediction = (distance / velocityMagnitude) * m_DistancePredictionMultiplier.Value;
            }

            // Predict the future by taking the velocity of the target and multiply it by the future prediction.
            var lastTargetPosition = m_TargetPosition;
            m_TargetPosition = m_Target.Value.transform.position;
            return m_TargetPosition + (m_TargetPosition - lastTargetPosition) * futurePrediction;
        }

        /// <summary>
        /// Updates the destination.
        /// </summary>
        /// <returns>Success when the agent arrives.</returns>
        public override TaskStatus OnUpdate()
        {
            if (m_Target == null || m_Target.Value == null) {
                return TaskStatus.Failure;
            }

            // --- 核心修改：基于距离的速度控制 ---
            
            // 1. 计算【直线距离】(非常重要，不用 NavMesh 的 remainingDistance)
            float distanceToTarget = Vector3.Distance(transform.position, m_Target.Value.transform.position);

            // 2. 检查是否已“到达” (即进入了停止范围)
            if (distanceToTarget <= m_Pathfinder.StoppingDistance) 
            {
                // 已经到达，强制停止并返回成功
                m_Pathfinder.m_NavMeshAgent.velocity = Vector3.zero; // 清除惯性
                m_Pathfinder.m_NavMeshAgent.isStopped = true;
                m_Pathfinder.m_NavMeshAgent.speed = 0f; // 速度设为零
                return TaskStatus.Success;
            }

            // 3. 检查是否在“减速缓冲区”
            if (distanceToTarget < m_SlowDownDistance.Value)
            {
                // 在缓冲区 (例如 2m 到 6m 之间)
                // 计算减速因子 (0.0 -> 1.0)
                // 距离 = 2m 时, factor = 0.0
                // 距离 = 6m 时, factor = 1.0
                float factor = (distanceToTarget - m_Pathfinder.StoppingDistance) / (m_SlowDownDistance.Value - m_Pathfinder.StoppingDistance);
                
                // 使用 Lerp 平滑地插值速度
                m_Pathfinder.m_NavMeshAgent.speed = Mathf.Lerp(m_MinSpeed.Value, m_OriginalMaxSpeed, factor);
                m_Pathfinder.m_NavMeshAgent.isStopped = false;
            }
            else
            {
                // 在缓冲区外，全速前进
                m_Pathfinder.m_NavMeshAgent.speed = m_OriginalMaxSpeed;
                m_Pathfinder.m_NavMeshAgent.isStopped = false;
            }
            // --- 核心修改结束 ---


            // 4. (原 Pursue 逻辑) 持续更新目标点（因为目标在移动）
            SetDestination(GetTargetDestination());

            return TaskStatus.Running;
        }

        /// <summary>
        /// Resets the task values back to their default.
        /// </summary>
        public override void Reset()
        {
            base.Reset();

            // 原有变量
            m_Target = null;
            m_DistancePrediction = 20;
            m_DistancePredictionMultiplier = 20;

            // 新增变量
            m_SlowDownDistance = 6f;
            m_MinSpeed = 0.5f;
        }
        
        /// <summary>
        /// 任务结束时（无论是成功到达，还是被Parallel Selector打断），彻底重置状态
        /// </summary>
        public override void OnEnd()
        {
            base.OnEnd();
    
            if (m_Pathfinder != null && m_Pathfinder.m_NavMeshAgent != null)
            {
                // 1. 【核心修复】立即物理刹车
                // 只有在 Agent 处于激活且在 NavMesh 上时才操作，防止报错
                if (m_Pathfinder.m_NavMeshAgent.isOnNavMesh && m_Pathfinder.m_NavMeshAgent.isActiveAndEnabled)
                {
                    // 强制停止寻路逻辑
                    m_Pathfinder.m_NavMeshAgent.isStopped = true;
            
                    // 抹除物理惯性 (这是导致滑步的罪魁祸首)
                    m_Pathfinder.m_NavMeshAgent.velocity = Vector3.zero;
            
                    // 清空当前的路径数据 (防止下一个任务开始前，Agent试图跑完旧路径)
                    m_Pathfinder.m_NavMeshAgent.ResetPath();
                }

                // 2. 恢复参数设置 (把 Agent 还原成标准状态，供下一个 Task 使用)
                m_Pathfinder.m_NavMeshAgent.autoBraking = true;
                m_Pathfinder.m_NavMeshAgent.speed = m_OriginalMaxSpeed; 
        
                // 注意：不要在这里设为 isStopped = false。
                // 下一个 Task (比如 Attack 或 Move) 开始时，
                // 它们会自动调用 SetDestination 或相关逻辑来启动 Agent。
                // 在这里保持 Stopped 是最安全的“待机”状态。
            }
        }
    }
}