using UnityEngine;
using Unity.Cinemachine;

namespace BaseGames.Camera
{
    /// <summary>
    /// 速度自适应 Lookahead 扩展。
    ///
    /// 玩家水平速度越快，Lookahead.Time 越接近 CameraArea 配置的最大值；
    /// 静止时衰减至最大值的 <see cref="_restScale"/> 倍，避免静止时镜头无谓偏移。
    ///
    /// 挂载位置：Persistent 场景中的 VCamA / VCamB GameObject。
    /// <see cref="CameraStateController.ConfigureSlot"/> 在每次切换区域时调用
    /// <see cref="SetConfiguredMax"/> 传入该区域的 LookaheadTime。
    /// </summary>
    [AddComponentMenu("Cinemachine/Extensions/Camera Adaptive Lookahead")]
    [DisallowMultipleComponent]
    public class CameraAdaptiveLookaheadExtension : CinemachineExtension
    {
        [Tooltip("静止时 Lookahead 缩减比例（0~1）。\n" +
                 "0 = 静止时完全无 Lookahead；0.25 = 静止时使用配置值的 25%。\n" +
                 "推荐 0.2~0.3。")]
        [Range(0f, 1f)]
        [SerializeField] private float _restScale = 0.25f;

        [Tooltip("达到最大 Lookahead 所需的水平速度（世界单位/秒）。\n" +
                 "玩家以此速度奔跑时 Lookahead.Time = 100% 配置值。推荐 10~15。")]
        [SerializeField] private float _speedAtFullLookahead = 12f;

        [Tooltip("水平速度估算的平滑强度。越大响应越快。推荐 4~6。")]
        [SerializeField] private float _speedSmoothing = 5f;

        // ── 内部状态 ──────────────────────────────────────────────────────────

        private float _configuredMaxTime = -1f;   // -1 = ConfigureSlot 尚未调用
        private float _estimatedSpeedX;
        private float _lastFollowX;
        private bool  _trackingInitialized;

        // ── 公开 API ──────────────────────────────────────────────────────────

        /// <summary>
        /// 由 <see cref="CameraStateController.ConfigureSlot"/> 调用，
        /// 传入当前 CameraArea 配置的最大 Lookahead 时长。
        /// </summary>
        public void SetConfiguredMax(float maxTime) => _configuredMaxTime = maxTime;

        // ── Extension ─────────────────────────────────────────────────────────

        protected override void PostPipelineStageCallback(
            CinemachineVirtualCameraBase vcam,
            CinemachineCore.Stage stage,
            ref CameraState state,
            float deltaTime)
        {
            if (stage != CinemachineCore.Stage.Body) return;

            // 编辑器预览时不运行
            if (deltaTime <= 0f)
            {
                _trackingInitialized = false;
                return;
            }

            // ConfigureSlot 尚未调用时跳过（避免覆盖默认值）
            if (_configuredMaxTime < 0f) return;

            // ── 估算玩家水平速度 ──────────────────────────────────────────────
            Transform follow = vcam.Follow;
            if (follow != null)
            {
                if (!_trackingInitialized)
                {
                    _lastFollowX         = follow.position.x;
                    _trackingInitialized = true;
                }

                float rawSpeedX  = Mathf.Abs(follow.position.x - _lastFollowX) / deltaTime;
                _lastFollowX     = follow.position.x;
                _estimatedSpeedX = Mathf.Lerp(_estimatedSpeedX, rawSpeedX, 1f - Mathf.Exp(-deltaTime * _speedSmoothing));
            }

            // ── 速度映射 → Lookahead 时长 ─────────────────────────────────────
            float fraction   = Mathf.Clamp01(_estimatedSpeedX / _speedAtFullLookahead);
            float scaledTime = Mathf.Lerp(_configuredMaxTime * _restScale, _configuredMaxTime, fraction);

            var composer = vcam.GetComponent<CinemachinePositionComposer>();
            if (composer == null) return;

            var lah  = composer.Lookahead;
            lah.Time = scaledTime;
            composer.Lookahead = lah;
        }

        /// <summary>
        /// 重置速度估算状态。在相机硬切时由 CameraStateController 调用，
        /// 避免上一区域的奔跑速度影响新区域的初始 Lookahead 量。
        /// </summary>
        public void ResetState()
        {
            _estimatedSpeedX     = 0f;
            _trackingInitialized = false;
        }
    }
}