using UnityEngine;

/// <summary>
/// 音频淡入淡出效果类（简化版）
/// 职责：管理音频的淡入淡出效果，与播放逻辑解耦
/// 设计：使用状态机模式，单一计时器，逻辑清晰
/// </summary>
public class AudioFadeEffect
{
    #region Enums
    
    /// <summary>
    /// 淡入淡出状态
    /// </summary>
    public enum FadeState
    {
        None,       // 无效果
        FadingIn,   // 正在淡入
        FadingOut,  // 正在淡出
    }
    
    #endregion
    
    #region Fields
    
    private FadeState _state = FadeState.None;
    private float _elapsedTime = 0f;        // 当前状态经过的时间
    private float _fadeInDuration = 4f;     // 淡入时长（秒）
    private float _fadeOutDuration = 4f;    // 淡出时长（秒）
    
    #endregion
    
    #region Properties
    
    /// <summary>
    /// 当前淡入淡出系数 (0-1)
    /// </summary>
    public float FadeValue { get; private set; } = 1f;
    
    /// <summary>
    /// 当前状态
    /// </summary>
    public FadeState State => _state;
    
    /// <summary>
    /// 是否正在淡入
    /// </summary>
    public bool IsFadingIn => _state == FadeState.FadingIn;
    
    /// <summary>
    /// 是否正在淡出
    /// </summary>
    public bool IsFadingOut => _state == FadeState.FadingOut;
    
    /// <summary>
    /// 是否有任何效果激活
    /// </summary>
    public bool IsActive => _state != FadeState.None;
    
    /// <summary>
    /// 淡入时长（秒）
    /// </summary>
    public float FadeInDuration
    {
        get => _fadeInDuration;
        set => _fadeInDuration = Mathf.Max(0.01f, value);
    }
    
    /// <summary>
    /// 淡出时长（秒）
    /// </summary>
    public float FadeOutDuration
    {
        get => _fadeOutDuration;
        set => _fadeOutDuration = Mathf.Max(0.01f, value);
    }
    
    #endregion
    
    #region Constructor
    
    /// <summary>
    /// 创建淡入淡出效果
    /// </summary>
    /// <param name="fadeInDuration">淡入时长（秒）</param>
    /// <param name="fadeOutDuration">淡出时长（秒）</param>
    public AudioFadeEffect(float fadeInDuration = 4f, float fadeOutDuration = 4f)
    {
        _fadeInDuration = Mathf.Max(0.01f, fadeInDuration);
        _fadeOutDuration = Mathf.Max(0.01f, fadeOutDuration);
        FadeValue = 1f;
    }
    
    #endregion
    
    #region Public Methods
    
    /// <summary>
    /// 开始淡入效果
    /// </summary>
    /// <param name="duration">淡入时长（秒），null 则使用默认值</param>
    public void StartFadeIn(float? duration = null)
    {
        if (duration.HasValue)
        {
            _fadeInDuration = Mathf.Max(0.01f, duration.Value);
        }
        
        _state = FadeState.FadingIn;
        _elapsedTime = 0f;
        FadeValue = 0f;
    }
    
    /// <summary>
    /// 开始淡出效果
    /// </summary>
    /// <param name="duration">淡出时长（秒），null 则使用默认值</param>
    /// <returns>如果已经在淡出中则返回 false</returns>
    public bool StartFadeOut(float? duration = null)
    {
        if (_state == FadeState.FadingOut)
            return false;
            
        if (duration.HasValue)
        {
            _fadeOutDuration = Mathf.Max(0.01f, duration.Value);
        }
        
        _state = FadeState.FadingOut;
        _elapsedTime = 0f;
        // FadeValue 保持当前值，从当前音量开始淡出
        
        return true;
    }
    
    /// <summary>
    /// 停止所有淡入淡出效果
    /// </summary>
    public void Stop()
    {
        _state = FadeState.None;
        _elapsedTime = 0f;
        FadeValue = 1f;
    }
    
    /// <summary>
    /// 重置到初始状态（无淡入淡出）
    /// </summary>
    public void Reset()
    {
        Stop();
    }
    
    /// <summary>
    /// 更新淡入淡出效果
    /// </summary>
    /// <param name="deltaTime">时间增量</param>
    /// <returns>是否应该停止播放（淡出完成）</returns>
    public bool Update(float deltaTime)
    {
        if (_state == FadeState.None)
        {
            FadeValue = 1f;
            return false;
        }
        
        _elapsedTime += deltaTime;
        
        switch (_state)
        {
            case FadeState.FadingIn:
                return UpdateFadeIn();
                
            case FadeState.FadingOut:
                return UpdateFadeOut();
                
            default:
                return false;
        }
    }
    
    /// <summary>
    /// 获取当前应用淡入淡出后的音量
    /// </summary>
    /// <param name="originalVolume">原始音量</param>
    /// <returns>应用淡入淡出系数后的音量</returns>
    public float ApplyFade(float originalVolume)
    {
        return originalVolume * FadeValue;
    }
    
    #endregion
    
    #region Private Methods
    
    /// <summary>
    /// 更新淡入
    /// </summary>
    private bool UpdateFadeIn()
    {
        if (_elapsedTime >= _fadeInDuration)
        {
            // 淡入完成
            FadeValue = 1f;
            _state = FadeState.None;
            return false;
        }
        
        // 计算淡入进度
        FadeValue = Mathf.Clamp01(_elapsedTime / _fadeInDuration);
        return false;
    }
    
    /// <summary>
    /// 更新淡出
    /// </summary>
    private bool UpdateFadeOut()
    {
        if (_elapsedTime >= _fadeOutDuration)
        {
            // 淡出完成
            FadeValue = 0f;
            _state = FadeState.None;
            return true; // 通知调用者应该停止播放
        }
        
        // 计算淡出进度（从当前值淡出到0）
        float progress = _elapsedTime / _fadeOutDuration;
        FadeValue = Mathf.Lerp(FadeValue, 0f, progress);
        
        return false;
    }
    
    #endregion
    
    #region Debug
    
    /// <summary>
    /// 获取调试信息
    /// </summary>
    public string GetDebugInfo()
    {
        return $"FadeEffect: State={_state}, Value={FadeValue:F2}, " +
               $"Elapsed={_elapsedTime:F2}s, " +
               $"Durations(In={_fadeInDuration:F1}s, Out={_fadeOutDuration:F1}s)";
    }
    
    #endregion
}