from typing import List
from .base import EffectProcessor

class TailEffect(EffectProcessor):
    """保留末尾效果处理器"""
    
    def validate_params(self) -> bool:
        """验证参数：保留的秒数"""
        if not self.params:
            return True  # 默认不截取
            
        try:
            tail_seconds = float(self.params)
            return tail_seconds >= 0
        except ValueError:
            return False
            
    def generate_filter_args(self, video_input: str, effect_index: int) -> tuple[List[str], str]:
        """生成保留末尾效果的滤镜参数"""
        if not self.validate_params():
            return [], video_input
            
        if not self.params:
            return [], video_input
            
        tail_seconds = float(self.params)
        if tail_seconds <= 0:
            return [], video_input
            
        output_stream = f"[v_eff{effect_index}]"
        
        # 使用reverse+trim+reverse的方法来精确获取最后N秒
        filter_args = [
            f"{video_input}reverse[v_rev{effect_index}]",
            f"[v_rev{effect_index}]trim=duration={tail_seconds}[v_trim{effect_index}]",
            f"[v_trim{effect_index}]reverse{output_stream}"
        ]
        
        return filter_args, output_stream
        
    def get_effect_name(self) -> str:
        return "tail"