import random
import pandas as pd
from io import BytesIO

class ProbabilityCalculator:
    @staticmethod
    def weighted_random_selection(students):
        """
        基于积分的加权随机点名算法
        积分越高，被点概率越低
        """
        if not students:
            raise ValueError("学生列表不能为空")
        
        base_weight = 100
        decay_factor = 8  # 积分衰减系数
        
        weights = []
        for student in students:
            # 计算权重衰减，确保最低权重为15
            score_deduction = min(student.total_score * decay_factor, 85)
            weight = max(base_weight - score_deduction, 15)
            weights.append({
                'student': student,
                'weight': weight
            })
        
        total_weight = sum(item['weight'] for item in weights)
        random_value = random.uniform(0, total_weight)
        
        current_sum = 0
        for item in weights:
            current_sum += item['weight']
            if current_sum >= random_value:
                return item['student']
        
        return weights[0]['student']  # 兜底返回第一个学生

class ScoreCalculator:
    @staticmethod
    def calculate_score(answer_type, performance):
        """
        根据回答类型和表现计算积分
        """
        score_map = {
            'repeat_question': {
                'correct': 0.5,
                'incorrect': -1
            },
            'answer_question': {
                'excellent': 3,
                'good': 2,
                'normal': 1,
                'poor': 0.5
            },
            'present': {
                'present': 1
            }
        }
        
        return score_map.get(answer_type, {}).get(performance, 0)

class ExcelService:
    @staticmethod
    def export_scores(students):
        """导出积分数据到Excel"""
        data = []
        for student in students:
            data.append({
                '学号': student.student_id,
                '姓名': student.name,
                '班级': student.class_name,
                '总积分': student.total_score
            })
        
        df = pd.DataFrame(data)
        output = BytesIO()
        with pd.ExcelWriter(output, engine='openpyxl') as writer:
            df.to_excel(writer, sheet_name='学生积分', index=False)
        output.seek(0)
        return output