# -*- coding: utf-8 -*-
"""SCD2 (Slowly Changing Dimension Type 2) 处理器"""
from datetime import datetime

class SCD2Handler:
    """SCD2历史记录处理器"""
    
    def __init__(self, db_ops):
        self.db = db_ops
    
    def upsert(self, table_name: str, natural_key: list, tracked_fields: list,
               record: dict, effective_date: datetime = None) -> str:
        """
        处理SCD2更新
        
        Args:
            table_name: 表名
            natural_key: 自然键字段列表
            tracked_fields: 需要跟踪变化的字段列表
            record: 记录数据
            effective_date: 生效日期
        
        Returns:
            操作类型: 'INSERT', 'UPDATE', 'UNCHANGED'
        """
        effective_date = effective_date or datetime.now()
        
        # 查找当前有效记录
        where_clause = " AND ".join([f"{k} = %({k})s" for k in natural_key])
        sql_select = f"""
        SELECT * FROM {table_name}
        WHERE {where_clause}
          AND valid_to IS NULL
        """
        
        # 使用 db 的 connection
        current = self.db.conn.cursor()
        current.execute(sql_select, record)
        existing = current.fetchone()
        
        if not existing:
            # 新记录：直接插入
            record["valid_from"] = effective_date
            record["valid_to"] = None
            record["is_current"] = True
            
            fields = list(record.keys())
            placeholders = ", ".join([f"%({f})s" for f in fields])
            sql_insert = f"""
            INSERT INTO {table_name} ({', '.join(fields)})
            VALUES ({placeholders})
            """
            current.execute(sql_insert, record)
            return 'INSERT'
        
        # 检查是否有变化
        has_changes = any(
            existing.get(field) != record.get(field)
            for field in tracked_fields
        )
        
        if not has_changes:
            return 'UNCHANGED'
        
        # 有变化：关闭旧记录，插入新记录
        update_where = " AND ".join([f"{k} = %({k})s" for k in natural_key])
        sql_close = f"""
        UPDATE {table_name}
        SET valid_to = %(effective_date)s,
            is_current = FALSE
        WHERE {update_where}
          AND valid_to IS NULL
        """
        record["effective_date"] = effective_date
        current.execute(sql_close, record)
        
        # 插入新记录
        record["valid_from"] = effective_date
        record["valid_to"] = None
        record["is_current"] = True
        
        fields = list(record.keys())
        if "effective_date" in fields:
            fields.remove("effective_date")
        placeholders = ", ".join([f"%({f})s" for f in fields])
        sql_insert = f"""
        INSERT INTO {table_name} ({', '.join(fields)})
        VALUES ({placeholders})
        """
        current.execute(sql_insert, record)
        
        return 'UPDATE'