"""Base transform node for data pipeline."""
from abc import ABC, abstractmethod
import sqlite3
import pandas as pd


class TransformContext:
    """Context object containing the dataframe for transformation."""
    
    def __init__(self, df: pd.DataFrame):
        self.df = df
    
    def get_dataframe(self) -> pd.DataFrame:
        """Get the pandas dataframe from the context."""
        return self.df


class TransformNode(ABC):
    """Abstract base class for transformation nodes.
    
    Each transform node implements a single transformation step
    that takes data from the database, transforms it, and 
    potentially writes results back.
    """
    
    @abstractmethod
    def run(self, con: sqlite3.Connection, context: TransformContext) -> TransformContext:
        """Execute the transformation.
        
        Args:
            con: SQLite database connection
            context: TransformContext containing the input dataframe
            
        Returns:
            TransformContext with the transformed dataframe
        """
        pass