'''
The etl module defines basic language primitives for manipulating Pandas
DataFrames. It takes a DataFrame in and outputs a transformed DataFrame.
You will implement several of the routines to perform these transformations.

Example Usage:

You can create DataFrame and create an ETL class that takes the DataFrame
as input.

>> df1 = pd.DataFrame([['Bob', 'Stewart'],
                       ['Anna', 'Davis'],
                       ['Jerry', 'Dole'],
                       ['John', 'Marsh']],
                      columns=["first_name", "last_name"])
>> etl = ETL(df1)

The add() function creates a new column with a specified value:

>> etl.add(colname="age", 0)
>> pw1.df
  first_name last_name  age
0        Bob   Stewart    0
1       Anna     Davis    0
2      Jerry      Dole    0
3       John     Marsh    0
'''

import pandas as pd
import re


class ETL:
    '''
    The class that defines ETL transformations for a single dataframe
    '''

    def __init__(self, df: pd.DataFrame):
        '''
        ETL objects are constructed with a source
        dataframe. These dataframes are manipulated
        in-place.
        '''

        #how to access the source dataframe
        self.df = df

        #stores a history of the transformations to the df
        self.transforms = []


    def add(self, colname, x):
        '''
        The add(colname, x) function adds a column with the specified name
        (colname) and a specified value (x). It adds this value to
        all rows of the dataframe. We've implemented this as an
        example to show you how to structure your ETL functions. 

        add *modifies* self.df as well as *returns* it
        '''

        #Test to see if colname is None, if so use a default colname
        self.df[colname] = x

        #append your changes to the transform list
        self.transforms.append(self.df.copy(deep=True))
        return self.df



    def drop(self, colname):
        '''
        The drop(colname) function returns a DataFrame 
        with the column (colname) removed.

        drop *modifies* self.df as well as *returns* it
        '''

        #YOUR CODE HERE

        self.transforms.append(self.df.copy(deep=True))
        return self.df

    def copy(self, colname, new_colname):
        '''
        copy(colname, new_colname) duplicates a column and 
        saves it to the new_colname.

        copy *modifies* self.df as well as *returns* it.
        '''

        #YOUR CODE HERE

        self.transforms.append(self.df.copy(deep=True))
        return self.df


    def split(self, colname, new_colname, splitter):
        '''
        split(colname, new_colname, splitter) takes a column
        splits the value on a delimiter. It replaces colname
        with the substrings that appear before the delimiter
        and puts the values after the delimiter in the 
        new_colname. If the string does not contain the delimiter
        then new_colname is assigned an empty string.

        split *modifies* self.df as well as *returns* it.
        '''

        #YOUR CODE HERE


        self.transforms.append(self.df.copy(deep=True))
        return self.df


    def merge(self, col1, col2, splitter):
        '''
        merge(col1, col2, splitter) replaces col1
        with the values of col1 and col2 concatenated,
        and seperated by the delimiter. The delimiter is
        ignored if either df.col1 or df.col2 is an empty 
        string.

        merge *modifies* self.df as well as *returns* it. 
        '''

        #YOUR CODE HERE


        self.transforms.append(self.df.copy(deep=True))
        return self.df


    def format(self, colname, fn):
        '''
        format applies an input function to every value in colname. fn
        is a *function*.

        format *modifies* self.df as well as *returns* it.
        '''
        
        #YOUR CODE HERE


        self.transforms.append(self.df.copy(deep=True))
        return self.df


    def divide(self, colname, new_colname1, new_colname2, condition):
        '''
        Divide conditionally divides a column, sending values that 
        satisfy the condition into one of two columns 
        (new_colname1 or new_colname2). condition is a Boolean function
        of values.

        See examples in the writeup.
        '''

        #YOUR CODE HERE

        self.transforms.append(self.df.copy(deep=True))
        return self.df