#!/usr/bin/env python3

""" Task3: implementation """

import numpy as np
import matplotlib.pyplot as plt

def plot_discrete_function(csvfile, delimiter, comments, pngfile):
    """   
    Reads a csv-file containing discretized value of a function (f), its derivative (df) and antiderivative (F) 
    and plots all three functions over the discrete value of the interval (x).
    
    Expected csv-column layout: 
      x, f, F, df

    Requirements for the plot:
    - axis labels     
    - a legend for the plotted data records

    Implementation hints: 
    - use numpy.loadtxt(...) for loading the data from the csvfile    
    - use Matplotlib for plotting

    Parameters
    ----------
    csvfile : string
        Name of the csv-file containing the discrete function
    delimiter: character
        Charater used to delimit individual values in the rows
    comments: character
        Charater (when used as first character in a row) denoting comment lines   
    pngfile : string
        Name of the file where the plot is saved
    """
    # load data from csv file
    data = np.loadtxt(csvfile, delimiter=delimiter, comments=comments)
    x = data[:, 0]
    f = data[:, 1]
    F = data[:, 2]
    df = data[:, 3]

    # plot the data
    plt.plot(x, f, label='f')
    plt.plot(x, F, label='F')
    plt.plot(x, df, label='df')
    plt.xlabel('x')
    plt.ylabel('y')
    plt.legend()
    plt.savefig(pngfile)
    plt.close('all')