#!/usr/bin/env python3

import sys
import argparse


parser = argparse.ArgumentParser(
	prog='CSV Transformer',
	description='Creates a new CSV from another CSV file with all desired (renamed) columns in the desired order.'
)
parser.add_argument('file', help='The CSV file to edit.')
parser.add_argument('-c', '--columns', required=True, help='The columns to keep, rename (=) or to add (+) comma separated (Example: "Test,One=Two,+Three")')
parser.add_argument('-o', '--output', help='The name of the output file (if not specified the output will be written to the console)')

args = parser.parse_args()

columns_wanted = args.columns.split(',')

with open(args.file, 'r') as file:
	csv = file.read()

lines = csv.split('\n')[:-1]
columns = lines[0].split(';')
new_head = []
column_to_column = []

for i,c in enumerate(columns_wanted):
	if c.find('=') != -1:
		old_name, new_name = c.split('=')
	else:
		old_name = c
		new_name = c

	new_head.append(new_name.replace('+', ''))

	if old_name.startswith('+'):
		index_old = None
	else:
		try:
			index_old = columns.index(old_name)
		except ValueError:
			print('Error: The column %s does not exist!' % (old_name))
			sys.exit(1)


	column_to_column.append(index_old)	

new_lines = []

for l in lines[1:]:
	new_line = []
	fields = l.split(';')

	for i,c in enumerate(column_to_column):
		if c is None:
			new_line.append('')
		else:
			new_line.append(fields[c])

	new_lines.append(';'.join(new_line))

output = ';'.join(new_head) + '\n' + '\n'.join(new_lines)

if args.output is None:
	print(output)
else:
	with open(args.output, 'w') as file:
		file.write(output)