ledger.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import csv
import datetime
import collections

import pytest


def ledger(path, cutoff=None):
    with open(path) as csvfile:
        result = collections.defaultdict(int)
        reader = csv.DictReader(csvfile, fieldnames=['date', 'payor', 'payee', 'amount'])
        for row in reader:
            amount = float(row['amount'])
            if cutoff is not None:
                date = datetime.datetime.strptime(row['date'], '%Y-%m-%d')
                if date > cutoff:
                    continue
            result[row['payor']] -= amount
            result[row['payee']] += amount
    return result


class TestLedger:
    @pytest.fixture
    def data(self, tmpdir):
        path = tmpdir.join('data.csv')
        with path.open('w') as csvfile:
            csvfile.write('2010-10-01,john,mary,50\n')
            csvfile.write('2011-10-01,mary,store,25\n')
            csvfile.write('2012-10-01,mary,store,100\n')
            csvfile.write('2013-10-01,sarah,mary,75\n')
        return path

    @pytest.fixture
    def bad_date_data(self, tmpdir):
        path = tmpdir.join('data.csv')
        with path.open('w') as csvfile:
            csvfile.write('2010-ten-one,john,mary,50\n')
        return path

    @pytest.fixture
    def bad_amount_data(self, tmpdir):
        path = tmpdir.join('data.csv')
        with path.open('w') as csvfile:
            csvfile.write('2010-10-01,john,mary,fifty\n')
        return path

    def test_no_date(self, data):
        assert ledger(data) == {
            'john': -50,
            'mary': 0,
            'sarah': -75,
            'store': 125,
        }

    def test_date(self, data):
        assert ledger(data, datetime.datetime(2012, 1, 1)) == {
            'john': -50,
            'mary': 25,
            'store': 25,
        }

    def test_bad_date(self, bad_date_data):
        with pytest.raises(ValueError):
            ledger(bad_date_data, datetime.datetime(2012, 1, 1))

    def test_bad_amount(self, bad_amount_data):
        with pytest.raises(ValueError):
            ledger(bad_amount_data)