sales_summary

import csv

def read_data():
    data = []

    with open('sales.csv','r') as sales_csv:
        spreadsheet = csv.reader(sales_csv)
        header = next(spreadsheet)

        for row in spreadsheet:
            data.append(row)

    return data

def run():
    data = read_data()
    sales = []
    months = []
    expenditure = []
    years = []

    for row in  data:
        year = int(row[0])
        sale = int(row[2])
        expense = int(row[3])
        months.append(row[1])
        sales.append(sale)
        years.append(year)
        expenditure.append(expense)

    total = sum(sales)
    average = total/len(sales)
    min_sale = months[sales.index(min(sales))]
    max_sale = months[sales.index(max(sales))]
    print('Total sales: {}'.format(total))

    with open('output_summary.csv','w',newline='') as f:
        writer = csv.writer(f)

        writer.writerow(['year','month', 'sales_change', 'expenditure_change'])
        writer.writerow([years[0], months[0],'',''])

        i = 1
        while i < len(sales):
            writer.writerow([years[i], months[i], ((sales[i]-sales[i-1])/sales[i-1])*100, ((expenditure[i]- expenditure[i-1])/expenditure[i-1])*100])

            i += 1

        writer.writerow([])
        writer.writerow(['Average:{}'.format(average)])
        writer.writerow(['Minimum sale month:{}'.format(min_sale)])
        writer.writerow(['Maximum sale month:{}'.format(max_sale)])
run()