import csv
import json


def f():
    map_by_prod = {}

    with open('SWE sample data - Q2 data.csv', 'r') as csv_file:
        lines = csv.reader(csv_file, delimiter=' ', quotechar='"')
        for row in lines:
            # print(row[0])
            line = json.loads(row[0])

            # by num of unique user
            if map_by_prod.get(line['product_id'], None) is None:
                map_by_prod[line['product_id']] = {
                    "num_user": {line['user_id']},
                    "quantity": line['quantity']
                }
            else:
                map_by_prod[line['product_id']]["num_user"].add(line['user_id'])
                map_by_prod[line['product_id']]["quantity"] += line['quantity']

    best_prod_by_num_user = ("", 0)
    best_prod_by_quantity = ("", 0)

    # sort takes nlog(n) time, might as well loop through it
    for (k, v) in map_by_prod.items():
        if v["quantity"] > best_prod_by_quantity[1]:
            best_prod_by_quantity = (k, v["quantity"])

        if len(v["num_user"]) > best_prod_by_num_user[1]:
            best_prod_by_num_user = (k, len(v["num_user"]))

    return (
        "Most popular product(s) based on the number of purchasers: {0} with {1} unique users."
            .format(best_prod_by_num_user[0], best_prod_by_num_user[1]),
        "Most popular product(s) based on the quantity of goods sold: {0} with {1} items sold."
            .format(best_prod_by_quantity[0], best_prod_by_quantity[1])
    )


print(f())