import collections.abc
import csv


class DataCollection(collections.abc.Sequence):
    def __init__(self, headers):
        self.headers = headers
        self.data = dict()
        for name in headers:
            self.data[name] = []

    def __len__(self):
        return len(self.data[self.headers[0]])

    def __getitem__(self, index):
        if isinstance(index, slice):
            value = DataCollection(self.headers)
        else:
            value = {}

        for name in self.headers:
            if isinstance(index, slice):
                value.data[name] = self.data[name][index]
            else:
                value[name] = self.data[name][index]
        return value

    def append(self, d):
        for name in self.headers:
            self.data[name].append(d[name])


def read_csv_as_dicts(filename, conversions):
    value = []
    with open(filename) as f:
        rows = csv.reader(f)
        headers = next(rows)
        for row in rows:
            value.append(
                {name: func(val) for name, func, val in zip(headers, conversions, row)}
            )
    return value


def read_csv_as_columns(filename, conversions):
    with open(filename) as f:
        rows = csv.reader(f)
        headers = next(rows)
        value = DataCollection(headers)
        for row in rows:
            value.append(
                {name: func(val) for name, func, val in zip(headers, conversions, row)}
            )
    return value


def read_csv_as_instances(filename, cls):
    """Read a CSV file into a list of instances"""
    records = []
    with open(filename) as f:
        rows = csv.reader(f)
        _ = next(rows)
        for row in rows:
            records.append(cls.from_row(row))
    return records