# api.py
import os
import csv
from copy import deepcopy

from marshmallow import Schema, fields, pre_load
from marshmallow.validate import Length, Range


class UserSchema(Schema):
    """Represent a *valid* user. """

    email = fields.Email(required=True)
    name = fields.Str(required=True, validate=Length(min=1))
    age = fields.Int(
        required=True, validate=Range(min=18, max=65)
    )
    role = fields.Str()

    @pre_load()
    def strip_name(self, data, **kwargs):
        data_copy = deepcopy(data)

        try:
            data_copy['name'] = data_copy['name'].strip()
        except (AttributeError, KeyError, TypeError):
            pass

        return data_copy


schema = UserSchema()


def export(filename, users, overwrite=True):
    """Export a CSV file.

    Create a CSV file and fill with valid users.  If `overwrite`
    is False and file already exists, raise IOError.
    """
    if not overwrite and os.path.isfile(filename):
        raise IOError(f"'{filename}' already exists.")

    valid_users = get_valid_users(users)
    write_csv(filename, valid_users)


def get_valid_users(users):
    """Yield one valid user at a time from users. """
    yield from filter(is_valid, users)


def is_valid(user):
    """Return whether or not the user is valid. """
    return not schema.validate(user)


def write_csv(filename, users):
    """Write a CSV given a filename and a list of users.

    The users are assumed to be valid for the given CSV structure.
    """
    fieldnames = ['email', 'name', 'age', 'role']

    with open(filename, 'w', newline='') as csvfile:
        writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
        writer.writeheader()

        for user in users:
            writer.writerow(user)