import os
import shutil
from urllib.parse import parse_qs, urlencode, urlsplit, urlunsplit

from django.db import transaction


def rename_file(instance, field_name, new_name, allow_missing_file=False):
    field = getattr(instance, field_name)
    current_name, extension = os.path.splitext(field.name)

    new_name_with_extension = "{}{}".format(new_name, extension)
    try:
        shutil.move(field.path, new_name_with_extension)
    except FileNotFoundError:
        if not allow_missing_file:
            raise
        print("Skipped missing file", field.path)
    initial_path = os.path.dirname(field.name)
    field.name = os.path.join(initial_path, new_name_with_extension)
    instance.save()
    return new_name_with_extension


def on_commit(f, *args, **kwargs):
    return transaction.on_commit(lambda: f(*args, **kwargs))


def set_query_parameter(url, **kwargs):
    """Given a URL, set or replace a query parameter and return the
    modified URL.

    >>> set_query_parameter('http://example.com?foo=bar&biz=baz', 'foo', 'stuff')
    'http://example.com?foo=stuff&biz=baz'
    """
    scheme, netloc, path, query_string, fragment = urlsplit(url)
    query_params = parse_qs(query_string)

    for param_name, param_value in kwargs.items():
        query_params[param_name] = [param_value]
    new_query_string = urlencode(query_params, doseq=True)

    return urlunsplit((scheme, netloc, path, new_query_string, fragment))