"""Reading a typed value out of the query string, without a 500.

WHY THIS EXISTS

List endpoints filtered like this:

    if type_id := request.args.get('typeid'):
        query = query.filter(Machine.machinetypeid == int(type_id))

`int('abc')` raises, nothing catches it, and the caller gets
500 INTERNAL_ERROR with a traceback in the log. A wrong query argument is the
caller's mistake and deserves a 400 saying which argument; a 500 says the server
is broken and sends whoever is reading the log looking for a fault that is not
there. The feature test run found the same shape in six places across five
plugins, which makes it a property of how list routes are written rather than of
any one route.

The helpers raise QueryArgError. Routes turn it into a 400 - or, more usually,
nothing does anything at all, because the app-level handler in
shopdb/__init__.py answers it. That is the point: a route should not have to
remember.

Deliberately NOT the same policy as get_pagination_params, which falls back to
a default for a bad page number. A nonsense page is harmless and the caller
still wants their list; a nonsense FILTER is not, because silently ignoring it
returns rows the caller believes they excluded.
"""

from flask import request


class QueryArgError(ValueError):
    """A query argument was present but not of the type the route needs."""

    def __init__(self, name, value, expected='a whole number'):
        self.name = name
        self.value = value
        super().__init__('%s must be %s (got %r)' % (name, expected, value))


def intarg(name, default=None, request_obj=None):
    """Read an integer query argument.

    Absent or empty -> default. Present but not an integer -> QueryArgError,
    which the app answers as a 400 naming the argument.
    """
    source = request_obj if request_obj is not None else request
    raw = source.args.get(name)
    if raw is None or raw == '':
        return default
    try:
        return int(raw)
    except (TypeError, ValueError):
        raise QueryArgError(name, raw)


def intargs(*names, request_obj=None):
    """Read several integer arguments at once; returns a dict of those present."""
    found = {}
    for name in names:
        value = intarg(name, request_obj=request_obj)
        if value is not None:
            found[name] = value
    return found