Parse query params.

    Parses, validates, and converts query into a consistent format.

    :keyword request: the bottle request
    :keyword standard_params: query params that are present in most of our
        (opinionated) APIs (ex. limit, offset, sort, q, and facets)
    :keyword filter_fields: list of field names to allow filtering on
    :keyword defaults: dict of params and their default values
    :retuns: dict of query params with supplied values (string or list)

def process_params(request, standard_params=STANDARD_QUERY_PARAMS,
                   filter_fields=None, defaults=None):
    """Parse query params.

    Parses, validates, and converts query into a consistent format.

    :keyword request: the bottle request
    :keyword standard_params: query params that are present in most of our
        (opinionated) APIs (ex. limit, offset, sort, q, and facets)
    :keyword filter_fields: list of field names to allow filtering on
    :keyword defaults: dict of params and their default values
    :retuns: dict of query params with supplied values (string or list)
    """
    if not filter_fields:
        filter_fields = []
    unfilterable = (set(request.query.keys()) - set(filter_fields) -
                    set(standard_params))
    if unfilterable:
        bottle.abort(400,
                     "The following query params were invalid: %s. "
                     "Try one (or more) of %s." %
                     (", ".join(unfilterable),
                      ", ".join(filter_fields)))
    query_fields = defaults or {}
    for key in request.query:
        if key in filter_fields:
            # turns ?netloc=this.com&netloc=that.com,what.net into
            # {'netloc': ['this.com', 'that.com', 'what.net']}
            matches = request.query.getall(key)
            matches = list(itertools.chain(*(k.split(',') for k in matches)))
            if len(matches) > 1:
                query_fields[key] = matches
            else:
                query_fields[key] = matches[0]
    if 'sort' in request.query:
        sort = request.query.getall('sort')
        sort = list(itertools.chain(*(
            comma_separated_strings(str(k)) for k in sort)))
        query_fields['sort'] = sort
    if 'q' in request.query:
        search = request.query.getall('q')
        search = list(itertools.chain(*(
            comma_separated_strings(k) for k in search
            if k)))
        query_fields['q'] = search
    return query_fields