同城外卖系统性价比评审中的转单版本与重试校验

from copy import deepcopy
def transfer(task, request):
    if request['region'] != task['region']:
        raise ValueError('region_mismatch')
    previous = task['receipts'].get(request['request_id'])
    payload = (request['from_rider'], request['to_rider'], request['version'])
    if previous is not None:
        if previous != payload:
            raise ValueError('request_conflict')
        return task
    if task['state'] != 'assigned':
        raise ValueError('handover_required')
    if request['version'] != task['version']:
        raise ValueError('stale_version')
    if request['from_rider'] != task['rider']:
        raise ValueError('rider_mismatch')
    if request['to_rider'] not in task['eligible_riders']:
        raise ValueError('rider_unavailable')
    result = deepcopy(task)
    result['rider'] = request['to_rider']
    result['version'] += 1
    result['receipts'][request['request_id']] = payload
    return result

if __name__ == '__main__':
    task = dict(region='east', state='assigned', rider='A', version=1,
                eligible_riders=['A', 'B'], receipts={})
    request = dict(region='east', request_id='R1', from_rider='A', to_rider='B', version=1)
    moved = transfer(task, request)
    assert (moved['rider'], moved['version']) == ('B', 2)
    assert transfer(moved, request) is moved
    assert task['rider'] == 'A'
    cases = [({**request, 'region':'west'}, task, 'region_mismatch'),
             ({**request, 'to_rider':'A'}, moved, 'request_conflict'),
             ({**request, 'request_id':'R2'}, moved, 'stale_version'),
             ({**request, 'from_rider':'C'}, task, 'rider_mismatch'),
             ({**request, 'to_rider':'C'}, task, 'rider_unavailable'),
             (request, {**task, 'state':'picked_up'}, 'handover_required')]
    for incoming, current, expected in cases:
        try:
            transfer(current, incoming)
        except ValueError as error:
            assert str(error) == expected
        else:
            raise AssertionError(expected)
    print('9 assertions passed; rider=B version=2; retries unchanged')