import xml.etree.ElementTree as ET

def create_student(xml_root, student_id):
    '''
    Vytvořte studenta dle loginu.
    Ujistěte se, že student neexistuje, jinak: raise Exception('student already exists')
    '''
    for student in xml_root.findall('student'):
        if student.get('student_id')==student_id:
            raise Exception('student already exists')
    new_student = ET.SubElement(xml_root, "student")
    new_student.set("student_id", student_id)
    return new_student

def remove_student(xml_root, student_id):
    '''
    Odstraňte studenta dle loginu
    '''
    for student in xml_root.findall('student'):
        if student.get('student_id')==student_id:
            xml_root.remove(student)
            return
    raise Exception('student does not exist')


def set_task_points(xml_root, student_id, task_id, points):
    '''
    Přepište body danému studentovi u jednoho tasku
    '''

    for student in xml_root.findall('student'):
        if student.get('student_id')==student_id:

            for task in student.findall('task'):
                if task.get('task_id')==task_id:
                    task.text=str(points)
                    return


            return
    raise Exception('student does not exist')


def create_task(xml_root, student_id, task_id, points):
    '''
    Pro daného studenta vytvořte task s body.
    Ujistěte se, že task (s task_id) u studenta neexistuje, jinak: raise Exception('task already exists')
    '''
    for student in xml_root.findall('student'):
        if student.get('student_id')==student_id:
            for task in student.findall('task'):
                if task.get('task_id')==task_id:
                    raise Exception('task already exists')
            new_task = ET.SubElement(student, 'task')
            new_task.set('task_id', task_id)
            new_task.text = str(points)
            return


def remove_task(xml_root, task_id):
    '''
    Napříč všemi studenty smažte task s daným task_id
    '''
    for student in xml_root.findall('student'):
        for task in student.findall('task'):
            if task.get('task_id')==task_id:
                student.remove(task)