# python standard library
from contextlib import contextmanager  # `with` statement in db sessions
import logging
from os import path

# user installed libraries
try:
    import bcrypt
    from sqlalchemy import create_engine
    from sqlalchemy.orm import sessionmaker
    import networkx as nx
    import yaml
except ImportError:
    logger.critical('Python package missing. See README.md for instructions.')
    sys.exit(1)

# this project
from models import Student, Answer, Topic, StudentTopic
from knowledge import Knowledge
from questions import QFactory
from tools import load_yaml

# setup logger for this module
logger = logging.getLogger(__name__)

# ============================================================================
# LearnApp - application logic
# ============================================================================
class LearnApp(object):
    def __init__(self):
        # online students
        self.online = {}

        # connect to database and check registered students
        self.setup_db('students.db')    # FIXME

        # build dependency graph
        self.build_dependency_graph('demo/config.yaml')  # FIXME

    # ------------------------------------------------------------------------
    def login(self, uid, try_pw):
        with self.db_session() as s:
            student =  s.query(Student).filter(Student.id == uid).one_or_none()

            if student is None:
                logger.info(f'User "{uid}" does not exist.')
                return False    # student does not exist or already loggeg in

            hashedtry = bcrypt.hashpw(try_pw.encode('utf-8'), student.password)
            if hashedtry != student.password:
                logger.info(f'User "{uid}" wrong password.')
                return False    # wrong password

            student_state = s.query(StudentTopic).filter(StudentTopic.student_id == uid).all()

            # success
            self.online[uid] = {
                'name': student.name,
                'number': student.id,
                'state': Knowledge(self.depgraph, student_state),
            }
            logger.info(f'User "{uid}" logged in')
            return True

    # ------------------------------------------------------------------------
    # logout
    def logout(self, uid):
        logger.info(f'User "{uid}" logged out')
        del self.online[uid]  # FIXME save current state

    # ------------------------------------------------------------------------
    def get_student_name(self, uid):
        return self.online[uid].get('name', '')

    # ------------------------------------------------------------------------
    # check answer and if correct returns new question, otherise returns None
    def check_answer(self, uid, answer):
        logger.debug(f'check_answer("{uid}", "{answer}")')
        knowledge = self.online[uid]['state']
        current_question = knowledge.check_answer(answer)

        if current_question is not None:
            logger.debug('check_answer: saving answer to db ...')
            with self.db_session() as s:
                s.add(Answer(
                    ref=current_question['ref'],
                    grade=current_question['grade'],
                    starttime=str(current_question['start_time']),
                    finishtime=str(current_question['finish_time']),
                    student_id=uid))
                s.commit()
            logger.debug('check_answer: saving done')

        logger.debug('check_answer: will return knowledge.new_question')
        return knowledge.new_question()

    # ------------------------------------------------------------------------
    # helper to manage db sessions using the `with` statement, for example
    #   with self.db_session() as s:  s.query(...)
    @contextmanager
    def db_session(self):
        session = self.Session()
        try:
            yield session
            session.commit()
        except Exception as e:
            session.rollback()
            raise e
        finally:
            session.close()

    # ------------------------------------------------------------------------
    # Receives a set of topics (strings like "math/algebra"),
    # and recursively adds dependencies to the dependency graph
    def build_dependency_graph(self, config_file):
        logger.debug(f'build_dependency_graph("{config_file}")')

        # Load configuration file
        try:
            with open(config_file, 'r') as f:
                logger.info(f'Loading configuration file "{config_file}"')
                config = yaml.load(f)
        except FileNotFoundError as e:
            logger.error(f'File not found: "{config_file}"')
            raise e

        prefix = config['path']     # FIXME default if does not exist?
        g = nx.DiGraph(path=prefix)

        # Build dependency graph
        deps = config.get('dependencies', {})
        for n,dd in deps.items():
            g.add_edges_from((n,d) for d in dd)

        # Builds factories for each node
        for n in g.nodes_iter():
            fullpath = path.join(prefix, n)
            # if name is directory defaults to "prefix/questions.yaml"
            if path.isdir(fullpath):
                filename = path.join(fullpath, "questions.yaml")

            if path.isfile(filename):
                logger.info(f'Loading questions from "{filename}"')
                questions = load_yaml(filename, default=[])
                for q in questions:
                    q['path'] = fullpath

                g.node[n]['factory'] = [QFactory(q) for q in questions]

        self.depgraph = g

    # ------------------------------------------------------------------------
    # setup and check database
    def setup_db(self, db):
        engine = create_engine(f'sqlite:///{db}', echo=False)
        self.Session = sessionmaker(bind=engine)
        try:
            with self.db_session() as s:
                n = s.query(Student).count()
        except Exception as e:
            logger.critical('Database not usable.')
            raise e
        else:
            logger.info(f'Database has {n} students registered.')