# python standard library
from os import path
import logging
from contextlib import contextmanager  # `with` statement in db sessions
import asyncio
from datetime import datetime
from random import random
from typing import Dict

# third party libraries
import bcrypt
import sqlalchemy as sa
import networkx as nx

# this project
from .models import Student, Answer, Topic, StudentTopic
from .student import StudentState
from .questions import QFactory
from .tools import load_yaml

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


# ============================================================================
class LearnException(Exception):
    pass


class DatabaseUnusableError(LearnException):
    pass


# ============================================================================
# LearnApp - application logic
# ============================================================================
class LearnApp(object):
    # ------------------------------------------------------------------------
    # helper to manage db sessions using the `with` statement, for example
    #   with self.db_session() as s:  s.query(...)
    # ------------------------------------------------------------------------
    @contextmanager
    def db_session(self, **kw):
        session = self.Session(**kw)
        try:
            yield session
            session.commit()
        except Exception:
            logger.error('!!! Database rollback !!!')
            session.rollback()
            raise
        finally:
            session.close()

    # ------------------------------------------------------------------------
    # init
    # ------------------------------------------------------------------------
    def __init__(self, config_files, prefix, db, check=False):
        self.db_setup(db)       # setup database and check students
        self.online = dict()    # online students

        self.deps = nx.DiGraph(prefix=prefix)
        for c in config_files:
            self.populate_graph(c)

        # factory is a dict with question generators for all topics
        self.factory = self.make_factory()    # {'qref': QFactory()}

        # if graph has topics that are not in the database, add them
        self.db_add_missing_topics(self.deps.nodes())

        if check:
            self.sanity_check_questions()

    # ------------------------------------------------------------------------
    def sanity_check_questions(self):
        logger.info('Starting sanity checks (may take a while...)')

        errors = 0
        for qref in self.factory:
            logger.debug(f'[sanity_check_questions] Checking "{qref}"...')
            try:
                q = self.factory[qref].generate()
            except Exception:
                logger.error(f'Failed to generate "{qref}".')
                errors += 1
                continue  # to next question

            if 'tests_right' in q:
                for t in q['tests_right']:
                    q['answer'] = t
                    q.correct()
                    if q['grade'] < 1.0:
                        logger.error(f'Failed right answer in "{qref}".')
                        errors += 1
                        continue  # to next test

            if 'tests_wrong' in q:
                for t in q['tests_wrong']:
                    q['answer'] = t
                    q.correct()
                    if q['grade'] >= 1.0:
                        logger.error(f'Failed wrong answer in "{qref}".')
                        errors += 1
                        continue  # to next test

        if errors > 0:
            logger.error(f'{errors:>6} errors found.')
            raise LearnException('Sanity checks')
        else:
            logger.info('     0 errors found.')

    # ------------------------------------------------------------------------
    # login
    # ------------------------------------------------------------------------
    async def login(self, uid, pw):
        with self.db_session() as s:
            found = s.query(Student.name, Student.password) \
                     .filter_by(id=uid) \
                     .one_or_none()

        # wait random time to minimize timing attacks
        await asyncio.sleep(random())

        loop = asyncio.get_running_loop()
        if found is None:
            logger.info(f'User "{uid}" does not exist')
            await loop.run_in_executor(None, bcrypt.hashpw, b'',
                                       bcrypt.gensalt())  # just spend time
            return False

        else:
            name, hashed_pw = found
            pw_ok = await loop.run_in_executor(None, bcrypt.checkpw,
                                               pw.encode('utf-8'), hashed_pw)

        if pw_ok:
            if uid in self.online:
                logger.warning(f'User "{uid}" already logged in')
                counter = self.online[uid]['counter']
            else:
                logger.info(f'User "{uid}" logged in')
                counter = 0

            # get topics of this student and set its current state
            with self.db_session() as s:
                tt = s.query(StudentTopic).filter_by(student_id=uid)

            state = {t.topic_id: {
                'level': t.level,
                'date': datetime.strptime(t.date, "%Y-%m-%d %H:%M:%S.%f")
                } for t in tt}

            self.online[uid] = {
                'number': uid,
                'name': name,
                'state': StudentState(deps=self.deps, factory=self.factory,
                                      state=state),
                'counter': counter + 1,  # counts simultaneous logins
                }

        else:
            logger.info(f'User "{uid}" wrong password')

        return pw_ok

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

    # ------------------------------------------------------------------------
    # change_password. returns True if password is successfully changed.
    # ------------------------------------------------------------------------
    async def change_password(self, uid, pw):
        if not pw:
            return False

        loop = asyncio.get_running_loop()
        pw = await loop.run_in_executor(None, bcrypt.hashpw,
                                        pw.encode('utf-8'), bcrypt.gensalt())

        with self.db_session() as s:
            u = s.query(Student).get(uid)
            u.password = pw

        logger.info(f'User "{uid}" changed password')
        return True

    # ------------------------------------------------------------------------
    # checks answer (updating student state) and returns grade.
    # ------------------------------------------------------------------------
    async def check_answer(self, uid, answer):
        knowledge = self.online[uid]['state']
        q, action = await knowledge.check_answer(answer)  # may move questions
        logger.info(f'User "{uid}" got {q["grade"]:.2} in "{q["ref"]}"')
        topic = knowledge.get_current_topic()

        # always save grade of answered question
        with self.db_session() as s:
            s.add(Answer(
                ref=q['ref'],
                grade=q['grade'],
                starttime=str(q['start_time']),
                finishtime=str(q['finish_time']),
                student_id=uid,
                topic_id=topic))
            logger.debug(f'[check_answer] Saved "{q["ref"]}" into database')

        if knowledge.topic_has_finished():
            # finished topic, save into database
            logger.info(f'User "{uid}" finished "{topic}"')
            level = knowledge.get_topic_level(topic)
            date = str(knowledge.get_topic_date(topic))

            with self.db_session() as s:
                a = s.query(StudentTopic) \
                    .filter_by(student_id=uid, topic_id=topic) \
                    .one_or_none()
                if a is None:
                    # insert new studenttopic into database
                    logger.debug('[check_answer] Database insert studenttopic')
                    t = s.query(Topic).get(topic)
                    u = s.query(Student).get(uid)
                    # association object
                    a = StudentTopic(level=level, date=date, topic=t,
                                     student=u)
                    u.topics.append(a)
                else:
                    # update studenttopic in database
                    logger.debug('[check_answer] Database update studenttopic')
                    a.level = level
                    a.date = date

                s.add(a)

            logger.debug(f'[check_answer] Saved topic "{topic}" into database')

        return q, action

    # ------------------------------------------------------------------------
    # Start new topic
    # ------------------------------------------------------------------------
    async def start_topic(self, uid, topic):
        student = self.online[uid]['state']
        try:
            await student.start_topic(topic)
        except Exception as e:
            logger.warning(f'User "{uid}" couldn\'t start "{topic}": {e}')
        else:
            logger.info(f'User "{uid}" started topic "{topic}"')

    # ------------------------------------------------------------------------
    # Fill db table 'Topic' with topics from the graph if not already there.
    # ------------------------------------------------------------------------
    def db_add_missing_topics(self, topics):
        with self.db_session() as s:
            new_topics = [Topic(id=t) for t in topics
                          if (t,) not in s.query(Topic.id)]

            if new_topics:
                s.add_all(new_topics)
                logger.info(f'Added {len(new_topics)} new topic(s) to the '
                            f'database')

    # ------------------------------------------------------------------------
    # setup and check database contents
    # ------------------------------------------------------------------------
    def db_setup(self, db):
        logger.info(f'Checking database "{db}":')
        engine = sa.create_engine(f'sqlite:///{db}', echo=False)
        self.Session = sa.orm.sessionmaker(bind=engine)
        try:
            with self.db_session() as s:
                n = s.query(Student).count()
                m = s.query(Topic).count()
                q = s.query(Answer).count()
        except Exception:
            logger.error(f'Database "{db}" not usable!')
            raise DatabaseUnusableError()
        else:
            logger.info(f'{n:6} students')
            logger.info(f'{m:6} topics')
            logger.info(f'{q:6} answers')

    # ============================================================================
    # Populates a digraph.
    #
    # Nodes are the topic references e.g. 'my/topic'
    #   g.node['my/topic']['name']      name of the topic
    #   g.node['my/topic']['questions'] list of question refs
    #
    # Edges are obtained from the deps defined in the YAML file for each topic.
    # ------------------------------------------------------------------------
    def populate_graph(self, conffile: str):
        logger.info(f'Populating graph from:  {conffile}...')
        config = load_yaml(conffile)    # course configuration

        # default attributes that apply to the topics
        default_file = config.get('file', 'questions.yaml')
        default_shuffle_questions = config.get('shuffle_questions', True)
        default_choose = config.get('choose', 9999)
        default_forgetting_factor = config.get('forgetting_factor', 1.0)
        default_maxtries = config.get('max_tries', 3)
        default_append_wrong = config.get('append_wrong', True)
        default_min_level = config.get('min_level', 0.01)  # to unlock topic

        # iterate over topics and populate graph
        topics = config.get('topics', {})
        g = self.deps       # dependency graph

        g.add_nodes_from(topics.keys())
        for tref, attr in topics.items():
            for d in attr.get('deps', []):
                if d not in g.nodes():
                    logger.error(f'Topic "{tref}" depends on "{d}" but it '
                                 f'does not exist')
                    raise LearnException()
                else:
                    g.add_edge(d, tref)

            t = g.node[tref]  # get current topic node
            t['type'] = attr.get('type', 'topic')
            t['name'] = attr.get('name', tref)
            t['path'] = path.join(g.graph['prefix'], tref)    # prefix/topic
            t['file'] = attr.get('file', default_file)        # questions.yaml
            t['shuffle_questions'] = attr.get('shuffle_questions',
                                              default_shuffle_questions)
            t['max_tries'] = attr.get('max_tries', default_maxtries)
            t['forgetting_factor'] = attr.get('forgetting_factor',
                                              default_forgetting_factor)
            t['min_level'] = attr.get('min_level', default_min_level)
            t['choose'] = attr.get('choose', default_choose)
            t['append_wrong'] = attr.get('append_wrong', default_append_wrong)
            t['questions'] = attr.get('questions', [])

        logger.info(f'Loaded {g.number_of_nodes()} topics')

    # ========================================================================
    # methods that do not change state (pure functions)
    # ========================================================================

    # ------------------------------------------------------------------------
    # Buils dictionary of question factories
    # ------------------------------------------------------------------------
    def make_factory(self) -> Dict[str, QFactory]:
        logger.info('Building questions factory...')
        factory = {}    # {'qref': QFactory()}
        g = self.deps
        for tref in g.nodes():
            t = g.node[tref]

            # load questions as list of dicts
            topicpath = path.join(g.graph['prefix'], tref)
            questions = load_yaml(path.join(topicpath, t['file']), default=[])

            # update refs to include topic as prefix.
            # refs are required to be unique only within the file.
            # undefined are set to topic:n, where n is the question number
            # within the file
            for i, q in enumerate(questions):
                qref = q.get('ref', str(i))  # ref or number
                q['ref'] = tref + ':' + qref
                q['path'] = topicpath
                q.setdefault('append_wrong', t['append_wrong'])

            # if questions are left undefined, include all.
            if not t['questions']:
                t['questions'] = [q['ref'] for q in questions]

            t['choose'] = min(t['choose'], len(t['questions']))

            for q in questions:
                if q['ref'] in t['questions']:
                    factory[q['ref']] = QFactory(q)

            logger.info(f'{len(t["questions"]):6} {tref}')

        logger.info(f'Factory contains {len(factory)} questions')
        return factory

    # ------------------------------------------------------------------------
    def get_login_counter(self, uid: str) -> int:
        return self.online[uid]['counter']

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

    # ------------------------------------------------------------------------
    def get_student_state(self, uid: str):
        return self.online[uid]['state'].get_knowledge_state()

    # ------------------------------------------------------------------------
    def get_student_progress(self, uid: str):
        return self.online[uid]['state'].get_topic_progress()

    # ------------------------------------------------------------------------
    def get_current_question(self, uid: str):
        return self.online[uid]['state'].get_current_question()     # dict

    # ------------------------------------------------------------------------
    def get_current_question_id(self, uid: str) -> str:
        return self.online[uid]['state'].get_current_question()['qid']

    # ------------------------------------------------------------------------
    def get_student_question_type(self, uid: str) -> str:
        return self.online[uid]['state'].get_current_question()['type']

    # ------------------------------------------------------------------------
    def get_student_topic(self, uid: str) -> str:
        return self.online[uid]['state'].get_current_topic()        # str

    # ------------------------------------------------------------------------
    def get_title(self) -> str:
        return self.deps.graph.get('title', '')  # FIXME

    # ------------------------------------------------------------------------
    def get_topic_name(self, ref: str) -> str:
        return self.deps.node[ref]['name']

    # ------------------------------------------------------------------------
    def get_current_public_dir(self, uid):
        topic = self.online[uid]['state'].get_current_topic()
        prefix = self.deps.graph['prefix']
        return path.join(prefix, topic, 'public')

    # ------------------------------------------------------------------------
    def get_rankings(self, uid):
        logger.info(f'User "{uid}" get rankings')
        with self.db_session() as s:
            students = s.query(Student.id, Student.name).all()
            # topic progress
            student_topics = s.query(StudentTopic.student_id,
                                     StudentTopic.topic_id,
                                     StudentTopic.level,
                                     StudentTopic.date).all()
            total_topics = s.query(Topic).count()

            # answer performance
            total = dict(s.query(Answer.student_id, sa.func.count(Answer.ref)).
                         group_by(Answer.student_id).
                         all())
            right = dict(s.query(Answer.student_id, sa.func.count(Answer.ref)).
                         filter(Answer.grade == 1.0).
                         group_by(Answer.student_id).
                         all())

        # compute percentage of right answers
        perf = {uid: right.get(uid, 0.0)/total[uid] for uid in total}

        # compute topic progress
        prog = {s[0]: 0.0 for s in students}
        now = datetime.now()
        for uid, topic, level, date in student_topics:
            date = datetime.strptime(date, "%Y-%m-%d %H:%M:%S.%f")
            prog[uid] += level**(now - date).days / total_topics

        rankings = [(uid, name, prog[uid], perf.get(uid, 0.0))
                    for uid, name in students if uid != '0']

        return sorted(rankings, key=lambda x: x[2], reverse=True)

    # ------------------------------------------------------------------------