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

# user installed libraries
import bcrypt
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
import networkx as nx
import yaml

# this project
from models import Student, Answer, Topic, StudentTopic
from knowledge import StudentKnowledge
from factory import QFactory
from tools import load_yaml

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


class LearnAppException(Exception):
    pass

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

        # dependency graph shared by all students
        self.deps = build_dependency_graph(conffile)

        # connect to database and checks for registered students
        self.db_setup(self.deps.graph['database'])

        # add topics from dependency graph to the database, if missing
        self.db_add_topics()

    # ------------------------------------------------------------------------
    # login
    # ------------------------------------------------------------------------
    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

            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

            # success
            logger.info(f'User "{uid}" logged in')

            tt = s.query(StudentTopic).filter(StudentTopic.student_id == uid)
            state = {}
            for t in tt:
                state[t.topic_id] = {
                    'level': t.level,
                    'date': datetime.strptime(t.date, "%Y-%m-%d %H:%M:%S.%f"),
                }

            self.online[uid] = {
                'name': student.name,
                'number': student.id,
                'state': StudentKnowledge(self.deps, state=state)
            }
            return True

    # ------------------------------------------------------------------------
    # logout
    # ------------------------------------------------------------------------
    def logout(self, uid):
        state = self.online[uid]['state'].state  # dict {node:level,...}

        # save state to database
        with self.db_session(autoflush=False) as s:

            # update existing associations and remove from state dict
            for a in s.query(StudentTopic).filter_by(student_id=uid):
                if a.topic_id in state:
                    d = state.pop(a.topic_id)
                    a.level = d['level'] #state.pop(a.topic_id)   # update
                    a.date = str(d['date'])
                    s.add(a)

            # insert the remaining ones
            u = s.query(Student).get(uid)
            for n,d in state.items():
                a = StudentTopic(level=d['level'], date=str(d['date']))
                t = s.query(Topic).get(n)
                if t is None: # create if topic doesn't exist yet
                    t = Topic(id=n)
                a.topic = t
                u.topics.append(a)
                s.add(a)

        del self.online[uid]
        logger.info(f'User "{uid}" logged out')

    # ------------------------------------------------------------------------
    # change_password
    # ------------------------------------------------------------------------
    def change_password(self, uid, pw):
        if not pw:
            return False

        with self.db_session() as s:
            u = s.query(Student).get(uid)
            u.password = bcrypt.hashpw(pw.encode('utf-8'), bcrypt.gensalt())
        logger.info(f'User "{uid}" changed password')
        return True

    # ------------------------------------------------------------------------
    # check answer and if correct returns new question, otherwise returns None
    # ------------------------------------------------------------------------
    def check_answer(self, uid, answer):
        knowledge = self.online[uid]['state']
        q = knowledge.check_answer(answer)

        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))
            s.commit()

        return q['grade']

    # ------------------------------------------------------------------------
    # Start new topic
    # ------------------------------------------------------------------------
    def start_topic(self, uid, topic):
        self.online[uid]['state'].init_topic(topic)

    # ------------------------------------------------------------------------
    # Fill db table 'Topic' with topics from the graph if not already there.
    # ------------------------------------------------------------------------
    def db_add_topics(self):
        with self.db_session() as s:
            tt = [t[0] for t in s.query(Topic.id)]  # db list of topics
            nn = self.deps.nodes() # topics in the graph
            s.add_all([Topic(id=n) for n in nn if n not in tt])

    # ------------------------------------------------------------------------
    # setup and check database
    # ------------------------------------------------------------------------
    def db_setup(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(f'Database "{db}" not usable.')
            sys.exit(1)
        else:
            logger.info(f'Database "{db}" has {n} students.')

    # ------------------------------------------------------------------------
    # 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 as e:
            session.rollback()
            raise e
        finally:
            session.close()



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


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

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

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

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

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

    # ------------------------------------------------------------------------
    def get_title(self):
        return self.deps.graph['title']

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

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



# ============================================================================
# Given configuration file, loads YAML on that file and builds a digraph.
# First, topics such as `computer/mips/exceptions` are added as nodes
# together with dependencies. Then, questions are loaded to a factory.
#
#   g.graph['path']         base path where topic directories are located
#   g.graph['title']        title defined in the configuration YAML
#   g.graph['database']     sqlite3 database file to use
#
# 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 defined in YAML
#   g.node['my/topic']['factory']   dict with question factories
# ----------------------------------------------------------------------------
def build_dependency_graph(config_file):
    # Load configuration file to a dict
    try:
        with open(config_file, 'r') as f:
            config = yaml.load(f)
    except FileNotFoundError:
        logger.critical(f'File not found: "{config_file}"')
        raise LearnAppException
    except yaml.scanner.ScannerError as err:
        logger.critical(f'Parsing YAML file "{config_file}": {err}')
        raise LearnAppException
    else:
        logger.info(f'Configuration file "{config_file}"')

    # create graph
    prefix = config.get('path', '.')
    title = config.get('title', '')
    database = config.get('database', 'students.db')
    g = nx.DiGraph(path=prefix, title=title, database=database)

    # iterate over topics and build graph
    topics = config.get('topics', {})
    for ref,attr in topics.items():
        g.add_node(ref)
        if isinstance(attr, dict):
            g.node[ref]['name'] = attr.get('name', ref)
            g.node[ref]['questions'] = attr.get('questions', [])
            g.add_edges_from((d,ref) for d in attr.get('deps', []))

    # iterate over topics and create question factories
    logger.info('Loading:')
    for tref in g.nodes():
        tnode = g.node[tref]  # current node (topic)
        fullpath = path.expanduser(path.join(prefix, tref))
        filename = path.join(fullpath, 'questions.yaml')

        loaded_questions = load_yaml(filename, default=[])  # list

        # if questions not in configuration then load all, preserving order
        if not tnode['questions']:
            tnode['questions'] = [q['ref'] for q in loaded_questions]

        # make questions factory (without repeating same question)
        tnode['factory'] = {}
        for q in loaded_questions:
            if q['ref'] in tnode['questions']:
                q['path'] = fullpath
                tnode['factory'][q['ref']] = QFactory(q)

        logger.info(f'{len(tnode["questions"]):4} questions from {tref}')

    return g