# python standard library
import random
from  datetime import datetime
import logging

# libraries
import networkx as nx

# this project
# import questions

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

# ----------------------------------------------------------------------------
# kowledge state of each student....??
# ----------------------------------------------------------------------------
class StudentKnowledge(object):
    # =======================================================================
    # methods that update state
    # =======================================================================

    def __init__(self, deps, state={}):
        # graph with topic dependencies shared between all students
        self.deps = deps

        # state only contains information on unlocked topics
        # {'topic_id': {'level':0.5, 'date': datetime}, ...}
        self.state = state

        # update state level based on the elapsed time (no dependencies... FIXME)
        now = datetime.now()
        for s in state.values():
            dt = now - s['date']
            s['level'] *= 0.975 ** dt.days


        # compute recommended sequence of topics  ['a', 'b', ...]
        self.topic_sequence = list(nx.topological_sort(self.deps))

        # select a topic to do and initialize questions
        # self.start_topic()


    # ------------------------------------------------------------------------
    # Unlock all topics whose dependencies are satisfied
    # ------------------------------------------------------------------------
    def unlock_topics(self):
        min_level = 0.01  # minimum level to unlock
        for topic in self.topic_sequence:
            if topic not in self.state:  # if locked
                pred = self.deps.predecessors(topic)
                if all(d in self.state and self.state[d]['level'] > min_level for d in pred): # dependencies done
                    self.state[topic] = {
                        'level': 0.0,
                        'date': datetime.now()
                        }
                    logger.debug(f'unlocked {topic}')


    # ------------------------------------------------------------------------
    # Recommends a topic to practice/learn from the state
    # ------------------------------------------------------------------------
    def recommend_topic(self):
        pass # FIXME

    # ------------------------------------------------------------------------
    # Start a new topic. If not provided, selects the first with level < 0.8
    # If all levels > 0.8, will stay in the last one forever...
    # ------------------------------------------------------------------------
    def start_topic(self, topic=''):
        # unlock topics whose dependencies are done
        logger.debug('start_topic ' + topic)

        self.unlock_topics()

        # choose topic
        if not topic:
            for topic in self.topic_sequence:
                unlocked = topic in self.state
                needs_work = unlocked and self.state[topic]['level'] < 0.8
                factory = self.deps.node[topic]['factory']
                if factory and (not unlocked or needs_work):
                    break

        # use given topic if possible
        else:
            unlocked = topic in self.state
            factory = self.deps.node[topic]['factory']
            if not factory or not unlocked:
                logger.debug(f'Can\'t start topic "{topic}".')
                return



        self.current_topic = topic
        logger.info(f'Topic set to "{topic}"')

        # generate question instances for current topic
        questionlist = self.deps.node[topic]['questions']
        self.questions = [factory[qref].generate() for qref in questionlist]
        self.current_question = self.questions.pop(0)  # FIXME crashes if questions==[]
        self.current_question['start_time'] = datetime.now()
        self.finished_questions = []

    # ------------------------------------------------------------------------
    # returns the current question with correction, time and comments updated
    # ------------------------------------------------------------------------
    def check_answer(self, answer):
        q = self.current_question
        q['finish_time'] = datetime.now()
        grade = q.correct(answer)
        logger.debug(f'Grade = {grade:.2} ({q["ref"]})')

        # new question if answer is correct
        if grade > 0.999:
            self.finished_questions.append(q)
            try:
                self.current_question = self.questions.pop(0) # FIXME empty?
            except IndexError:
                self.current_question = None
                self.state[self.current_topic] = {
                    'level': 1.0,
                    'date': datetime.now()
                }
                self.start_topic()
            else:
                self.current_question['start_time'] = datetime.now()
        else:
            factory = self.deps.node[self.current_topic]['factory']
            self.questions.append(factory[q['ref']].generate())

        return q


    # ========================================================================
    # pure functions of the state (no side effects)
    # ========================================================================

    # ------------------------------------------------------------------------
    def get_current_question(self):
        return self.current_question

    # ------------------------------------------------------------------------
    def get_current_topic(self):
        return self.current_topic

    # ------------------------------------------------------------------------
    # Return list of tuples (topic, level).
    # Levels are in the interval [0, 1] or None if the topic is locked.
    # Topics unlocked but not yet done have level 0.0.
    # Example:  [('topic_A', 0.9), ('topic_B', None), ...]
    # ------------------------------------------------------------------------
    def get_knowledge_state(self):
        return [{
            'ref': ref,
            'name': self.deps.nodes[ref]['name'],
            'level': self.state[ref]['level'] if ref in self.state else None
            } for ref in self.topic_sequence ]

        # ts = []
        # for ref in self.topic_sequence:
        #     ts.append({
        #         'ref': ref,
        #         'name': self.deps.nodes[ref]['name'],
        #         'level': self.state[ref]['level'] if ref in self.state else None
        #         })
        # return ts

    # ------------------------------------------------------------------------
    def get_topic_progress(self):
        return len(self.finished_questions) / (1 + len(self.finished_questions) + len(self.questions))