# coding=utf-8

import operator
import threading
import prolog.engine
import db
from . import problems

__all__ = ['PrologSession']

def format_prolog_output(reply, output):
    messages = [text for text in map(operator.itemgetter(1), output)]
    # When an engine is destroyed, a nested data object has the actual query result.
    event = reply['event']
    if event == 'destroy':
        reply = reply['data']
        event = reply['event']

    if event == 'success':
        messages.append(prolog.engine.pretty_vars(reply['data'][0]))
        return messages, 'ok', True and reply['more']
    if event == 'failure':
        messages.append('false')
        return messages, 'ok', False
    if event == 'error':
        # Remove potential module name (engine ID) from the error message.
        messages.append('error: ' + reply['data'].replace("'{}':".format(reply['id']), ''))
        return messages, 'error', False

    return messages, 'ok', False  # TODO: is it possible to reach this return statement?


class PrologSession(object):
    """Abstracts a Prolog session.
    Only public methods are available to the outside world due to the use of multiprocessing managers.
    Therefore prefix any private methods with an underscore (_).
    No properties are accessible; use getters and setters instead.
    Values are passed by value instead of by reference (deep copy!).
    """
    def __init__(self, user_session):
        self._user_session = user_session  # the owning session
        self._access_lock = threading.Lock()
        self._engine_id = None
        self._problem_id = -1

    def run(self, code):
        with self._access_lock:
            if self._engine_id is not None:
                prolog.engine.stop(self._engine_id)
                self._engine_id = None
            reply, output = prolog.engine.create(code=code)
            if reply.get('event') != 'create':
                raise Exception('System error: could not create a prolog engine')
            self._engine_id = reply['id']
            messages = [text for text in map(operator.itemgetter(1), output)]
            status = 'error' if 'error' in map(operator.itemgetter(0), output) else 'ok'
            return messages, status, False

    def query(self, query):
        with self._access_lock:
            if self._engine_id is None:
                return ['Prolog is not running'], 'error', False
            try:
                return format_prolog_output(*prolog.engine.ask(self._engine_id, query))
            except Exception as e:
                return [str(e)], 'error', False

    def step(self):
        with self._access_lock:
            if self._engine_id is None:
                return ['Prolog is not running'], 'error', False
            try:
                return format_prolog_output(*prolog.engine.next(self._engine_id))
            except Exception as e:
                return [str(e)], 'error', False

    def end(self):
        """Stops the Prolog engine."""
        with self._access_lock:
            if self._engine_id is not None:
                prolog.engine.stop(self._engine_id)
                self._engine_id = None
                self._problem_id = -1
            return [], 'ok', False

    def __del__(self):
        #  no locking needed if GC is removing us, as there cannot be any concurrent access by definition
        if hasattr(self, '_engine_id') and (self._engine_id is not None):
            prolog.engine.stop(self._engine_id)
            self._engine_id = None

    def run_for_user(self, user_id, problem_id, program, query):
        """A "shorthand" method to start a Prolog session, load correct solutions of all user's solved
        problems and the given program, and ask a query.
        """
        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                cur.execute('select l.id, l.identifier, g.identifier, p.identifier from problem p inner join problem_group g on g.id = p.problem_group_id inner join language l on l.id = p.language_id where p.id = %s', (problem_id,))
                row = cur.fetchone()
                language_id = row[0]
                language = row[1]
                problem_group = row[2]
                problem = row[3]
                cur.execute('select g.identifier, p.identifier from solution s inner join problem p on p.id = s.problem_id inner join problem_group g on g.id = p.problem_group_id where s.codeq_user_id = %s and s.done = True and s.problem_id != %s and p.language_id = %s', (user_id, problem_id, language_id))
                solved_problems = cur.fetchall()
            finally:
                cur.close()
        finally:
            conn.commit()
            db.return_connection(conn)

        other_solutions = problems.solutions_for_problems(language, solved_problems)
        problem_module = problems.load_problem(language, problem_group, problem, 'common')
        problem_facts = problems.get_facts(language, problem_module) or ''
        code = other_solutions + problem_facts + program
        messages, status, have_more = self.run(code)
        if status == 'ok':
            more_messages, status, have_more = self.query(query)
            messages.extend(more_messages)
        self._problem_id = problem_id
#        self._user_session.update_solution(problem_id, [], program)  # TODO
        return messages, status, have_more