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path: root/server/prolog_session.py
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# coding=utf-8

import operator
import threading
import prolog.engine
import server.user_session
from db.models import CodeqUser, Problem
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):
        self._access_lock = threading.Lock()
        self._engine_id = None
        self._problem_id = -1
        self._sent_hints = []

    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
            engine_id, output = prolog.engine.create(code=code)
            if not engine_id:
                raise Exception('System error: could not create a prolog engine')
            self._engine_id = engine_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.destroy(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.destroy(self._engine_id)
            self._engine_id = None

    def hint(self, sid, problem_id, program):
        session = server.user_session.get_session_by_id(sid)
        language, problem_group, problem = Problem.get_identifier(problem_id)
        language_module = problems.load_language(language, 'common')
        problem_module = problems.load_problem(language, problem_group, problem, 'common')

        solved_problems = [p for p in CodeqUser.solved_problems(session.get_uid(), language)
                             if p != (problem_group, problem)]
        hints = []
        if hasattr(language_module, 'hint'):
            hints = language_module.hint(program, solved_problems)
        if not hints and hasattr(problem_module, 'hint'):
            hints = problem_module.hint(program, solved_problems)
        if not hints:
            hints = [{'id': 'no_hint'}]

        self._instantiate_and_save_hints(language_module, problem_module, hints)
        return hints

    def test(self, sid, problem_id, program):
        session = server.user_session.get_session_by_id(sid)
        language, problem_group, problem = Problem.get_identifier(problem_id)
        language_module = problems.load_language(language, 'common')
        problem_module = problems.load_problem(language, problem_group, problem, 'common')

        solved_problems = [p for p in CodeqUser.solved_problems(session.get_uid(), language)
                             if p != (problem_group, problem)]
        try:
            passed, hints = problem_module.test(program, solved_problems)
        except AttributeError as ex:
            hints = [{'id': 'system_error', 'args': {'message': 'test function does not exist'}}]

        self._instantiate_and_save_hints(language_module, problem_module, hints)
        return hints

    # Add hint parameters (such as message index) based on hint class. Append
    # the finalized hints to the list of sent hints.
    def _instantiate_and_save_hints(self, language_mod, problem_mod, hints):
        with self._access_lock:
            for hint in hints:
                for mod in [language_mod, problem_mod]:
                    if hasattr(mod, 'hint_type') and hint['id'] in mod.hint_type:
                        hint_type = mod.hint_type[hint['id']]
                        hint_type.instantiate(hint, self._sent_hints)
            self._sent_hints.extend(hints)

    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.
        """
        language, problem_group, problem = Problem.get_identifier(problem_id)
        problem_module = problems.load_problem(language, problem_group, problem, 'common')

        solved_problems = [p for p in CodeqUser.solved_problems(user_id, language)
                                   if p != (problem_group, problem)]
        other_solutions = problems.solutions_for_problems(language, solved_problems)
        problem_facts = problems.get_facts(language, problem_module) or ''
        code = program + '\n' + other_solutions + '\n' + problem_facts

        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
        return messages, status, have_more

    def get_problem_id(self):
        return self._problem_id