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# coding=utf-8

import uuid
import threading  # multiprocessing.managers.BaseManager uses threading to serve incoming requests
import hashlib
import base64
import random
from . import prolog_session
from . import python_session
from . import problems
import db
from errors.session import NoSuchSession, AuthenticationFailed
import psycopg2.extras

__all__ = ['get_session_by_id', 'get_or_create_session', 'UserSession']

sessions = {}  # maps session IDs to session objects

module_access_lock = threading.Lock()  # use this lock to access the sessions dictionary

class UserSession(object):
    """Abstracts a user 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, uid, username):
        self._access_lock = threading.Lock()
        self.sid = uuid.uuid4().hex
        self.uid = uid
        self.username = username
        self.prolog_session = None
        self.python_session = None

    def destroy(self):
        """Destroys the session."""
        with self._access_lock:
            with module_access_lock:
                del sessions[self.sid]
            if self.prolog_session is not None:
                self.prolog_session.end()
                self.prolog_session = None
            if self.python_session is not None:
                self.python_session.destroy()
                self.python_session = None
            # TODO: add any cleanups as features are added!

    def get_sid(self):
        return self.sid

    def get_uid(self):
        return self.uid

    def get_prolog(self):
        with self._access_lock:
            if self.prolog_session is None:
                self.prolog_session = prolog_session.PrologSession()  # lazy init
            return self.prolog_session

    def get_python(self):
        with self._access_lock:
            if self.python_session is None:
                self.python_session = python_session.PythonSession()  # lazy init
            return self.python_session

    def get_problem_data(self, language, problem_group, problem):
        mod = problems.load_problem(language, problem_group, problem, 'sl')
        mod_language = problems.load_language(language, 'sl')

        # Get generic and problem-specific hints.
        hint = dict(mod_language.hint)
        hint.update(mod.hint)

        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                cur.execute("select l.id, l.name, g.id, g.name, p.id, p.name from problem p inner join language l on l.id = p.language_id inner join problem_group g on g.id = p.problem_group_id where l.identifier = %s and g.identifier = %s and p.identifier = %s", (language, problem_group, problem))
                row = cur.fetchone()
                problem_id = row[4]
                result = {
                    'language': {'id': row[0], 'identifier': language, 'name': row[1]},
                    'problem_group': {'id': row[2], 'identifier': problem_group, 'name': row[3]},
                    'problem': {'id': problem_id, 'identifier': problem, 'name': row[5], 'slug': mod.slug, 'description': mod.description, 'hint': hint}
                }
                cur.execute("select content from solution where problem_id = %s and codeq_user_id = %s", (problem_id, self.uid))
                row = cur.fetchone()
                if row:
                    result['solution'] = row[0]
                else:
                    result['solution'] = ''
                return result
            finally:
                cur.close()
        finally:
            conn.commit()
            db.return_connection(conn)

    def update_solution(self, problem_id, trace, solution):
        if (trace is None) and (solution is None):
            return
        conn = db.get_connection()
        try:
            cur = conn.cursor()
            try:
                # TODO: convert to upsert with postgresql 9.5 to eliminate the small window where it's possible for more than one concurrent insert to execute
                cur.execute('select id, trace, content from solution where codeq_user_id = %s and problem_id = %s for update', (self.uid, problem_id))
                row = cur.fetchone()
                if row:
                    if row[1]:
                        new_trace = row[1]
                        if trace:
                            new_trace.extend(trace)
                    else:
                        new_trace = trace
                    new_solution = row[2] if solution is None else solution
                    cur.execute('update solution set content = %s, trace = %s where id = %s', (new_solution, psycopg2.extras.Json(new_trace), row[0]))
                else:
                    # this is the first entry
                    cur.execute('insert into solution (done, content, problem_id, codeq_user_id, trace) values (%s, %s, %s, %s, %s)', (False, solution, problem_id, self.uid, psycopg2.extras.Json(trace)))
            finally:
                cur.close()
            conn.commit()
        except:
            conn.rollback()
            raise
        finally:
            db.return_connection(conn)

    def __del__(self):
        #  no locking needed if GC is removing us, as there cannot be any concurrent access by definition
        if hasattr(self, 'prolog_session') and (self.prolog_session is not None):
            self.prolog_session.end()
            self.prolog_session = None
        if hasattr(self, 'python_session') and (self.python_session is not None):
            self.python_session.destroy()
            self.python_session = None
        # TODO: add any cleanups as features are added!

def get_session_by_id(sid):
    with module_access_lock:
        s = sessions.get(sid, None)
        if s is None:
            raise NoSuchSession('There is no session with SID {}'.format(sid))
        return s

def get_or_create_session(uid, username, sid=None):
    with module_access_lock:
        if sid is not None:
            s = sessions.get(sid)
            if s is not None:
                return s
        s = UserSession(uid, username)
        sessions[s.sid] = s
        return s

def authenticate_and_create_session(username, password):
    conn = db.get_connection()
    try:
        cur = conn.cursor()
        try:
            cur.execute('select id, password from codeq_user where username = %s', (username,))
            row = cur.fetchone()
            if row is None:
                raise AuthenticationFailed('No such user: {}'.format(username))
            if verify_password(password, row[1]):
                return get_or_create_session(row[0], username)
            raise AuthenticationFailed('Password mismatch')
        finally:
            cur.close()
    finally:
        conn.commit()
        db.return_connection(conn)

def verify_password(plain_password, encrypted_password):
    elts = encrypted_password.split('$')
    if len(elts) != 4:
        return False
    if elts[0] != 'pbkdf2_sha256':
        return False
    try:
        rounds = int(elts[1])
    except:
        return False
    enc = hashlib.pbkdf2_hmac('sha256', plain_password.encode('utf-8'), elts[2].encode('utf-8'), rounds)
    return base64.b64encode(enc).decode('utf-8') == elts[3]

_salt_chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
_salt_chars_len = len(_salt_chars)
def encrypt_password(plain_password):
    rounds = 20000
    chosen_chars = []
    for i in range(0, 12):
        chosen_chars.append(_salt_chars[random.randrange(0, _salt_chars_len)])
    salt = ''.join(chosen_chars)
    enc = hashlib.pbkdf2_hmac('sha256', plain_password.encode('utf-8'), salt.encode('utf-8'), rounds)
    return '{0}${1}${2}${3}'.format('pbkdf2_sha256', rounds, salt, base64.b64encode(enc).decode('utf-8'))

random.seed()

# TODO: add a session timeout timer