#!/usr/bin/env python3

# python standard library
from os import path
import sys
import base64
import uuid
import logging.config
import argparse
import mimetypes
import signal
import asyncio
import functools

# user installed libraries
import tornado.ioloop
import tornado.web
import tornado.httpserver
from tornado.escape import to_unicode

# this project
from learnapp import LearnApp
from tools import load_yaml, md_to_html

# ----------------------------------------------------------------------------
# Decorator used to restrict access to the administrator
# ----------------------------------------------------------------------------
def admin_only(func):
    @functools.wraps(func)
    def wrapper(self, *args, **kwargs):
        if self.current_user != '0':
            raise tornado.web.HTTPError(403)  # forbidden
        else:
            func(self, *args, **kwargs)
    return wrapper


# ============================================================================
# WebApplication - Tornado Web Server
# ============================================================================
class WebApplication(tornado.web.Application):
    def __init__(self, learnapp, debug=False):
        handlers = [
            (r'/login',         LoginHandler),
            (r'/logout',        LogoutHandler),
            (r'/change_password', ChangePasswordHandler),
            (r'/question',      QuestionHandler),       # renders each question
            (r'/topic/(.+)',    TopicHandler),          # start a topic
            (r'/file/(.+)',     FileHandler),           # serve files, images, etc
            (r'/',              RootHandler),           # show list of topics
        ]
        settings = {
            'template_path': path.join(path.dirname(__file__), 'templates'),
            'static_path':   path.join(path.dirname(__file__), 'static'),
            'static_url_prefix': '/static/',
            'xsrf_cookies': True,
            'cookie_secret': base64.b64encode(uuid.uuid4().bytes),
            'login_url': '/login',
            'debug': debug,
        }
        super().__init__(handlers, **settings)
        self.learn = learnapp


# ============================================================================
# Handlers
# ============================================================================

# ----------------------------------------------------------------------------
# Base handler common to all handlers.
# ----------------------------------------------------------------------------
class BaseHandler(tornado.web.RequestHandler):
    @property
    def learn(self):
        return self.application.learn

    def get_current_user(self):
        cookie = self.get_secure_cookie('user')
        if cookie:
            counter = self.get_secure_cookie('counter')
            uid = cookie.decode('utf-8')
            if counter.decode('utf-8') == str(self.learn.get_login_counter(uid)):
                return uid

# ----------------------------------------------------------------------------
# /auth/login  and  /auth/logout
# ----------------------------------------------------------------------------
class LoginHandler(BaseHandler):
    def get(self):
        self.render('login.html', error='')

    async def post(self):
        uid = self.get_body_argument('uid')
        pw = self.get_body_argument('pw')

        login_ok = await self.learn.login(uid, pw)

        if login_ok:
            self.set_secure_cookie('user', uid)  # expires_days=30
            self.set_secure_cookie('counter', str(self.learn.get_login_counter(uid)))
            self.redirect('/')
        else:
            self.render('login.html', error='Número ou senha incorrectos')


# ----------------------------------------------------------------------------
class LogoutHandler(BaseHandler):
    @tornado.web.authenticated
    def get(self):
        self.clear_cookie('user')
        self.clear_cookie('counter')
        self.redirect('/')

    def on_finish(self):
        self.learn.logout(self.current_user)


# ----------------------------------------------------------------------------
class ChangePasswordHandler(BaseHandler):
    @tornado.web.authenticated
    async def post(self):
        uid = self.current_user
        pw = self.get_body_arguments('new_password')[0]

        changed_ok = await self.learn.change_password(uid, pw)
        if changed_ok:
            notification = to_unicode(self.render_string('notification.html', type='success', msg='A password foi alterada!'))
        else:
            notification = to_unicode(self.render_string('notification.html', type='danger', msg='A password não foi alterada!'))
        self.write({'msg': notification})


# ----------------------------------------------------------------------------
# Main page:  /
# Shows a list of topics and proficiency (stars, locked).
# ----------------------------------------------------------------------------
class RootHandler(BaseHandler):
    @tornado.web.authenticated
    def get(self):
        uid = self.current_user
        self.render('maintopics-table.html',
            uid=uid,
            name=self.learn.get_student_name(uid),
            state=self.learn.get_student_state(uid),
            title=self.learn.get_title(),
            )


# ----------------------------------------------------------------------------
# Start a given topic:  /topic/...
# ----------------------------------------------------------------------------
class TopicHandler(BaseHandler):
    SUPPORTED_METHODS = ['GET']

    @tornado.web.authenticated
    async def get(self, topic):
        uid = self.current_user

        try:
            await self.learn.start_topic(uid, topic)
        except KeyError:
            self.redirect('/')
        else:
            self.render('topic.html',
                uid=uid,
                name=self.learn.get_student_name(uid),
                )


# ----------------------------------------------------------------------------
# Serves files from the /public subdir of the topics.
# Based on https://bhch.github.io/posts/2017/12/serving-large-files-with-tornado-safely-without-blocking/
# ----------------------------------------------------------------------------

# FIXME error in many situations... images are not shown...
# seems to happen when the browser sends two GET requests at the same time
class FileHandler(BaseHandler):
    SUPPORTED_METHODS = ['GET']

    @tornado.web.authenticated
    # async
    def get(self, filename):
        uid = self.current_user
        public_dir = self.learn.get_current_public_dir(uid)
        filepath = path.expanduser(path.join(public_dir, filename))

        try:
            f = open(filepath, 'rb')
        except FileNotFoundError:
            logging.error(f'File not found: {filepath}')
        except PermissionError:
            logging.error(f'No permission: {filepath}')
        else:
            content_type = mimetypes.guess_type(filename)
            self.set_header("Content-Type", content_type[0])
            # divide the file into chunks and write one chunk at a time, so
            # that the write does not block the ioloop for very long.
            with f:
                data = f.read()
                self.write(data)
                # await self.flush()
                self.flush()


# ----------------------------------------------------------------------------
# respond to AJAX to get a JSON question
# ----------------------------------------------------------------------------
class QuestionHandler(BaseHandler):
    SUPPORTED_METHODS = ['GET', 'POST']

    templates = {
        'checkbox':         'question-checkbox.html',
        'radio':            'question-radio.html',
        'text':             'question-text.html',
        'text-regex':       'question-text.html',
        'numeric-interval': 'question-text.html',
        'textarea':         'question-textarea.html',
        # -- information panels --
        'information':      'question-information.html',
        'info':             'question-information.html',
        'success':          'question-success.html',
    }

    # --- get question to render
    @tornado.web.authenticated
    def get(self):
        logging.debug('QuestionHandler.get()')
        user = self.current_user
        q = self.learn.get_current_question(user)

        if q is not None:
            question_html = to_unicode(self.render_string(self.templates[q['type']],
                question=q, md=md_to_html))
            response = {
                'method': 'new_question',
                'params': {
                    'type': q['type'],
                    'question': question_html,
                    'progress': self.learn.get_student_progress(user),
                    'tries': q['tries'],
                    }
                }

        else:
            finished_topic_html = to_unicode(self.render_string('finished_topic.html'))
            response = {
                'method': 'finished_topic',
                'params': {
                    'question': finished_topic_html
                    }
                }

        self.write(response)

    # --- post answer, returns what to do next: shake, new_question, finished
    @tornado.web.authenticated
    async def post(self):
        logging.debug('QuestionHandler.post()')
        user = self.current_user
        answer = self.get_body_arguments('answer')  # list

        # answers are returned in a list. fix depending on question type
        qtype = self.learn.get_student_question_type(user)
        if qtype in ('success', 'information', 'info'):
            answer = None
        elif qtype == 'radio' and not answer:
            answer = None
        elif qtype != 'checkbox':   # radio, text, textarea, ...
            answer = answer[0]

        # check answer (nonblocking) and get corrected question
        q, action = await self.learn.check_answer(user, answer)

        response = {'method': action, 'params': {}}

        if action == 'right':   # get next question in the topic
            comments_html = self.render_string('comments-right.html',
                comments=q['comments'], md=md_to_html)

            response['params'] = {
                'type': q['type'],
                'progress': self.learn.get_student_progress(user),
                'comments': to_unicode(comments_html),
                'tries': q['tries'],
                }

        elif action == 'try_again':
            comments_html = self.render_string('comments.html',
                comments=q['comments'], md=md_to_html)

            response['params'] = {
                    'type': q['type'],
                    'progress': self.learn.get_student_progress(user),
                    'comments': to_unicode(comments_html),
                    'tries': q['tries'],
                    }

        elif action == 'wrong':  # no more tries
            comments_html = to_unicode(self.render_string('comments.html',
                comments=q['comments'], md=md_to_html))
            solution_html = to_unicode(self.render_string('solution.html',
                solution=q['solution'], md=md_to_html))

            response['params'] = {
                'type': q['type'],
                'progress': self.learn.get_student_progress(user),
                'comments': comments_html,
                'solution': solution_html,
                'tries': q['tries'],
                }

        else:
            logging.error(f'Unknown action: {action}')

        self.write(response)


# ----------------------------------------------------------------------------
# Signal handler to catch Ctrl-C and abort server
# ----------------------------------------------------------------------------
def signal_handler(signal, frame):
    r = input(' --> Stop webserver? (yes/no) ').lower()
    if r == 'yes':
        tornado.ioloop.IOLoop.current().stop()
        logging.critical('Webserver stopped.')
        sys.exit(0)
    else:
        logging.info('Abort canceled...')


# -------------------------------------------------------------------------
# Tornado web server
# ----------------------------------------------------------------------------
def main():
    # --- Commandline argument parsing
    argparser = argparse.ArgumentParser(description='Server for online learning. Enrolled students and topics have to be previously configured. Please read the documentation included with this software before running the server.')
    argparser.add_argument('conffile', type=str, nargs='+',
        help='Topics configuration file in YAML format.')
    argparser.add_argument('--prefix', type=str, default='demo',
        help='Path prefix under which the topic directories can be found, e.g. ~/topics')
    argparser.add_argument('--port', type=int, default=8443,
        help='Port to be used by the HTTPS server, e.g. 8443')
    argparser.add_argument('--db', type=str, default='students.db',
        help='SQLite3 database file, e.g. students.db')
    argparser.add_argument('--debug', action='store_true',
        help='Enable debug messages')
    arg = argparser.parse_args()

    # --- Setup logging
    logger_file = 'logger-debug.yaml' if arg.debug else 'logger.yaml'
    SERVER_PATH = path.dirname(path.realpath(__file__))
    LOGGER_CONF = path.join(SERVER_PATH, f'config/{logger_file}')

    try:
        logging.config.dictConfig(load_yaml(LOGGER_CONF))
    except:
        print('An error ocurred while setting up the logging system.')
        sys.exit(1)

    logging.info('====================================================')

    # --- start application
    logging.info('Starting App')
    try:
        learnapp = LearnApp(arg.conffile, prefix=arg.prefix, db=arg.db)
    except Exception as e:
        logging.critical('Failed to start backend application')
        raise e

    # --- create web application
    logging.info('Starting Web App (tornado)')
    try:
        webapp = WebApplication(learnapp, debug=arg.debug)
    except Exception as e:
        logging.critical('Failed to start web application.')
        raise e

    # --- create webserver
    try:
        http_server = tornado.httpserver.HTTPServer(webapp,
            ssl_options={
                "certfile": "certs/cert.pem",
                "keyfile": "certs/privkey.pem"
            })
    except ValueError:
        logging.critical('Certificates cert.pem and privkey.pem not found')
        sys.exit(1)
    else:
        http_server.listen(arg.port)
        logging.info(f'Listening on port {arg.port}.')

    # --- run webserver
    logging.info('Webserver running...  (Ctrl-C to stop)')
    signal.signal(signal.SIGINT, signal_handler)

    try:
        tornado.ioloop.IOLoop.current().start()  # running...
    except Exception:
        logging.critical('Webserver stopped.')
        tornado.ioloop.IOLoop.current().stop()
        raise


# ----------------------------------------------------------------------------
if __name__ == "__main__":
    main()