# -*- coding: UTF-8 -*-
import re
import os
import sys
from collections import defaultdict
from postomaat.shared import ScannerPlugin, DUNNO, string_to_actioncode, apply_template
from postomaat.plugins.ratelimit.strategies import AVAILABLE_STRATEGIES, AVAILABLE_BACKENDS

if sys.version_info > (3,):
    unicode = str #pylint: disable=C0103


class Limiter(object):
    def __init__(self):
        self.name = None
        self.strategy = None
        self.max = -1 # negative value: no limit
        self.timespan = 1
        self.fields = []
        self.regex = None
        self.skip = None
        self.action = DUNNO
        self.message = 'Limit exceeded'

    def __str__(self):
        return "<Limiter name={name:s} rate={limit:d}/{timespan:d} fields={fields:s}>".format(
            name=self.name,
            limit=self.max,
            timespan=self.timespan,
            fields=",".join(self.fields)
        )


class RateLimitPlugin(ScannerPlugin):
    def __init__(self, config, section=None):
        ScannerPlugin.__init__(self, config, section)
        self.requiredvars = {

            'limiterfile': {
                'default': '/etc/postomaat/conf.d/ratelimit.conf',
                'description': 'file based rate limits',
            },

            'backendtype':{
                'default': 'memory',
                'description': 'type of backend where the events are stored. memory is only recommended for low traffic standalone systems. alternatives are: redis, sqlalchemy' #pylint: disable=C0301
            },

            'backendconfig':{
                'default': '',
                'description': 'backend specific configuration. sqlalchemy: the database url, redis: redis://:[password]@hostname:6379/0' #pylint: disable=C0301
            }

        }

        self.logger = self._logger()
        self.backends = dict()
        self.reqired_strategies = list()
        self.limiters = None
        self.logger.info("RateLimit plugin available backends: %s",
            ' '.join([str(k) + " => " + str(AVAILABLE_BACKENDS[k].keys()) for k in AVAILABLE_BACKENDS.keys()]))

    def load_limiter_config(self, text):
        patt = re.compile(r'^limit\s+name=(?P<name>[^\s]+)\s+strategy=(?P<strategy>[^\s]+)\s+rate=(?P<max>\-?\d{1,10})\/(?P<time>\d{1,10})\s+fields=(?P<fieldlist>[^\s]+)(\s+match=\/(?P<matchregex>.+)\/(\s+skip=(?P<skiplist>[^\s]+))?)?\s+action=(?P<action>[^\s]+)\s+message=(?P<message>.*)$') #pylint: disable=C0301
        limiters = []
        lineno = 0
        for line in text.split('\n'):
            lineno += 1
            line = line.strip()
            if line.startswith('#') or line.strip() == '':
                continue
            match = patt.match(line)
            if match is None:
                self.logger.error('cannot parse limiter config line %d', lineno)
                continue
            gdict = match.groupdict()
            limiter = Limiter()
            limiter.name = gdict['name']
            limiter.strategy = gdict['strategy']
            limiter.max = int(gdict['max'])
            limiter.timespan = int(gdict['time'])
            limiter.fields = gdict['fieldlist'].split(',')
            limiter.regex = gdict['matchregex']
            if gdict['skiplist'] is not None:
                limiter.skip = gdict['skiplist'].split(',')
            action = string_to_actioncode(gdict['action'])
            if action is None:
                self.logger.error('Limiter config line %d: invalid action %s',
                                  lineno, gdict['action'])
            limiter.action = action
            limiter.message = gdict['message']

            if limiter.strategy not in AVAILABLE_STRATEGIES:
                self.logger.error('Limiter config line %d: invalid strategy %s',
                                  lineno, gdict['strategy'])
            else:
                self.reqired_strategies.append(limiter.strategy)

            limiters.append(limiter)
        return limiters

    def load_backends(self):
        """ Of all the AVAILABLE_BACKENDS
        load only the backends required by limiters
        """
        for strategy in self.reqired_strategies:
            btype = self.config.get(self.section, 'backendtype')
            if strategy in self.backends:
                return
            if btype not in AVAILABLE_BACKENDS[strategy]:
                self.logger.error('RateLimit backend %s not available for strategy %s', btype, strategy)
                return
            backendconfig = self.config.get(self.section, 'backendconfig')
            
            try:
                backend_instance = AVAILABLE_BACKENDS[strategy][btype](backendconfig)
                self.backends.update(
                    {
                        strategy: backend_instance
                    }
                )
            except Exception as ex:
                error = type(ex).__name__, ex.message
                self.logger.error('Failed to load backend %s.%s error %s', strategy, btype, error)


    def examine(self, suspect):
        if self.limiters is None:
            filename = self.config.get(self.section, 'limiterfile')
            if not os.path.exists(filename):
                self.logger.error('Limiter config file %s not found', filename)
                return
            with open(filename) as filehandle:
                limiterconfig = filehandle.read()
            limiters = self.load_limiter_config(limiterconfig)
            self.limiters = limiters
            self.logger.info('Found %d limiter configurations', len(limiters))
            
            self.load_backends()

        skiplist = []
        for limiter in self.limiters:
            if limiter.name in skiplist: # check if this limiter is skipped by a previous one
                self.logger.debug('limiter %s skipped due to previous match', limiter.name)
                continue

            #get field values
            allfieldsavailable = True
            fieldvalues = []
            for fieldname in limiter.fields:
                if hasattr(suspect, fieldname):
                    fieldvalues.append(getattr(suspect, fieldname))
                elif suspect.get_tag(fieldname):
                    fieldvalues.append(str(suspect.get_tag(fieldname)))
                else:
                    allfieldsavailable = False
                    self.logger.debug('Skipping limiter %s - suspect field or tag %s not available',
                                      limiter.name, fieldname)
                    break
            if not allfieldsavailable: #rate limit can not be applied
                continue

            checkval = ','.join(fieldvalues)
            if limiter.regex is not None:
                if re.match(limiter.regex, checkval):
                    if limiter.skip is not None:
                        skiplist.extend(limiter.skip)
                else: #no match, skip this limiter
                    self.logger.debug('Skipping limiter %s - regex does not match', limiter.name)
                    continue

            eventname = limiter.name+checkval
            timespan = limiter.timespan

            if limiter.max < 0: #no limit
                continue

            try:
                (allow, count) = self.backends[limiter.strategy].check_allowed(eventname, limiter.max, timespan)
                self.logger.debug('Limiter event %s count: %d', eventname, count)
                if not allow:
                    return limiter.action, apply_template(limiter.message, suspect)
            except Exception as ex:
                error = type(ex).__name__, ex.message
                self.logger.error('Failed to run limitter backend for strategy "%s" eventname %s error %s',
                                  limiter.strategy,
                                  eventname,
                                  error)