'''
date_interpreter.py - The module contains the MailIterator class.

Copyright (c) 2012 Intra2net AG
Author: Plamen Dimitrov

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
'''

import datetime, time
import re
import logging

#reg expressions
RECEIVED_DATE = re.compile(r'(0?[1-9]|[1-2][0-9]|3[01])\s+([A-Z][a-z][a-z])\s+'
        r'(19[0-9]{2}|[2-9][0-9]{3}|[0-9]{2})\s+(2[0-3]|[0-1][0-9]):([0-5][0-9])(?::(60|[0-5][0-9]))?\s*'
        r'(?:([-\+])([0-9]{2})([0-5][0-9]))*')
INTERNAL_DATE = re.compile(r'(?P<day>[ 0123][0-9])-(?P<mon>[A-Z][a-z][a-z])-(?P<year>[0-9][0-9][0-9][0-9])'
        r' (?P<hour>[0-9][0-9]):(?P<min>[0-9][0-9]):(?P<sec>[0-9][0-9])'
        r' (?P<zonen>[-+])(?P<zoneh>[0-9][0-9])(?P<zonem>[0-9][0-9])')
CONTROL_SYMBOLS = re.compile(r'[\n\r\t]')

class DateInterpreter:
    """This class extracts dates from imap server responses and compares them.
    This class contains only static methods."""

    def __init__(self):
        return

    @classmethod
    def extract_internal_date(cls, fetchresult):
        """Extracts the internal date from INTERNALDATE, returns datetime."""
        return datetime.datetime.fromtimestamp(time.mktime(fetchresult))

    @classmethod
    def extract_received_date(cls, fetchresult):
        """Extracts the first date from RECEIVED, returns datetime."""
        fetchresult = CONTROL_SYMBOLS.sub('', fetchresult[0][1].decode("utf-8"))
        received_dates = RECEIVED_DATE.findall(fetchresult)
        if(len(received_dates)==0):
            return ""
        else: received_date = received_dates[0]
        logging.debug("Retrieved date %s from header %s.", received_date, fetchresult)
        month = datetime.datetime.strptime(received_date[1],'%b').month

        if(received_date[3]!=""):
            hours = int(received_date[3])
        else: hours = 0
        if(received_date[4]!=""):
            minutes = int(received_date[4])
        else: minutes = 0
        if(received_date[5]!=""):
            seconds = int(received_date[5])
        else: seconds = 0

        if(received_date[6]!=""):
            zonen = received_date[6]
        else: zonen = b'+'
        if(received_date[7]!=""):
            zoneh = int(received_date[7])
        else: zoneh = 0
        if(received_date[8]!=""):
            zonem = int(received_date[8])
        else: zonem = 0
        # subtract time zone to get unified time
        zone = (zoneh * 60 + zonem) * 60
        if(zonen == b'-'):
            zone = -zone

        time_tuple = (int(received_date[2]), month, int(received_date[0]), hours, minutes, seconds, -1, -1, -1)
        #'mktime' assumes arg in local timezone, so add timezone/altzone
        utc = time.mktime(time_tuple)
        #adjust to DST
        if(time.daylight and time.localtime(utc)[-1]):
            zone = zone + time.altzone
        else:
            zone = zone + time.timezone

        received_time_tuple = time.localtime(utc - zone)
        converted_received_date = datetime.datetime.fromtimestamp(time.mktime(received_time_tuple))
        return converted_received_date

    @classmethod
    def compare_dates(cls, date1, date2, tolerance=1800):
        """Compares datetime objects for deviation given certain tolerance."""
        """Returns 1 if there is a significant difference."""
        logging.debug("Comparing dates %s <> %s.", date1, date2)
        timedelta = abs(date1 - date2)
        if(timedelta.total_seconds()>tolerance):
            return True
        else:
            return False