import eventlet
imapclient = eventlet.import_patched('imapclient')

import os.path as path
import sys
import traceback
import logging
from logging.handlers import RotatingFileHandler
import ConfigParser
import email
from time import sleep
from datetime import datetime, time


# Setup the log handlers to stdout and file.
log = logging.getLogger('imap_monitor')
log.setLevel(logging.DEBUG)
formatter = logging.Formatter(
    '%(asctime)s | %(name)s | %(levelname)s | %(message)s'
    )
handler_stdout = logging.StreamHandler(sys.stdout)
handler_stdout.setLevel(logging.DEBUG)
handler_stdout.setFormatter(formatter)
log.addHandler(handler_stdout)
handler_file = RotatingFileHandler(
	'imap_monitor.log',
	mode='a',
	maxBytes=1048576,
	backupCount=9,
	encoding='UTF-8',
	delay=True
	)
handler_file.setLevel(logging.DEBUG)
handler_file.setFormatter(formatter)
log.addHandler(handler_file)

# TODO: Support SMTP log handling for CRITICAL errors.


def process_email(mail_, download_, log_):
	"""Email processing to be done here. mail_ is the Mail object passed to this
	function. download_ is the path where attachments may be downloaded to.
	log_ is the logger object.
	
	"""
	log_.info(mail_['subject'])
	return 'return meaningful result here'
	
def main():
	log.info('... script started')
	while True:
		# <--- Start of configuration section
		
		# Read config file - halt script on failure
		try:
			config_file = open('imap_monitor.ini','r+')
		except IOError:
			log.critical('configuration file is missing')
			break
		config = ConfigParser.SafeConfigParser()
		config.readfp(config_file)
		
		# Retrieve IMAP host - halt script if section 'imap' or value 
		# missing
		try:
			host = config.get('imap', 'host')
		except ConfigParser.NoSectionError:
			log.critical('no "imap" section in configuration file')
			break
		except ConfigParser.NoOptionError:
			log.critical('no IMAP host specified in configuration file')
			break
		
		# Retrieve IMAP username - halt script if missing
		try:
			username = config.get('imap', 'username')
		except ConfigParser.NoOptionError:
			log.critical('no IMAP username specified in configuration file')
			break
		
		# Retrieve IMAP password - halt script if missing
		try:
			password = config.get('imap', 'password')
		except ConfigParser.NoOptionError:
			log.critical('no IMAP password specified in configuration file')
			break
		
		# Retrieve IMAP SSL setting - warn if missing, halt if not boolean
		try:
			ssl = config.getboolean('imap', 'ssl')
		except ConfigParser.NoOptionError:
			# Default SSL setting to False if missing
			log.warning('no IMAP SSL setting specified in configuration file')
			ssl = False
		except ValueError:
			log.critical('IMAP SSL setting invalid - not boolean')
			break
		
		# Retrieve IMAP folder to monitor - warn if missing
		try:
			folder = config.get('imap', 'folder')
		except ConfigParser.NoOptionError:
			# Default folder to monitor to 'INBOX' if missing
			log.warning('no IMAP folder specified in configuration file')
			folder = 'INBOX'
			
		# Retrieve path for downloads - halt if section of value missing
		try:
			download = config.get('path', 'download')
		except ConfigParser.NoSectionError:
			log.critical('no "path" section in configuration')
			break
		except ConfigParser.NoOptionError:
			# If value is None or specified path not existing, warn and default
			# to script path
			log.warn('no download path specified in configuration')
			download = None
		finally:
			download = download if (
				download and path.exists(download)
				) else path.abspath(__file__)
		log.info('setting path for email downloads - {0}'.format(download))
		
		while True:
			# <--- Start of IMAP server connection loop
			
			# Attempt connection to IMAP server
			log.info('connecting to IMAP server - {0}'.format(host))
			try:
				imap = imapclient.IMAPClient(host, use_uid=True, ssl=ssl)
			except Exception:
				# If connection attempt to IMAP server fails, retry
				etype, evalue = sys.exc_info()[:2]
				estr = traceback.format_exception_only(etype, evalue)
				logstr = 'failed to connect to IMAP server - '
				for each in estr:
					logstr += '{0}; '.format(each.strip('\n'))
				log.error(logstr)
				sleep(10)
				continue
			log.info('server connection established')
			
			# Attempt login to IMAP server
			log.info('logging in to IMAP server - {0}'.format(username))
			try:
				result = imap.login(username, password)
				log.info('login successful - {0}'.format(result))
			except Exception:
				# Halt script when login fails
				etype, evalue = sys.exc_info()[:2]
				estr = traceback.format_exception_only(etype, evalue)
				logstr = 'failed to login to IMAP server - '
				for each in estr:
					logstr += '{0}; '.format(each.strip('\n'))
				log.critical(logstr)
				break
			
			# Select IMAP folder to monitor
			log.info('selecting IMAP folder - {0}'.format(folder))
			try:
				result = imap.select_folder(folder)
				log.info('folder selected')
			except Exception:
				# Halt script when folder selection fails
				etype, evalue = sys.exc_info()[:2]
				estr = traceback.format_exception_only(etype, evalue)
				logstr = 'failed to select IMAP folder - '
				for each in estr:
					logstr += '{0}; '.format(each.strip('\n'))
				log.critical(logstr)
				break
			
			# Retrieve and process all unread messages. Should errors occur due
			# to loss of connection, attempt restablishing connection 
			try:
				result = imap.search('UNSEEN')
			except Exception:
				continue
			log.info('{0} unread messages seen - {1}'.format(
				len(result), result
				))
			for each in result:
				try:
					result = imap.fetch(each, ['RFC822'])
				except Exception:
					log.error('failed to fetch email - {0}'.format(each))
					continue
				mail = email.message_from_string(result[each]['RFC822'])
				try:
					process_email(mail, download, log)
					log.info('processing email {0} - {1}'.format(
						each, mail['subject']
						))
				except Exception:
					log.error('failed to process email {0}'.format(each))
					raise
					continue
					
			while True:
				# <--- Start of mail monitoring loop
				
				# After all unread emails are cleared on initial login, start
				# monitoring the folder for new email arrivals and process 
				# accordingly. Use the IDLE check combined with occassional NOOP
				# to refresh. Should errors occur in this loop (due to loss of
				# connection), return control to IMAP server connection loop to
				# attempt restablishing connection instead of halting script.
				imap.idle()
				# TODO: Remove hard-coded IDLE timeout; place in config file
				result = imap.idle_check(5*60)
				if result:
					imap.idle_done()
					result = imap.search('UNSEEN')
					log.info('{0} new unread messages - {1}'.format(
						len(result),result
						))
					for each in result:
						fetch = imap.fetch(each, ['RFC822'])
						mail = email.message_from_string(
							fetch[each]['RFC822']
							)
						try:
							process_email(mail, download, log)
							log.info('processing email {0} - {1}'.format(
								each, mail['subject']
								))
						except Exception:
							log.error(
								'failed to process email {0}'.format(each))
							raise
							continue
				else:
					imap.idle_done()
					imap.noop()
					log.info('no new messages seen')
				# End of mail monitoring loop --->
				continue
				
			# End of IMAP server connection loop --->
			break
			
		# End of configuration section --->
		break
	log.info('script stopped ...')

if __name__ == '__main__':
	main()