# Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
# MIT License. See license.txt

from __future__ import unicode_literals
import time
import _socket, poplib
import frappe
from frappe import _
from frappe.utils import extract_email_id, convert_utc_to_user_timezone, now, cint, cstr, strip
from frappe.utils.scheduler import log
from email_reply_parser import EmailReplyParser
from email.header import decode_header
from frappe.utils.file_manager import get_random_filename

class EmailSizeExceededError(frappe.ValidationError): pass
class EmailTimeoutError(frappe.ValidationError): pass
class TotalSizeExceededError(frappe.ValidationError): pass
class LoginLimitExceeded(frappe.ValidationError): pass

class POP3Server:
	"""Wrapper for POP server to pull emails."""
	def __init__(self, args=None):
		self.setup(args)

	def setup(self, args=None):
		# overrride
		self.settings = args or frappe._dict()

	def check_mails(self):
		# overrride
		return True

	def process_message(self, mail):
		# overrride
		pass

	def connect(self):
		"""Connect to **Email Account**."""
		try:
			if cint(self.settings.use_ssl):
				self.pop = Timed_POP3_SSL(self.settings.host, timeout=frappe.conf.get("pop_timeout"))
			else:
				self.pop = Timed_POP3(self.settings.host, timeout=frappe.conf.get("pop_timeout"))

			self.pop.user(self.settings.username)
			self.pop.pass_(self.settings.password)

			# connection established!
			return True

		except _socket.error:
			# Invalid mail server -- due to refusing connection
			frappe.msgprint(_('Invalid Mail Server. Please rectify and try again.'))
			raise

		except poplib.error_proto, e:
			if self.is_temporary_system_problem(e):
				return False

			else:
				frappe.msgprint(_('Invalid User Name or Support Password. Please rectify and try again.'))
				raise

	def get_messages(self):
		"""Returns new email messages in a list."""
		if not self.check_mails():
			return # nothing to do

		frappe.db.commit()

		if not self.connect():
			return []

		try:
			# track if errors arised
			self.errors = False
			self.latest_messages = []
			pop_list = self.pop.list()[1]
			num = num_copy = len(pop_list)

			# WARNING: Hard coded max no. of messages to be popped
			if num > 20: num = 20

			# size limits
			self.total_size = 0
			self.max_email_size = cint(frappe.local.conf.get("max_email_size"))
			self.max_total_size = 5 * self.max_email_size

			for i, pop_meta in enumerate(pop_list):
				# do not pull more than NUM emails
				if (i+1) > num:
					break

				try:
					self.retrieve_message(pop_meta, i+1)
				except (TotalSizeExceededError, EmailTimeoutError, LoginLimitExceeded):
					break

			# WARNING: Mark as read - message number 101 onwards from the pop list
			# This is to avoid having too many messages entering the system
			num = num_copy
			if num > 100 and not self.errors:
				for m in xrange(101, num+1):
					self.pop.dele(m)

		except Exception, e:
			if self.has_login_limit_exceeded(e):
				pass

			else:
				raise

		finally:
			# no matter the exception, pop should quit if connected
			self.pop.quit()

		return self.latest_messages

	def retrieve_message(self, pop_meta, msg_num):
		incoming_mail = None
		try:
			self.validate_pop(pop_meta)
			msg = self.pop.retr(msg_num)

			self.latest_messages.append(b'\n'.join(msg[1]))

		except (TotalSizeExceededError, EmailTimeoutError):
			# propagate this error to break the loop
			self.errors = True
			raise

		except Exception, e:
			if self.has_login_limit_exceeded(e):
				self.errors = True
				raise LoginLimitExceeded, e

			else:
				# log performs rollback and logs error in scheduler log
				log("receive.get_messages", self.make_error_msg(msg_num, incoming_mail))
				self.errors = True
				frappe.db.rollback()

				self.pop.dele(msg_num)
		else:
			self.pop.dele(msg_num)

	def has_login_limit_exceeded(self, e):
		return "-ERR Exceeded the login limit" in strip(cstr(e.message))

	def is_temporary_system_problem(self, e):
		messages = (
			"-ERR [SYS/TEMP] Temporary system problem. Please try again later.",
			"Connection timed out",
		)
		for message in messages:
			if message in strip(cstr(e.message)):
				return True
		return False

	def validate_pop(self, pop_meta):
		# throttle based on email size
		if not self.max_email_size:
			return

		m, size = pop_meta.split()
		size = cint(size)

		if size < self.max_email_size:
			self.total_size += size
			if self.total_size > self.max_total_size:
				raise TotalSizeExceededError
		else:
			raise EmailSizeExceededError

	def make_error_msg(self, msg_num, incoming_mail):
		error_msg = "Error in retrieving email."
		if not incoming_mail:
			try:
				# retrieve headers
				incoming_mail = Email(b'\n'.join(self.pop.top(msg_num, 5)[1]))
			except:
				pass

		if incoming_mail:
			error_msg += "\nDate: {date}\nFrom: {from_email}\nSubject: {subject}\n".format(
				date=incoming_mail.date, from_email=incoming_mail.from_email, subject=incoming_mail.subject)

		return error_msg

class Email:
	"""Wrapper for an email."""
	def __init__(self, content):
		"""Parses headers, content, attachments from given raw message.

		:param content: Raw message."""
		import email, email.utils
		import datetime


		self.raw = content
		self.mail = email.message_from_string(self.raw)

		self.text_content = ''
		self.html_content = ''
		self.attachments = []
		self.parse()
		self.set_content_and_type()
		self.set_subject()

		self.from_email = extract_email_id(self.mail["From"])
		self.from_real_name = email.utils.parseaddr(self.mail["From"])[0]

		if self.mail["Date"]:
			utc = email.utils.mktime_tz(email.utils.parsedate_tz(self.mail["Date"]))
			utc_dt = datetime.datetime.utcfromtimestamp(utc)
			self.date = convert_utc_to_user_timezone(utc_dt).strftime('%Y-%m-%d %H:%M:%S')
		else:
			self.date = now()

	def parse(self):
		"""Walk and process multi-part email."""
		for part in self.mail.walk():
			self.process_part(part)

	def set_subject(self):
		"""Parse and decode `Subject` header."""
		import email.header
		_subject = email.header.decode_header(self.mail.get("Subject", "No Subject"))
		self.subject = _subject[0][0] or ""
		if _subject[0][1]:
			self.subject = self.subject.decode(_subject[0][1])
		else:
			# assume that the encoding is utf-8
			self.subject = self.subject.decode("utf-8")

		if not self.subject:
			self.subject = "No Subject"

	def set_content_and_type(self):
		self.content, self.content_type = '[Blank Email]', 'text/plain'
		if self.html_content:
			self.content, self.content_type = self.html_content, 'text/html'
		else:
			self.content, self.content_type = EmailReplyParser.parse_reply(self.text_content), 'text/plain'

	def process_part(self, part):
		"""Parse email `part` and set it to `text_content`, `html_content` or `attachments`."""
		content_type = part.get_content_type()
		charset = part.get_content_charset()
		if not charset: charset = self.get_charset(part)

		if content_type == 'text/plain':
			self.text_content += self.get_payload(part, charset)

		if content_type == 'text/html':
			self.html_content += self.get_payload(part, charset)

		if part.get_filename():
			self.get_attachment(part, charset)

	def get_charset(self, part):
		"""Detect chartset."""
		charset = part.get_content_charset()
		if not charset:
			import chardet
			charset = chardet.detect(str(part))['encoding']

		return charset

	def get_payload(self, part, charset):
		try:
			return unicode(part.get_payload(decode=True),str(charset),"ignore")
		except LookupError:
			return part.get_payload()

	def get_attachment(self, part, charset):
		fcontent = part.get_payload(decode=True)

		if fcontent:
			content_type = part.get_content_type()
			fname = part.get_filename()
			if fname:
				try:
					fname = cstr(decode_header(fname)[0][0])
				except:
					fname = get_random_filename(content_type=content_type)
			else:
				fname = get_random_filename(content_type=content_type)

			self.attachments.append({
				'content_type': content_type,
				'fname': fname,
				'fcontent': fcontent,
			})

	def save_attachments_in_doc(self, doc):
		"""Save email attachments in given document."""
		from frappe.utils.file_manager import save_file, MaxFileSizeReachedError
		for attachment in self.attachments:
			try:
				save_file(attachment['fname'], attachment['fcontent'],
					doc.doctype, doc.name)
			except MaxFileSizeReachedError:
				# WARNING: bypass max file size exception
				pass
			except frappe.DuplicateEntryError:
				# same file attached twice??
				pass

	def get_thread_id(self):
		"""Extract thread ID from `[]`"""
		import re
		l = re.findall('(?<=\[)[\w/-]+', self.subject)
		return l and l[0] or None

class TimerMixin(object):
	def __init__(self, *args, **kwargs):
		self.timeout = kwargs.pop('timeout', 0.0)
		self.elapsed_time = 0.0
		self._super.__init__(self, *args, **kwargs)
		if self.timeout:
			# set per operation timeout to one-fifth of total pop timeout
			self.sock.settimeout(self.timeout / 5.0)

	def _getline(self, *args, **kwargs):
		start_time = time.time()
		ret = self._super._getline(self, *args, **kwargs)

		self.elapsed_time += time.time() - start_time
		if self.timeout and self.elapsed_time > self.timeout:
			raise EmailTimeoutError

		return ret

	def quit(self, *args, **kwargs):
		self.elapsed_time = 0.0
		return self._super.quit(self, *args, **kwargs)

class Timed_POP3(TimerMixin, poplib.POP3):
	_super = poplib.POP3

class Timed_POP3_SSL(TimerMixin, poplib.POP3_SSL):
	_super = poplib.POP3_SSL
