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

from __future__ import unicode_literals
import six
from six import iteritems, text_type
from six.moves import range
import time, _socket, poplib, imaplib, email, email.utils, datetime, chardet, re
from email_reply_parser import EmailReplyParser
from email.header import decode_header
import frappe
from frappe import _, safe_decode, safe_encode
from frappe.utils import (extract_email_id, convert_utc_to_user_timezone, now,
	cint, cstr, strip, markdown, parse_addr)
from frappe.utils.scheduler import log
from frappe.core.doctype.file.file import get_random_filename, MaxFileSizeReachedError

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

class EmailServer:
	"""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**."""
		if cint(self.settings.use_imap):
			return self.connect_imap()
		else:
			return self.connect_pop()

	def connect_imap(self):
		"""Connect to IMAP"""
		try:
			if cint(self.settings.use_ssl):
				self.imap = Timed_IMAP4_SSL(self.settings.host, timeout=frappe.conf.get("pop_timeout"))
			else:
				self.imap = Timed_IMAP4(self.settings.host, timeout=frappe.conf.get("pop_timeout"))
			self.imap.login(self.settings.username, 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 Exception as e:
			frappe.msgprint(_('Cannot connect: {0}').format(str(e)))
			raise

	def connect_pop(self):
		#this method return pop connection
		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:
			# log performs rollback and logs error in Error Log
			log("receive.connect_pop")

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

		except poplib.error_proto as 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

		uid_list = []

		try:
			# track if errors arised
			self.errors = False
			self.latest_messages = []
			self.seen_status = {}
			self.uid_reindexed = False

			uid_list = email_list = self.get_new_mails()

			if not email_list:
				return

			num = num_copy = len(email_list)

			# WARNING: Hard coded max no. of messages to be popped
			if num > 50: num = 50

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

				try:
					self.retrieve_message(message_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 not cint(self.settings.use_imap):
				if num > 100 and not self.errors:
					for m in range(101, num+1):
						self.pop.dele(m)

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

			else:
				raise

		finally:
			# no matter the exception, pop should quit if connected
			if cint(self.settings.use_imap):
				self.imap.logout()
			else:
				self.pop.quit()

		out = { "latest_messages": self.latest_messages }
		if self.settings.use_imap:
			out.update({
				"uid_list": uid_list,
				"seen_status": self.seen_status,
				"uid_reindexed": self.uid_reindexed
			})

		return out

	def get_new_mails(self):
		"""Return list of new mails"""
		if cint(self.settings.use_imap):
			email_list = []
			self.check_imap_uidvalidity()

			readonly = False if self.settings.email_sync_rule == "UNSEEN" else True

			self.imap.select("Inbox", readonly=readonly)
			response, message = self.imap.uid('search', None, self.settings.email_sync_rule)
			if message[0]:
				email_list =  message[0].split()
		else:
			email_list = self.pop.list()[1]

		return email_list

	def check_imap_uidvalidity(self):
		# compare the UIDVALIDITY of email account and imap server
		uid_validity = self.settings.uid_validity

		response, message = self.imap.status("Inbox", "(UIDVALIDITY UIDNEXT)")
		current_uid_validity = self.parse_imap_response("UIDVALIDITY", message[0]) or 0

		uidnext = int(self.parse_imap_response("UIDNEXT", message[0]) or "1")
		frappe.db.set_value("Email Account", self.settings.email_account, "uidnext", uidnext)

		if not uid_validity or uid_validity != current_uid_validity:
			# uidvalidity changed & all email uids are reindexed by server
			frappe.db.sql(
				"""update `tabCommunication` set uid=-1 where communication_medium='Email'
				and email_account=%s""", (self.settings.email_account,)
			)
			frappe.db.sql(
				"""update `tabEmail Account` set uidvalidity=%s, uidnext=%s where
				name=%s""", (current_uid_validity, uidnext, self.settings.email_account)
			)

			# uid validity not found pulling emails for first time
			if not uid_validity:
				self.settings.email_sync_rule = "UNSEEN"
				return

			sync_count = 100 if uid_validity else int(self.settings.initial_sync_count)
			from_uid = 1 if uidnext < (sync_count + 1) or (uidnext - sync_count) < 1 else uidnext - sync_count
			# sync last 100 email
			self.settings.email_sync_rule = "UID {}:{}".format(from_uid, uidnext)
			self.uid_reindexed = True

		elif uid_validity == current_uid_validity:
			return

	def parse_imap_response(self, cmd, response):
		pattern = r"(?<={cmd} )[0-9]*".format(cmd=cmd)
		match = re.search(pattern, response.decode('utf-8'), re.U | re.I)
		if match:
			return match.group(0)
		else:
			return None

	def retrieve_message(self, message_meta, msg_num=None):
		incoming_mail = None
		try:
			self.validate_message_limits(message_meta)

			if cint(self.settings.use_imap):
				status, message = self.imap.uid('fetch', message_meta, '(BODY.PEEK[] BODY.PEEK[HEADER] FLAGS)')
				raw = message[0]

				self.get_email_seen_status(message_meta, raw[0])
				self.latest_messages.append(raw[1])
			else:
				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 as e:
			if self.has_login_limit_exceeded(e):
				self.errors = True
				raise LoginLimitExceeded(e)

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

				if not cint(self.settings.use_imap):
					self.pop.dele(msg_num)
				else:
					# mark as seen if email sync rule is UNSEEN (syncing only unseen mails)
					if self.settings.email_sync_rule == "UNSEEN":
						self.imap.uid('STORE', message_meta, '+FLAGS', '(\\SEEN)')
		else:
			if not cint(self.settings.use_imap):
				self.pop.dele(msg_num)
			else:
				# mark as seen if email sync rule is UNSEEN (syncing only unseen mails)
				if self.settings.email_sync_rule == "UNSEEN":
					self.imap.uid('STORE', message_meta, '+FLAGS', '(\\SEEN)')

	def get_email_seen_status(self, uid, flag_string):
		""" parse the email FLAGS response """
		if not flag_string:
			return None

		flags = []
		for flag in imaplib.ParseFlags(flag_string) or []:
			pattern = re.compile("\w+")
			match = re.search(pattern, frappe.as_unicode(flag))
			flags.append(match.group(0))

		if "Seen" in flags:
			self.seen_status.update({ uid: "SEEN" })
		else:
			self.seen_status.update({ uid: "UNSEEN" })

	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)) or message in strip(cstr(getattr(e, 'strerror', ''))):
				return True
		return False

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

		m, size = message_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

	def update_flag(self, uid_list={}):
		""" set all uids mails the flag as seen  """

		if not uid_list:
			return

		if not self.connect():
			return

		self.imap.select("Inbox")
		for uid, operation in iteritems(uid_list):
			if not uid: continue

			op = "+FLAGS" if operation == "Read" else "-FLAGS"
			try:
				self.imap.uid('STORE', uid, op, '(\\SEEN)')
			except Exception:
				continue

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

		:param content: Raw message."""
		self.raw = safe_encode(content) if six.PY2 else safe_decode(content)
		self.mail = email.message_from_string(self.raw)


		self.text_content = ''
		self.html_content = ''
		self.attachments = []
		self.cid_map = {}
		self.parse()
		self.set_content_and_type()
		self.set_subject()
		self.set_from()
		self.message_id = (self.mail.get('Message-ID') or "").strip(" <>")

		if self.mail["Date"]:
			try:
				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')
			except:
				self.date = now()
		else:
			self.date = now()
		if self.date > now():
			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."""
		_subject = decode_header(self.mail.get("Subject", "No Subject"))
		self.subject = _subject[0][0] or ""
		if _subject[0][1]:
			self.subject = safe_decode(self.subject, _subject[0][1])
		else:
			# assume that the encoding is utf-8
			self.subject = safe_decode(self.subject)[:140]

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

	def set_from(self):
		# gmail mailing-list compatibility
		# use X-Original-Sender if available, as gmail sometimes modifies the 'From'
		_from_email = self.decode_email(self.mail.get("X-Original-From") or self.mail["From"])
		_reply_to = self.decode_email(self.mail.get("Reply-To"))

		if _reply_to and not frappe.db.get_value('Email Account', {"email_id":_reply_to}, 'email_id'):
			self.from_email = extract_email_id(_reply_to)
		else:
			self.from_email = extract_email_id(_from_email)

		if self.from_email:
			self.from_email = self.from_email.lower()

		self.from_real_name = parse_addr(_from_email)[0] if "@" in _from_email else _from_email

	def decode_email(self, email):
		if not email: return
		decoded = ""
		for part, encoding in decode_header(frappe.as_unicode(email).replace("\""," ").replace("\'"," ")):
			if encoding:
				decoded += part.decode(encoding)
			else:
				decoded += safe_decode(part)
		return decoded

	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.read(self.text_content).text.replace("\n","\n\n"), '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()
		if content_type == 'text/plain':
			self.text_content += self.get_payload(part)

		elif content_type == 'text/html':
			self.html_content += self.get_payload(part)

		elif content_type == 'message/rfc822':
			# sent by outlook when another email is sent as an attachment to this email
			self.show_attached_email_headers_in_content(part)

		elif part.get_filename() or 'image' in content_type:
			self.get_attachment(part)

	def show_attached_email_headers_in_content(self, part):
		# get the multipart/alternative message
		try:
		    from html import escape  # python 3.x
		except ImportError:
		    from cgi import escape  # python 2.x

		message = list(part.walk())[1]
		headers = []
		for key in ('From', 'To', 'Subject', 'Date'):
			value = cstr(message.get(key))
			if value:
				headers.append('{label}: {value}'.format(label=_(key), value=escape(value)))

		self.text_content += '\n'.join(headers)
		self.html_content += '<hr>' + '\n'.join('<p>{0}</p>'.format(h) for h in headers)

		if not message.is_multipart() and message.get_content_type()=='text/plain':
			# email.parser didn't parse it!
			text_content = self.get_payload(message)
			self.text_content += text_content
			self.html_content += markdown(text_content)

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

		return charset

	def get_payload(self, part):
		charset = self.get_charset(part)

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

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

		if fcontent:
			content_type = part.get_content_type()
			fname = part.get_filename()
			if fname:
				try:
					fname = fname.replace('\n', ' ').replace('\r', '')
					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,
			})

			cid = (part.get("Content-Id") or "").strip("><")
			if cid:
				self.cid_map[fname] = cid

	def save_attachments_in_doc(self, doc):
		"""Save email attachments in given document."""
		saved_attachments = []

		for attachment in self.attachments:
			try:
				_file = frappe.get_doc({
					"doctype": "File",
					"file_name": attachment['fname'],
					"attached_to_doctype": doc.doctype,
					"attached_to_name": doc.name,
					"is_private": 1,
					"content": attachment['fcontent']})
				_file.save()
				saved_attachments.append(_file)

				if attachment['fname'] in self.cid_map:
					self.cid_map[_file.name] = self.cid_map[attachment['fname']]

			except MaxFileSizeReachedError:
				# WARNING: bypass max file size exception
				pass
			except frappe.DuplicateEntryError:
				# same file attached twice??
				pass

		return saved_attachments

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


# fix due to a python bug in poplib that limits it to 2048
poplib._MAXLINE = 20480
imaplib._MAXLINE = 20480

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
class Timed_IMAP4(TimerMixin, imaplib.IMAP4):
	_super = imaplib.IMAP4

class Timed_IMAP4_SSL(TimerMixin, imaplib.IMAP4_SSL):
	_super = imaplib.IMAP4_SSL