#!/usr/bin/python
# Copyright 2015 (c) Anna Schumaker.
#
import re
import slack
import sys
from email.parser import Parser

headers = Parser().parsestr(sys.stdin.read())


#
# Only allow replies that come from the slack user's email address.
#
sender = headers.get("sender", headers.get("from"))
match  = re.search("<(.*?)@(.*?)>", sender)
addr   = match.group(0)[1:-1] if match else sender
if addr.replace(".", "") != slack.user().email().replace(".", ""):
    print("Reply not from user!")
    sys.exit(1)


#
# Find the message payload (this is tricky for multipart messages)
#
if headers.is_multipart():
    for part in headers.get_payload():
        if part.get_content_type() == "text/plain":
            payload = part.get_payload(decode = True)
else:
    payload = headers.get_payload(decode = True)

if type(payload) is bytes:
    payload = payload.decode()

#
# Find the thread id in the message payload
#
reply = "--- Reply above this line ---(\s*?)thread=(.*?)\n"
match = re.search(reply, payload)
if match == None:
    print("Reply line missing!")
    sys.exit(1)

thread_id = match.group(0).rsplit("=")[-1].rstrip()


#
# Parse the message payload to find the text that was sent.
# Note that we make the following assumptions:
#
# - Quoted text will always begin with ">"
# - The email reply will always have "Reply sent on <whenever>" text
#
message = re.sub("^>(.*?)\n", "", payload, flags=re.MULTILINE).rstrip()
split   = message.split("\n")
message = "\n".join(split[:-1]).rstrip()


#
# Post the message to the thread
#
thread = slack.find_thread(thread_id)
if thread == None:
    print("No such thread: %s!" % thread_id)
    sys.exit(1)

if thread.post(message) == False:
    print("Error posting to thread: %s" % thread_id)
    sys.exit(1)