from django.db import models
from django.utils.crypto import get_random_string
from django.core.mail import EmailMessage, get_connection
from django.conf import settings

import hashlib


def generate_message_token():
    # /!\ birthday problem
    return get_random_string(length=32)


def hexdigest_sha256(*args):
    r = hashlib.sha256()
    for arg in args:
        r.update(str(arg).encode('utf-8'))
    return r.hexdigest()


class MessageCorrespondent(models.Model):
    email = models.EmailField()
    token = models.CharField(max_length=64, default=generate_message_token, unique=True)


class MessageThread(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    token = models.CharField(max_length=64, default=generate_message_token, unique=True)


class Message(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    thread = models.ForeignKey(MessageThread)
    author = models.EmailField(blank=True)
    content = models.TextField(blank=True)
    token = models.CharField(max_length=64, default=generate_message_token, unique=True)

    class Meta:
        ordering = ['created']

    def send_notification(self, subject, sender, dests, reply_to=None, message_id=None, reference=None):
        messages = []
        for dest_name, dest_email in dests:
            correspondent, created = MessageCorrespondent.objects.get_or_create(email=dest_email)
            token = self.thread.token + correspondent.token + hexdigest_sha256(settings.SECRET_KEY, self.thread.token, correspondent.token)[:16]
            sender_name, sender_email = sender
            if reply_to:
                reply_to_name, reply_to_email = reply_to
                reply_to_list = ['%s <%s>' % (reply_to_name, reply_to_email.format(token=token))]
            else:
                reply_to_list = []
            headers = dict()
            if message_id:
                headers.update({
                    'Message-ID': message_id.format(id=self.token),
                })
            if message_id and reference:
                headers.update({
                    'References': message_id.format(id=reference),
                })
            messages.append(EmailMessage(
                subject=subject,
                body=self.content,
                from_email='%s <%s>' % (sender_name, sender_email),
                to=['%s <%s>' % (dest_name, dest_email)],
                reply_to=reply_to_list,
                headers=headers,
            ))
        connection = get_connection()
        connection.send_messages(messages)

    def __str__(self):
        return "Message from %s" % self.author