import os.path
import re
import mimetypes

from email.mime.base import MIMEBase
from django.core.mail import EmailMultiAlternatives, SafeMIMEMultipart
from django.conf import settings

# Source: https://djangosnippets.org/snippets/2215/
class EmailMultiRelated(EmailMultiAlternatives):
    """
    A version of EmailMessage that makes it easy to send multipart/related
    messages. For example, including text and HTML versions with inline images.
    """
    related_subtype = 'related'

    def __init__(self, subject='', body='', from_email=None, to=None, bcc=None,
            connection=None, attachments=None, headers=None, alternatives=None):
        # self.related_ids = []
        self.related_attachments = []
        super(EmailMultiRelated, self).__init__(subject, body, from_email, to, bcc, connection, attachments, headers, alternatives)

    def attach_related(self, filename=None, content=None, mimetype=None):
        """
        Attaches a file with the given filename and content. The filename can
        be omitted and the mimetype is guessed, if not provided.

        If the first parameter is a MIMEBase subclass it is inserted directly
        into the resulting message attachments.
        """
        if isinstance(filename, MIMEBase):
            assert content == mimetype == None
            self.related_attachments.append(filename)
        else:
            assert content is not None
            self.related_attachments.append((filename, content, mimetype))

    def attach_related_file(self, path, mimetype=None):
        """Attaches a file from the filesystem."""
        filename = os.path.basename(path)
        content = open(path, 'rb').read()
        if mimetype is None:
            mimetypes.init()
            mimetype = mimetypes.guess_type(filename)[0]
        self.attach_related(filename, content, mimetype)

    def _create_message(self, msg):
        return self._create_attachments(self._create_related_attachments(self._create_alternatives(msg)))

    def _create_alternatives(self, msg):
        for i, (content, mimetype) in enumerate(self.alternatives):
            if mimetype == 'text/html':
                for filename, _, _ in self.related_attachments:
                    content = re.sub(r'(?<!cid:)%s' % re.escape(filename), 'cid:%s' % filename, content)
                self.alternatives[i] = (content, mimetype)

        return super(EmailMultiRelated, self)._create_alternatives(msg)

    def _create_related_attachments(self, msg):
        encoding = self.encoding or settings.DEFAULT_CHARSET
        if self.related_attachments:
            body_msg = msg
            msg = SafeMIMEMultipart(_subtype=self.related_subtype, encoding=encoding)
            if self.body:
                msg.attach(body_msg)
            for related in self.related_attachments:
                msg.attach(self._create_related_attachment(*related))
        return msg

    def _create_related_attachment(self, filename, content, mimetype=None):
        """
        Convert the filename, content, mimetype triple into a MIME attachment
        object. Adjust headers to use Content-ID where applicable.
        Taken from http://code.djangostudy.com/ticket/4771
        """
        attachment = super(EmailMultiRelated, self)._create_attachment(filename, content, mimetype)
        if filename:
            mimetype = attachment['Content-Type']
            del(attachment['Content-Type'])
            del(attachment['Content-Disposition'])
            attachment.add_header('Content-Disposition', 'inline', filename=filename)
            attachment.add_header('Content-Type', mimetype, name=filename)
            attachment.add_header('Content-ID', '<%s>' % filename)
        return attachment