## $Id: smtp.py 7819 2012-03-08 22:28:46Z henrik $
##
## Copyright (C) 2012 Uli Fouquet & Henrik Bettermann
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
##
"""
Email (SMTP) services for Kofa.

Note About Encodings
--------------------

All functions in this module expect any raw strings passed in to be
encoded 'utf-8' (if you pass in unicode objects instead, this is not a
problem).

This is because we cannot easily tell from a raw string (it is in fact
only a byte stream) what encoding it has. In latin-1 and utf-8, for
instance, there exist some chars (byte values) that have different
meanings in both encodings. If we see such a char in a byte stream:
what is it meant to represent? The respective character from latin1 or
the one from utf-8?

We therefore interpret all internally used raw strings to be encoded as
utf-8.

The functions in here nevertheless try hard to produce output (mail
parts, headers, etc.) encoded in the least complex manner. For
instance if you pass in some address or mail body that is
representable (correctly) as ASCII or latin-1, we will turn the text
into that encoding (given, you passed it in as utf-8) to stay as
compatible as possible with old mailers that do not understand utf-8.

"""
import grok
import logging
from email.Header import Header
from email.Utils import formataddr
from email.mime.text import MIMEText
from zope.component import getUtility
from zope.sendmail.interfaces import IMailDelivery
from waeup.kofa.interfaces import IMailService

class DefaultMailService(grok.GlobalUtility):
    """Returns a :class:`zope.sendmail.IMailDelivery`.

    Searches a site from current request (if applicable) and returns
    the mail delivery set for this site or a fake mailer that does not
    really send mail (for testing, evaluating, etc.).
    """
    grok.implements(IMailService)

    def __call__(self):
        name = 'No email service'
        site = grok.getSite()
        if site is not None:
            config = site['configuration']
            name = getattr(config, 'smtp_mailer', name)
        return getUtility(IMailDelivery, name=name)

class FakeSMTPDelivery(grok.GlobalUtility):
    """A fake mail delivery for testing etc.

    Instead of sending real mails, this mailer only logs received
    messages to the ``test.smtp`` logger.
    """
    grok.implements(IMailDelivery)
    grok.name('No email service')

    def send(self, fromaddr, toaddrs, message):
        logger = logging.getLogger('test.smtp')
        rcpts = ', '.join([x.decode('utf-8') for x in toaddrs])
        logger.info(
            u"Sending email from %s to %s:" % (
                fromaddr.decode('utf-8'), rcpts))
        logger.info(u"Message:")
        for line in message.split('\n'):
            logger.info(u"msg: " + line.decode('utf-8'))
        return 'fake-message-id@example.com'

CHARSETS = ('US-ASCII', 'ISO-8859-1', 'UTF-8')

def encode_header_item(item):
    if not isinstance(item, unicode):
        item = unicode(item, 'utf-8')
    return str(Header(item, 'iso-8859-1')) # try ascii, then latin1, then utf-8

def encode_address(addr, name=u''):
    """Turn email address parts into a single valid email string.

    The given email address and the name are turned into a single
    (byte stream) string, suitable for use with ``To:`` or ``From:``
    headers in emails.

    Any encodings to a mailer-readable format are performed.

    Preferred input format is unicode, although also raw strings (byte
    streams) work as long as they are decodable from UTF-8.

    That means: if you pass in non-unicode string, take care to
    deliver utf-8 encoded strings (or plain ASCII).

    Returns a single (raw) string like "My Name <my@sample.com>".
    """
    addr = encode_header_item(addr)
    name = encode_header_item(name)
    return formataddr((name, addr))

def encode_body(text):
    """Build MIME message part from text.

    You can pass unicode objects or simple strings as text.

    .. warn:: If the input is a simple string, this string is expected
              to be encoded 'utf-8'!

    Returns a MIMEText object.
    """
    if not isinstance(text, unicode):
        text = unicode(text, 'utf-8')
    charset = CHARSETS[-1] # fallback
    for charset in CHARSETS:
        try:
            text = text.encode(charset)
        except UnicodeError:
            pass # try next encoding
        else:
            break
    return MIMEText(text, 'plain', charset)

def send_mail(from_name, from_addr, rcpt_name, rcpt_addr,
              subject, body, config=None):
    """Send mail.
    """
    # format message
    body = encode_body(body)
    body["From"] = encode_address(from_addr, from_name)
    body["To"] = encode_address(rcpt_addr, rcpt_name)
    body["Subject"] = encode_header_item(subject)

    mailer = getUtility(IMailService)
    result = mailer().send(from_addr, [rcpt_addr], body.as_string())
    return result