import mimetypes
from base64 import b64encode
from email.mime.base import MIMEBase
from email.utils import parseaddr

import six
from django.core.mail.message import sanitize_address, DEFAULT_ATTACHMENT_MIME_TYPE


UNSET = object()  # Used as non-None default value


def combine(*args):
    """
    Combines all non-UNSET args, by shallow merging mappings and concatenating sequences

    >>> combine({'a': 1, 'b': 2}, UNSET, {'b': 3, 'c': 4}, UNSET)
    {'a': 1, 'b': 3, 'c': 4}
    >>> combine([1, 2], UNSET, [3, 4], UNSET)
    [1, 2, 3, 4]
    >>> combine({'a': 1}, None, {'b': 2})  # None suppresses earlier args
    {'b': 2}
    >>> combine()
    UNSET

    """
    result = UNSET
    for value in args:
        if value is None:
            # None is a request to suppress any earlier values
            result = UNSET
        elif value is not UNSET:
            if result is UNSET:
                try:
                    result = value.copy()  # will shallow merge if dict-like
                except AttributeError:
                    result = value  # will concatenate if sequence-like
            else:
                try:
                    result.update(value)  # shallow merge if dict-like
                except AttributeError:
                    result += value  # concatenate if sequence-like
    return result


def last(*args):
    """Returns the last of its args which is not UNSET.

    (Essentially `combine` without the merge behavior)

    >>> last(1, 2, UNSET, 3, UNSET, UNSET)
    3
    >>> last(1, 2, None, UNSET)  # None suppresses earlier args
    UNSET
    >>> last()
    UNSET

    """
    for value in reversed(args):
        if value is None:
            # None is a request to suppress any earlier values
            return UNSET
        elif value is not UNSET:
            return value
    return UNSET


class ParsedEmail(object):
    """A sanitized, full email address with separate name and email properties"""

    def __init__(self, address, encoding):
        self.address = sanitize_address(address, encoding)
        self._name = None
        self._email = None

    def _parse(self):
        if self._email is None:
            self._name, self._email = parseaddr(self.address)

    def __str__(self):
        return self.address

    @property
    def name(self):
        self._parse()
        return self._name

    @property
    def email(self):
        self._parse()
        return self._email


class Attachment(object):
    """A normalized EmailMessage.attachments item with additional functionality

    Normalized to have these properties:
    name: attachment filename; may be empty string; will be Content-ID for inline attachments
    content
    mimetype: the content type; guessed if not explicit
    inline: bool, True if attachment has a Content-ID header
    """

    def __init__(self, attachment, encoding):
        # Note that an attachment can be either a tuple of (filename, content, mimetype)
        # or a MIMEBase object. (Also, both filename and mimetype may be missing.)
        self._attachment = attachment
        self.encoding = encoding  # should we be checking attachment["Content-Encoding"] ???
        self.inline = False

        if isinstance(attachment, MIMEBase):
            self.name = attachment.get_filename()
            self.content = attachment.get_payload(decode=True)
            self.mimetype = attachment.get_content_type()
            # Treat image attachments that have content ids as inline:
            if attachment.get_content_maintype() == "image" and attachment["Content-ID"] is not None:
                self.inline = True
                self.name = attachment["Content-ID"]
        else:
            (self.name, self.content, self.mimetype) = attachment

        # Guess missing mimetype from filename, borrowed from
        # django.core.mail.EmailMessage._create_attachment()
        if self.mimetype is None and self.name is not None:
            self.mimetype, _ = mimetypes.guess_type(self.name)
        if self.mimetype is None:
            self.mimetype = DEFAULT_ATTACHMENT_MIME_TYPE

    @property
    def b64content(self):
        """Content encoded as a base64 ascii string"""
        content = self.content
        if isinstance(content, six.text_type):
            content = content.encode(self.encoding)
        return b64encode(content).decode("ascii")