import mimetypes
import os
from email import (
    charset as Charset, encoders as Encoders, generator, message_from_string,
)
from email.errors import InvalidHeaderDefect, NonASCIILocalPartDefect
from email.header import Header
from email.headerregistry import Address
from email.message import Message
from email.mime.base import MIMEBase
from email.mime.message import MIMEMessage
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.utils import formatdate, getaddresses, make_msgid, parseaddr
from io import BytesIO, StringIO

from django.conf import settings
from django.core.mail.utils import DNS_NAME
from django.utils.encoding import force_text

# Don't BASE64-encode UTF-8 messages so that we avoid unwanted attention from
# some spam filters.
utf8_charset = Charset.Charset('utf-8')
utf8_charset.body_encoding = None  # Python defaults to BASE64
utf8_charset_qp = Charset.Charset('utf-8')
utf8_charset_qp.body_encoding = Charset.QP

# Default MIME type to use on attachments (if it is not explicitly given
# and cannot be guessed).
DEFAULT_ATTACHMENT_MIME_TYPE = 'application/octet-stream'

RFC5322_EMAIL_LINE_LENGTH_LIMIT = 998


class BadHeaderError(ValueError):
    pass


# Header names that contain structured address data (RFC #5322)
ADDRESS_HEADERS = {
    'from',
    'sender',
    'reply-to',
    'to',
    'cc',
    'bcc',
    'resent-from',
    'resent-sender',
    'resent-to',
    'resent-cc',
    'resent-bcc',
}


def forbid_multi_line_headers(name, val, encoding):
    """Forbids multi-line headers, to prevent header injection."""
    encoding = encoding or settings.DEFAULT_CHARSET
    val = force_text(val)
    if '\n' in val or '\r' in val:
        raise BadHeaderError("Header values can't contain newlines (got %r for header %r)" % (val, name))
    try:
        val.encode('ascii')
    except UnicodeEncodeError:
        if name.lower() in ADDRESS_HEADERS:
            val = ', '.join(sanitize_address(addr, encoding) for addr in getaddresses((val,)))
        else:
            val = Header(val, encoding).encode()
    else:
        if name.lower() == 'subject':
            val = Header(val).encode()
    return name, val


def split_addr(addr, encoding):
    """
    Split the address into local part and domain, properly encoded.

    When non-ascii characters are present in the local part, it must be
    MIME-word encoded. The domain name must be idna-encoded if it contains
    non-ascii characters.
    """
    if '@' in addr:
        localpart, domain = addr.split('@', 1)
        # Try to get the simplest encoding - ascii if possible so that
        # to@example.com doesn't become =?utf-8?q?to?=@example.com. This
        # makes unit testing a bit easier and more readable.
        try:
            localpart.encode('ascii')
        except UnicodeEncodeError:
            localpart = Header(localpart, encoding).encode()
        domain = domain.encode('idna').decode('ascii')
    else:
        localpart = Header(addr, encoding).encode()
        domain = ''
    return (localpart, domain)


def sanitize_address(addr, encoding):
    """
    Format a pair of (name, address) or an email address string.
    """
    if not isinstance(addr, tuple):
        addr = parseaddr(force_text(addr))
    nm, addr = addr
    localpart, domain = None, None
    nm = Header(nm, encoding).encode()
    try:
        addr.encode('ascii')
    except UnicodeEncodeError:  # IDN or non-ascii in the local part
        localpart, domain = split_addr(addr, encoding)

    # An `email.headerregistry.Address` object is used since
    # email.utils.formataddr() naively encodes the name as ascii (see #25986).
    if localpart and domain:
        address = Address(nm, username=localpart, domain=domain)
        return str(address)

    try:
        address = Address(nm, addr_spec=addr)
    except (InvalidHeaderDefect, NonASCIILocalPartDefect):
        localpart, domain = split_addr(addr, encoding)
        address = Address(nm, username=localpart, domain=domain)
    return str(address)


class MIMEMixin:
    def as_string(self, unixfrom=False, linesep='\n'):
        """Return the entire formatted message as a string.
        Optional `unixfrom' when True, means include the Unix From_ envelope
        header.

        This overrides the default as_string() implementation to not mangle
        lines that begin with 'From '. See bug #13433 for details.
        """
        fp = StringIO()
        g = generator.Generator(fp, mangle_from_=False)
        g.flatten(self, unixfrom=unixfrom, linesep=linesep)
        return fp.getvalue()

    def as_bytes(self, unixfrom=False, linesep='\n'):
        """Return the entire formatted message as bytes.
        Optional `unixfrom' when True, means include the Unix From_ envelope
        header.

        This overrides the default as_bytes() implementation to not mangle
        lines that begin with 'From '. See bug #13433 for details.
        """
        fp = BytesIO()
        g = generator.BytesGenerator(fp, mangle_from_=False)
        g.flatten(self, unixfrom=unixfrom, linesep=linesep)
        return fp.getvalue()


class SafeMIMEMessage(MIMEMixin, MIMEMessage):

    def __setitem__(self, name, val):
        # message/rfc822 attachments must be ASCII
        name, val = forbid_multi_line_headers(name, val, 'ascii')
        MIMEMessage.__setitem__(self, name, val)


class SafeMIMEText(MIMEMixin, MIMEText):

    def __init__(self, _text, _subtype='plain', _charset=None):
        self.encoding = _charset
        MIMEText.__init__(self, _text, _subtype=_subtype, _charset=_charset)

    def __setitem__(self, name, val):
        name, val = forbid_multi_line_headers(name, val, self.encoding)
        MIMEText.__setitem__(self, name, val)

    def set_payload(self, payload, charset=None):
        if charset == 'utf-8':
            has_long_lines = any(
                len(l.encode('utf-8')) > RFC5322_EMAIL_LINE_LENGTH_LIMIT
                for l in payload.splitlines()
            )
            # Quoted-Printable encoding has the side effect of shortening long
            # lines, if any (#22561).
            charset = utf8_charset_qp if has_long_lines else utf8_charset
        MIMEText.set_payload(self, payload, charset=charset)


class SafeMIMEMultipart(MIMEMixin, MIMEMultipart):

    def __init__(self, _subtype='mixed', boundary=None, _subparts=None, encoding=None, **_params):
        self.encoding = encoding
        MIMEMultipart.__init__(self, _subtype, boundary, _subparts, **_params)

    def __setitem__(self, name, val):
        name, val = forbid_multi_line_headers(name, val, self.encoding)
        MIMEMultipart.__setitem__(self, name, val)


class EmailMessage:
    """
    A container for email information.
    """
    content_subtype = 'plain'
    mixed_subtype = 'mixed'
    encoding = None     # None => use settings default

    def __init__(self, subject='', body='', from_email=None, to=None, bcc=None,
                 connection=None, attachments=None, headers=None, cc=None,
                 reply_to=None):
        """
        Initialize a single email message (which can be sent to multiple
        recipients).

        All string arguments used to create the message can be strings
        or UTF-8 bytestrings. The SafeMIMEText class will handle any
        necessary encoding conversions.
        """
        if to:
            if isinstance(to, str):
                raise TypeError('"to" argument must be a list or tuple')
            self.to = list(to)
        else:
            self.to = []
        if cc:
            if isinstance(cc, str):
                raise TypeError('"cc" argument must be a list or tuple')
            self.cc = list(cc)
        else:
            self.cc = []
        if bcc:
            if isinstance(bcc, str):
                raise TypeError('"bcc" argument must be a list or tuple')
            self.bcc = list(bcc)
        else:
            self.bcc = []
        if reply_to:
            if isinstance(reply_to, str):
                raise TypeError('"reply_to" argument must be a list or tuple')
            self.reply_to = list(reply_to)
        else:
            self.reply_to = []
        self.from_email = from_email or settings.DEFAULT_FROM_EMAIL
        self.subject = subject
        self.body = body
        self.attachments = attachments or []
        self.extra_headers = headers or {}
        self.connection = connection

    def get_connection(self, fail_silently=False):
        from django.core.mail import get_connection
        if not self.connection:
            self.connection = get_connection(fail_silently=fail_silently)
        return self.connection

    def message(self):
        encoding = self.encoding or settings.DEFAULT_CHARSET
        msg = SafeMIMEText(self.body, self.content_subtype, encoding)
        msg = self._create_message(msg)
        msg['Subject'] = self.subject
        msg['From'] = self.extra_headers.get('From', self.from_email)
        msg['To'] = self.extra_headers.get('To', ', '.join(map(force_text, self.to)))
        if self.cc:
            msg['Cc'] = ', '.join(map(force_text, self.cc))
        if self.reply_to:
            msg['Reply-To'] = self.extra_headers.get('Reply-To', ', '.join(map(force_text, self.reply_to)))

        # Email header names are case-insensitive (RFC 2045), so we have to
        # accommodate that when doing comparisons.
        header_names = [key.lower() for key in self.extra_headers]
        if 'date' not in header_names:
            # formatdate() uses stdlib methods to format the date, which use
            # the stdlib/OS concept of a timezone, however, Django sets the
            # TZ environment variable based on the TIME_ZONE setting which
            # will get picked up by formatdate().
            msg['Date'] = formatdate(localtime=settings.EMAIL_USE_LOCALTIME)
        if 'message-id' not in header_names:
            # Use cached DNS_NAME for performance
            msg['Message-ID'] = make_msgid(domain=DNS_NAME)
        for name, value in self.extra_headers.items():
            if name.lower() in ('from', 'to'):  # From and To are already handled
                continue
            msg[name] = value
        return msg

    def recipients(self):
        """
        Returns a list of all recipients of the email (includes direct
        addressees as well as Cc and Bcc entries).
        """
        return [email for email in (self.to + self.cc + self.bcc) if email]

    def send(self, fail_silently=False):
        """Sends the email message."""
        if not self.recipients():
            # Don't bother creating the network connection if there's nobody to
            # send to.
            return 0
        return self.get_connection(fail_silently).send_messages([self])

    def attach(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.

        For a text/* mimetype (guessed or specified), when a bytes object is
        specified as content, it will be decoded as UTF-8. If that fails,
        the mimetype will be set to DEFAULT_ATTACHMENT_MIME_TYPE and the
        content is not decoded.
        """
        if isinstance(filename, MIMEBase):
            assert content is None
            assert mimetype is None
            self.attachments.append(filename)
        else:
            assert content is not None

            if not mimetype:
                mimetype, _ = mimetypes.guess_type(filename)
                if not mimetype:
                    mimetype = DEFAULT_ATTACHMENT_MIME_TYPE
            basetype, subtype = mimetype.split('/', 1)

            if basetype == 'text':
                if isinstance(content, bytes):
                    try:
                        content = content.decode('utf-8')
                    except UnicodeDecodeError:
                        # If mimetype suggests the file is text but it's
                        # actually binary, read() raises a UnicodeDecodeError.
                        mimetype = DEFAULT_ATTACHMENT_MIME_TYPE

            self.attachments.append((filename, content, mimetype))

    def attach_file(self, path, mimetype=None):
        """
        Attaches a file from the filesystem.

        The mimetype will be set to the DEFAULT_ATTACHMENT_MIME_TYPE if it is
        not specified and cannot be guessed.

        For a text/* mimetype (guessed or specified), the file's content
        will be decoded as UTF-8. If that fails, the mimetype will be set to
        DEFAULT_ATTACHMENT_MIME_TYPE and the content is not decoded.
        """
        filename = os.path.basename(path)

        with open(path, 'rb') as file:
            content = file.read()
            self.attach(filename, content, mimetype)

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

    def _create_attachments(self, msg):
        if self.attachments:
            encoding = self.encoding or settings.DEFAULT_CHARSET
            body_msg = msg
            msg = SafeMIMEMultipart(_subtype=self.mixed_subtype, encoding=encoding)
            if self.body:
                msg.attach(body_msg)
            for attachment in self.attachments:
                if isinstance(attachment, MIMEBase):
                    msg.attach(attachment)
                else:
                    msg.attach(self._create_attachment(*attachment))
        return msg

    def _create_mime_attachment(self, content, mimetype):
        """
        Converts the content, mimetype pair into a MIME attachment object.

        If the mimetype is message/rfc822, content may be an
        email.Message or EmailMessage object, as well as a str.
        """
        basetype, subtype = mimetype.split('/', 1)
        if basetype == 'text':
            encoding = self.encoding or settings.DEFAULT_CHARSET
            attachment = SafeMIMEText(content, subtype, encoding)
        elif basetype == 'message' and subtype == 'rfc822':
            # Bug #18967: per RFC2046 s5.2.1, message/rfc822 attachments
            # must not be base64 encoded.
            if isinstance(content, EmailMessage):
                # convert content into an email.Message first
                content = content.message()
            elif not isinstance(content, Message):
                # For compatibility with existing code, parse the message
                # into an email.Message object if it is not one already.
                content = message_from_string(content)

            attachment = SafeMIMEMessage(content, subtype)
        else:
            # Encode non-text attachments with base64.
            attachment = MIMEBase(basetype, subtype)
            attachment.set_payload(content)
            Encoders.encode_base64(attachment)
        return attachment

    def _create_attachment(self, filename, content, mimetype=None):
        """
        Converts the filename, content, mimetype triple into a MIME attachment
        object.
        """
        attachment = self._create_mime_attachment(content, mimetype)
        if filename:
            try:
                filename.encode('ascii')
            except UnicodeEncodeError:
                filename = ('utf-8', '', filename)
            attachment.add_header('Content-Disposition', 'attachment',
                                  filename=filename)
        return attachment


class EmailMultiAlternatives(EmailMessage):
    """
    A version of EmailMessage that makes it easy to send multipart/alternative
    messages. For example, including text and HTML versions of the text is
    made easier.
    """
    alternative_subtype = 'alternative'

    def __init__(self, subject='', body='', from_email=None, to=None, bcc=None,
                 connection=None, attachments=None, headers=None, alternatives=None,
                 cc=None, reply_to=None):
        """
        Initialize a single email message (which can be sent to multiple
        recipients).

        All string arguments used to create the message can be strings or UTF-8
        bytestrings. The SafeMIMEText class will handle any necessary encoding
        conversions.
        """
        super().__init__(
            subject, body, from_email, to, bcc, connection, attachments,
            headers, cc, reply_to,
        )
        self.alternatives = alternatives or []

    def attach_alternative(self, content, mimetype):
        """Attach an alternative content representation."""
        assert content is not None
        assert mimetype is not None
        self.alternatives.append((content, mimetype))

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

    def _create_alternatives(self, msg):
        encoding = self.encoding or settings.DEFAULT_CHARSET
        if self.alternatives:
            body_msg = msg
            msg = SafeMIMEMultipart(_subtype=self.alternative_subtype, encoding=encoding)
            if self.body:
                msg.attach(body_msg)
            for alternative in self.alternatives:
                msg.attach(self._create_mime_attachment(*alternative))
        return msg
