import datetime
import email.header
import logging
import os

from django.conf import settings


logger = logging.getLogger(__name__)


def get_settings():
    return {
        'strip_unallowed_mimetypes': getattr(
            settings,
            'DJANGO_MAILBOX_STRIP_UNALLOWED_MIMETYPES',
            False
        ),
        'allowed_mimetypes': getattr(
            settings,
            'DJANGO_MAILBOX_ALLOWED_MIMETYPES',
            [
                'text/plain',
                'text/html'
            ]
        ),
        'text_stored_mimetypes': getattr(
            settings,
            'DJANGO_MAILBOX_TEXT_STORED_MIMETYPES',
            [
                'text/plain',
                'text/html'
            ]
        ),
        'altered_message_header': getattr(
            settings,
            'DJANGO_MAILBOX_ALTERED_MESSAGE_HEADER',
            'X-Django-Mailbox-Altered-Message'
        ),
        'attachment_interpolation_header': getattr(
            settings,
            'DJANGO_MAILBOX_ATTACHMENT_INTERPOLATION_HEADER',
            'X-Django-Mailbox-Interpolate-Attachment'
        ),
        'attachment_upload_to': getattr(
            settings,
            'DJANGO_MAILBOX_ATTACHMENT_UPLOAD_TO',
            'mailbox_attachments/%Y/%m/%d/'
        ),
        'store_original_message': getattr(
            settings,
            'DJANGO_MAILBOX_STORE_ORIGINAL_MESSAGE',
            False
        ),
        'compress_original_message': getattr(
            settings,
            'DJANGO_MAILBOX_COMPRESS_ORIGINAL_MESSAGE',
            False
        ),
        'original_message_compression': getattr(
            settings,
            'DJANGO_MAILBOX_ORIGINAL_MESSAGE_COMPRESSION',
            6
        ),
        'default_charset': getattr(
            settings,
            'DJANGO_MAILBOX_DEFAULT_CHARSET',
            'iso8859-1',
        )
    }


def convert_header_to_unicode(header):
    default_charset = get_settings()['default_charset']

    def _decode(value, encoding):
        if isinstance(value, str):
            return value
        if not encoding or encoding == 'unknown-8bit':
            encoding = default_charset
        return value.decode(encoding, 'replace')

    try:
        return ''.join(
            [
                (
                    _decode(bytestr, encoding)
                ) for bytestr, encoding in email.header.decode_header(header)
            ]
        )
    except UnicodeDecodeError:
        logger.exception(
            'Errors encountered decoding header %s into encoding %s.',
            header,
            default_charset,
        )
        return header.decode(default_charset, 'replace')


def get_body_from_message(message, maintype, subtype):
    """
    Fetchs the body message matching main/sub content type.
    """
    body = ''
    for part in message.walk():
        if part.get('content-disposition', '').startswith('attachment;'):
            continue
        if part.get_content_maintype() == maintype and \
                part.get_content_subtype() == subtype:
            charset = part.get_content_charset()
            this_part = part.get_payload(decode=True)
            if charset:
                try:
                    this_part = this_part.decode(charset, 'replace')
                except LookupError:
                    this_part = this_part.decode('ascii', 'replace')
                    logger.warning(
                        'Unknown encoding %s encountered while decoding '
                        'text payload.  Interpreting as ASCII with '
                        'replacement, but some data may not be '
                        'represented as the sender intended.',
                        charset
                    )
                except ValueError:
                    this_part = this_part.decode('ascii', 'replace')
                    logger.warning(
                        'Error encountered while decoding text '
                        'payload from an incorrectly-constructed '
                        'e-mail; payload was converted to ASCII with '
                        'replacement, but some data may not be '
                        'represented as the sender intended.'
                    )
            else:
                this_part = this_part.decode('ascii', 'replace')

            body += this_part

    return body


def get_attachment_save_path(instance, filename):
    settings = get_settings()

    path = settings['attachment_upload_to']
    if '%' in path:
        path = datetime.datetime.utcnow().strftime(path)

    return os.path.join(
        path,
        filename,
    )