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,
    )