# Copyright (C) 2011-2012  Patrick Totzke <patricktotzke@gmail.com>
# This file is released under the GNU GPL, version 3 or a later revision.
# For further details see the COPYING file

import codecs
import email
import email.charset as charset
import email.policy
from functools import cached_property
import logging
import os
import subprocess

from datetime import datetime

from urwid.util import detected_encoding

from ..mail.attachment import Attachment
from .. import crypto
from .. import helper
from ..errors import GPGProblem
from ..settings.const import settings
from ..utils.mailcap import MailcapHandler

charset.add_charset('utf-8', charset.QP, charset.QP, 'utf-8')

_APP_PGP_SIG = 'application/pgp-signature'
_APP_PGP_ENC = 'application/pgp-encrypted'

def _render_part_external(payload, ctype, params, filename):
    """
    renders a non-multipart email part into displayable plaintext by piping its
    payload through an external script. The handler itself is determined by
    the mailcap entry for this part's ctype.
    """
    h = MailcapHandler(payload, ctype, params, filename, 'copiousoutput')
    if not h or h.needs_terminal:
        return

    def decode(buf):
        return buf.decode(detected_encoding, errors = 'backslashreplace')

    with h:
        logging.debug('Rendering part %s: %s', ctype, h.cmd)

        try:
            result = subprocess.run(h.cmd, shell = True, check = True,
                                    capture_output = True, input = h.stdin,
                                    stdin = None if h.stdin else subprocess.DEVNULL)
        except subprocess.CalledProcessError as e:
            logging.error('Calling mailcap handler "%s" failed with code %d: %s',
                          h.cmd, e.returncode, decode(e.stderr))
            return None

        return decode(result.stdout)

class _MessageHeaders:
    _msg = None

    def __init__(self, msg):
        self._msg = msg

    def __contains__(self, key):
        return key in self._msg

    # workaround for https://bugs.python.org/issue39100
    def _exc_is_bp39100(self, e):
        if (e.args and len(e.args) >= 1 and
            'Group' in e.args[0] and 'local_part' in e.args[0]):
            logging.error('Working around Python bug 39100')
            return True
        return False

    def _get_all_wrapper(self, key, failobj = None):
        try:
            return self._msg.get_all(key, failobj)
        except AttributeError as e:
            if self._exc_is_bp39100(e):
                return []
            raise

    def __getitem__(self, key):
        if not key in self._msg:
            raise KeyError(key)
        return self._get_all_wrapper(key)

    def get(self, key):
        """
        Get the value of the first header with the name equal to key,
        None if the header is not present.
        """
        try:
            return self._msg.get(key)
        except AttributeError as e:
            if self._exc_is_bp39100(e):
                return []
            raise

    def get_all(self, key):
        """
        Get the list of all values of the header with the name equal to key,
        empty list of the header is not present.
        """
        return self._get_all_wrapper(key, [])

    def keys(self):
        try:
            return self._msg.keys()
        except AttributeError as e:
            if self._exc_is_bp39100(e):
                return []
            raise

    def items(self):
        try:
            return self._msg.items()
        except AttributeError as e:
            if self._exc_is_bp39100(e):
                return []
            raise

class _MimeTree:
    _part = None

    # content-type: (maintype, subtype)
    # may differ from that indicated in _part,
    # e.g. when it reports octet-stream, but we guess
    # something more specific
    _ctype_val = None

    is_signed     = False
    is_encrypted  = False
    sig_valid     = None
    sig_trusted   = None
    signer_id     = None
    crypt_error   = None

    is_alternative = False

    headers    = None
    children   = None
    attachment = None

    def __init__(self, part, session_keys = None):
        self._part = part
        self.headers = _MessageHeaders(self._part)

        if part.is_multipart():
            st = part.get_content_subtype()

            # handle signed/encrypted messages
            if st == 'signed' and part.get_param('protocol') == _APP_PGP_SIG:
                return self._handle_signed_pgp(session_keys)
            elif st == 'encrypted':
                return self._handle_encrypted(session_keys)

            # for all other cases, we just put all the sub-parts into children
            # multipart/alternative are flagged as such
            # everything else is treated as multipart/mixed
            if st == 'alternative':
                self.is_alternative = True

            children = []
            for part in part.iter_parts():
                children.append(_MimeTree(part, session_keys))
            self.children = children
        else:
            if self.content_maintype == 'text':
                self._fixup_charset()

            cd = part.get_content_disposition()
            fn = part.get_filename()
            if cd == 'attachment' or fn is not None:
                data   = part.get_content()
                params = part.get_params()

                # make sure data is always a byte-sequence
                if isinstance(data, str):
                    data = data.encode('utf-8', errors = 'replace')
                    params = [p for p in params if p[0] != 'charset'] + \
                             [('charset', 'utf-8')]

                self.attachment = Attachment(data, self.content_type,
                                             fn, params)

    def __str__(self):
        return 'MimePart(%s)' % self.content_type

    def _fixup_charset(self):
        """
        If a text MIME part declares an invalid or no charset, replace it
        with UTF-8.
        """
        charset = self._part.get_param('charset')
        if charset is not None:
            try:
                return codecs.lookup(charset)
            except LookupError:
                pass

        self._part.set_param('charset', 'utf-8')

    def render_str(self, alt_preference = None):
        if self.children is not None:
            if self.is_alternative and len(self.children) > 0:
                child = None
                for ch in self.children:
                    if ch.content_type == alt_preference:
                        child = ch
                        break
                if child is None:
                    child = self.children[0]
                return child.render_str(alt_preference)

            parts = []
            for ch in self.children:
                part = ch.render_str(alt_preference)
                if part:
                    parts.append(part)
            return '\n'.join(parts)

        content = self._part.get_content()

        # try procesing content with an external program
        rendered = _render_part_external(content, self.content_type,
                                         self._part.get_params(),
                                         self.filename)
        if rendered:
            return rendered

        # return text parts without a handler as-is
        if self.content_maintype == 'text':
            if not isinstance(content, str):
                content = content.decode('utf-8', errors = 'backslashreplace')
            return content

        return None

    @property
    def raw_data(self):
        return self._part.as_bytes()

    @property
    def _ctype(self):
        if self._ctype_val is None:
            ctype = self._part.get_content_type()

            # replace underspecified mime description by a better guess
            if ctype in ['octet/stream', 'application/octet-stream',
                         'application/octetstream']:
                ctype = helper.guess_mimetype(self._part.get_content())
                logging.debug('Overriding octet-stream content type to %s', ctype)

            maintype, _, subtype = ctype.partition('/')
            self._ctype_val = (maintype, subtype)

        return self._ctype_val

    @property
    def content_type(self):
        return '/'.join(self._ctype)
    @property
    def content_maintype(self):
        return self._ctype[0]
    @property
    def content_subtype(self):
        return self._ctype[1]

    @property
    def filename(self):
        return self._part.get_filename()

    def _handle_signed_pgp(self, session_keys):
        """
        Handle PGP-signed data.

        RFC 3156 is quite strict:
        * exactly two messages
        * the second is of type 'application/pgp-signature'
        * the second contains the detached signature
        """
        self.is_signed = True
        payload = list(self._part.iter_parts())

        if len(payload) != 2:
            self.crypt_error = 'expected exactly two messages, got %d' % len(payload)
            return

        self.children = [_MimeTree(payload[0], session_keys)]

        ct = payload[1].get_content_type()
        if ct != _APP_PGP_SIG:
            self.crypt_error = 'expected Content-Type: {0}, got: {1}'.format(
                _APP_PGP_SIG, ct)
            return

        # TODO: RFC 3156 says the alg has to be lower case, but I've seen a message
        # with 'PGP-'. maybe we should be more permissive here, or maybe not, this
        # is crypto stuff...
        micalg = self._part.get_param('micalg', '')
        if not micalg.startswith('pgp-'):
            self.crypt_error = 'expected micalg=pgp-..., got: {0}'.format(micalg)
            return

        part_data = payload[0].as_bytes()
        sig_data  = payload[1].get_content()

        # verify the signature
        sig     = None
        gpg_err = None
        try:
            sigs = crypto.verify_detached(part_data, sig_data)
            self.sig_valid = True
            if len(sigs) == 1:
                sig = sigs[0]
            else:
                gpg_err = 'exactly one signature expected'
        except GPGProblem as e:
            self.sig_valid = False
            gpg_err = str(e)

        # get the signer
        if sig is not None:
            self.signer_id, self.sig_trusted = self._sig_check_key(sig.fpr)

        if gpg_err:
            self.crypt_error = gpg_err

    def _sig_check_key(self, fingerprint):
        try:
            key = crypto.get_key(fingerprint)
            for uid in key.uids:
                if crypto.check_uid_validity(key, uid.email):
                    return uid.uid, True

            # No trusted uid found
            sig_from = key.uids[0].uid
        except GPGProblem:
            sig_from = fingerprint

        return sig_from, False

    def _handle_encrypted(self, session_keys):
        """
        Handle encrypted messages.

        RFC 3156 is quite strict:
        * exactly two parts
        * the first is of type 'application/pgp-encrypted'
        * the first contains 'Version: 1'
        * the second is of type 'application/octet-stream'
        * the second contains the encrypted and possibly signed data
        """
        self.is_encrypted = True
        payload = list(self._part.iter_parts())

        if len(payload) != 2:
            self.crypt_error = 'expected exactly two messages, got %d' % len(payload)
            return

        part_control = payload[0]
        part_body    = payload[1]

        ct = part_control.get_content_type()
        if ct != _APP_PGP_ENC:
            self.crypt_error = 'expected Content-Type: %s, got: %s' % (_APP_PGP_ENC, ct)
            return

        want = 'application/octet-stream'
        ct = part_body.get_content_type()
        if ct != want:
            self.crypt_error = 'expected Content-Type: %s, got: %s' % (want, ct)
            return

        payload = part_body.get_content()
        try:
            sigs, d = crypto.decrypt_verify(payload, session_keys)
        except GPGProblem as e:
            # signature verification failures end up here too if the combined
            # method is used, currently this prevents the interpretation of the
            # recovered plain text mail. maybe that's a feature.
            self.crypt_error = 'Failed to decrypt message: %s' % str(e)
            sigs = None
            d    = None

        if d:
            child = email.message_from_bytes(d, policy = email.policy.SMTP)
            self.children = [_MimeTree(child, session_keys)]

        if sigs:
            self.is_signed = True
            self.sig_valid = True
            if len(sigs) == 1:
                self.signer_id, self.sig_trusted = self._sig_check_key(sigs[0].fpr)

class Message:
    """
    a persistent notmuch message object.
    It it uses a :class:`~alot.db.DBManager` for cached manipulation
    and lazy lookups.
    """

    """the :class:`~alot.db.Thread` this Message belongs to"""
    thread = None

    """value of the Date header value as :class:`~datetime.datetime`"""
    date = None

    """value of the Message-Id header (str)"""
    id = None

    """Paths to all files corresponding to this message"""
    filenames = None

    """this message's depth in the thread tree"""
    depth = None

    """A list of replies to this message"""
    replies = None

    """
    This message parent in the list (i.e. the message this message is a reply
    to). None when this message is top-level.
    """
    parent = None

    _session_keys = None

    _nm_from = None
    "From header stored in the database"

    def __init__(self, dbman, thread, msg, depth):
        """
        :param dbman: db manager that is used for further lookups
        :type dbman: alot.db.DBManager
        :param thread: this messages thread
        :type thread: :class:`~alot.db.Thread`
        :param msg: the wrapped message
        :type msg: notmuch.database.Message
        :param depth: depth of this message in the thread tree (0 for toplevel
                      messages, 1 for their replies etc.)
        :type depth int
        """
        self._dbman = dbman
        self.id = msg.messageid
        self.thread = thread
        self.depth   = depth
        try:
            self.date = datetime.fromtimestamp(msg.date)
        except ValueError:
            self.date = None

        self.filenames = list(msg.filenamesb())
        if len(self.filenames) == 0:
            raise ValueError('No filenames for a message returned')

        session_keys = []
        for name, value in msg.properties.getall('session-key', exact = True):
            session_keys.append(value)
        self._session_keys = session_keys

        self._tags    = set(msg.tags)
        try:
            self._nm_from = msg.header('from')
        except LookupError:
            self._nm_from = None

    def __str__(self):
        """prettyprint the message"""
        aname, aaddress = self.get_author()
        if not aname:
            aname = aaddress
        return "%s (%s)" % (aname, self.get_datestring())

    def __hash__(self):
        """needed for sets of Messages"""
        return hash(self.id)

    def __eq__(self, other):
        if isinstance(other, type(self)):
            return self.id == other.id
        return NotImplemented

    @cached_property
    def body(self):
        """
        A MimeTree object containing the body of the message.
        """
        return _MimeTree(self._email, self._session_keys)

    @property
    def headers(self):
        """
        The object providing access to the email's headers.
        """
        return self.body.headers

    @property
    def filename(self):
        return self.filenames[0]

    @cached_property
    def _email(self):
        try:
            with open(self.filename, 'rb') as f:
                mail = email.message_from_bytes(f.read(), policy = email.policy.SMTP)
        except IOError:
            warning = b"Subject: Caution!\n"\
                      b"Message file is no longer accessible:\n%s" % self.filename
            mail = email.message_from_bytes(warning, policy = email.policy.SMTP)

        return mail

    def as_bytes(self):
        return self._email.as_bytes()

    def get_tags(self):
        """returns tags attached to this message as set of strings"""
        return self._tags

    def get_datestring(self):
        """
        returns reformated datestring for this message.

        It uses :meth:`SettingsManager.represent_datetime` to represent
        this messages `Date` header

        :rtype: str
        """
        if self.date is None:
            return None
        return settings.represent_datetime(self.date)

    def get_author(self):
        """
        returns realname and address of this messages author

        :rtype: (str,str)
        """
        sender = self._nm_from
        if sender is None:
            sender = self.headers.get('Sender')

        if not sender:
            if 'draft' in self._tags:
                acc = settings.get_accounts()[0]
                sender = '"{}" <{}>'.format(acc.realname, str(acc.address))
            else:
                sender = '"Unknown" <>'

        return email.utils.parseaddr(sender)

    def tags_add(self, tags):
        """
        Asynchronously add tags to message

        :param tags: a set of tags to be added
        :type tags: set of str
        """
        def myafterwards(fut):
            self._tags = self._tags.union(tags)

        fut = self._dbman.tags_add('id:' + self.id, tags)
        fut.add_done_callback(myafterwards)
        return fut

    def tags_set(self, tags):
        """
        Asynchronously set tags for a message

        :param tags: a set of new tags to replace the existing set
        :type tags: set of str
        """
        def myafterwards(fut):
            self._tags = set(tags)

        fut = self._dbman.tags_set('id:' + self.id, tags)
        fut.add_done_callback(myafterwards)
        return fut

    def tags_remove(self, tags):
        """Asynchronously remove tags from message

        :param tags: a set of tags to be removed
        :type tags: set of str
        """
        def myafterwards(fut):
            self._tags = self._tags.difference(tags)

        fut = self._dbman.tags_remove('id:' + self.id, tags)
        fut.add_done_callback(myafterwards)
        return fut

    def iter_attachments(self):
        """
        Iterate over all the attachments in this message.
        """
        def tree_walk(mime_tree):
            if mime_tree.attachment:
                yield mime_tree.attachment

            if mime_tree.children is not None:
                for ch in mime_tree.children:
                    yield from tree_walk(ch)

        yield from tree_walk(self.body)

    def get_body_text(self):
        """
        Returns a string view of a Message.

        This consults :ref:`prefer_plaintext <prefer-plaintext>`
        to determine if a "text/plain" alternative is preferred over a "text/html"
        part.

        :returns: The combined text of any parts to be used
        :rtype: str
        """
        if settings.get('prefer_plaintext'):
            alt_preference = 'text/plain'
        else:
            alt_preference = 'text/html'

        return self.body.render_str(alt_preference)

    def matches(self, querystring):
        """tests if this messages is in the resultset for `querystring`"""
        searchfor = '( {} ) AND id:{}'.format(querystring, self.id)
        return self._dbman.count_messages(searchfor) > 0

    def parents(self):
        """
        A generator iterating over this message's parents up to the topmost
        level.
        """
        m = self.parent
        while m:
            yield m
            m = m.parent