# Copyright (C) 2001-2006 Python Software Foundation

# Author: Barry Warsaw

# Contact: email-sig@python.org

"""Classes to generate plain text from a message object tree."""

__all__ = ['Generator', 'DecodedGenerator']

import re

import sys

import time

import random

import warnings

from cStringIO import StringIO

from email.header import Header

UNDERSCORE = '_'

NL = '\n'

fcre = re.compile(r'^From ', re.MULTILINE)

def _is8bitstring(s):

    if isinstance(s, str):

        try:

            unicode(s, 'us-ascii')

        except UnicodeError:

            return True

    return False

class Generator:

    """Generates output from a Message object tree.

    This basic generator writes the message to the given file object as plain

    text.

    """

    #

    # Public interface

    #

    def __init__(self, outfp, mangle_from_=True, maxheaderlen=78):

        """Create the generator for message flattening.

        outfp is the output file-like object for writing the message to.  It

        must have a write() method.

        Optional mangle_from_ is a flag that, when True (the default), escapes

        From_ lines in the body of the message by putting a `>' in front of

        them.

        Optional maxheaderlen specifies the longest length for a non-continued

        header.  When a header line is longer (in characters, with tabs

        expanded to 8 spaces) than maxheaderlen, the header will split as

        defined in the Header class.  Set maxheaderlen to zero to disable

        header wrapping.  The default is 78, as recommended (but not required)

        by RFC 2822.

        """

        self._fp = outfp

        self._mangle_from_ = mangle_from_

        self._maxheaderlen = maxheaderlen

    def write(self, s):

        # Just delegate to the file object

        self._fp.write(s)

    def flatten(self, msg, unixfrom=False):

        """Print the message object tree rooted at msg to the output file

        specified when the Generator instance was created.

        unixfrom is a flag that forces the printing of a Unix From_ delimiter

        before the first object in the message tree.  If the original message

        has no From_ delimiter, a `standard' one is crafted.  By default, this

        is False to inhibit the printing of any From_ delimiter.

        Note that for subobjects, no From_ line is printed.

        """

        if unixfrom:

            ufrom = msg.get_unixfrom()

            if not ufrom:

                ufrom = 'From nobody ' + time.ctime(time.time())

            print >> self._fp, ufrom

        self._write(msg)

    def clone(self, fp):

        """Clone this generator with the exact same options."""

        return self.__class__(fp, self._mangle_from_, self._maxheaderlen)

    #

    # Protected interface - undocumented ;/

    #

    def _write(self, msg):

        # We can't write the headers yet because of the following scenario:

        # say a multipart message includes the boundary string somewhere in

        # its body.  We'd have to calculate the new boundary /before/ we write

        # the headers so that we can write the correct Content-Type:

        # parameter.

        #

        # The way we do this, so as to make the _handle_*() methods simpler,

        # is to cache any subpart writes into a StringIO.  The we write the

        # headers and the StringIO contents.  That way, subpart handlers can

        # Do The Right Thing, and can still modify the Content-Type: header if

        # necessary.

        oldfp = self._fp

        try:

            self._fp = sfp = StringIO()

            self._dispatch(msg)

        finally:

            self._fp = oldfp

        # Write the headers.  First we see if the message object wants to

        # handle that itself.  If not, we'll do it generically.

        meth = getattr(msg, '_write_headers', None)

        if meth is None:

            self._write_headers(msg)

        else:

            meth(self)

        self._fp.write(sfp.getvalue())

    def _dispatch(self, msg):

        # Get the Content-Type: for the message, then try to dispatch to

        # self._handle_<maintype>_<subtype>().  If there's no handler for the

        # full MIME type, then dispatch to self._handle_<maintype>().  If

        # that's missing too, then dispatch to self._writeBody().

        main = msg.get_content_maintype()

        sub = msg.get_content_subtype()

        specific = UNDERSCORE.join((main, sub)).replace('-', '_')

        meth = getattr(self, '_handle_' + specific, None)

        if meth is None:

            generic = main.replace('-', '_')

            meth = getattr(self, '_handle_' + generic, None)

            if meth is None:

                meth = self._writeBody

        meth(msg)

    #

    # Default handlers

    #

    def _write_headers(self, msg):

        for h, v in msg.items():

            print >> self._fp, '%s:' % h,

            if self._maxheaderlen == 0:

                # Explicit no-wrapping

                print >> self._fp, v

            elif isinstance(v, Header):

                # Header instances know what to do

                print >> self._fp, v.encode()

            elif _is8bitstring(v):

                # If we have raw 8bit data in a byte string, we have no idea

                # what the encoding is.  There is no safe way to split this

                # string.  If it's ascii-subset, then we could do a normal

                # ascii split, but if it's multibyte then we could break the

                # string.  There's no way to know so the least harm seems to

                # be to not split the string and risk it being too long.

                print >> self._fp, v

            else:

                # Header's got lots of smarts, so use it.

                print >> self._fp, Header(

                    v, maxlinelen=self._maxheaderlen,

                    header_name=h, continuation_ws='\t').encode()

        # A blank line always separates headers from body

        print >> self._fp

    #

    # Handlers for writing types and subtypes

    #

    def _handle_text(self, msg):

        payload = msg.get_payload()

        if payload is None:

            return

        if not isinstance(payload, basestring):

            raise TypeError('string payload expected: %s' % type(payload))

        if self._mangle_from_:

            payload = fcre.sub('>From ', payload)

        self._fp.write(payload)

    # Default body handler

    _writeBody = _handle_text

    def _handle_multipart(self, msg):

        # The trick here is to write out each part separately, merge them all

        # together, and then make sure that the boundary we've chosen isn't

        # present in the payload.

        msgtexts = []

        subparts = msg.get_payload()

        if subparts is None:

            subparts = []

        elif isinstance(subparts, basestring):

            # e.g. a non-strict parse of a message with no starting boundary.

            self._fp.write(subparts)

            return

        elif not isinstance(subparts, list):

            # Scalar payload

            subparts = [subparts]

        for part in subparts:

            s = StringIO()

            g = self.clone(s)

            g.flatten(part, unixfrom=False)

            msgtexts.append(s.getvalue())

        # Now make sure the boundary we've selected doesn't appear in any of

        # the message texts.

        alltext = NL.join(msgtexts)

        # BAW: What about boundaries that are wrapped in double-quotes?

        boundary = msg.get_boundary(failobj=_make_boundary(alltext))

        # If we had to calculate a new boundary because the body text

        # contained that string, set the new boundary.  We don't do it

        # unconditionally because, while set_boundary() preserves order, it

        # doesn't preserve newlines/continuations in headers.  This is no big

        # deal in practice, but turns out to be inconvenient for the unittest

        # suite.

        if msg.get_boundary() <> boundary:

            msg.set_boundary(boundary)

        # If there's a preamble, write it out, with a trailing CRLF

        if msg.preamble is not None:

            print >> self._fp, msg.preamble

        # dash-boundary transport-padding CRLF

        print >> self._fp, '--' + boundary

        # body-part

        if msgtexts:

            self._fp.write(msgtexts.pop(0))

        # *encapsulation

        # --> delimiter transport-padding

        # --> CRLF body-part

        for body_part in msgtexts:

            # delimiter transport-padding CRLF

            print >> self._fp, '\n--' + boundary

            # body-part

            self._fp.write(body_part)

        # close-delimiter transport-padding

        self._fp.write('\n--' + boundary + '--')

        if msg.epilogue is not None:

            print >> self._fp

            self._fp.write(msg.epilogue)

    def _handle_message_delivery_status(self, msg):

        # We can't just write the headers directly to self's file object

        # because this will leave an extra newline between the last header

        # block and the boundary.  Sigh.

        blocks = []

        for part in msg.get_payload():

            s = StringIO()

            g = self.clone(s)

            g.flatten(part, unixfrom=False)

            text = s.getvalue()

            lines = text.split('\n')

            # Strip off the unnecessary trailing empty line

            if lines and lines[-1] == '':

                blocks.append(NL.join(lines[:-1]))

            else:

                blocks.append(text)

        # Now join all the blocks with an empty line.  This has the lovely

        # effect of separating each block with an empty line, but not adding

        # an extra one after the last one.

        self._fp.write(NL.join(blocks))

    def _handle_message(self, msg):

        s = StringIO()

        g = self.clone(s)

        # The payload of a message/rfc822 part should be a multipart sequence

        # of length 1.  The zeroth element of the list should be the Message

        # object for the subpart.  Extract that object, stringify it, and

        # write it out.

        g.flatten(msg.get_payload(0), unixfrom=False)

        self._fp.write(s.getvalue())

_FMT = '[Non-text (%(type)s) part of message omitted, filename %(filename)s]'

class DecodedGenerator(Generator):

    """Generator a text representation of a message.

    Like the Generator base class, except that non-text parts are substituted

    with a format string representing the part.

    """

    def __init__(self, outfp, mangle_from_=True, maxheaderlen=78, fmt=None):

        """Like Generator.__init__() except that an additional optional

        argument is allowed.

        Walks through all subparts of a message.  If the subpart is of main

        type `text', then it prints the decoded payload of the subpart.

        Otherwise, fmt is a format string that is used instead of the message

        payload.  fmt is expanded with the following keywords (in

        %(keyword)s format):

        type       : Full MIME type of the non-text part

        maintype   : Main MIME type of the non-text part

        subtype    : Sub-MIME type of the non-text part

        filename   : Filename of the non-text part

        description: Description associated with the non-text part

        encoding   : Content transfer encoding of the non-text part

        The default value for fmt is None, meaning

        [Non-text (%(type)s) part of message omitted, filename %(filename)s]

        """

        Generator.__init__(self, outfp, mangle_from_, maxheaderlen)

        if fmt is None:

            self._fmt = _FMT

        else:

            self._fmt = fmt

    def _dispatch(self, msg):

        for part in msg.walk():

            maintype = part.get_content_maintype()

            if maintype == 'text':

                print >> self, part.get_payload(decode=True)

            elif maintype == 'multipart':

                # Just skip this

                pass

            else:

                print >> self, self._fmt % {

                    'type'       : part.get_content_type(),

                    'maintype'   : part.get_content_maintype(),

                    'subtype'    : part.get_content_subtype(),

                    'filename'   : part.get_filename('[no filename]'),

                    'description': part.get('Content-Description',

                                            '[no description]'),

                    'encoding'   : part.get('Content-Transfer-Encoding',

                                            '[no encoding]'),

                    }

# Helper

_width = len(repr(sys.maxint-1))

_fmt = '%%0%dd' % _width

def _make_boundary(text=None):

    # Craft a random boundary.  If text is given, ensure that the chosen

    # boundary doesn't appear in the text.

    token = random.randrange(sys.maxint)

    boundary = ('=' * 15) + (_fmt % token) + '=='

    if text is None:

        return boundary

    b = boundary

    counter = 0

    while True:

        cre = re.compile('^--' + re.escape(b) + '(--)?$', re.MULTILINE)

        if not cre.search(text):

            break

        b = boundary + '.' + str(counter)

        counter += 1

    return b