"""Generic MIME writer.

This module defines the class MimeWriter.  The MimeWriter class implements

a basic formatter for creating MIME multi-part files.  It doesn't seek around

the output file nor does it use large amounts of buffer space. You must write

the parts out in the order that they should occur in the final file.

MimeWriter does buffer the headers you add, allowing you to rearrange their

order.

"""

import mimetools

__all__ = ["MimeWriter"]

class MimeWriter:

    """Generic MIME writer.

    Methods:

    __init__()

    addheader()

    flushheaders()

    startbody()

    startmultipartbody()

    nextpart()

    lastpart()

    A MIME writer is much more primitive than a MIME parser.  It

    doesn't seek around on the output file, and it doesn't use large

    amounts of buffer space, so you have to write the parts in the

    order they should occur on the output file.  It does buffer the

    headers you add, allowing you to rearrange their order.

    General usage is:

    f = <open the output file>

    w = MimeWriter(f)

    ...call w.addheader(key, value) 0 or more times...

    followed by either:

    f = w.startbody(content_type)

    ...call f.write(data) for body data...

    or:

    w.startmultipartbody(subtype)

    for each part:

        subwriter = w.nextpart()

        ...use the subwriter's methods to create the subpart...

    w.lastpart()

    The subwriter is another MimeWriter instance, and should be

    treated in the same way as the toplevel MimeWriter.  This way,

    writing recursive body parts is easy.

    Warning: don't forget to call lastpart()!

    XXX There should be more state so calls made in the wrong order

    are detected.

    Some special cases:

    - startbody() just returns the file passed to the constructor;

      but don't use this knowledge, as it may be changed.

    - startmultipartbody() actually returns a file as well;

      this can be used to write the initial 'if you can read this your

      mailer is not MIME-aware' message.

    - If you call flushheaders(), the headers accumulated so far are

      written out (and forgotten); this is useful if you don't need a

      body part at all, e.g. for a subpart of type message/rfc822

      that's (mis)used to store some header-like information.

    - Passing a keyword argument 'prefix=<flag>' to addheader(),

      start*body() affects where the header is inserted; 0 means

      append at the end, 1 means insert at the start; default is

      append for addheader(), but insert for start*body(), which use

      it to determine where the Content-Type header goes.

    """

    def __init__(self, fp):

        self._fp = fp

        self._headers = []

    def addheader(self, key, value, prefix=0):

        """Add a header line to the MIME message.

        The key is the name of the header, where the value obviously provides

        the value of the header. The optional argument prefix determines

        where the header is inserted; 0 means append at the end, 1 means

        insert at the start. The default is to append.

        """

        lines = value.split("\n")

        while lines and not lines[-1]: del lines[-1]

        while lines and not lines[0]: del lines[0]

        for i in range(1, len(lines)):

            lines[i] = "    " + lines[i].strip()

        value = "\n".join(lines) + "\n"

        line = key + ": " + value

        if prefix:

            self._headers.insert(0, line)

        else:

            self._headers.append(line)

    def flushheaders(self):

        """Writes out and forgets all headers accumulated so far.

        This is useful if you don't need a body part at all; for example,

        for a subpart of type message/rfc822 that's (mis)used to store some

        header-like information.

        """

        self._fp.writelines(self._headers)

        self._headers = []

    def startbody(self, ctype, plist=[], prefix=1):

        """Returns a file-like object for writing the body of the message.

        The content-type is set to the provided ctype, and the optional

        parameter, plist, provides additional parameters for the

        content-type declaration.  The optional argument prefix determines

        where the header is inserted; 0 means append at the end, 1 means

        insert at the start. The default is to insert at the start.

        """

        for name, value in plist:

            ctype = ctype + ';\n %s=\"%s\"' % (name, value)

        self.addheader("Content-Type", ctype, prefix=prefix)

        self.flushheaders()

        self._fp.write("\n")

        return self._fp

    def startmultipartbody(self, subtype, boundary=None, plist=[], prefix=1):

        """Returns a file-like object for writing the body of the message.

        Additionally, this method initializes the multi-part code, where the

        subtype parameter provides the multipart subtype, the boundary

        parameter may provide a user-defined boundary specification, and the

        plist parameter provides optional parameters for the subtype.  The

        optional argument, prefix, determines where the header is inserted;

        0 means append at the end, 1 means insert at the start. The default

        is to insert at the start.  Subparts should be created using the

        nextpart() method.

        """

        self._boundary = boundary or mimetools.choose_boundary()

        return self.startbody("multipart/" + subtype,

                              [("boundary", self._boundary)] + plist,

                              prefix=prefix)

    def nextpart(self):

        """Returns a new instance of MimeWriter which represents an

        individual part in a multipart message.

        This may be used to write the part as well as used for creating

        recursively complex multipart messages. The message must first be

        initialized with the startmultipartbody() method before using the

        nextpart() method.

        """

        self._fp.write("\n--" + self._boundary + "\n")

        return self.__class__(self._fp)

    def lastpart(self):

        """This is used to designate the last part of a multipart message.

        It should always be used when writing multipart messages.

        """

        self._fp.write("\n--" + self._boundary + "--\n")

if __name__ == '__main__':

    import test.test_MimeWriter