"""A readline()-style interface to the parts of a multipart message.

The MultiFile class makes each part of a multipart message "feel" like

an ordinary file, as long as you use fp.readline().  Allows recursive

use, for nested multipart messages.  Probably best used together

with module mimetools.

Suggested use:

real_fp = open(...)

fp = MultiFile(real_fp)

"read some lines from fp"

fp.push(separator)

while 1:

        "read lines from fp until it returns an empty string" (A)

        if not fp.next(): break

fp.pop()

"read remaining lines from fp until it returns an empty string"

The latter sequence may be used recursively at (A).

It is also allowed to use multiple push()...pop() sequences.

If seekable is given as 0, the class code will not do the bookkeeping

it normally attempts in order to make seeks relative to the beginning of the

current file part.  This may be useful when using MultiFile with a non-

seekable stream object.

"""

__all__ = ["MultiFile","Error"]

class Error(Exception):

    pass

class MultiFile:

    seekable = 0

    def __init__(self, fp, seekable=1):

        self.fp = fp

        self.stack = []

        self.level = 0

        self.last = 0

        if seekable:

            self.seekable = 1

            self.start = self.fp.tell()

            self.posstack = []

    def tell(self):

        if self.level > 0:

            return self.lastpos

        return self.fp.tell() - self.start

    def seek(self, pos, whence=0):

        here = self.tell()

        if whence:

            if whence == 1:

                pos = pos + here

            elif whence == 2:

                if self.level > 0:

                    pos = pos + self.lastpos

                else:

                    raise Error, "can't use whence=2 yet"

        if not 0 <= pos <= here or \

                        self.level > 0 and pos > self.lastpos:

            raise Error, 'bad MultiFile.seek() call'

        self.fp.seek(pos + self.start)

        self.level = 0

        self.last = 0

    def readline(self):

        if self.level > 0:

            return ''

        line = self.fp.readline()

        # Real EOF?

        if not line:

            self.level = len(self.stack)

            self.last = (self.level > 0)

            if self.last:

                raise Error, 'sudden EOF in MultiFile.readline()'

            return ''

        assert self.level == 0

        # Fast check to see if this is just data

        if self.is_data(line):

            return line

        else:

            # Ignore trailing whitespace on marker lines

            marker = line.rstrip()

        # No?  OK, try to match a boundary.

        # Return the line (unstripped) if we don't.

        for i, sep in enumerate(reversed(self.stack)):

            if marker == self.section_divider(sep):

                self.last = 0

                break

            elif marker == self.end_marker(sep):

                self.last = 1

                break

        else:

            return line

        # We only get here if we see a section divider or EOM line

        if self.seekable:

            self.lastpos = self.tell() - len(line)

        self.level = i+1

        if self.level > 1:

            raise Error,'Missing endmarker in MultiFile.readline()'

        return ''

    def readlines(self):

        list = []

        while 1:

            line = self.readline()

            if not line: break

            list.append(line)

        return list

    def read(self): # Note: no size argument -- read until EOF only!

        return ''.join(self.readlines())

    def next(self):

        while self.readline(): pass

        if self.level > 1 or self.last:

            return 0

        self.level = 0

        self.last = 0

        if self.seekable:

            self.start = self.fp.tell()

        return 1

    def push(self, sep):

        if self.level > 0:

            raise Error, 'bad MultiFile.push() call'

        self.stack.append(sep)

        if self.seekable:

            self.posstack.append(self.start)

            self.start = self.fp.tell()

    def pop(self):

        if self.stack == []:

            raise Error, 'bad MultiFile.pop() call'

        if self.level <= 1:

            self.last = 0

        else:

            abslastpos = self.lastpos + self.start

        self.level = max(0, self.level - 1)

        self.stack.pop()

        if self.seekable:

            self.start = self.posstack.pop()

            if self.level > 0:

                self.lastpos = abslastpos - self.start

    def is_data(self, line):

        return line[:2] != '--'

    def section_divider(self, str):

        return "--" + str

    def end_marker(self, str):

        return "--" + str + "--"