import re

import xml.parsers.expat as expat

import streams

class ConsecXmlInputStream(streams.TracedStream):

    '''Wraps an input stream, inserting EOF after each consecutive XML document

    '''

    def __init__(self, stream):

        self.eof = False

        self.root_close_tag = None

        def trace(line):

            if self.root_close_tag == None: # before XML document

                match = re.match(r'^<(?!\?)([^\s>]+)', line)

                if match: self.root_close_tag = '</'+match.group(1)+'>'

            else: # inside XML document

                if line.rstrip().endswith(self.root_close_tag):

                    self.root_close_tag = None # now outside XML document

                    self.eof = True # next read will produce EOF

        streams.TracedStream.__init__(self, trace, stream)

    def readline(self):

        if self.eof:

            self.eof = False

            return '' # don't read from underlying stream

        else: return streams.TracedStream.readline(self)

    def read(self, n): return self.readline() # forward all reads to readline()

def parse_next(stream):

    '''Parses the next document in a consecutive sequence of XML documents.

    @return The next document's root, or None if no more documents available

    '''

    try: return minidom.parse(ConsecXmlInputStream(stream)).documentElement

    except expat.ExpatError, e:

        if str(e).startswith('no element found:'): return None # no more docs

        else: raise e

def docs_iter(stream): return iter(lambda: parse_next(stream), None)