# Source code for ly.document

    # This file is part of python-ly, https://pypi.python.org/pypi/python-ly
    #
    # Copyright (c) 2013 - 2015 by Wilbert Berendsen
    #
    # This program is free software; you can redistribute it and/or
    # modify it under the terms of the GNU General Public License
    # as published by the Free Software Foundation; either version 2
    # of the License, or (at your option) any later version.
    #
    # This program is distributed in the hope that it will be useful,
    # but WITHOUT ANY WARRANTY; without even the implied warranty of
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    # GNU General Public License for more details.
    #
    # You should have received a copy of the GNU General Public License
    # along with this program; if not, write to the Free Software
    # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
    # See http://www.gnu.org/licenses/ for more information.

    """
    DocumentBase and Document
    =========================

    Represents a LilyPond source document (the text contents).

    The Document implementation keeps the document in a (unicode) text string,
    but you can inherit from the DocumentBase class to support other
    representations of the text content.

    Modifying is preferably done inside a context (the with statement), e.g.:

    .. code-block:: python

        d = Document('some string')
        with d:
            d[5:5] = 'different '
        d.plaintext()  --> 'some different string'

    Changes are applied when the context is exited, also the modified part of the
    document is re-tokenized. Changes may not overlap.

    You may modify the document outside a context, in which case the document is
    re-tokenized immediately. This is much slower however when performing multiple
    changes after each other.

    The tokens(block) method returns a tuple of tokens for the specified block.
    Depending on the implementation, a block describes a line in the LilyPond
    source document. It is not expected to have any methods, except that the
    '==' operator is supported between two blocks, and returns True if both
    refer to the same line of text in the source document.

    Cursor
    ======

    Defines a range or position in a Document.

    Runner
    ======

    A Runner allows iterating back and forth over the tokens of a document.

    Source
    ======

    Iterate over tokens in a (part of a) Document, with or without state.

    """

    from __future__ import unicode_literals
    from __future__ import absolute_import

    import io
    import sys
    import operator
    import collections
    import weakref

    import ly.lex

    class DocumentBase(object):
        """Abstract base class for Document instances.

        You should inherit the following methods:

        setplaintext
        __len__
        __getitem__
        block
        index
        position
        text
        tokens
        isvalid
        initial_state
        state_end
        apply_changes

        You may inherit (e.g. to get speed improvements):

        plaintext
        next_block
        previous_block
        blocks_forward
        blocks_backward
        state

        You may use the following attributes:

        filename (None)   # can represent the filename of the document on disk
        encoding (None)   # can represent the encoding of the document when reading/writing to disk

        """

        filename = None
        encoding = None

        def __init__(self):
            """Constructor"""
            self._writing = 0
            self._changes = collections.defaultdict(list)
            self._cursors = weakref.WeakSet()

        def __bool__(self):
            return True

        __nonzero__ = __bool__      # py2 compat

        def __iter__(self):
            """Iter over all blocks."""
            return self.blocks_forward(self[0])

        def __len__(self):
            """Return the number of blocks"""
            raise NotImplementedError()

        def __getitem__(self, index):
            """Return the block at the specified index."""
            raise NotImplementedError()

        def plaintext(self):
            """The document contents as a plain text string."""
            return '\n'.join(map(self.text, self))

        def setplaintext(self, text):
            """Sets the document contents to the text string."""
            raise NotImplementedError()

        def size(self):
            """Return the number of characters in the document."""
            last_block = self[len(self) - 1]
            return self.position(last_block) + len(self.text(last_block))

        def block(self, position):
            """Return the text block at the specified character position.

            The text block itself has no methods, but it can be used as an
            argument to other methods of this class.

            (Blocks do have to support the '==' operator.)

            """
            raise NotImplementedError()

        def index(self, block):
            """Return the linenumber of the block (starting with 0)."""
            raise NotImplementedError()

        def blocks_forward(self, block):
            """Iter forward starting with the specified block."""
            while self.isvalid(block):
                yield block
                block = self.next_block(block)

        def blocks_backward(self, block):
            """Iter backwards starting with the specified block."""
            while self.isvalid(block):
                yield block
                block = self.previous_block(block)

        def position(self, block):
            """Return the position of the specified block."""
            raise NotImplementedError()

        def text(self, block):
            """Return the text of the specified block."""
            raise NotImplementedError()

        def next_block(self, block):
            """Return the next block, which may be invalid."""
            index = self.index(block)
            if index < len(self) - 1:
                return self[index + 1]

        def previous_block(self, block):
            """Return the previous block, which may be invalid."""
            index = self.index(block)
            if index > 0:
                return self[index - 1]

        def isvalid(self, block):
            """Return True if the block is a valid block."""
            raise NotImplementedError()

        def isblank(self, block):
            """Return True if the block is empty or blank."""
            t = self.text(block)
            return not t or t.isspace()

        def __enter__(self):
            """Start the context for modifying the document."""
            self._writing += 1
            return self

        def __exit__(self, exc_type, exc_val, exc_tb):
            """Exit the context for modifying."""
            if exc_type is not None:
                # cancel all edits when an exception occurred
                self._writing = 0
                self._changes.clear()
            elif self._writing == 1:
                if self._changes:
                    self._sort_changes()
                    self.update_cursors()
                    self.apply_changes()
                    del self._changes_list
                self._writing = 0
            elif self._writing > 1:
                self._writing -= 1

        def _register_cursor(self, cursor):
            """Make a weak reference to the cursor.

            This is called by the constructor of the Cursor.
            The Cursor gets updated when the document is changed.

            """
            self._cursors.add(cursor)

        def check_changes(self):
            """Debugging method that checks for overlapping edits."""
            pos = self.size()
            for start, end, text in self._changes_list:
                if end > pos:
                    if len(text) > 12:
                        text = text[:10] + '...'
                    raise ValueError("overlapping edit: {0}-{1}: {2}".format(start, end, text))
                pos = start

        def _sort_changes(self):
            """Sort all the changes and put them in the _changes_list."""
            self._changes_list = [(start, end, text)
                for start, items in sorted(self._changes.items(), reverse=True)
                for end, text in reversed(sorted(items,
                    key=lambda i: (i[0] is None, i[0])))]
            self._changes.clear()

        def update_cursors(self):
            """Updates the position of the registered Cursor instances."""
            for start, end, text in self._changes_list:
                for c in self._cursors:
                    if c.start > start:
                        if end is None or end >= c.start:
                            c.start = start
                        else:
                            c.start += start + len(text) - end
                    if c.end is not None and c.end >= start:
                        if end is None or end >= c.end:
                            c.end = start + len(text)
                        else:
                            c.end += start + len(text) - end

        def apply_changes(self):
            """Apply the changes and update the tokens."""
            raise NotImplementedError()

        def tokens(self, block):
            """Return the tuple of tokens of the specified block.

            The pos and end attributes of every token point to the position
            of the token in the block.

            """
            raise NotImplementedError()

        def tokens_with_position(self, block):
            """Return a tuple of tokens of the specified block.

            The pos and end attributes of every token point to the position
            in the Document, instead of to the position in the current block.

            This makes it easier to iterate over tokens and change the document.

            """
            pos = self.position(block)
            return tuple(type(t)(t, pos + t.pos) for t in self.tokens(block))

        def initial_state(self):
            """Return the state at the beginning of the document."""
            raise NotImplementedError()

        def state(self, block):
            """Return the state at the start of the specified block."""
            prev = self.previous_block(block)
            if self.isvalid(prev):
                return self.state_end(prev)
            return self.initial_state()

        def state_end(self, block):
            """Return the state at the end of the specified block."""
            raise NotImplementedError()

        def __setitem__(self, key, text):
            """Change the text pointed to in key (integer or slice).

            If start > stop in the slice (and stop is not None), start and stop
            are swapped. (This is different than usual Python behaviour, where
            stop is set to start if it was lower.)

            """
            if isinstance(key, slice):
                start = key.start or 0
                end = key.stop
                if end is not None and start > end:
                    start, end = end, start
            else:
                start = key
                end = start + 1
            text = text.replace('\r', '')
            if text or start != end:
                self._changes[start].append((end, text))
                # when a change is made outside context manager, apply immediately
                if self._writing == 0:
                    self._sort_changes()
                    self.update_cursors()
                    self.apply_changes()
                    del self._changes_list

        def __delitem__(self, key):
            """Remove the range of text."""
            self[key] = ""

    class Document(DocumentBase):
        """A plain text LilyPond source document that auto-updates the tokens.

        The modified attribute is set to True as soon as the document is changed,
        but the setplaintext() method sets it to False.

        """
        modified = False

        def __init__(self, text='', mode=None):
            super(Document, self).__init__()
            self._fridge = ly.lex.Fridge()
            self._mode = mode
            self._guessed_mode = None
            self.setplaintext(text)

        @classmethod
        def load(cls, filename, encoding='utf-8', mode=None):
            """Load the document from a file, using the specified encoding and mode."""
            with io.open(filename, encoding=encoding) as f:
                doc = cls(f.read(), mode)
            doc.filename = filename
            return doc

        def copy(self):
            """Return a full copy of the document."""
            doc = Document(self.plaintext(), self.mode())
            doc.filename = self.filename
            doc.encoding = self.encoding
            doc.modified = self.modified
            return doc

        def __len__(self):
            """Return the number of blocks"""
            return len(self._blocks)

        def __getitem__(self, index):
            """Return the block at the specified index."""
            return self._blocks[index]

        def setmode(self, mode):
            """Sets the mode to one of the ly.lex modes.

            Use None to auto-determine the mode.

            """
            if mode not in ly.lex.modes:
                mode = None
            if mode == self._mode:
                return
            self._mode, old_mode = mode, self._mode
            if not mode:
                self._guessed_mode = ly.lex.guessMode(self.plaintext())
                if self._guessed_mode == old_mode:
                    return
            elif not old_mode:
                if mode == self._guessed_mode:
                    return
            self._update_all_tokens()

        def mode(self):
            """Return the mode (lilypond, html, etc). None means automatic mode."""
            return self._mode

        def setplaintext(self, text):
            """Set the text of the document, sets modified to False."""
            text = text.replace('\r', '')
            lines = text.split('\n')
            self._blocks = [_Block(t, n) for n, t in enumerate(lines)]
            pos = 0
            for b in self._blocks:
                b.position = pos
                pos += len(b.text) + 1
            if not self._mode:
                self._guessed_mode = ly.lex.guessMode(text)
            self._update_all_tokens()
            self.modified = False

        def _update_all_tokens(self):
            state = self.initial_state()
            for b in self._blocks:
                b.tokens = tuple(state.tokens(b.text))
                b.state = self._fridge.freeze(state)

        def initial_state(self):
            """Return the state at the beginning of the document."""
            return ly.lex.state(self._mode or self._guessed_mode)

        def state_end(self, block):
            """Return the state at the end of the specified block."""
            return self._fridge.thaw(block.state)

        def block(self, position):
            """Return the text block at the specified character position."""
            if 0 <= position <= self._blocks[-1].position + len(self._blocks[-1].text):
                lo = 0
                hi = len(self._blocks)
                while lo < hi:
                    mid = (lo + hi) // 2
                    if position < self._blocks[mid].position:
                        hi = mid
                    else:
                        lo = mid + 1
                return self._blocks[lo-1]

        def index(self, block):
            """Return the linenumber of the block (starting with 0)."""
            return block.index

        def position(self, block):
            """Return the position of the specified block."""
            return block.position

        def text(self, block):
            """Return the text of the specified block."""
            return block.text

        def isvalid(self, block):
            """Return True if the block is a valid block."""
            return bool(block)

        def tokens(self, block):
            """Return the tuple of tokens of the specified block."""
            return block.tokens

        def apply_changes(self):
            for start, end, text in self._changes_list:
                s = self.block(start)
                # first remove the old contents
                if end is None:
                    # all text to the end should be removed
                    s.text = s.text[:start - s.position]
                    del self._blocks[s.index+1:]
                else:
                    # remove until the end position
                    e = self.block(end)
                    s.text = s.text[:start - s.position] + e.text[end - e.position:]
                    del self._blocks[s.index+1:e.index+1]
                # now insert the new stuff
                if text:
                    lines = text.split('\n')
                    lines[-1] += s.text[start - s.position:]
                    s.text = s.text[:start - s.position] + lines[0]
                    self._blocks[s.index+1:s.index+1] = map(_Block, lines[1:])
                # make sure this line gets reparsed
                s.tokens = None

            # update the position of all the new blocks
            pos = s.position
            for i, b in enumerate(self._blocks[s.index:], s.index):
                b.index = i
                b.position = pos
                pos += len(b.text) + 1

            self.modified = True

            # if the initial state has changed, reparse everything
            if not self._mode:
                mode = ly.lex.guessMode(self.plaintext())
                if mode != self._guessed_mode:
                    self._guessed_mode = mode
                    self._update_all_tokens()
                    return

            # update the tokens starting at block s
            state = self.state(s)
            reparse = False
            for block in self._blocks[s.index:]:
                if reparse or block.tokens is None:
                    block.tokens = tuple(state.tokens(block.text))
                    frozen = self._fridge.freeze(state)
                    reparse = block.state != frozen
                    block.state = frozen
                else:
                    state = self._fridge.thaw(block.state)

    class _Block(object):
        """A line of text.

        This class is only used by the Document implementation.

        """

        position = sys.maxsize  # prevent picking those blocks before updating pos
        state    = None
        tokens   = None

        def __init__(self, text="", index=-1):
            self.text = text
            self.index = index

    class Cursor(object):
        """Defines a certain range (selection) in a Document.

        You may change the start and end attributes yourself. Both must be an
        integer, end may also be None, denoting the end of the document.

        As long as you keep a reference to the Cursor, its positions are updated
        when the document changes. When text is inserted at the start position,
        it remains the same. But when text is inserted at the end of a cursor,
        the end position moves along with the new text. E.g.:

        .. code-block:: python

            d = Document('hi there, folks!')
            c = Cursor(d, 8, 8)
            with d:
                d[8:8] = 'new text'
            c.start, c.end --> (8, 16)

        Many tools in the ly module use this object to describe (part of) a
        document.

        """
        def __init__(self, doc, start=0, end=None):
            self._d = doc
            self.start = start
            self.end = end
            doc._register_cursor(self)

        @property
        def document(self):
            return self._d

        def start_block(self):
            """Return the block the start attribute points at."""
            return self._d.block(self.start)

        def end_block(self):
            """Return the block the end attribute points at."""
            if self.end is None:
                return self._d[len(self._d)-1]
            return self._d.block(self.end)

        def blocks(self):
            """Iterate over the selected blocks.

            If there are multiple blocks and the cursor ends on the first
            position of the last selected block, that block is not included.

            """
            if self.end == self.start:
                yield self.start_block()
            else:
                for b in self._d.blocks_forward(self.start_block()):
                    if self.end is not None and self._d.position(b) >= self.end:
                        break
                    yield b

        def text(self):
            """Convenience method to return the selected text."""
            return self._d.plaintext()[self.start:self.end]

        def text_before(self):
            """Return text before the cursor in it's start block."""
            b = self.start_block()
            pos = self.start - self._d.position(b)
            return self._d.text(b)[:pos]

        def text_after(self):
            """Return text after the cursor in it's end block."""
            if self.end is None:
                return ""
            b = self.end_block()
            pos = self.end - self._d.position(b)
            return self._d.text(b)[pos:]

        def has_selection(self):
            """Return True when there is some text selected."""
            end = self.end
            if end is None:
                end = self._d.size()
            return self.start != end

        def select_all(self):
            """Select all text."""
            self.start, self.end = 0, None

        def select_end_of_block(self):
            """Move end to the end of the block."""
            if self.end is not None:
                end = self.end_block()
                self.end = self._d.position(end) + len(self._d.text(end))

        def select_start_of_block(self):
            """Move start to the start of the block."""
            start = self.start_block()
            self.start = self._d.position(start)

        def lstrip(self, chars=None):
            """Move start to the right, like Python's lstrip() string method."""
            if self.has_selection():
                text = self.text()
                self.start += len(text) - len(text.lstrip(chars))

        def rstrip(self, chars=None):
            """Move end to the left, like Python's lstrip() string method."""
            if self.has_selection():
                text = self.text()
                end = self._d.size() if self.end is None else self.end
                end -= len(text) - len(text.rstrip(chars))
                if end < self._d.size():
                    self.end = end

        def strip(self, chars=None):
            """Strip chars from the selection, like Python's strip() method."""
            self.rstrip(chars)
            self.lstrip(chars)

    class Runner(object):
        """Iterates back and forth over tokens.

        A Runner can stop anywhere and remembers its current token.

        """
        def __init__(self, doc, tokens_with_position=False):
            """Create and init with Document.

            If tokens_with_position is True, uses the tokens_with_position()
            method to get the tokens, else (by default), the tokens() method is
            used.

            The Runner is initialized at position 0. Alternatively, you can use
            the 'at' classmethod to construct a Runner at a specific cursor
            position.

            """
            self._doc = doc
            self._wp = tokens_with_position
            self.move_to_block(doc[0])

        @classmethod
        def at(cls, cursor, after_token=False, tokens_with_position=False):
            """Create and init from a Cursor.

            The Runner is positioned so that yielding forward starts with the
            first complete token after the cursor's start position.

            Set after_token to True if you want to position the cursor after the
            token, so that it gets yielded when you go backward.

            If tokens_with_position is True, uses the tokens_with_position()
            method to get the tokens, else (by default), the tokens() method is
            used.

            """
            runner = cls(cursor.document, tokens_with_position)
            runner.set_position(cursor.start, after_token)
            return runner

        @property
        def document(self):
            """Return our Document."""
            return self._doc

        def set_position(self, position, after_token=False):
            """Positions the Runner at the specified position.

            Set after_token to True if you want to position the cursor after the
            token, so that it gets yielded when you go backward.

            """
            block = self._doc.block(position)
            self.move_to_block(block)
            if after_token:
                for t in self.forward_line():
                    if self.position() + len(t) >= position:
                        self._index += 1
                        break
            else:
                for t in self.forward_line():
                    if self.position() + len(t) > position:
                        self._index -= 1
                        break

        def move_to_block(self, block, at_end=False):
            """Positions the Runner at the start of the given text block.

            If at_end == True, the iterator is positioned past the end of the block.

            """
            if self._doc.isvalid(block):
                self.block = block
                method = self._doc.tokens_with_position if self._wp else self._doc.tokens
                self._tokens = method(block)
                self._index = len(self._tokens) if at_end else -1
                return True

        def _newline(self):
            """(Internal) Create a Newline token at the end of the current block."""
            pos = len(self._doc.text(self.block))
            if self._wp:
                pos += self._doc.position(self.block)
            return ly.lex.Newline('\n', pos)

        def next(self, current_block=False):
            """Return the next token or False if there is no more token.
            If current_block=True stop at the end of the current block."""
            if self._index < len(self._tokens) - 1:
                self._index += 1
                return self._tokens[self._index]
            elif current_block or not self.next_block():
                return False
            else:
                return self._newline()

        def previous(self, current_block=False):
            """Return the previous token or False if there is no more token.
            If current_block=True stop at the beginning of the current block."""
            if self._index > 0:
                self._index -= 1
                return self._tokens[self._index]
            elif current_block or not self.previous_block():
                return False
            else: return self._newline()

        def _forward(self, current_block):
            """Internal method to yield tokens in forward direction.
            current_block determines whether this is globally or limited
            to the current block."""
            while True:
                token = self.next(current_block)
                if not token:
                    break
                yield token

        def forward_line(self):
            """Yields tokens in forward direction in the current block."""
            for token in self._forward(current_block=True):
                yield token

        def forward(self):
            """Yields tokens in forward direction across blocks."""
            for token in self._forward(current_block=False):
                yield token

        def _backward(self, current_block):
            """Internal method to yield tokens in backward direction.
            current_block determines whether this is globally or limited
            to the current block."""
            while True:
                token = self.previous(current_block)
                if not token:
                    break
                yield token

        def backward_line(self):
            """Yields tokens in backward direction in the current block."""
            for token in self._backward(current_block=True):
                yield token

        def backward(self):
            """Yields tokens in backward direction across blocks."""
            for token in self._backward(current_block=False):
                yield token

        def previous_block(self, at_end=True):
            """Go to the previous block, positioning the cursor at the end by default.

            Returns False if there was no previous block, else True.

            """
            return self.move_to_block(self._doc.previous_block(self.block), at_end)

        def next_block(self, at_end=False):
            """Go to the next block, positioning the cursor at the start by default.

            Returns False if there was no next block, else True.

            """
            return self.move_to_block(self._doc.next_block(self.block), at_end)

        def token(self):
            """Re-returns the last yielded token."""
            if self._tokens:
                index = self._index
                if index < 0:
                    index = 0
                elif index >= len(self._tokens):
                    index = len(self._tokens) - 1
                return self._tokens[index]

        def position(self):
            """Returns the position of the current token."""
            if self._tokens:
                pos = self.token().pos
                if not self._wp:
                    pos += self._doc.position(self.block)
                return pos
            else:
                return self._d.position(self.block)

        def copy(self):
            """Return a new Runner at the current position."""
            obj = type(self)(self._doc, self._wp)
            obj.block = self.block
            obj._tokens = self._tokens
            obj._index = self._index
            return obj

    OUTSIDE = -1
    PARTIAL = 0
    INSIDE  = 1

    class Source(object):
        """Helper iterator.

        Iterates over the (block, tokens) tuples from a Document (or a part
        thereof). Stores the current block in the block attribute and the tokens
        (which also is a generator) in the tokens attribute.

        Iterating over the source object itself just yields the tokens, while the
        block attribute contains the current block.

        You can also iterate over the tokens attribute, which will yield the
        remaining tokens of the current block and then stop.

        If you specify a state, the tokens will update the state. If you specify
        state = True, the state will be taken from the document.

        """

        def __init__(self, cursor, state=None, partial=INSIDE, tokens_with_position=False):
            """Initialize the iterator.

            cursor is a Cursor instance, describing a Document and a selected range
            state is, if given, a ly.lex.State instance or True (in which case the
                state is taken from the document).

            The following keyword arguments can be used:

            partial is either OUTSIDE, PARTIAL, or INSIDE:
                OUTSIDE: tokens that touch the selected range are also yielded
                PARTIAL: tokens that overlap the start or end positions are yielded
                INSIDE:  (default) yield only tokens fully contained in the range
            The partial argument only makes sense if start or end are specified.

            If tokens_with_position is True, uses the
            document.tokens_with_position() method to get the tokens from the
            cursor's document, else (by default), the document.tokens() method is
            used.

            """
            self._pushback = False
            self._last = None
            self._doc = document = cursor.document
            start_block = document.block(cursor.start)
            self._wp = tokens_with_position
            tokens_method = document.tokens_with_position if tokens_with_position else document.tokens

            # start, end predicates
            start_pred, end_pred = {
                OUTSIDE: (
                    lambda t: t.end < start_pos,
                    lambda t: t.pos > end_pos,
                ),
                PARTIAL: (
                    lambda t: t.end <= start_pos,
                    lambda t: t.pos >= end_pos,
                ),
                INSIDE: (
                    lambda t: t.pos < start_pos,
                    lambda t: t.end > end_pos,
                ),
            }[partial]

            # if a state is given, use it (True: pick state from doc)
            if state:
                if state is True:
                    state = document.state(start_block)
                def token_source(block):
                    for t in tokens_method(block):
                        state.follow(t)
                        yield t
            else:
                def token_source(block):
                    return iter(tokens_method(block))
            self.state = state

            # where to start
            if cursor.start:
                start_pos = cursor.start
                if not tokens_with_position:
                    start_pos -= document.position(start_block)
                # token source for first block
                def source_start(block):
                    source = token_source(block)
                    for t in source:
                        if not start_pred(t):
                            yield t
                            for t in source:
                                yield t
            else:
                source_start = token_source

            # where to end
            if cursor.end is not None:
                end_block = cursor.end_block()
                end_pos = cursor.end
                if not tokens_with_position:
                    end_pos -= document.position(end_block)
                def source_end(source):
                    for t in source:
                        if end_pred(t):
                            break
                        yield t

            # generate the tokens
            def generator():
                source = source_start
                block = start_block
                if cursor.end is not None:
                    while block != end_block:
                        yield block, source(block)
                        source = token_source
                        block = document.next_block(block)
                    yield block, source_end(source(block))
                else:
                    for block in document.blocks_forward(start_block):
                        yield block, source(block)
                        source = token_source
            gen = generator()

            if tokens_with_position:
                def newline():
                    pos = document.position(self.block) - 1
                    return ly.lex.Newline('\n', pos)
            else:
                def newline():
                    pos = len(document.text(document.previous_block(self.block)))
                    return ly.lex.Newline('\n', pos)

            # initialize block and tokens
            for self.block, self.tokens in gen:
                break
            # keep them going after the first line
            def g():
                for t in self.tokens:
                    yield t
                for self.block, self.tokens in gen:
                    yield newline()
                    for t in self.tokens:
                        yield t
            self._gen = g()

        def __iter__(self):
            return self

        def __next__(self):
            if self._pushback:
                self._pushback = False
                return self._last
            i = self._last = next(self._gen)
            return i

        next = __next__

        def pushback(self, pushback=True):
            """Yields the last yielded token again on the next request.

            This can be called multiple times, but only the last token will be
            yielded again. You can also undo a call to pushback() using
            pushback(False).

            """
            self._pushback = pushback

        def token(self):
            """Re-returns the last yielded token."""
            return self._last

        @property
        def document(self):
            """Return our Document."""
            return self._doc

        def position(self, token):
            """Returns the position of the token in the current block.

            If the iterator was instantiated with tokens_with_position == True,
            this position is the same as the token.pos attribute, and the current
            block does not matter. (In that case you'll probably not use this
            method.)

            """
            pos = token.pos
            if not self._wp:
                pos += self._doc.position(self.block)
            return pos

        def until_parser_end(self):
            """Yield the tokens until the current parser is quit.

            You can only use this method if you have a State enabled.

            """
            depth = self.state.depth()
            for t in self:
                yield t
                if self.state.depth() < depth and not self._pushback:
                    break

        def consume(self, iterable, position):
            """Consumes iterable (supposed to be reading from us) until position.

            Returns the last token if that overlaps position.

            """
            if self._doc.position(self.block) < position:
                for t in iterable:
                    pos = self.position(t)
                    end = pos + len(t)
                    if end == position:
                        return
                    elif end > position:
                        return t