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# Emitter expects events obeying the following grammar:
# stream ::= STREAM-START document* STREAM-END
# document ::= DOCUMENT-START node DOCUMENT-END
# node ::= SCALAR | sequence | mapping
# sequence ::= SEQUENCE-START node* SEQUENCE-END
# mapping ::= MAPPING-START (node node)* MAPPING-END

__all__ = ['Emitter', 'EmitterError']

from error import YAMLError
from events import *

class EmitterError(YAMLError):
    pass

class ScalarAnalysis(object):
    def __init__(self, scalar, empty, multiline,
            allow_flow_plain, allow_block_plain,
            allow_single_quoted, allow_double_quoted,
            allow_block):
        self.scalar = scalar
        self.empty = empty
        self.multiline = multiline
        self.allow_flow_plain = allow_flow_plain
        self.allow_block_plain = allow_block_plain
        self.allow_single_quoted = allow_single_quoted
        self.allow_double_quoted = allow_double_quoted
        self.allow_block = allow_block

class Emitter(object):

    DEFAULT_TAG_PREFIXES = {
        u'!' : u'!',
        u'tag:yaml.org,2002:' : u'!!',
    }

    def __init__(self, stream, canonical=None, indent=None, width=None,
            allow_unicode=None, line_break=None):

        # The stream should have the methods `write` and possibly `flush`.
        self.stream = stream

        # Encoding can be overriden by STREAM-START.
        self.encoding = None

        # Emitter is a state machine with a stack of states to handle nested
        # structures.
        self.states = []
        self.state = self.expect_stream_start

        # Current event and the event queue.
        self.events = []
        self.event = None

        # The current indentation level and the stack of previous indents.
        self.indents = []
        self.indent = None

        # Flow level.
        self.flow_level = 0

        # Contexts.
        self.root_context = False
        self.sequence_context = False
        self.mapping_context = False
        self.simple_key_context = False

        # Characteristics of the last emitted character:
        #  - current position.
        #  - is it a whitespace?
        #  - is it an indention character
        #    (indentation space, '-', '?', or ':')?
        self.line = 0
        self.column = 0
        self.whitespace = True
        self.indention = True

        # Whether the document requires an explicit document indicator
        self.open_ended = False

        # Formatting details.
        self.canonical = canonical
        self.allow_unicode = allow_unicode
        self.best_indent = 2
        if indent and 1 < indent < 10:
            self.best_indent = indent
        self.best_width = 80
        if width and width > self.best_indent*2:
            self.best_width = width
        self.best_line_break = u'\n'
        if line_break in [u'\r', u'\n', u'\r\n']:
            self.best_line_break = line_break

        # Tag prefixes.
        self.tag_prefixes = None

        # Prepared anchor and tag.
        self.prepared_anchor = None
        self.prepared_tag = None

        # Scalar analysis and style.
        self.analysis = None
        self.style = None

    def dispose(self):
        # Reset the state attributes (to clear self-references)
        self.states = []
        self.state = None

    def emit(self, event):
        self.events.append(event)
        while not self.need_more_events():
            self.event = self.events.pop(0)
            self.state()
            self.event = None

    # In some cases, we wait for a few next events before emitting.

    def need_more_events(self):
        if not self.events:
            return True
        event = self.events[0]
        if isinstance(event, DocumentStartEvent):
            return self.need_events(1)
        elif isinstance(event, SequenceStartEvent):
            return self.need_events(2)
        elif isinstance(event, MappingStartEvent):
            return self.need_events(3)
        else:
            return False

    def need_events(self, count):
        level = 0