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# Scanner produces tokens of the following types:
# STREAM-START
# STREAM-END
# DIRECTIVE(name, value)
# DOCUMENT-START
# DOCUMENT-END
# BLOCK-SEQUENCE-START
# BLOCK-MAPPING-START
# BLOCK-END
# FLOW-SEQUENCE-START
# FLOW-MAPPING-START
# FLOW-SEQUENCE-END
# FLOW-MAPPING-END
# BLOCK-ENTRY
# FLOW-ENTRY
# KEY
# VALUE
# ALIAS(value)
# ANCHOR(value)
# TAG(value)
# SCALAR(value, plain, style)
#
# Read comments in the Scanner code for more details.
#

__all__ = ['Scanner', 'ScannerError']

from error import MarkedYAMLError
from tokens import *

class ScannerError(MarkedYAMLError):
    pass

class SimpleKey(object):
    # See below simple keys treatment.

    def __init__(self, token_number, required, index, line, column, mark):
        self.token_number = token_number
        self.required = required
        self.index = index
        self.line = line
        self.column = column
        self.mark = mark

class Scanner(object):

    def __init__(self):
        """Initialize the scanner."""
        # It is assumed that Scanner and Reader will have a common descendant.
        # Reader do the dirty work of checking for BOM and converting the
        # input data to Unicode. It also adds NUL to the end.
        #
        # Reader supports the following methods
        #   self.peek(i=0)       # peek the next i-th character
        #   self.prefix(l=1)     # peek the next l characters
        #   self.forward(l=1)    # read the next l characters and move the pointer.

        # Had we reached the end of the stream?
        self.done = False

        # The number of unclosed '{' and '['. `flow_level == 0` means block
        # context.
        self.flow_level = 0

        # List of processed tokens that are not yet emitted.
        self.tokens = []

        # Add the STREAM-START token.
        self.fetch_stream_start()

        # Number of tokens that were emitted through the `get_token` method.
        self.tokens_taken = 0

        # The current indentation level.
        self.indent = -1

        # Past indentation levels.
        self.indents = []

        # Variables related to simple keys treatment.

        # A simple key is a key that is not denoted by the '?' indicator.
        # Example of simple keys:
        #   ---
        #   block simple key: value
        #   ? not a simple key:
        #   : { flow simple key: value }
        # We emit the KEY token before all keys, so when we find a potential
        # simple key, we try to locate the corresponding ':' indicator.
        # Simple keys should be limited to a single line and 1024 characters.

        # Can a simple key start at the current position? A simple key may
        # start:
        # - at the beginning of the line, not counting indentation spaces
        #       (in block context),
        # - after '{', '[', ',' (in the flow context),
        # - after '?', ':', '-' (in the block context).
        # In the block context, this flag also signifies if a block collection
        # may start at the current position.
        self.allow_simple_key = True

        # Keep track of possible simple keys. This is a dictionary. The key
        # is `flow_level`; there can be no more that one possible simple key
        # for each level. The value is a SimpleKey record:
        #   (token_number, required, index, line, column, mark)
        # A simple key may start with ALIAS, ANCHOR, TAG, SCALAR(flow),
        # '[', or '{' tokens.
        self.possible_simple_keys = {}

    # Public methods.

    def check_token(self, *choices):
        # Check if the next token is one of the given types.
        while self.need_more_tokens():
            self.fetch_more_tokens()
        if self.tokens:
            if not choices:
                return True
            for choice in choices:
                if isinstance(self.tokens[0], choice):
                    return True
        return False

    def peek_token(self):
        # Return the next token, but do not delete if from the queue.
        while self.n