# -*- coding: utf-8 -*-
"""
    scanner
    ~~~~~~~

    This library implements a regex based scanner.

    :copyright: 2006-2007 by Armin Ronacher, Georg Brandl.
    :license: BSD license.
"""
import re


class EndOfText(RuntimeError):
    """
    Raise if end of text is reached and the user
    tried to call a match function.
    """


class Scanner(object):
    """
    Simple scanner

    All method patterns are regular expression strings (not
    compiled expressions!)
    """

    def __init__(self, text, flags=0):
        """
        :param text:    The text which should be scanned
        :param flags:   default regular expression flags
        """
        self.data = text
        self.data_length = len(text)
        self.start_pos = 0
        self.pos = 0
        self.flags = flags
        self.last = None
        self.match = None
        self._re_cache = {}

    def eos(self):
        """`True` if the scanner reached the end of text."""
        return self.pos >= self.data_length
    eos = property(eos, eos.__doc__)

    def check(self, pattern):
        """
        Apply `pattern` on the current position and return
        the match object. (Doesn't touch pos). Use this for
        lookahead.
        """
        if self.eos:
            raise EndOfText()
        if pattern not in self._re_cache:
            self._re_cache[pattern] = re.compile(pattern, self.flags)
        return self._re_cache[pattern].match(self.data, self.pos)

    def test(self, pattern):
        """Apply a pattern on the current position and check
        if it patches. Doesn't touch pos."""
        return self.check(pattern) is not None

    def scan(self, pattern):
        """
        Scan the text for the given pattern and update pos/match
        and related fields. The return value is a boolen that
        indicates if the pattern matched. The matched value is
        stored on the instance as ``match``, the last value is
        stored as ``last``. ``start_pos`` is the position of the
        pointer before the pattern was matched, ``pos`` is the
        end position.
        """
        if self.eos:
            raise EndOfText()
        if pattern not in self._re_cache:
            self._re_cache[pattern] = re.compile(pattern, self.flags)
        self.last = self.match
        m = self._re_cache[pattern].match(self.data, self.pos)
        if m is None:
            return False
        self.start_pos = m.start()
        self.pos = m.end()
        self.match = m
        return True

    def get_char(self):
        """Scan exactly one char."""
        self.scan('.')

    def __repr__(self):
        return '<%s %d/%d>' % (
            self.__class__.__name__,
            self.pos,
            self.data_length
        )