#!/usr/bin/python3

from collections import namedtuple
from heapq import heappush, heappop
import itertools

# A simple priority queue based on the heapq class.
class PQueue(object):
    REMOVED = '<removed-task>'      # placeholder for a removed task

    def __init__(self):
        self.pq = []                         # list of entries arranged in a heap
        self.entry_finder = {}               # mapping of tasks to entries
        self.counter = itertools.count()     # unique sequence count
        self.size = 0

    def push(self, task, priority=0):
        'Add a new task or update the priority of an existing task'
        if task in self.entry_finder:
            self.remove(task)
        else:
            self.size += 1
        entry = [priority, next(self.counter), task]
        self.entry_finder[task] = entry
        heappush(self.pq, entry)

    def remove(self, task):
        'Mark an existing task as REMOVED.  Raise KeyError if not found.'
        entry = self.entry_finder.pop(task)
        entry[-1] = self.REMOVED
        self.size -= 1

    def pop(self):
        'Remove and return the lowest priority task. Raise KeyError if empty.'
        while self.pq:
            priority, count, task = heappop(self.pq)
            if task is not self.REMOVED:
                del self.entry_finder[task]
                self.size -= 1
                return task
        return None

    def __len__(self):
        return self.size

# Stores a token's type and value, and optionally the position of the first
# character in the lexed stream.
class Token(namedtuple('Token', ['type', 'val', 'pos'])):
    __slots__ = ()

    # Custom constructor to support default parameters.
    def __new__(cls, type, val='', pos=None):
        return super(Token, cls).__new__(cls, type, val, pos)

    def __str__(self):
        return self.val

    # Ignore position when comparing tokens. There is probably a cleaner way of
    # doing these.
    __eq__ = lambda x, y: x[0] == y[0] and x[1] == y[1]
    __ne__ = lambda x, y: x[0] != y[0] or x[1] != y[1]
    __lt__ = lambda x, y: tuple.__lt__(x[0:2], y[0:2])
    __le__ = lambda x, y: tuple.__le__(x[0:2], y[0:2])
    __ge__ = lambda x, y: tuple.__ge__(x[0:2], y[0:2])
    __gt__ = lambda x, y: tuple.__gt__(x[0:2], y[0:2])

    # Only hash token's value (we don't care about position, and types are
    # determined by values).
    def __hash__(self):
        return hash(self[1])

# Return [n]th line in [text].
def get_line(text, n):
    lines = text.split('\n')
    if n >= 0 and n < len(lines):
        return lines[n]
    return None

# Indent each line in [text] by [indent] spaces.
def indent(text, indent=2):
    return '\n'.join([' '*indent+line for line in text.split('\n')])