#!/usr/bin/python3
#
#


# What direction the mouse is facing
NORTH = 0
EAST = 1
SOUTH = 2
WEST = 3

# N:-1 E:0 S:+1 W:0
FORWARD_ROW = (-1, 0, +1, 0)
# N:0 E:1 S:0 W:-1
FORWARD_COL = (0, +1, 0, -1)


class Mouse(object):
    def __init__(self):
        # We always start at (15, 0)
        self.r = 15
        self.c = 0

        # Starting direction is always north
        self.d = NORTH

        # How many total moves?
        self.moves = 0

    def reset(self):
        ### unclear whether we want to keep this, when considering
        ### the idea of "navigate back to start"
        self.r = 15
        self.c = 0
        self.d = NORTH
        self.moves = 0

    def turn_right(self):
        self.d =  (self.d + 1) & 3
    def turn_around(self):
        self.d =  (self.d + 2) & 3  # or ^= 2
    def turn_left(self):
        self.d =  (self.d + 3) & 3

    def turn_towards(self, r, c):
        ### robot instructions should be inserted here. Just set our
        ### direction immediately.
        if r < self.r:
            self.d = NORTH
        elif c > self.c:
            self.d = EAST
        elif r > self.r:
            self.d = SOUTH
        else:
            assert c < self.c
            self.d = WEST

    def forward(self):
        # Caller should not have moved self forward, to an impossible
        # location. Double-check.
        assert ( (self.d == NORTH and self.r > 0)
                 or (self.d == EAST and self.c < 15)
                 or (self.d == SOUTH and self.r < 15)
                 or (self.d == WEST and self.c > 0) )

        self.r += FORWARD_ROW[self.d]
        self.c += FORWARD_COL[self.d]

        self.moves += 1


class Path(object):
    def __init__(self):
        self.crumbs = [ ]

    def moved_to(self, r, c):
        # If we have returned to a prior location on our path, then
        # cut out all the wandering.
        try:
            ### something is broken. hold on this.
            raise ValueError
            i = self.crumbs.index((r, c))
            print('IDX:', i)
            print('OLD:', self.crumbs)
            # Delete the found location (about to be added), and all
            # locations after that. Thus, our crumbs have no loops.
            del self.crumbs[i:]
            print('NEW:', self.crumbs)
        except ValueError:
            pass

        self.crumbs.append((r, c))

    def retreat(self):
        # Yield all locations, starting at the end of the path.
        for _ in range(len(self.crumbs)):
            yield self.crumbs.pop()