"""Mutable Linked Lists"""

class Link:
    empty = ()

    def __init__(self, first, rest=empty):
        if not (rest is Link.empty or isinstance(rest, Link)):
            raise ValueError('rest must be Link or empty')
        self.first = first
        self.rest = rest

    def __repr__(self):
        if self.rest is Link.empty:
            return 'Link({})'.format(
                self.first)
        else:
            return 'Link({}, {})'.format(
                self.first, repr(self.rest))

    def __len__(self):
        return 1 + len(self.rest)  # Where's the base case??

    def __getitem__(self, i):
        if i == 0:
            return self.first
        elif self.rest is Link.empty:
            raise IndexError('linked list index out of range')
        else:
            # return self.rest.__getitem__(i-1)
            return self.rest[i-1]

    def __setitem__(self, i, val):
        if i == 0:
            self.first = val
        elif self.rest is Link.empty:
            raise IndexError('linked list assignment index out of range')
        else:
            self.rest[i-1] = val

    def map(self, f):
        self.first = f(self.first)
        if self.rest is not Link.empty:
            self.rest.map(f)

    def __contains__(self, e):
        if self.first == e:
            return True
        elif self.rest is Link.empty:
            return False
        else:
            return e in self.rest

    @property
    def second(self):
        return self.rest.first

    @second.setter
    def second(self, value):
        self.rest.first = value

def create_long_ll(n):
    head = Link.empty
    while n > 0:
        head = Link(n, head)
        n -= 1
    return head

# Last demo
s = Link(1, Link(2))
t = Link(3, Link(4))
s.first = 10 # mutate
s
s.rest.rest = t # change pointer
s
u = Link(1)
u.rest = u # self referencing
u.first
u.rest.first
u.rest.rest.first
v = Link(s, t)
v
t.first = 30 # affects both
v