from contextlib import contextmanager
from .utils import hashable
from .dispatch import dispatch

_global_logic_variables = set()  # type: ignore[var-annotated]
_glv = _global_logic_variables


class Var:
    """ Logic Variable """

    _id = 1

    def __new__(cls, *token):
        if len(token) == 0:
            token = "_%s" % Var._id  # type: ignore[assignment]
            Var._id += 1
        elif len(token) == 1:
            token = token[0]

        obj = object.__new__(cls)
        obj.token = token  # type: ignore[attr-defined]
        return obj

    def __str__(self):
        return "~" + str(self.token)  # type: ignore[attr-defined]
    __repr__ = __str__

    def __eq__(self, other):
        return type(self) == type(other) and self.token == other.token  # type: ignore[attr-defined]

    def __hash__(self):
        return hash((type(self), self.token))  # type: ignore[attr-defined]


def var():
    return lambda *args: Var(*args)


def vars():
    return lambda n: [var() for i in range(n)]


@dispatch(Var)
def isvar(v):
    return True

isvar


@dispatch(object)  # type: ignore[no-redef]
def isvar(o):
    return not not _glv and hashable(o) and o in _glv


@contextmanager
def variables(*variables):
    """
    Context manager for logic variables

    Example:
        >>> # xdoctest: +SKIP("undefined vars")
        >>> from __future__ import with_statement
        >>> with variables(1):
        ...     print(isvar(1))
        True
        >>> print(isvar(1))
        False
        >>> # Normal approach
        >>> from unification import unify
        >>> x = var('x')
        >>> unify(x, 1)
        {~x: 1}
        >>> # Context Manager approach
        >>> with variables('x'):
        ...     print(unify('x', 1))
        {'x': 1}
    """
    old_global_logic_variables = _global_logic_variables.copy()
    _global_logic_variables.update(set(variables))
    try:
        yield
    finally:
        _global_logic_variables.clear()
        _global_logic_variables.update(old_global_logic_variables)