"""
Models here are intended to be passed to :meth:`~manticore.core.state.State.invoke_model`, not invoked directly.
"""

from .core.cpu.abstractcpu import ConcretizeArgument
from .utils.helpers import issymbolic
from .core.smtlib.solver import solver
from .core.smtlib.operators import ITEBV, ZEXTEND


VARIADIC_FUNC_ATTR = '_variadic'

def isvariadic(model):
    """
    :param callable model: Function model
    :return: Whether `model` models a variadic function
    :rtype: bool
    """
    return getattr(model, VARIADIC_FUNC_ATTR, False)

def variadic(func):
    """
    A decorator used to mark a function model as variadic. This function should
    take two parameters: a :class:`~manticore.core.state.State` object, and
    a generator object for the arguments.

    :param callable func: Function model
    """
    setattr(func, VARIADIC_FUNC_ATTR, True)
    return func

def _find_zero(cpu, constrs, ptr):
    """
    Helper for finding the closest NULL or, effectively NULL byte from a starting address.

    :param Cpu cpu:
    :param ConstraintSet constrs: Constraints for current `State`
    :param int ptr: Address to start searching for a zero from
    :return: Offset from `ptr` to first byte that is 0 or an `Expression` that must be zero
    """

    offset = 0
    while True:
        byt = cpu.read_int(ptr + offset, 8)

        if issymbolic(byt):
            if not solver.can_be_true(constrs, byt != 0):
                break
        else:
            if byt == 0:
                break

        offset += 1

    return offset


def strcmp(state, s1, s2):
    """
    strcmp symbolic model.

    Algorithm: Walks from end of string (minimum offset to NULL in either string)
    to beginning building tree of ITEs each time either of the
    bytes at current offset is symbolic.

    Points of Interest:
    - We've been building up a symbolic tree but then encounter two
      concrete bytes that differ. We can throw away the entire symbolic
      tree!
    - If we've been encountering concrete bytes that match
      at the end of the string as we walk forward, and then we encounter
      a pair where one is symbolic, we can forget about that 0 `ret` we've
      been tracking and just replace it with the symbolic subtraction of
      the two

    :param State state: Current program state
    :param int s1: Address of string 1
    :param int s2: Address of string 2
    :return: Symbolic strcmp result
    :rtype: Expression or int
    """

    cpu = state.cpu

    if issymbolic(s1):
        raise ConcretizeArgument(state.cpu, 1)
    if issymbolic(s2):
        raise ConcretizeArgument(state.cpu, 2)

    s1_zero_idx = _find_zero(cpu, state.constraints, s1)
    s2_zero_idx = _find_zero(cpu, state.constraints, s2)
    min_zero_idx = min(s1_zero_idx, s2_zero_idx)

    ret = None

    for offset in xrange(min_zero_idx, -1, -1):
        s1char = ZEXTEND(cpu.read_int(s1 + offset, 8), cpu.address_bit_size)
        s2char = ZEXTEND(cpu.read_int(s2 + offset, 8), cpu.address_bit_size)

        if issymbolic(s1char) or issymbolic(s2char):
            if ret is None or (not issymbolic(ret) and ret == 0):
                ret = s1char - s2char
            else:
                ret = ITEBV(cpu.address_bit_size, s1char != s2char, s1char - s2char, ret)
        else:
            if s1char != s2char:
                ret = s1char - s2char
            elif ret is None:
                ret = 0

    return ret


def strlen(state, s):
    """
    strlen symbolic model.

    Algorithm: Walks from end of string not including NULL building ITE tree when current byte is symbolic.

    :param State state: current program state
    :param int s: Address of string
    :return: Symbolic strlen result
    :rtype: Expression or int
    """

    cpu = state.cpu

    if issymbolic(s):
        raise ConcretizeArgument(state.cpu, 1)

    zero_idx = _find_zero(cpu, state.constraints, s)

    ret = zero_idx

    for offset in xrange(zero_idx-1, -1, -1):
        byt = cpu.read_int(s + offset, 8)
        if issymbolic(byt):
            ret = ITEBV(cpu.address_bit_size, byt == 0, offset, ret)

    return ret
