import logging

from .paged_memory_mixin import PagedMemoryMixin
from ....errors import SimSegfaultException, SimMemoryError
from ....sim_options import STRICT_PAGE_ACCESS

l = logging.getLogger(__name__)


class StackAllocationMixin(PagedMemoryMixin):
    """
    This mixin adds automatic allocation for a stack region based on the stack_end and stack_size parameters.
    """

    # TODO: multiple stacks. this scheme should scale p well
    # TODO tbh this should be handled by an actual fault handler in simos or something
    def __init__(self, stack_end=None, stack_size=None, stack_perms=None, **kwargs):
        super().__init__(**kwargs)
        self._red_pageno = (stack_end - 1) // self.page_size if stack_end is not None else None
        self._remaining_stack = stack_size
        self._stack_perms = stack_perms

    def copy(self, memo):
        o = super().copy(memo)
        o._red_pageno = self._red_pageno
        o._remaining_stack = self._remaining_stack
        o._stack_perms = self._stack_perms
        return o

    def allocate_stack_pages(self, addr: int, size: int, **kwargs):
        """
        Pre-allocates pages for the stack without triggering any logic related to reading from them.

        :param addr: The highest address that should be mapped
        :param size: The number of bytes to be allocated. byte 1 is the one at addr, byte 2 is the one before that, and
                     so on.
        :return: A list of the new page objects
        """
        # weird off-by-ones here. we want to calculate the last byte requested, find its pageno, and then use that to
        # determine what the last page allocated will be and then how many pages are touched
        pageno = addr // self.page_size
        if pageno != self._red_pageno:
            raise SimMemoryError("Trying to allocate stack space in a place that isn't the top of the stack")
        num = pageno - ((addr - size + 1) // self.page_size) + 1

        result = []
        for _ in range(num):
            new_red_pageno = (self._red_pageno - 1) % ((1 << self.state.arch.bits) // self.page_size)
            if new_red_pageno in self._pages:
                raise SimSegfaultException(self._red_pageno * self.page_size, "stack collided with heap")

            if self._remaining_stack is not None and self._remaining_stack < self.page_size:
                raise SimSegfaultException(self._red_pageno * self.page_size, "exhausted stack quota")

            l.debug("Allocating new stack page at %#x", self._red_pageno * self.page_size)
            result.append(
                PagedMemoryMixin._initialize_default_page(
                    self, self._red_pageno, permissions=self._stack_perms, **kwargs
                )
            )
            self._pages[self._red_pageno] = result[-1]

            self._red_pageno = new_red_pageno
            if self._remaining_stack is not None:
                self._remaining_stack -= self.page_size

        return result

    def _initialize_page(self, pageno: int, **kwargs):
        if pageno != self._red_pageno or STRICT_PAGE_ACCESS not in self.state.options:
            return super()._initialize_page(pageno, **kwargs)

        return self.allocate_stack_pages((pageno + 1) * self.page_size - 1, self.page_size)[0]
