from sploit.arch import arch, itob
from sploit.types.index_entry import IndexEntry

_PLACEHOLDER_MAGIC = b"\xef"

class PayloadEntry(IndexEntry):
    """Base class for dynamic Payload entries"""

    def __repr__(self):
        """Return human-readable entry description."""
        return f"{self.__class__.__name__}{self.__dict__}"

    def payload_insert(self, payload):
        """
        Called on insert into a payload object.

        Override this method to perform any initialization which requires a
        reference to the payload object.  self.base is set to the insertion
        location.
        """
        pass

    def payload_bytes(self, payload):
        """
        Called to generate bytes for this entry.

        Override this method to generate and return the binary output for this
        dynamic payload entry.  self.base is set to the current entry address
        or offset.
        """
        return b""

# Concrete payload entry definitions

class pointer(PayloadEntry):
    """Generate an integer which is always a fixed offset from self.base."""

    def __init__(self, target=None):
        self.target = target

    def payload_insert(self, payload):
        if self.target is None:
            self.target = self.base
        self.target -= self.base

    def payload_bytes(self, payload):
        return itob(self.target + self.base)

class padlen(PayloadEntry):
    """Generate padding to reach a target payload length."""

    def __init__(self, size, data=None):
        self.size = size
        self.data = data

    def _gen_padding(self, size):
        data = self.data or arch.nopcode
        if size < 0:
            raise ValueError("padding: Available space is negative")
        if (size := size / len(data)) != int(size):
            raise ValueError("padding: Element does not divide the space evenly")
        return data * int(size)

    def payload_bytes(self, payload):
        return self._gen_padding(self.size - (self.base - payload.base))

class padabs(padlen):
    """Generate padding to reach a target absolute address."""

    def payload_bytes(self, payload):
        return self._gen_padding(self.size - self.base)

class padrel(padlen):
    """Generate a fixed length of padding (aka: length relative to self)."""

    def payload_bytes(self, payload):
        return self._gen_padding(self.size)

class padalign(padlen):
    """Generate padding to reach next aligned address."""

    def __init__(self, size=None, data=None):
        self.size = size
        self.data = data

    def payload_bytes(self, payload):
        size = self.size or arch.alignment
        return self._gen_padding(-self.base % size)

class placeholder(padlen):
    """Generate fixed length of magic bytes, one word length by default."""

    def __init__(self, size=None):
        self.size = size
        self.data = _PLACEHOLDER_MAGIC

    def payload_bytes(self, payload):
        size = self.size or arch.wordsize
        return self._gen_padding(size)