import enum
from destruct import Struct

from .util import MultiEnum
from .common import CLIToken, CLITableType


class CILFormat(enum.Enum):
    Tiny = 2
    Extended = 3

class CILFlags(enum.Flag):
    MoreSections   = 0x8
    InitLocals     = 0x10 

class CILAttributes(MultiEnum):
    format      = (CILFormat, 0b0011)
    flags       = (CILFlags,  0x0FF0 | 0b1100)
    header_size = (int,       0xF000, 12)

class CILTinyHeader(Struct, nocopy=True):
    attribs    = Static(CILAttributes(CILFormat.Tiny.value))
    stack_size = Static(0)
    code_size  = Process(UInt(8), lambda v: v >> 2)
    vars       = Static(None)
    code       = Data()

    def on_attribs(self, spec, context):
        self.attribs.header_size = 1

    def on_code_size(self, spec, context):
        spec.code.length = self.code_size

class CILExtendedHeader(Struct, nocopy=True):
    attribs    = Enum(CILAttributes, UInt(16))
    stack_size = UInt(16)
    code_size  = UInt(32)
    vars       = CLIToken
    _pad       = Data()
    code       = Data()

    def on_attribs(self, spec, context):
        self.attribs.header_size *= 4
        spec._pad.length = self.attribs.header_size - 12

    def on_code_size(self, spec, context):
        spec.code.length = self.code_size


def determine_header(b):
    format = CILFormat(b[0] & 0b11)
    if format == CILFormat.Tiny:
        return CILTinyHeader
    else:
        return CILExtendedHeader