from dataclasses import dataclass
import struct

@dataclass
class triangle_strip:
    mask: int
    shadow: int
    skip: int
    triangle_strip_start: int

    def __init__(self, value):
        assert (value >> 31) & 1 == 0, value

        self.mask = (value >> 25) & 0b111111
        self.shadow = (value >> 24) & 0b1
        self.skip = (value >> 21) & 0b111
        self.triangle_strip_start = (value & 0x1fffff) << 2

@dataclass
class triangle_array:
    number_of_triangles: int
    shadow: int
    skip: int
    triangle_array_start: int

    def __init__(self, value):
        assert (value >> 29) & 0b111 == 0b100, value

        self.number_of_triangles = (value >> 25) & 0b1111
        self.shadow = (value >> 24) & 0b1
        self.skip = (value >> 21) & 0b111
        self.triangle_array_start = (value & 0x1fffff) << 2

@dataclass
class quad_array:
    number_of_quads: int
    shadow: int
    skip: int
    quad_array_start: int

    def __init__(self, value):
        assert (value >> 29) & 0b111 == 0b101, value

        self.number_of_quads = (value >> 25) & 0b1111
        self.shadow = (value >> 24) & 0b1
        self.skip = (value >> 21) & 0b111
        self.quad_array_start = (value & 0x1fffff) << 2

@dataclass
class object_pointer_block_link:
    end_of_list: int
    next_pointer_block: int

    def __init__(self, value):
        assert (value >> 29) & 0b111 == 0b111, value
        assert (value >> 0) & 0b11 == 0b00, value

        self.end_of_list = (value >> 28) & 1
        self.next_pointer_block = value & 0xffffff


def decode_ol_entry(mem, offset):
    value, = struct.unpack("<I", mem[offset:offset+4])
    selector = (value >> 29) & 0b111

    if selector == 0b111:
        return object_pointer_block_link(value)
    elif selector == 0b101:
        return quad_array(value)
    elif selector == 0b100:
        return triangle_array(value)
    elif (value >> 31) & 1 == 0:
        return triangle_strip(value)
    else:
        assert False, value