import io
import struct

class Reader:
    def __init__(self, file, chunk_id: str, parent=None, indent=0):
        self.file = file
        self.size: int = 0
        self.size_pos = None
        self.parent = parent
        self.header = chunk_id
        self.indent = "  " * indent


    def __enter__(self):
        self.size_pos = self.file.tell()
        self.file.seek(4,1) #skip header, will add check later
        self.size = self.read_u32()

        padding_length = 4 - (self.size % 4) if self.size % 4 > 0 else 0
        self.end_pos = self.size_pos + padding_length + self.size + 8

        print(self.indent + "Begin " + self.header + ", Size: " + str(self.size) + ", Pos: " + str(self.size_pos))

        return self


    def __exit__(self, exc_type, exc_value, traceback):
        if self.size > self.MAX_SIZE:
            raise OverflowError(f".msh file overflowed max size. size = {self.size} MAX_SIZE = {self.MAX_SIZE}")

        print(self.indent + "End   " + self.header)
        self.file.seek(self.end_pos)



    def read_bytes(self,num_bytes):
        return self.file.read(num_bytes)


    def read_string(self):
        last_byte = self.read_bytes(1)
        result = b''
        while last_byte[0] != 0x0:
            result += last_byte
            last_byte = self.read_bytes(1)

        return result.decode("utf-8")

    def read_i8(self, num=1):
        buf = self.read_bytes(num)
        result = struct.unpack(f"<{num}b", buf)
        return result[0] if num == 1 else result

    def read_u8(self, num=1):
        buf = self.read_bytes(num)
        result = struct.unpack(f"<{num}B", buf)
        return result[0] if num == 1 else result

    def read_i16(self, num=1):
        buf = self.read_bytes(num * 2)
        result = struct.unpack(f"<{num}h", buf)
        return result[0] if num == 1 else result

    def read_u16(self, num=1):
        buf = self.read_bytes(num * 2)
        result = struct.unpack(f"<{num}H", buf)
        return result[0] if num == 1 else result

    def read_i32(self, num=1):
        buf = self.read_bytes(num * 4)
        result = struct.unpack(f"<{num}i", buf)
        return result[0] if num == 1 else result

    def read_u32(self, num=1):
        buf = self.read_bytes(num * 4) 
        result = struct.unpack(f"<{num}I", buf)
        return result[0] if num == 1 else result

    def read_f32(self, num=1):
        buf = self.read_bytes(num * 4)
        result = struct.unpack(f"<{num}f", buf)
        return result[0] if num == 1 else result



    def read_child(self, child_id: str):
        child = Reader(self.file, chunk_id=child_id, parent=self, indent=int(len(self.indent) / 2) + 1)
        return child


    def skip_bytes(self,num):
        self.file.seek(num,1)


    def peak_next_header(self):
        buf = self.read_bytes(4);
        self.file.seek(-4,1)
        return buf.decode("utf-8")


    def could_have_child(self):
    	return self.end_pos - self.file.tell() >= 8



    MAX_SIZE: int = 2147483647 - 8

'''
with open("/Users/will/Desktop/spacedoortest/spa1_prop_impdoor.msh", "rb") as tst_stream:
    with Reader(tst_stream, "HEDR") as hedr:
        print(hedr.peak_next_header())
'''