import struct

class AFrame:
    def __init__(self, data: bytes):
        self.valid = False
        self.data_id = 0
        self.data_len = 0
        self.payload = b""

        # A帧最小长度: 4+4+4+4+4+4 + 8 + 2 = 34
        if len(data) < 34:
            return

        try:
            # 大端解包
            magic, dlen, dir_, data_id, ptype, sat = struct.unpack('>IIIIII', data[:24])
            payload = data[24:-2]
            tail = data[-2:]

            if magic != 0xEB90EB90 or tail != 0x4C3A.to_bytes(2, 'big'):
                return

            self.valid = True
            self.data_id = data_id
            self.data_len = dlen
            self.payload = payload
        except:
            pass

    def get_doubles(self):
        doubles = []
        buf = self.payload
        while len(buf) >= 8:
            d = struct.unpack('>d', buf[:8])[0]
            doubles.append(d)
            buf = buf[8:]
        return doubles