import bluetooth
import bluetooth._bluetooth as bt
import struct
import array
import fcntl


class BluetoothRSSI(object):
    """Object class for getting the RSSI value of a Bluetooth address.
    Reference: https://github.com/dagar/bluetooth-proximity
    """
    def __init__(self, addr, dev_id=0):
        self.addr = addr
        self.hci_sock = bt.hci_open_dev(dev_id)
        self.hci_fd = self.hci_sock.fileno()
        self.bt_sock = bluetooth.BluetoothSocket(bluetooth.L2CAP)
        self.bt_sock.settimeout(10)
        self.connected = False
        self.cmd_pkt = None

    def prep_cmd_pkt(self):
        """Prepares the command packet for requesting RSSI"""
        reqstr = struct.pack(
            "6sB17s", bt.str2ba(self.addr), bt.ACL_LINK, "\0" * 17)
        request = array.array("c", reqstr)
        handle = fcntl.ioctl(self.hci_fd, bt.HCIGETCONNINFO, request, 1)
        handle = struct.unpack("8xH14x", request.tostring())[0]
        self.cmd_pkt = struct.pack('H', handle)

    def connect(self):
        """Connects to the Bluetooth address"""
        self.bt_sock.connect_ex((self.addr, 1))  # PSM 1 - Service Discovery
        self.connected = True

    def get_rssi(self):
        """Gets the current RSSI value.

        @return: The RSSI value (float) or None if the device connection fails
                 (i.e. the device is nowhere nearby).
        """
        try:
            # Only do connection if not already connected
            if not self.connected:
                self.connect()
            if self.cmd_pkt is None:
                self.prep_cmd_pkt()
            # Send command to request RSSI
            rssi = bt.hci_send_req(
                self.hci_sock, bt.OGF_STATUS_PARAM,
                bt.OCF_READ_RSSI, bt.EVT_CMD_COMPLETE, 4, self.cmd_pkt)
            rssi = struct.unpack('b', rssi[3])[0]
            return rssi
        except IOError:
            # Happens if connection fails (e.g. device is not in range)
            self.connected = False
            return None