import usocket as socket
import ustruct as struct
from ubinascii import hexlify

class MQTTException(Exception):
pass

class MQTTClient:

def __init__(self, client_id, server, port=0, user=None, password=None, keepalive=0,
             ssl=False, ssl_params={}):
    if port == 0:
        port = 8883 if ssl else 1883
    self.client_id = client_id
    self.sock = None
    self.addr = socket.getaddrinfo(server, port)[0][-1]
    self.ssl = ssl
    self.ssl_params = ssl_params
    self.pid = 0
    self.cb = None
    self.user = user
    self.pswd = password
    self.keepalive = keepalive
    self.lw_topic = None
    self.lw_msg = None
    self.lw_qos = 0
    self.lw_retain = False

def _send_str(self, s):
    self.sock.write(struct.pack("!H", len(s)))
    self.sock.write(s)

def _recv_len(self):
    n = 0
    sh = 0
    while 1:
        b = self.sock.read(1)[0]
        n |= (b & 0x7f) << sh
        if not b & 0x80:
            return n
        sh += 7

def set_callback(self, f):
    self.cb = f

def set_last_will(self, topic, msg, retain=False, qos=0):
    assert 0 <= qos <= 2
    assert topic
    self.lw_topic = topic
    self.lw_msg = msg
    self.lw_qos = qos
    self.lw_retain = retain

def connect(self, clean_session=True):
    sock = socket.socket()
    self.sock_connect(self.addr)
    if self.ssl:
        import ussl
        self.sock_connect = ussl.wrap_socket(self.sock, **self.ssl_params)
    msg = bytearray(b"\x10\0\0\x04MQTT\x04\x02\0\0")
    msg[1] = 10 + 2 + len(self.client_id)
    msg[9] = clean_session << 1
    if self.user is not None:
        msg[1] += 2 + len(self.user) + 2 + len(self.pswd)
        msg[9] |= 0xC0
    if self.keepalive:
        assert self.keepalive < 65536
        msg[10] |= self.keepalive >> 8
        msg[11] |= self.keepalive & 0x00FF
    if self.lw_topic:
        msg[1] += 2 + len(self.lw_topic) + 2 + len(self.lw_msg)
        msg[9] |= 0x4 | (self.lw_qos & 0x1) << 3 | (self.lw_qos & 0x2) << 3
        msg[9] |= self.lw_retain << 5
    self.sock.write(msg)
    #print(hex(len(msg)), hexlify(msg, ":"))
    self._send_str(self.client_id)
    if self.lw_topic:
        self._send_str(self.lw_topic)
        self._send_str(self.lw_msg)
    if self.user is not None:
        self._send_str(self.user)
        self._send_str(self.pswd)
    resp = self.sock.read(4)
    assert resp[0] == 0x20 and resp[1] == 0x02
    if resp[3] != 0:
        raise MQTTException(resp[3])
    return resp[2] & 1

def disconnect(self):
    self.sock.write(b"\xe0\0")
    self.sock.close()

def ping(self):
    self.sock.write(b"\xc0\0")

def publish(self, topic, msg, retain=False, qos=0):
    pkt = bytearray(b"\x30\0\0\0")
    pkt[0] |= qos << 1 | retain
    sz = 2 + len(topic) + len(msg)
    if qos > 0:
        sz += 2
    assert sz < 2097152
    i = 1
    while sz > 0x7f:
        pkt[i] = (sz & 0x7f) | 0x80
        sz >>= 7
        i += 1
    pkt[i] = sz
    #print(hex(len(pkt)), hexlify(pkt, ":"))
    self.sock.write(pkt, i + 1)
    self._send_str(topic)
    if qos > 0:
        self.pid += 1
        pid = self.pid
        struct.pack_into("!H", pkt, 0, pid)
        self.sock.write(pkt, 2)
    self.sock.write(msg)
    if qos == 1:
        while 1:
            op = self.wait_msg()
            if op == 0x40:
                sz = self.sock.read(1)
                assert sz == b"\x02"
                rcv_pid = self.sock.read(2)
                rcv_pid = rcv_pid[0] << 8 | rcv_pid[1]
                if pid == rcv_pid:
                    return
    elif qos == 2:
        assert 0

def subscribe(self, topic, qos=0):
    assert self.cb is not None, "Subscribe callback is not set"
    pkt = bytearray(b"\x82\0\0\0")
    self.pid += 1
    struct.pack_into("!BH", pkt, 1, 2 + 2 + len(topic) + 1, self.pid)
    #print(hex(len(pkt)), hexlify(pkt, ":"))
    self.sock.write(pkt)
    self._send_str(topic)
    self.sock.write(qos.to_bytes(1, 'little'))
    while 1:
        op = self.wait_msg()
        if op == 0x90:
            resp = self.sock.read(4)
            #print(resp)
            assert resp[1] == pkt[2] and resp[2] == pkt[3]
            if resp[3] == 0x80:
                raise MQTTException(resp[3])
            return

# Wait for a single incoming MQTT message and process it.
# Subscribed messages are delivered to a callback previously
# set by .set_callback() method. Other (internal) MQTT
# messages processed internally.
def wait_msg(self):
    res = self.sock.read(1)
    self.sock.setblocking(True)
    if res is None:
        return None
    if res == b"":
        raise OSError(-1)
    if res == b"\xd0":  # PINGRESP
        sz = self.sock.read(1)[0]
        assert sz == 0
        return None
    op = res[0]
    if op & 0xf0 != 0x30:
        return op
    sz = self._recv_len()
    topic_len = self.sock.read(2)
    topic_len = (topic_len[0] << 8) | topic_len[1]
    topic = self.sock.read(topic_len)
    sz -= topic_len + 2
    if op & 6:
        pid = self.sock.read(2)
        pid = pid[0] << 8 | pid[1]
        sz -= 2
    msg = self.sock.read(sz)
    self.cb(topic, msg)
    if op & 6 == 2:
        pkt = bytearray(b"\x40\x02\0\0")
        struct.pack_into("!H", pkt, 2, pid)
        self.sock.write(pkt)
    elif op & 6 == 4:
        assert 0

# Checks whether a pending message from server is available.
# If not, returns immediately with None. Otherwise, does
# the same processing as wait_msg.
def check_msg(self):
    self.sock.setblocking(False)
    return self.wait_msg()