"""Exports a BLE based UART as a socket."""

import asyncio
import logging
from typing import Set, Sequence, Optional

import bleak
import prometheus_client
import click
import txdbus.error
import systemd_stopper

log = logging.getLogger('janet.bleasync')

# Lists the UUIDs used for the receive and TX characteristics.
_RX_UUIDS = set(('0000ffe1-0000-1000-8000-00805f9b34fb',
                 '0000fff1-0000-1000-8000-00805f9b34fb'))
_TX_UUIDS = set(('0000ffe1-0000-1000-8000-00805f9b34fb',
                 '0000fff2-0000-1000-8000-00805f9b34fb'))

# Maximum number of bytes per write.
_TX_CAP = 20
# bleak.connect seems to lock up on concurrent connect() calls.
_LOCK = asyncio.Lock()

_CONNECTED = prometheus_client.Gauge(
    'blebridge_connected',
    'Bridge is connected to the Bluetooth device',
    labelnames=('mac', ))
_CLIENTS = prometheus_client.Gauge('blebridge_client_count',
                                   'Number of connected socket clients',
                                   labelnames=('mac', ))
_SENT = prometheus_client.Counter('blebridge_sent_bytes',
                                  'Number of bytes sent over Bluetooth',
                                  labelnames=('mac', ))
_RECEIVED = prometheus_client.Counter(
    'blebridge_received_bytes',
    'Number of bytes received over Bluetooth',
    labelnames=('mac', ))


class Bridge:
    def __init__(self, address: str, port: int):
        self._address = address
        self._port = port

        self._device = bleak.BleakClient(address)
        self._writers: Set[asyncio.StreamWriter] = set()
        self._tx: asyncio.Queue[bytearray] = asyncio.Queue()
        self._stop = asyncio.Event()
        self._stopped = asyncio.Event()
        self._lock = asyncio.Lock()

    def _notify(self, unused_sender, data):
        """Handles data that arrives over Bluetooth."""
        _RECEIVED.labels(self._address).inc(len(data))

        for writer in list(self._writers):
            try:
                writer.write(data)
            except Exception as ex:
                log.warning(
                    'Exception while writing data to the client, removing',
                    exc_info=ex)
                self._writers.remove(writer)

    async def _client(self, reader, writer):
        """Handles a single client socket connection."""
        with _CLIENTS.labels(self._address).track_inprogress():
            self._writers.add(writer)
            try:
                while True:
                    got = await reader.read(100)
                    if not got:
                        log.info('client closed')
                        return
                    await self._tx.put(bytearray(got))
            except BrokenPipeError as ex:
                log.info('broken pipe error, closing')
            finally:
                self._writers.remove(writer)
                writer.close()

    async def run(self):
        """Runs the main loop."""
        server = await asyncio.start_server(self._client, None, self._port)
        s = asyncio.create_task(server.serve_forever())

        try:
            while not self._stop.is_set():
                try:
                    await self.ble()
                except bleak.exc.BleakError as ex:
                    log.info('Caught BLE exception, retrying', exc_info=ex)
                except txdbus.error.DBusException as ex:
                    log.info('Caught DBus exception, retrying', exc_info=ex)

                if not self._stop.is_set():
                    await asyncio.sleep(5)

        except Exception as ex:
            log.warning('Unhandled exception, closing', exc_info=ex)
            raise
        finally:
            server.close()
            self._stopped.set()

    def _disconnected(self, unused_client) -> None:
        log.info('Bridge: notified of disconnect')
        self._tx.put_nowait(bytearray())

    async def ble(self):
        """Connects and handles the Bluetooth connection."""
        if self._stop.is_set():
            return

        async with _LOCK:
            log.info(f'connecting to {self._address}')
            await self._device.connect()

        with _CONNECTED.labels(self._address).track_inprogress():
            log.info(f'Bridge: connected to {self._address}')
            try:
                self._device.set_disconnected_callback(self._disconnected)

                tx_uuid = None
                rx_uuid = None

                services = await self._device.get_services()
                for service in services:
                    for ch in service.characteristics:
                        if ch.uuid in _TX_UUIDS:
                            tx_uuid = ch.uuid
                        if ch.uuid in _RX_UUIDS:
                            rx_uuid = ch.uuid

                if not tx_uuid or not rx_uuid:
                    log.warning('tx_uuid or rx_uuid not found, giving up')
                    return

                await self._device.start_notify(rx_uuid, self._notify)
                while True:
                    if self._stop.is_set():
                        return
                    if not await self._device.is_connected():
                        return

                    tx = await self._tx.get()
                    if not tx:
                        continue
                    for i in range(0, len(tx), _TX_CAP):
                        await self._device.write_gatt_char(
                            tx_uuid, tx[i:i + _TX_CAP])
                    _SENT.labels(self._address).inc(len(tx))
            finally:
                if await self._device.is_connected():
                    await self._device.disconnect()
                log.info('Bridge: disconnected')

    async def stop(self):
        self._stop.set()
        await self._tx.put(None)
        await self._stopped.wait()
        log.info('Bridge: stopped')


@click.command()
@click.option('--mac',
              type=str,
              required=True,
              multiple=True,
              help='MAC address to connect to.')
@click.option('--port',
              type=int,
              default=9876,
              help='Port number to listen on.')
@click.option('--prometheus-port',
              type=int,
              default=7011,
              help='Port number to listen for monitoring on.')
def main(mac: Sequence[str], port: int, prometheus_port: Optional[int]):
    logging.basicConfig(
        format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
        level=logging.INFO)

    if prometheus_port:
        prometheus_client.start_http_server(prometheus_port)

    bridges = [Bridge(mac, port + i) for i, mac in enumerate(mac)]

    loop = asyncio.get_event_loop()
    systemd_stopper.install(callback=loop.stop)

    try:
        loop.run_until_complete(
            asyncio.wait([bridge.run() for bridge in bridges]))
    except (KeyboardInterrupt, RuntimeError):
        pass

    loop = asyncio.get_event_loop()
    loop.run_until_complete(asyncio.wait([bridge.stop()
                                          for bridge in bridges]))


if __name__ == '__main__':
    main()