"""Persistentní Modbus TCP klient na sdílené Waveshare / RS485 bráně (jedno spojení + lock)."""

from __future__ import annotations

import asyncio
import logging
from collections.abc import AsyncIterator
from contextlib import asynccontextmanager

from pymodbus.client import AsyncModbusTcpClient

logger = logging.getLogger(__name__)


class ModbusBatch:
    """Více read/write pod jedním držením locku (žádný jiný task na stejném klientovi mezi nimi)."""

    def __init__(self, owner: PersistentModbusClient) -> None:
        self._o = owner

    async def read_register(self, address: int) -> int:
        return await self._o._read_register_locked(address)

    async def read_register_signed(self, address: int) -> int:
        raw = await self.read_register(address)
        return raw - 65536 if raw > 32767 else raw

    async def write_register(self, address: int, value: int) -> bool:
        return await self._o._write_register_locked(address, value)

    async def write_registers(self, address: int, values: list[int]) -> bool:
        return await self._o._write_registers_locked(address, values)


class PersistentModbusClient:
    """
    Jedno persistentní TCP spojení na převodník.
    Serializuje všechny požadavky přes asyncio.Lock().
    Automaticky reconnectuje při výpadku.
    """

    def __init__(self, host: str, port: int, device_id: int = 1) -> None:
        self.host = host
        self.port = port
        self.device_id = device_id
        self._client: AsyncModbusTcpClient | None = None
        self._lock = asyncio.Lock()

    async def _ensure_connected(self) -> None:
        if self._client is not None and self._client.connected:
            return
        if self._client is not None:
            self._client.close()
            self._client = None
        logger.info("Modbus connecting %s:%s dev=%s", self.host, self.port, self.device_id)
        self._client = AsyncModbusTcpClient(
            self.host,
            port=self.port,
            timeout=5,
            retries=2,
        )
        await self._client.connect()
        if not self._client.connected:
            self._client.close()
            self._client = None
            raise ConnectionError(f"Cannot connect Modbus {self.host}:{self.port}")
        logger.info("Modbus connected %s:%s", self.host, self.port)

    async def _read_register_locked(self, address: int) -> int:
        if self._client is None or not self._client.connected:
            await self._ensure_connected()
        assert self._client is not None
        try:
            r = await self._client.read_holding_registers(
                address, count=1, device_id=self.device_id
            )
            if r.isError() or not getattr(r, "registers", None):
                raise OSError(f"Read error 0x{address:04X}: {r!r}")
            return int(r.registers[0])
        except Exception as e:
            logger.warning("Modbus read 0x%04X failed: %s", address, e)
            self._client.close()
            self._client = None
            raise

    async def _write_registers_locked(self, address: int, values: list[int]) -> bool:
        if self._client is None or not self._client.connected:
            await self._ensure_connected()
        assert self._client is not None
        try:
            clamped = [max(0, min(65535, int(v))) for v in values]
            r = await self._client.write_registers(
                address, clamped, device_id=self.device_id
            )
            if r.isError():
                raise OSError(f"Write error 0x{address:04X}={clamped}: {r!r}")
            return True
        except Exception as e:
            logger.warning(
                "Modbus write_registers 0x%04X failed: %s", address, e
            )
            self._client.close()
            self._client = None
            raise

    async def _write_register_locked(self, address: int, value: int) -> bool:
        if self._client is None or not self._client.connected:
            await self._ensure_connected()
        assert self._client is not None
        try:
            v = max(0, min(65535, int(value)))
            r = await self._client.write_register(address, v, device_id=self.device_id)
            if r.isError():
                raise OSError(f"Write error 0x{address:04X}={v}: {r!r}")
            return True
        except Exception as e:
            logger.warning("Modbus write 0x%04X=%s failed: %s", address, value, e)
            self._client.close()
            self._client = None
            raise

    async def read_register(self, address: int) -> int:
        async with self._lock:
            await self._ensure_connected()
            return await self._read_register_locked(address)

    async def read_register_signed(self, address: int) -> int:
        raw = await self.read_register(address)
        return raw - 65536 if raw > 32767 else raw

    async def write_register(self, address: int, value: int) -> bool:
        async with self._lock:
            await self._ensure_connected()
            return await self._write_register_locked(address, value)

    async def write_registers(self, address: int, values: list[int]) -> bool:
        """FC 0x10 – povinné pro Deye registry 60–499 (jeden i více registrů)."""
        async with self._lock:
            await self._ensure_connected()
            return await self._write_registers_locked(address, values)

    @asynccontextmanager
    async def batch(self) -> AsyncIterator[ModbusBatch]:
        """Drží lock pro více po sobě jdoucích operací (telemetrie vs. control na stejné bráně)."""
        async with self._lock:
            await self._ensure_connected()
            yield ModbusBatch(self)

    def close(self) -> None:
        if self._client is not None:
            self._client.close()
            self._client = None


_clients: dict[str, PersistentModbusClient] = {}
_registry_lock = asyncio.Lock()


async def get_modbus_client(
    host: str, port: int, device_id: int = 1
) -> PersistentModbusClient:
    key = f"{host}:{port}:{device_id}"
    async with _registry_lock:
        if key not in _clients:
            _clients[key] = PersistentModbusClient(host, port, device_id)
        return _clients[key]