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

from __future__ import annotations

import asyncio
import hashlib
import logging
import os
from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from pathlib import Path

from pymodbus.client import AsyncModbusTcpClient

try:
    import fcntl

    _FCNTL = True
except ImportError:
    fcntl = None  # type: ignore[assignment]
    _FCNTL = False

logger = logging.getLogger(__name__)

_flock_warned = False


_BACKEND_ROOT = Path(__file__).resolve().parent.parent
_DEFAULT_LOCK_DIR = _BACKEND_ROOT / ".ems-modbus-locks"


def _gateway_lock_path(host: str, port: int) -> Path:
    # Výchozí = backend/.ems-modbus-locks (v Dockeru /app → mount ./backend), aby flock sdílel
    # hostitel + kontejner při dvou backend procesech na stejné bráně; přepiš EMS_MODBUS_LOCK_DIR.
    base = Path(os.getenv("EMS_MODBUS_LOCK_DIR", str(_DEFAULT_LOCK_DIR)))
    h = hashlib.sha256(f"{host.strip()}:{int(port)}".encode()).hexdigest()[:20]
    return base / f"{h}.lock"


@asynccontextmanager
async def _gateway_exclusive(host: str, port: int):
    """
    Jedna RS485 linka přes levné TCP↔serial brány nesmí obsluhovat dva procesy najednou —
    odpovědi pak mají cizí transaction_id (např. 22 vs 54000). flock serializuje napříč PID.
    Vypnout: EMS_MODBUS_DISABLE_FLOCK=1 (nebo neexistující fcntl, např. Windows).
    """
    global _flock_warned
    port_i = int(port)
    host_s = host.strip()
    if (
        not _FCNTL
        or os.getenv("EMS_MODBUS_DISABLE_FLOCK", "").lower() in ("1", "true", "yes")
    ):
        if not _FCNTL and not _flock_warned:
            logger.warning(
                "Modbus: fcntl nedostupný — meziprocesová serializace na bránu %s:%s "
                "neaktivní (riziko kolizí při dvou masterech)",
                host_s,
                port_i,
            )
            _flock_warned = True
        yield
        return

    path = _gateway_lock_path(host_s, port_i)
    path.parent.mkdir(parents=True, exist_ok=True)
    f = open(path, "a+b")  # noqa: SIM115
    try:
        await asyncio.to_thread(fcntl.flock, f.fileno(), fcntl.LOCK_EX)
        yield
    finally:
        try:
            await asyncio.to_thread(fcntl.flock, f.fileno(), fcntl.LOCK_UN)
        except OSError:
            pass
        f.close()


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

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

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

    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 read_holding_registers(self, address: int, count: int) -> list[int]:
        """Jedna PDU (FC3) pro po sobě jdoucí registry — méně kolizí na RS485 bránách."""
        return await self._o._read_holding_registers_locked(
            address, count, self._device_id
        )

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

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


class PersistentModbusClient:
    """
    Jedno persistentní TCP spojení na převodník (host:port).
    Unit ID se předává u každé operace — serial servery často nezvládají
    paralelní TCP sockety na stejnou bránu (pližící se transaction_id mismatch).
    Serializuje všechny požadavky přes asyncio.Lock().
    """

    def __init__(self, host: str, port: int) -> None:
        self.host = host.strip()
        self.port = int(port)
        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", self.host, self.port)
        self._client = AsyncModbusTcpClient(
            self.host,
            port=self.port,
            timeout=8,
            retries=3,
        )
        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, device_id: 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=int(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 _read_holding_registers_locked(
        self, address: int, count: int, device_id: int
    ) -> list[int]:
        if count < 1 or count > 125:
            raise ValueError(f"invalid holding register count: {count}")
        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=count, device_id=int(device_id)
            )
            if r.isError() or not getattr(r, "registers", None):
                raise OSError(f"Read error 0x{address:04X} x{count}: {r!r}")
            if len(r.registers) != count:
                raise OSError(
                    f"Read 0x{address:04X}: expected {count} regs, got {len(r.registers)}"
                )
            return [int(x) for x in r.registers]
        except Exception as e:
            logger.warning(
                "Modbus read 0x%04X count=%s failed: %s", address, count, e
            )
            self._client.close()
            self._client = None
            raise

    async def _write_registers_locked(
        self, address: int, values: list[int], device_id: 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=int(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, device_id: 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=int(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, device_id: int = 1) -> int:
        async with _gateway_exclusive(self.host, self.port):
            async with self._lock:
                await self._ensure_connected()
                return await self._read_register_locked(address, device_id)

    async def read_register_signed(self, address: int, device_id: int = 1) -> int:
        raw = await self.read_register(address, device_id)
        return raw - 65536 if raw > 32767 else raw

    async def write_register(self, address: int, value: int, device_id: int = 1) -> bool:
        async with _gateway_exclusive(self.host, self.port):
            async with self._lock:
                await self._ensure_connected()
                return await self._write_register_locked(address, value, device_id)

    async def write_registers(
        self, address: int, values: list[int], device_id: int = 1
    ) -> bool:
        """FC 0x10 – povinné pro Deye registry 60–499 (jeden i více registrů)."""
        async with _gateway_exclusive(self.host, self.port):
            async with self._lock:
                await self._ensure_connected()
                return await self._write_registers_locked(address, values, device_id)

    async def force_disconnect(self) -> None:
        """Uzavře socket pod lockem (např. před retry po chybě)."""
        async with _gateway_exclusive(self.host, self.port):
            async with self._lock:
                if self._client is not None:
                    self._client.close()
                    self._client = None

    @asynccontextmanager
    async def batch(self, device_id: int = 1) -> AsyncIterator[ModbusBatch]:
        """Drží lock pro více po sobě jdoucích operací (telemetrie vs. control na stejné bráně)."""
        async with _gateway_exclusive(self.host, self.port):
            async with self._lock:
                await self._ensure_connected()
                yield ModbusBatch(self, int(device_id))

    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) -> PersistentModbusClient:
    """Jedno TCP spojení na převodník podle host:port (unit ID u jednotlivých volání)."""
    key = f"{host.strip()}:{int(port)}"
    async with _registry_lock:
        if key not in _clients:
            _clients[key] = PersistentModbusClient(host.strip(), port)
        return _clients[key]