"""
serial_port.py — Minimal 8N1 serial port using only the Python standard library.
Replaces pyserial for TrueNAS environments where pip is unavailable.
"""

import fcntl
import os
import select
import termios
import time
from typing import Optional


class SerialPort:
    BAUD_MAP = {
        9600:   termios.B9600,
        19200:  termios.B19200,
        38400:  termios.B38400,
        57600:  termios.B57600,
        115200: termios.B115200,
    }

    def __init__(self, port: str, baudrate: int = 115200, timeout: float = 5.0):
        self.port     = port
        self.baudrate = baudrate
        self.timeout  = timeout
        self._fd: Optional[int] = None
        self._saved_attrs       = None

    # ── Open / close ──────────────────────────────────────────────────────────
    def open(self):
        try:
            self._fd = os.open(self.port, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
        except OSError as e:
            raise OSError(f"Cannot open {self.port}: {e}") from e

        # Switch back to blocking mode now that O_NOCTTY is set
        flags = fcntl.fcntl(self._fd, fcntl.F_GETFL)
        fcntl.fcntl(self._fd, fcntl.F_SETFL, flags & ~os.O_NONBLOCK)

        self._saved_attrs = termios.tcgetattr(self._fd)

        # Raw 8N1: iflag, oflag, cflag, lflag, ispeed, ospeed, cc
        attrs = list(termios.tcgetattr(self._fd))
        baud  = self.BAUD_MAP.get(self.baudrate, termios.B115200)

        attrs[0] = termios.IGNBRK                               # iflag
        attrs[1] = 0                                             # oflag
        attrs[2] = termios.CS8 | termios.CREAD | termios.CLOCAL # cflag
        attrs[3] = 0                                             # lflag (raw)
        attrs[4] = baud                                          # ispeed
        attrs[5] = baud                                          # ospeed
        attrs[6][termios.VMIN]  = 0
        attrs[6][termios.VTIME] = min(int(self.timeout * 10), 255)

        termios.tcsetattr(self._fd, termios.TCSANOW, attrs)
        termios.tcflush(self._fd, termios.TCIOFLUSH)

    def close(self):
        if self._fd is not None:
            try:
                if self._saved_attrs:
                    termios.tcsetattr(self._fd, termios.TCSADRAIN, self._saved_attrs)
                os.close(self._fd)
            except OSError:
                pass
            finally:
                self._fd = None

    @property
    def is_open(self) -> bool:
        return self._fd is not None

    # ── Read / write ──────────────────────────────────────────────────────────
    def write(self, data: bytes):
        if self._fd is None:
            raise OSError("Port is not open")
        os.write(self._fd, data)

    def read_chunk(self, size: int = 4096) -> bytes:
        if self._fd is None:
            raise OSError("Port is not open")
        try:
            return os.read(self._fd, size)
        except OSError:
            return b""

    def read_until_quiet(self, quiet_period: float = 0.5,
                         timeout: Optional[float] = None) -> str:
        """
        Read until no new bytes arrive for `quiet_period` seconds,
        or until `timeout` (default: self.timeout) seconds have elapsed.
        Pass a longer timeout for operations like curl that take more time.
        """
        output   = b""
        deadline = time.monotonic() + (timeout if timeout is not None else self.timeout)
        last_rx  = time.monotonic()

        while True:
            now = time.monotonic()
            if now >= deadline:
                break
            if output and (now - last_rx) >= quiet_period:
                break

            wait = min(deadline - now, quiet_period)
            ready, _, _ = select.select([self._fd], [], [], wait)
            if ready:
                chunk = self.read_chunk()
                if chunk:
                    output  += chunk
                    last_rx  = time.monotonic()

        return output.decode("utf-8", errors="replace")

    def send_line(self, cmd: str = "", delay: float = 0.3):
        self.write((cmd + "\r\n").encode("utf-8"))
        time.sleep(delay)

    # ── Context manager ───────────────────────────────────────────────────────
    def __enter__(self):
        self.open()
        return self

    def __exit__(self, *_):
        self.close()