"""
Mock serial port for tests and simulations.

This module provides :class:`MockSerial`, a lightweight stand-in for
``pyserial.Serial`` that can be injected where real UART hardware would
otherwise be needed.
"""

from __future__ import annotations

# ─── standard lib ────────────────────────────────────────────────────────
import random
import time
from typing import Callable, Optional

# ─── first-party ─────────────────────────────────────────────────────────
from measurement_acquisition.crc import Crc

# ─── types ───────────────────────────────────────────────────────────────
FrameFn = Callable[[], bytes]


def _default_frame() -> bytes:
    """Return a pseudo-random frame with a valid CRC byte."""
    time.sleep(1)  # mimic 1-second sampling cadence
    mu, sigma = 2.5, 1.5
    msb = int(round(random.gauss(mu, sigma))) % 55
    lsb = int(round(random.gauss(mu, sigma))) % 55
    frame = [5, 1, msb, lsb, 0]  # [START, LEN, MSB, LSB, CRC]
    frame[4] = Crc.calculate(frame[:-1])
    return bytes(frame)


class SerialException(Exception):
    """Raised when the virtual port is mis-used (e.g. read after close)."""


class MockSerial:  # pylint: disable=too-few-public-methods
    """
    Minimal drop-in replacement for ``pyserial.Serial``.

    Only the subset of functionality required by *measurement_acquisition*
    is implemented.
    """

    # ── construction ────────────────────────────────────────────────────
    def __init__(  # noqa: D401
        self,
        port: str,
        baudrate: int,
        timeout: Optional[float] = None,
        *,
        frame_fn: FrameFn = _default_frame,
        **_ignored,  # keep signature parity   # pylint: disable=unused-argument
    ) -> None:
        """Instantiate a mock serial port with the given parameters."""
        self.port = port
        self.baudrate = baudrate
        self.timeout = timeout
        self._is_open = True
        self._frame_fn = frame_fn
        self._tx_log: list[bytes] = []

    # ── pyserial-compatible API ─────────────────────────────────────────
    @property
    def is_open(self) -> bool:
        """Return ``True`` while the virtual port is open."""
        return self._is_open

    def flushInput(self) -> None:  # noqa: N802 (keep camelCase for API)
        """Discard unread bytes (no-op in this stub)."""

    def read(self, size: int = 1) -> bytes:  # pylint: disable=unused-argument
        """Return one full frame generated by *frame_fn*."""
        if not self._is_open:
            raise SerialException("Port is closed")
        return self._frame_fn()

    def write(self, data: bytes) -> int:
        """Record *data* in the internal TX log and echo it to RX."""
        if not self._is_open:
            raise SerialException("Port is closed")
        self._tx_log.append(bytes(data))
        return len(data)

    def close(self) -> None:
        """Mark the port as closed."""
        self._is_open = False