"""Backend template for implementing custom Modbus communication.

This template provides the complete interface for implementing a new Modbus backend.
Copy this file and implement all TODO sections with your backend library.

All functions use multipledispatch with a custom backend tag for type-based routing.
"""

from typing import List, Union
from multipledispatch import dispatch
import logging

from atmospyre.sensors.sensor import (
    ModbusBackendTag,
    modbusbackend_namespace,
    Byteorder,
    ModbusMode,
    Parity,
    Stopbits,
)

logger = logging.getLogger(__name__)

# ============================================================================
# BACKEND TAG DEFINITION
# ============================================================================


class CustomBackendTag(ModbusBackendTag):
    """Backend tag for your custom Modbus library.

    This tag is used by multipledispatch to route operations to your
    backend implementation. Create one instance and pass it to sensors.

    Examples
    --------
    >>> from atmospyre.sensors.backends.custom import CustomBackendTag
    >>> backend = CustomBackendTag()
    >>> sensor = GMP252(port='/dev/ttyUSB0', backend_tag=backend)
    """

    pass


# ============================================================================
# SECTION 1: ENUM MAPPING FUNCTIONS (4 required)
# ============================================================================
# Convert generic enums to backend-specific constants


@dispatch(Byteorder, CustomBackendTag, namespace=modbusbackend_namespace)
def _get_byteorder(byteorder_enum: Byteorder, backend_tag: CustomBackendTag):
    """Map generic Byteorder enum to backend byte order constant.

    Parameters
    ----------
    byteorder_enum : Byteorder
        Generic byte order enumeration (ABCD, BADC, CDAB, DCBA)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    Any
        Your backend's byte order constant

    Notes
    -----
    Map these values:
    - Byteorder.ABCD: Big-endian (most significant byte first)
    - Byteorder.BADC: Big-endian with byte swap
    - Byteorder.CDAB: Little-endian with byte swap
    - Byteorder.DCBA: Little-endian (least significant byte first)
    """
    # TODO: Implement byte order mapping
    raise NotImplementedError("Implement _get_byteorder for your backend")


@dispatch(ModbusMode, CustomBackendTag, namespace=modbusbackend_namespace)
def _get_modbus_mode(modbus_mode_enum: ModbusMode, backend_tag: CustomBackendTag):
    """Map generic ModbusMode enum to backend mode constant.

    Parameters
    ----------
    modbus_mode_enum : ModbusMode
        Generic Modbus mode (RTU or ASCII)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    Any
        Your backend's Modbus mode constant

    Notes
    -----
    Map these values:
    - ModbusMode.RTU: Binary Modbus RTU mode
    - ModbusMode.ASCII: ASCII-encoded Modbus ASCII mode
    """
    # TODO: Implement Modbus mode mapping
    raise NotImplementedError("Implement _get_modbus_mode for your backend")


@dispatch(Parity, CustomBackendTag, namespace=modbusbackend_namespace)
def _get_parity(parity_enum: Parity, backend_tag: CustomBackendTag):
    """Map generic Parity enum to backend parity constant.

    Parameters
    ----------
    parity_enum : Parity
        Generic parity mode (NONE, EVEN, ODD, MARK, SPACE)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    Any
        Your backend's parity constant
    """
    # TODO: Implement parity mapping
    raise NotImplementedError("Implement _get_parity for your backend")


@dispatch(Stopbits, CustomBackendTag, namespace=modbusbackend_namespace)
def _get_stopbits(stopbits_enum: Stopbits, backend_tag: CustomBackendTag):
    """Map generic Stopbits enum to backend stop bits constant.

    Parameters
    ----------
    stopbits_enum : Stopbits
        Generic stop bits (ONE, ONE_POINT_FIVE, TWO)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    Any
        Your backend's stop bits constant
    """
    # TODO: Implement stop bits mapping
    raise NotImplementedError("Implement _get_stopbits for your backend")


# ============================================================================
# SECTION 2: INSTRUMENT LIFECYCLE (3 required)
# ============================================================================
# Create, configure, and cleanup instrument instances


@dispatch(str, int, CustomBackendTag, namespace=modbusbackend_namespace)
def _create_instrument(port: str, slave_address: int, backend_tag: CustomBackendTag):
    """Create and return your backend's Modbus client instance.

    Called before each read/write operation.

    Parameters
    ----------
    port : str
        Serial port name (e.g., '/dev/ttyACM0', 'COM3')
    slave_address : int
        Modbus slave address (1-247)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    Any
        Your backend's unconfigured client/instrument instance

    Notes
    -----
    Return a fresh instance - do not configure it here.
    Configuration happens in _setup_instrument.
    """
    # TODO: Create and return your backend's Modbus client
    raise NotImplementedError("Implement _create_instrument for your backend")


@dispatch(
    object,
    int,
    Stopbits,
    int,
    Parity,
    ModbusMode,
    float,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _setup_instrument(
    instrument,
    baudrate: int,
    stopbits: Stopbits,
    bytesize: int,
    parity: Parity,
    modbus_mode: ModbusMode,
    timeout: float,
    backend_tag: CustomBackendTag,
) -> None:
    """Configure instrument with serial communication parameters.

    Called immediately after _create_instrument.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance (from _create_instrument)
    baudrate : int
        Serial baudrate (e.g., 9600, 19200, 115200)
    stopbits : Stopbits
        Number of stop bits
    bytesize : int
        Number of data bits (typically 8)
    parity : Parity
        Parity setting
    modbus_mode : ModbusMode
        Modbus mode (RTU or ASCII)
    timeout : float
        Serial timeout in seconds
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Important
    ---------
    MUST set equivalent of close_port_after_each_call=True to prevent
    serial port conflicts when multiple sensors share the same port.
    """
    # TODO: Configure your backend's instrument
    # Use mapping functions: _get_stopbits, _get_parity, _get_modbus_mode
    raise NotImplementedError("Implement _setup_instrument for your backend")


@dispatch(object, CustomBackendTag, namespace=modbusbackend_namespace)
def _open_port(instrument, backend_tag: CustomBackendTag) -> None:
    """Open the serial port explicitly.

    Called by the context manager before read/write operations.
    For backends with automatic port management, this can be a no-op.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If opening the port fails

    Notes
    -----
    - Check if port exists before opening
    - Check if already open before attempting to open
    - Log debug messages for troubleshooting
    - Raise IOError if opening fails (don't silently fail)

    Examples
    --------
    >>> # For minimalmodbus:
    >>> if instrument and hasattr(instrument, 'serial') and instrument.serial:
    ...     try:
    ...         if not instrument.serial.is_open:
    ...             instrument.serial.open()
    ...     except Exception as e:
    ...         logger.warning(f"Failed to open port: {e}")
    ...         raise
    """
    # TODO: Implement port opening for your backend
    raise NotImplementedError("Implement _open_port for your backend")


@dispatch(object, CustomBackendTag, namespace=modbusbackend_namespace)
def _close_port(instrument, backend_tag: CustomBackendTag) -> None:
    """Close the serial port explicitly.

    Called by the context manager after read/write operations.
    For backends with automatic port management, this can be a no-op.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Notes
    -----
    - Check if port exists before closing
    - Check if currently open before attempting to close
    - Catch and ignore exceptions (cleanup should never fail)
    - Log debug messages for troubleshooting

    Examples
    --------
    >>> # For minimalmodbus:
    >>> if instrument and hasattr(instrument, 'serial') and instrument.serial:
    ...     try:
    ...         if instrument.serial.is_open:
    ...             instrument.serial.close()
    ...     except Exception as e:
    ...         logger.warning(f"Failed to close port: {e}")
    """
    # TODO: Implement port closing for your backend
    raise NotImplementedError("Implement _close_port for your backend")


@dispatch(object, CustomBackendTag, namespace=modbusbackend_namespace)
def _cleanup_instrument(instrument, backend_tag: CustomBackendTag) -> None:
    """Close instrument and release serial port resources.

    Called after each read/write operation in a finally block.
    Must be defensive and never raise exceptions.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Notes
    -----
    - Check if instrument exists before accessing
    - Check if port exists and is open before closing
    - Catch and ignore all exceptions
    - This allows other sensors to use the same port
    - This is the final cleanup, called after _close_port

    Examples
    --------
    >>> # For minimalmodbus:
    >>> if instrument is not None:
    ...     if hasattr(instrument, 'serial') and instrument.serial is not None:
    ...         if hasattr(instrument.serial, 'is_open'):
    ...             try:
    ...                 if instrument.serial.is_open:
    ...                     instrument.serial.close()
    ...             except Exception:
    ...                 pass  # Silently ignore cleanup errors
    """
    # TODO: Close and cleanup your backend's instrument
    raise NotImplementedError("Implement _cleanup_instrument for your backend")


# ============================================================================
# SECTION 3: BIT OPERATIONS (4 required)
# ============================================================================
# Read/write individual and multiple bits (coils/discrete inputs)


@dispatch(object, object, object, CustomBackendTag, namespace=modbusbackend_namespace)
def _read_bit(
    instrument, address: int, functioncode: int, backend_tag: CustomBackendTag
) -> int:
    """Read one bit from the slave (coil or discrete input).

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Bit register address (0-based)
    functioncode : int
        Modbus function code (1: read coils, 2: read discrete inputs)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    int
        Bit value (0 or 1)

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement single bit read
    raise NotImplementedError("Implement _read_bit for your backend")


@dispatch(
    object, object, object, object, CustomBackendTag, namespace=modbusbackend_namespace
)
def _write_bit(
    instrument,
    address: int,
    value: int,
    functioncode: int,
    backend_tag: CustomBackendTag,
) -> None:
    """Write one bit to the slave (coil).

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Bit register address (0-based)
    value : int
        Value to write (0 or 1)
    functioncode : int
        Modbus function code (5: write single coil, 15: write multiple)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement single bit write
    raise NotImplementedError("Implement _write_bit for your backend")


@dispatch(
    object, object, object, object, CustomBackendTag, namespace=modbusbackend_namespace
)
def _read_bits(
    instrument,
    address: int,
    number_of_bits: int,
    functioncode: int,
    backend_tag: CustomBackendTag,
) -> List[int]:
    """Read multiple bits from the slave (coils or discrete inputs).

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting bit register address (0-based)
    number_of_bits : int
        Number of bits to read
    functioncode : int
        Modbus function code (1: read coils, 2: read discrete inputs)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    List[int]
        List of bit values (0 or 1)

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement multiple bits read
    raise NotImplementedError("Implement _read_bits for your backend")


@dispatch(object, object, object, CustomBackendTag, namespace=modbusbackend_namespace)
def _write_bits(
    instrument, address: int, values: List[int], backend_tag: CustomBackendTag
) -> None:
    """Write multiple bits to the slave (coils).

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting bit register address (0-based)
    values : List[int]
        List of values to write (0 or 1)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement multiple bits write
    raise NotImplementedError("Implement _write_bits for your backend")


# ============================================================================
# SECTION 4: 16-BIT REGISTER OPERATIONS (4 required)
# ============================================================================
# Read/write 16-bit signed/unsigned integers with optional decimal scaling


@dispatch(
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _read_register(
    instrument,
    address: int,
    number_of_decimals: int,
    functioncode: int,
    signed: bool,
    backend_tag: CustomBackendTag,
) -> Union[int, float]:
    """Read a 16-bit integer from a single register.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Register address (0-based)
    number_of_decimals : int
        Decimal scaling (divide by 10^number_of_decimals)
    functioncode : int
        Modbus function code (3: holding, 4: input)
    signed : bool
        Interpret as signed (-32768 to 32767) or unsigned (0 to 65535)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    int or float
        Register value (int if number_of_decimals=0, else float)

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    If number_of_decimals > 0, divide raw value by 10^number_of_decimals.
    Example: raw=235, decimals=1 → returns 23.5
    """
    # TODO: Implement 16-bit register read with decimal scaling
    raise NotImplementedError("Implement _read_register for your backend")


@dispatch(
    object,
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _write_register(
    instrument,
    address: int,
    value: Union[int, float],
    number_of_decimals: int,
    functioncode: int,
    signed: bool,
    backend_tag: CustomBackendTag,
) -> None:
    """Write a 16-bit integer to a single register.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Register address (0-based)
    value : int or float
        Value to write
    number_of_decimals : int
        Decimal scaling (multiply by 10^number_of_decimals before writing)
    functioncode : int
        Modbus function code (6: single, 16: multiple)
    signed : bool
        Interpret as signed or unsigned
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    If number_of_decimals > 0, multiply value by 10^number_of_decimals.
    Example: value=23.5, decimals=1 → writes 235
    """
    # TODO: Implement 16-bit register write with decimal scaling
    raise NotImplementedError("Implement _write_register for your backend")


@dispatch(
    object, object, object, object, CustomBackendTag, namespace=modbusbackend_namespace
)
def _read_registers(
    instrument,
    address: int,
    number_of_registers: int,
    functioncode: int,
    backend_tag: CustomBackendTag,
) -> List[int]:
    """Read multiple 16-bit integers from consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    number_of_registers : int
        Number of registers to read (max ~125)
    functioncode : int
        Modbus function code (3: holding, 4: input)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    List[int]
        List of register values (unsigned 16-bit: 0-65535)

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement multiple registers read
    raise NotImplementedError("Implement _read_registers for your backend")


@dispatch(object, object, object, CustomBackendTag, namespace=modbusbackend_namespace)
def _write_registers(
    instrument, address: int, values: List[int], backend_tag: CustomBackendTag
) -> None:
    """Write multiple 16-bit integers to consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    values : List[int]
        List of values to write (max ~123)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    Typically uses function code 16 (write multiple registers).
    """
    # TODO: Implement multiple registers write
    raise NotImplementedError("Implement _write_registers for your backend")


# ============================================================================
# SECTION 5: 32/64-BIT LONG INTEGER OPERATIONS (2 required)
# ============================================================================
# Read/write 32-bit and 64-bit signed/unsigned integers


@dispatch(
    object,
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _read_long(
    instrument,
    address: int,
    functioncode: int,
    signed: bool,
    byteorder: Byteorder,
    number_of_registers: int,
    backend_tag: CustomBackendTag,
) -> int:
    """Read a 32-bit or 64-bit integer from consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    functioncode : int
        Modbus function code (3: holding, 4: input)
    signed : bool
        Interpret as signed or unsigned
    byteorder : Byteorder
        Byte order (use _get_byteorder to convert)
    number_of_registers : int
        Number of registers (2: 32-bit, 4: 64-bit)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    int
        32-bit or 64-bit integer value

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    Use _get_byteorder to convert Byteorder enum to backend constant.
    """
    # TODO: Implement long integer read with byte order handling
    raise NotImplementedError("Implement _read_long for your backend")


@dispatch(
    object,
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _write_long(
    instrument,
    address: int,
    value: int,
    signed: bool,
    byteorder: Byteorder,
    number_of_registers: int,
    backend_tag: CustomBackendTag,
) -> None:
    """Write a 32-bit or 64-bit integer to consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    value : int
        Value to write
    signed : bool
        Interpret as signed or unsigned
    byteorder : Byteorder
        Byte order (use _get_byteorder to convert)
    number_of_registers : int
        Number of registers (2: 32-bit, 4: 64-bit)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement long integer write with byte order handling
    raise NotImplementedError("Implement _write_long for your backend")


# ============================================================================
# SECTION 6: 32/64-BIT FLOAT OPERATIONS (2 required)
# ============================================================================
# Read/write 32-bit single precision and 64-bit double precision floats


@dispatch(
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _read_float(
    instrument,
    address: int,
    functioncode: int,
    number_of_registers: int,
    byteorder: Byteorder,
    backend_tag: CustomBackendTag,
) -> float:
    """Read a floating point number from consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    functioncode : int
        Modbus function code (3: holding, 4: input)
    number_of_registers : int
        Number of registers (2: 32-bit float, 4: 64-bit double)
    byteorder : Byteorder
        Byte order (use _get_byteorder to convert)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    float
        Floating point value

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    Use _get_byteorder to convert Byteorder enum to backend constant.
    32-bit (single precision): number_of_registers=2
    64-bit (double precision): number_of_registers=4
    """
    # TODO: Implement float read with byte order handling
    raise NotImplementedError("Implement _read_float for your backend")


@dispatch(
    object,
    object,
    object,
    object,
    object,
    CustomBackendTag,
    namespace=modbusbackend_namespace,
)
def _write_float(
    instrument,
    address: int,
    value: Union[int, float],
    number_of_registers: int,
    byteorder: Byteorder,
    backend_tag: CustomBackendTag,
) -> None:
    """Write a floating point number to consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    value : float or int
        Value to write
    number_of_registers : int
        Number of registers (2: 32-bit float, 4: 64-bit double)
    byteorder : Byteorder
        Byte order (use _get_byteorder to convert)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails
    """
    # TODO: Implement float write with byte order handling
    raise NotImplementedError("Implement _write_float for your backend")


# ============================================================================
# SECTION 7: STRING OPERATIONS (2 required)
# ============================================================================
# Read/write ASCII strings from/to consecutive registers (2 chars per register)


@dispatch(
    object, object, object, object, CustomBackendTag, namespace=modbusbackend_namespace
)
def _read_string(
    instrument,
    address: int,
    number_of_registers: int,
    functioncode: int,
    backend_tag: CustomBackendTag,
) -> str:
    """Read an ASCII string from consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    number_of_registers : int
        Number of registers to read
    functioncode : int
        Modbus function code (3: holding, 4: input)
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Returns
    -------
    str
        ASCII string

    Raises
    ------
    IOError
        If communication with device fails

    Notes
    -----
    Each 16-bit register holds 2 ASCII characters.
    To read N characters, use number_of_registers = ceil(N/2).
    """
    # TODO: Implement string read (2 chars per register)
    raise NotImplementedError("Implement _read_string for your backend")


@dispatch(
    object, object, object, object, CustomBackendTag, namespace=modbusbackend_namespace
)
def _write_string(
    instrument,
    address: int,
    textstring: str,
    number_of_registers: int,
    backend_tag: CustomBackendTag,
) -> None:
    """Write an ASCII string to consecutive registers.

    Parameters
    ----------
    instrument : Any
        Your backend's client instance
    address : int
        Starting register address (0-based)
    textstring : str
        ASCII string to write (max 2*number_of_registers characters)
    number_of_registers : int
        Number of registers allocated for the string
    backend_tag : CustomBackendTag
        Backend tag for dispatch

    Raises
    ------
    IOError
        If communication with device fails
    ValueError
        If textstring is too long for allocated registers

    Notes
    -----
    Each register holds 2 characters.
    Shorter strings are typically padded with spaces.
    """
    # TODO: Implement string write (2 chars per register)
    raise NotImplementedError("Implement _write_string for your backend")
