"""Encapsulated Interface (MEI) Transport Messages."""
from __future__ import annotations

import struct

from pymodbus.constants import DeviceInformation, ExcCodes, MoreData
from pymodbus.datastore import ModbusDeviceContext

from .decoders import DecodePDU
from .device import DeviceInformationFactory, ModbusControlBlock
from .exceptionresponse import ExceptionResponse
from .pdu import ModbusPDU


_MCB = ModbusControlBlock()


class _OutOfSpaceException(Exception):
    """Internal out of space exception."""

    # This exception exists here as a simple, local way to manage response
    # length control for the only MODBUS command which requires it under
    # standard, non-error conditions.
    #
    # See Page 5/50 of MODBUS Application Protocol Specification V1.1b3.

    def __init__(self, oid: int) -> None:
        self.oid = oid
        super().__init__()
        self.oid = oid


class ReadDeviceInformationRequest(ModbusPDU):
    """ReadDeviceInformationRequest."""

    function_code = 0x2B
    sub_function_code = 0x0E
    rtu_frame_size = 7

    def __init__(self, read_code: int | None = None, object_id: int = 0, dev_id: int = 1, transaction_id: int = 0) -> None:
        """Initialize a new instance."""
        super().__init__(transaction_id=transaction_id, dev_id=dev_id)
        self.read_code = read_code or DeviceInformation.BASIC
        self.object_id = object_id

    def encode(self) -> bytes:
        """Encode the request packet."""
        packet = struct.pack(
            ">BBB", self.sub_function_code, self.read_code, self.object_id
        )
        return packet

    @classmethod
    def decode_sub_function_code(cls, data: bytes) -> int:
        """Decode sub function code (1 byte)."""
        return int(data[2])

    def decode(self, data: bytes) -> None:
        """Decode data part of the message."""
        self.sub_function_code, self.read_code, self.object_id = struct.unpack(">BBB", data[:3])

    async def update_datastore(self, _context: ModbusDeviceContext) -> ModbusPDU:
        """Run a read exception status request against the store."""
        if not 0x00 <= self.object_id <= 0xFF:
            return ExceptionResponse(self.function_code, ExcCodes.ILLEGAL_VALUE)
        if not 0x00 <= self.read_code <= 0x04:
            return ExceptionResponse(self.function_code, ExcCodes.ILLEGAL_VALUE)

        information = DeviceInformationFactory.get(_MCB, self.read_code, self.object_id)
        return ReadDeviceInformationResponse(read_code=self.read_code, information=information, dev_id=self.dev_id, transaction_id=self.transaction_id)


class ReadDeviceInformationResponse(ModbusPDU):
    """ReadDeviceInformationResponse."""

    function_code = 0x2B
    sub_function_code = 0x0E

    @classmethod
    def calculateRtuFrameSize(cls, data: bytes) -> int:
        """Calculate the size of the message."""
        size = 8  # skip the header information
        if (data_len := len(data)) < size:
            return 999
        count = int(data[7])

        while count > 0:
            if data_len < size+2:
                return 998
            _, object_length = struct.unpack(">BB", data[size : size + 2])
            size += object_length + 2
            count -= 1
        return size + 2

    def __init__(self, read_code: int | None = None, information: dict | None = None, dev_id: int = 1, transaction_id: int = 0) -> None:
        """Initialize a new instance."""
        super().__init__(transaction_id=transaction_id, dev_id=dev_id)
        self.read_code = read_code or DeviceInformation.BASIC
        self.information = information or {}
        self.number_of_objects = 0
        self.conformity = 0x83  # I support everything right now
        self.next_object_id = 0x00
        self.more_follows = MoreData.NOTHING
        self.space_left = 253 - 6

    def _encode_object(self, object_id: int, data: bytes | ModbusPDU) -> bytes:
        """Encode object."""
        if not isinstance(data, bytes):
            data = data.encode()
        data_len = len(data)
        self.space_left -= 2 + data_len
        if self.space_left <= 0:
            raise _OutOfSpaceException(object_id)
        encoded_obj = struct.pack(">BB", object_id, data_len)
        encoded_obj += data
        self.number_of_objects += 1
        return encoded_obj

    def encode(self) -> bytes:
        """Encode the response."""
        packet = struct.pack(
            ">BBB", self.sub_function_code, self.read_code, self.conformity
        )
        objects = b""
        try:
            for object_id, data in iter(self.information.items()):
                if isinstance(data, list):
                    for item in data:
                        objects += self._encode_object(object_id, item)
                else:
                    objects += self._encode_object(object_id, data)
        except _OutOfSpaceException as exc:
            self.next_object_id = exc.oid
            self.more_follows = MoreData.KEEP_READING

        packet += struct.pack(
            ">BBB", self.more_follows, self.next_object_id, self.number_of_objects
        )
        packet += objects
        return packet

    @classmethod
    def decode_sub_function_code(cls, data: bytes) -> int:
        """Decode sub function code (1 byte)."""
        return int(data[2])

    def decode(self, data: bytes) -> None:
        """Decode a the response."""
        params = struct.unpack(">BBBBBB", data[0:6])
        self.sub_function_code, self.read_code = params[0:2]
        self.conformity, self.more_follows = params[2:4]
        self.next_object_id, self.number_of_objects = params[4:6]
        self.information, count = {}, 6  # skip the header information

        while count < len(data):
            object_id, object_length = struct.unpack(">BB", data[count : count + 2])
            count += object_length + 2
            if object_id not in self.information:
                self.information[object_id] = data[count - object_length : count]
            elif isinstance(self.information[object_id], list):
                self.information[object_id].append(data[count - object_length : count])
            else:
                self.information[object_id] = [
                    self.information[object_id],
                    data[count - object_length : count],
                ]

DecodePDU.add_pdu(ReadDeviceInformationRequest, ReadDeviceInformationResponse)
DecodePDU.add_sub_pdu(ReadDeviceInformationRequest, ReadDeviceInformationResponse)