// SPDX-FileCopyrightText: Copyright (c) 2017-2024 slowtec GmbH <post@slowtec.de>
// SPDX-License-Identifier: MIT OR Apache-2.0

#[cfg(feature = "rtu")]
pub(crate) mod rtu;

#[cfg(feature = "tcp")]
pub(crate) mod tcp;

use std::{
    borrow::Cow,
    error,
    fmt::{self, Display},
};

use crate::bytes::Bytes;

/// A Modbus function code.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FunctionCode {
    /// Modbus Function Code: `01` (`0x01`).
    ReadCoils,
    /// Modbus Function Code: `02` (`0x02`).
    ReadDiscreteInputs,

    /// Modbus Function Code: `05` (`0x05`).
    WriteSingleCoil,
    /// Modbus Function Code: `06` (`0x06`).
    WriteSingleRegister,

    /// Modbus Function Code: `03` (`0x03`).
    ReadHoldingRegisters,
    /// Modbus Function Code: `04` (`0x04`).
    ReadInputRegisters,

    /// Modbus Function Code: `15` (`0x0F`).
    WriteMultipleCoils,
    /// Modbus Function Code: `16` (`0x10`).
    WriteMultipleRegisters,

    /// Modbus Function Code: `22` (`0x16`).
    MaskWriteRegister,

    /// Modbus Function Code: `23` (`0x17`).
    ReadWriteMultipleRegisters,

    /// Custom Modbus Function Code.
    Custom(u8),
}

impl FunctionCode {
    /// Create a new [`FunctionCode`] with `value`.
    #[must_use]
    pub const fn new(value: u8) -> Self {
        match value {
            0x01 => FunctionCode::ReadCoils,
            0x02 => FunctionCode::ReadDiscreteInputs,
            0x05 => FunctionCode::WriteSingleCoil,
            0x06 => FunctionCode::WriteSingleRegister,
            0x03 => FunctionCode::ReadHoldingRegisters,
            0x04 => FunctionCode::ReadInputRegisters,
            0x0F => FunctionCode::WriteMultipleCoils,
            0x10 => FunctionCode::WriteMultipleRegisters,
            0x16 => FunctionCode::MaskWriteRegister,
            0x17 => FunctionCode::ReadWriteMultipleRegisters,
            code => FunctionCode::Custom(code),
        }
    }

    /// Get the [`u8`] value of the current [`FunctionCode`].
    #[must_use]
    pub const fn value(self) -> u8 {
        match self {
            FunctionCode::ReadCoils => 0x01,
            FunctionCode::ReadDiscreteInputs => 0x02,
            FunctionCode::WriteSingleCoil => 0x05,
            FunctionCode::WriteSingleRegister => 0x06,
            FunctionCode::ReadHoldingRegisters => 0x03,
            FunctionCode::ReadInputRegisters => 0x04,
            FunctionCode::WriteMultipleCoils => 0x0F,
            FunctionCode::WriteMultipleRegisters => 0x10,
            FunctionCode::MaskWriteRegister => 0x16,
            FunctionCode::ReadWriteMultipleRegisters => 0x17,
            FunctionCode::Custom(code) => code,
        }
    }
}

impl Display for FunctionCode {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.value().fmt(f)
    }
}

/// A Modbus protocol address is represented by 16 bit from `0` to `65535`.
///
/// This *protocol address* uses 0-based indexing, while the *coil address* or
/// *register address* is often specified as a number with 1-based indexing.
/// Please consult the specification of your devices if 1-based coil/register
/// addresses need to be converted to 0-based protocol addresses by subtracting 1.
pub type Address = u16;

/// A Coil represents a single bit.
///
/// - `true` is equivalent to `ON`, `1` and `0xFF00`.
/// - `false` is equivalent to `OFF`, `0` and `0x0000`.
pub(crate) type Coil = bool;

/// Modbus uses 16 bit for its data items.
///
/// Transmitted using a big-endian representation.
pub(crate) type Word = u16;

/// Number of items to process.
pub type Quantity = u16;

/// A request represents a message from the client (master) to the server (slave).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Request<'a> {
    /// A request to read multiple coils.
    /// The first parameter is the address of the first coil to read.
    /// The second parameter is the number of coils to read.
    ReadCoils(Address, Quantity),

    /// A request to read multiple discrete inputs
    /// The first parameter is the address of the first discrete input to read.
    /// The second parameter is the number of discrete inputs to read.
    ReadDiscreteInputs(Address, Quantity),

    /// A request to write a single coil.
    /// The first parameter is the address of the coil.
    /// The second parameter is the value to write to the coil.
    WriteSingleCoil(Address, Coil),

    /// A request to write multiple coils.
    /// The first parameter is the address of the first coil to write.
    /// The second parameter is the vector of values to write to the coils.
    WriteMultipleCoils(Address, Cow<'a, [Coil]>),

    /// A request to read multiple input registers.
    /// The first parameter is the address of the first input register to read.
    /// The second parameter is the number of input registers to read.
    ReadInputRegisters(Address, Quantity),

    /// A request to read multiple holding registers.
    /// The first parameter is the address of the first holding register to read.
    /// The second parameter is the number of holding registers to read.
    ReadHoldingRegisters(Address, Quantity),

    /// A request to write a single register.
    /// The first parameter is the address of the register to read.
    /// The second parameter is the value to write to the register.
    WriteSingleRegister(Address, Word),

    /// A request to write to multiple registers.
    /// The first parameter is the address of the first register to write.
    /// The second parameter is the vector of values to write to the registers.
    WriteMultipleRegisters(Address, Cow<'a, [Word]>),

    /// A request to set or clear individual bits of a holding register.
    /// The first parameter is the address of the holding register.
    /// The second parameter is the AND mask.
    /// The third parameter is the OR mask.
    MaskWriteRegister(Address, Word, Word),

    /// A request to simultaneously read multiple registers and write multiple registers.
    /// The first parameter is the address of the first register to read.
    /// The second parameter is the number of registers to read.
    /// The third parameter is the address of the first register to write.
    /// The fourth parameter is the vector of values to write to the registers.
    ReadWriteMultipleRegisters(Address, Quantity, Address, Cow<'a, [Word]>),

    /// A raw Modbus request.
    /// The first parameter is the Modbus function code.
    /// The second parameter is the raw bytes of the request.
    Custom(u8, Cow<'a, [u8]>),

    /// A poison pill for stopping the client service and to release
    /// the underlying transport, e.g. for disconnecting from an
    /// exclusively used serial port.
    ///
    /// This is an ugly workaround, because `tokio-proto` does not
    /// provide other means to gracefully shut down the `ClientService`.
    /// Otherwise the bound transport is never freed as long as the
    /// executor is active, even when dropping the Modbus client
    /// context.
    Disconnect,
}

impl<'a> Request<'a> {
    /// Converts the request into an owned instance with `'static'` lifetime.
    #[must_use]
    pub fn into_owned(self) -> Request<'static> {
        use Request::*;

        match self {
            ReadCoils(addr, qty) => ReadCoils(addr, qty),
            ReadDiscreteInputs(addr, qty) => ReadDiscreteInputs(addr, qty),
            WriteSingleCoil(addr, coil) => WriteSingleCoil(addr, coil),
            WriteMultipleCoils(addr, coils) => {
                WriteMultipleCoils(addr, Cow::Owned(coils.into_owned()))
            }
            ReadInputRegisters(addr, qty) => ReadInputRegisters(addr, qty),
            ReadHoldingRegisters(addr, qty) => ReadHoldingRegisters(addr, qty),
            WriteSingleRegister(addr, word) => WriteSingleRegister(addr, word),
            WriteMultipleRegisters(addr, words) => {
                WriteMultipleRegisters(addr, Cow::Owned(words.into_owned()))
            }
            MaskWriteRegister(addr, and_mask, or_mask) => {
                MaskWriteRegister(addr, and_mask, or_mask)
            }
            ReadWriteMultipleRegisters(addr, qty, write_addr, words) => {
                ReadWriteMultipleRegisters(addr, qty, write_addr, Cow::Owned(words.into_owned()))
            }
            Custom(func, bytes) => Custom(func, Cow::Owned(bytes.into_owned())),
            Disconnect => Disconnect,
        }
    }

    /// Get the [`FunctionCode`] of the [`Request`].
    #[must_use]
    pub const fn function_code(&self) -> FunctionCode {
        use Request::*;

        match self {
            ReadCoils(_, _) => FunctionCode::ReadCoils,
            ReadDiscreteInputs(_, _) => FunctionCode::ReadDiscreteInputs,

            WriteSingleCoil(_, _) => FunctionCode::WriteSingleCoil,
            WriteMultipleCoils(_, _) => FunctionCode::WriteMultipleCoils,

            ReadInputRegisters(_, _) => FunctionCode::ReadInputRegisters,
            ReadHoldingRegisters(_, _) => FunctionCode::ReadHoldingRegisters,

            WriteSingleRegister(_, _) => FunctionCode::WriteSingleRegister,
            WriteMultipleRegisters(_, _) => FunctionCode::WriteMultipleRegisters,

            MaskWriteRegister(_, _, _) => FunctionCode::MaskWriteRegister,

            ReadWriteMultipleRegisters(_, _, _, _) => FunctionCode::ReadWriteMultipleRegisters,

            Custom(code, _) => FunctionCode::Custom(*code),

            Disconnect => unreachable!(),
        }
    }
}

/// A Modbus request with slave included
#[cfg(feature = "server")]
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SlaveRequest<'a> {
    /// Slave Id from the request
    pub slave: crate::slave::SlaveId,
    /// A `Request` enum
    pub request: Request<'a>,
}

#[cfg(feature = "server")]
impl<'a> SlaveRequest<'a> {
    /// Converts the request into an owned instance with `'static'` lifetime.
    #[must_use]
    pub fn into_owned(self) -> SlaveRequest<'static> {
        let Self { slave, request } = self;
        SlaveRequest {
            slave,
            request: request.into_owned(),
        }
    }
}

/// The data of a successful request.
///
/// ReadCoils/ReadDiscreteInputs: The length of the result Vec is always a
/// multiple of 8. Only the values of the first bits/coils that have actually
/// been requested are defined. The value of the remaining bits depend on the
/// server implementation and those coils should be should be ignored.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Response {
    /// Response to a ReadCoils request
    /// The parameter contains the coil values that have been read
    /// See also the note above regarding the vector length
    ReadCoils(Vec<Coil>),

    /// Response to a ReadDiscreteInputs request
    /// The parameter contains the discrete input values that have been read
    /// See also the note above regarding the vector length
    ReadDiscreteInputs(Vec<Coil>),

    /// Response to a WriteSingleCoil request
    /// The first parameter contains the address of the coil that has been written to
    /// The second parameter contains the value that has been written to the coil the given address
    WriteSingleCoil(Address, Coil),

    /// Response to a WriteMultipleCoils request
    /// The first parameter contains the address at the start of the range that has been written to
    /// The second parameter contains the amount of values that have been written
    WriteMultipleCoils(Address, Quantity),

    /// Response to a ReadInputRegisters request
    /// The parameter contains the register values that have been read
    ReadInputRegisters(Vec<Word>),

    /// Response to a ReadHoldingRegisters request
    /// The parameter contains the register values that have been read
    ReadHoldingRegisters(Vec<Word>),

    /// Response to a WriteSingleRegister request
    /// The first parameter contains the address of the register that has been written to
    /// The second parameter contains the value that has been written to the register at the given address
    WriteSingleRegister(Address, Word),

    /// Response to a WriteMultipleRegisters request
    /// The first parameter contains the address at the start of the register range that has been written to
    /// The second parameter contains the amount of register that have been written
    WriteMultipleRegisters(Address, Quantity),

    /// Response MaskWriteRegister
    /// The first parameter is the address of the holding register.
    /// The second parameter is the AND mask.
    /// The third parameter is the OR mask.
    MaskWriteRegister(Address, Word, Word),

    /// Response to a ReadWriteMultipleRegisters request
    /// The parameter contains the register values that have been read as part of the read instruction
    ReadWriteMultipleRegisters(Vec<Word>),

    /// Response to a raw Modbus request
    /// The first parameter contains the returned Modbus function code
    /// The second parameter contains the bytes read following the function code
    Custom(u8, Bytes),
}

impl Response {
    /// Get the [`FunctionCode`] of the [`Response`].
    #[must_use]
    pub const fn function_code(&self) -> FunctionCode {
        use Response::*;

        match self {
            ReadCoils(_) => FunctionCode::ReadCoils,
            ReadDiscreteInputs(_) => FunctionCode::ReadDiscreteInputs,

            WriteSingleCoil(_, _) => FunctionCode::WriteSingleCoil,
            WriteMultipleCoils(_, _) => FunctionCode::WriteMultipleCoils,

            ReadInputRegisters(_) => FunctionCode::ReadInputRegisters,
            ReadHoldingRegisters(_) => FunctionCode::ReadHoldingRegisters,

            WriteSingleRegister(_, _) => FunctionCode::WriteSingleRegister,
            WriteMultipleRegisters(_, _) => FunctionCode::WriteMultipleRegisters,

            MaskWriteRegister(_, _, _) => FunctionCode::MaskWriteRegister,

            ReadWriteMultipleRegisters(_) => FunctionCode::ReadWriteMultipleRegisters,

            Custom(code, _) => FunctionCode::Custom(*code),
        }
    }
}

/// A server (slave) exception.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum Exception {
    IllegalFunction = 0x01,
    IllegalDataAddress = 0x02,
    IllegalDataValue = 0x03,
    ServerDeviceFailure = 0x04,
    Acknowledge = 0x05,
    ServerDeviceBusy = 0x06,
    MemoryParityError = 0x08,
    GatewayPathUnavailable = 0x0A,
    GatewayTargetDevice = 0x0B,
}

impl From<Exception> for u8 {
    fn from(from: Exception) -> Self {
        from as u8
    }
}

impl Exception {
    pub(crate) fn description(&self) -> &str {
        use crate::frame::Exception::*;

        match *self {
            IllegalFunction => "Illegal function",
            IllegalDataAddress => "Illegal data address",
            IllegalDataValue => "Illegal data value",
            ServerDeviceFailure => "Server device failure",
            Acknowledge => "Acknowledge",
            ServerDeviceBusy => "Server device busy",
            MemoryParityError => "Memory parity error",
            GatewayPathUnavailable => "Gateway path unavailable",
            GatewayTargetDevice => "Gateway target device failed to respond",
        }
    }
}

/// A server (slave) exception response.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ExceptionResponse {
    pub function: FunctionCode,
    pub exception: Exception,
}

/// Represents a message from the client (slave) to the server (master).
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct RequestPdu<'a>(pub(crate) Request<'a>);

impl<'a> From<Request<'a>> for RequestPdu<'a> {
    fn from(from: Request<'a>) -> Self {
        RequestPdu(from)
    }
}

impl<'a> From<RequestPdu<'a>> for Request<'a> {
    fn from(from: RequestPdu<'a>) -> Self {
        from.0
    }
}

/// Represents a message from the server (slave) to the client (master).
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct ResponsePdu(pub(crate) Result<Response, ExceptionResponse>);

impl From<Response> for ResponsePdu {
    fn from(from: Response) -> Self {
        ResponsePdu(Ok(from))
    }
}

impl From<ExceptionResponse> for ResponsePdu {
    fn from(from: ExceptionResponse) -> Self {
        ResponsePdu(Err(from))
    }
}

impl From<Result<Response, ExceptionResponse>> for ResponsePdu {
    fn from(from: Result<Response, ExceptionResponse>) -> Self {
        ResponsePdu(from.map(Into::into).map_err(Into::into))
    }
}

#[cfg(any(
    feature = "rtu-over-tcp-server",
    feature = "rtu-server",
    feature = "tcp-server"
))]
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct OptionalResponsePdu(pub(crate) Option<ResponsePdu>);

#[cfg(any(
    feature = "rtu-over-tcp-server",
    feature = "rtu-server",
    feature = "tcp-server"
))]
impl<T> From<Option<T>> for OptionalResponsePdu
where
    T: Into<ResponsePdu>,
{
    fn from(from: Option<T>) -> Self {
        Self(from.map(Into::into))
    }
}

#[cfg(any(feature = "rtu-server", feature = "tcp-server"))]
impl<T> From<T> for OptionalResponsePdu
where
    T: Into<ResponsePdu>,
{
    fn from(from: T) -> Self {
        Self(Some(from.into()))
    }
}

impl From<ResponsePdu> for Result<Response, ExceptionResponse> {
    fn from(from: ResponsePdu) -> Self {
        from.0
    }
}

impl fmt::Display for Exception {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.description())
    }
}

impl error::Error for Exception {
    fn description(&self) -> &str {
        self.description()
    }
}

impl fmt::Display for ExceptionResponse {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Modbus function {}: {}", self.function, self.exception)
    }
}

impl error::Error for ExceptionResponse {
    fn description(&self) -> &str {
        self.exception.description()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn new_function_code() {
        assert_eq!(FunctionCode::ReadCoils, FunctionCode::new(0x01));
        assert_eq!(FunctionCode::ReadDiscreteInputs, FunctionCode::new(0x02));

        assert_eq!(FunctionCode::WriteSingleCoil, FunctionCode::new(0x05));
        assert_eq!(FunctionCode::WriteSingleRegister, FunctionCode::new(0x06));

        assert_eq!(FunctionCode::ReadHoldingRegisters, FunctionCode::new(0x03));
        assert_eq!(FunctionCode::ReadInputRegisters, FunctionCode::new(0x04));

        assert_eq!(FunctionCode::WriteMultipleCoils, FunctionCode::new(0x0F));
        assert_eq!(
            FunctionCode::WriteMultipleRegisters,
            FunctionCode::new(0x10)
        );

        assert_eq!(FunctionCode::MaskWriteRegister, FunctionCode::new(0x016));

        assert_eq!(
            FunctionCode::ReadWriteMultipleRegisters,
            FunctionCode::new(0x017)
        );

        assert_eq!(FunctionCode::Custom(70), FunctionCode::new(70));
    }

    #[test]
    fn function_code_values() {
        assert_eq!(FunctionCode::ReadCoils.value(), 0x01);
        assert_eq!(FunctionCode::ReadDiscreteInputs.value(), 0x02);

        assert_eq!(FunctionCode::WriteSingleCoil.value(), 0x05);
        assert_eq!(FunctionCode::WriteSingleRegister.value(), 0x06);

        assert_eq!(FunctionCode::ReadHoldingRegisters.value(), 0x03);
        assert_eq!(FunctionCode::ReadInputRegisters.value(), 0x04);

        assert_eq!(FunctionCode::WriteMultipleCoils.value(), 0x0F);
        assert_eq!(FunctionCode::WriteMultipleRegisters.value(), 0x10);

        assert_eq!(FunctionCode::MaskWriteRegister.value(), 0x016);

        assert_eq!(FunctionCode::ReadWriteMultipleRegisters.value(), 0x017);

        assert_eq!(FunctionCode::Custom(70).value(), 70);
    }

    #[test]
    fn function_code_from_request() {
        use Request::*;

        assert_eq!(ReadCoils(0, 0).function_code(), FunctionCode::ReadCoils);
        assert_eq!(
            ReadDiscreteInputs(0, 0).function_code(),
            FunctionCode::ReadDiscreteInputs
        );

        assert_eq!(
            WriteSingleCoil(0, true).function_code(),
            FunctionCode::WriteSingleCoil
        );
        assert_eq!(
            WriteMultipleCoils(0, Cow::Borrowed(&[])).function_code(),
            FunctionCode::WriteMultipleCoils
        );

        assert_eq!(
            ReadInputRegisters(0, 0).function_code(),
            FunctionCode::ReadInputRegisters
        );
        assert_eq!(
            ReadHoldingRegisters(0, 0).function_code(),
            FunctionCode::ReadHoldingRegisters
        );

        assert_eq!(
            WriteSingleRegister(0, 0).function_code(),
            FunctionCode::WriteSingleRegister
        );
        assert_eq!(
            WriteMultipleRegisters(0, Cow::Borrowed(&[])).function_code(),
            FunctionCode::WriteMultipleRegisters
        );

        assert_eq!(
            MaskWriteRegister(0, 0, 0).function_code(),
            FunctionCode::MaskWriteRegister
        );

        assert_eq!(
            ReadWriteMultipleRegisters(0, 0, 0, Cow::Borrowed(&[])).function_code(),
            FunctionCode::ReadWriteMultipleRegisters
        );

        assert_eq!(Custom(88, Cow::Borrowed(&[])).function_code().value(), 88);
    }

    #[test]
    fn function_code_from_response() {
        use Response::*;

        assert_eq!(ReadCoils(vec![]).function_code(), FunctionCode::ReadCoils);
        assert_eq!(
            ReadDiscreteInputs(vec![]).function_code(),
            FunctionCode::ReadDiscreteInputs
        );

        assert_eq!(
            WriteSingleCoil(0x0, false).function_code(),
            FunctionCode::WriteSingleCoil
        );
        assert_eq!(
            WriteMultipleCoils(0x0, 0x0).function_code(),
            FunctionCode::WriteMultipleCoils
        );

        assert_eq!(
            ReadInputRegisters(vec![]).function_code(),
            FunctionCode::ReadInputRegisters
        );
        assert_eq!(
            ReadHoldingRegisters(vec![]).function_code(),
            FunctionCode::ReadHoldingRegisters
        );

        assert_eq!(
            WriteSingleRegister(0, 0).function_code(),
            FunctionCode::WriteSingleRegister
        );
        assert_eq!(
            WriteMultipleRegisters(0, 0).function_code(),
            FunctionCode::WriteMultipleRegisters
        );

        assert_eq!(
            MaskWriteRegister(0, 0, 0).function_code(),
            FunctionCode::MaskWriteRegister
        );

        assert_eq!(
            ReadWriteMultipleRegisters(vec![]).function_code(),
            FunctionCode::ReadWriteMultipleRegisters
        );

        assert_eq!(
            Custom(99, Bytes::from_static(&[])).function_code().value(),
            99
        );
    }
}