dcc-rs 0.2.0

// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! This module provides types and serialisers for each packet type
//! defined by the NMRA standard.

use crate::Error;
use bitvec::prelude::*;

/// Convenient Result wrapper
pub type Result<T> = core::result::Result<T, Error>;

struct Preamble(BitArr!(for 14, in u8, Msb0));

/// Buffer long enough to serialise any common DCC packet into
pub type SerialiseBuffer = BitArr!(for 43, in u8, Msb0);

impl Default for Preamble {
    fn default() -> Self {
        Self(BitArray::from([0xff, 0xff]))
    }
}

/// Possible directions, usually referenced to the "forward" direction
/// of a loco
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "use-defmt", derive(defmt::Format))]
pub enum Direction {
    /// Forward
    Forward,
    /// Backward
    Backward,
}

impl Default for Direction {
    fn default() -> Self {
        Self::Forward
    }
}

impl Direction {
    /// Switches a direction to the opposite one
    pub fn toggle(&mut self) {
        use Direction::*;
        *self = match *self {
            Forward => Backward,
            Backward => Forward,
        }
    }
}

/// Speed and Direction packet. Used to command a loco to move in the
/// given direction at the given speed.
///
/// The speed part of the instruction is five bits wide, with the bits
/// ordered `04321`, where `0` is LSB and `4` is MSB. The speed
/// instructions are defined by the following list:
/// ```ignore
///  0 4321 | meaning
///  ---------------------------------------------
///  0 0000 | stop
///  1 0000 | also stop
///  0 0001 | e-stop
///  1 0001 | also e-stop
///  0 0010 | speed 1 (0x04)
///   ...   |   ...
///  1 1111 | speed 28 (0x1f)
/// ```
pub struct SpeedAndDirection {
    address: u8,
    instruction: u8,
    ecc: u8,
}

impl SpeedAndDirection {
    /// Builder interface for `SpeedAndDirection`. Use of the Builder
    /// pattern ensures that only valid packets are produced.
    pub fn builder() -> SpeedAndDirectionBuilder {
        SpeedAndDirectionBuilder::default()
    }

    /// Serialise the packed into the provided buffer
    pub fn serialise(&self, buf: &mut SerialiseBuffer) -> Result<usize> {
        buf[0..16].copy_from_bitslice([0xff, 0xfe].view_bits::<Msb0>()); // preamble
        buf.set(15, false); // start bit
        buf[16..24].copy_from_bitslice([self.address].view_bits::<Msb0>());
        buf.set(24, false); // data start bit
        buf[25..33].copy_from_bitslice([self.instruction].view_bits::<Msb0>());
        buf.set(33, false); // ecc start bit
        buf[34..42].copy_from_bitslice([self.ecc].view_bits::<Msb0>());

        buf.set(42, true); // stop bit

        Ok(43)
    }
}

/// Builder used to construct a SpeedAndDirection packet
#[derive(Default)]
pub struct SpeedAndDirectionBuilder {
    address: Option<u8>,
    speed: Option<u8>,
    e_stop: bool,
    direction: Option<Direction>,
}

impl SpeedAndDirectionBuilder {
    /// Sets the address. In short mode the address has to be between 1
    /// and 126. Returns `Error::InvalidAddress` if the provided address
    /// is outside this range.
    pub fn address(&mut self, address: u8) -> Result<&mut Self> {
        if address == 0 || address > 0x7f {
            Err(Error::InvalidAddress)
        } else {
            self.address = Some(address);
            Ok(self)
        }
    }

    /// Sets the speed. In short mode the speed has to be between 0 and
    /// 16. Returns `Error::InvalidSpeed` if the provided speed is outside
    /// this range.
    pub fn speed(&mut self, speed: u8) -> Result<&mut Self> {
        if speed > 28 {
            Err(Error::InvalidSpeed)
        } else {
            self.speed = Some(speed);
            Ok(self)
        }
    }

    /// Sets the direction
    pub fn direction(&mut self, direction: Direction) -> &mut Self {
        self.direction = Some(direction);
        self
    }

    /// Sends the e-stop signal. Overrides any other set speed value
    pub fn e_stop(&mut self, e_stop: bool) -> &mut Self {
        self.e_stop = e_stop;
        self
    }

    /// Build a `SpeedAndDirection` packet using the provided values,
    /// falling back to sensible defaults if not all fields have been
    /// provided.
    ///
    /// Defaults:
    /// * `speed = 0`
    /// * `direction = Forward`
    /// * `address = 3`
    /// * `headlight = false`
    pub fn build(&mut self) -> SpeedAndDirection {
        let address = self.address.unwrap_or(3);
        // add the weird offset to the speed
        let speed = match self.speed {
            Some(0) | None => 0,
            Some(speed) => speed + 3,
        };
        #[cfg(test)]
        eprintln!("Speed is {speed} = {speed:08b}");
        let mut instruction = 0b0100_0000; // packet type
        if let Direction::Forward = self.direction.unwrap_or_default() {
            instruction |= 0b0010_0000;
        }

        // e-stop overrides other speed setting
        if self.e_stop {
            instruction |= 0x01;
        } else {
            // upper four bits of speed
            instruction |= (speed >> 1) & 0x0f;

            // LSB of speed
            instruction |= (speed & 0x01) << 4;
        }

        let ecc = address ^ instruction;
        SpeedAndDirection {
            address,
            instruction,
            ecc,
        }
    }
}

/// A Reset packet is one in which the address, instruction, and ECC are
/// all zero. All decoders will, upon receiving this packet, reset to their
/// normal power-up state. Any speed or direction will be cleared and
/// locomotives stopped.
pub struct Reset;

impl Reset {
    /// Serialise the packed into the provided buffer
    pub fn serialise(&self, buf: &mut SerialiseBuffer) -> Result<usize> {
        buf[0..16].copy_from_bitslice([0xff, 0xfe].view_bits::<Msb0>()); // preamble
        buf.set(15, false); // start bit
        buf[16..24].copy_from_bitslice([0x00].view_bits::<Msb0>());
        buf.set(24, false); // data start bit
        buf[25..33].copy_from_bitslice([0x00].view_bits::<Msb0>());
        buf.set(33, false); // ecc start bit
        buf[34..42].copy_from_bitslice([0x00].view_bits::<Msb0>());
        buf.set(42, true); // stop bit

        Ok(43)
    }
}

/// An Idle packet is one in which the address is 0xff and instruction 0x00.
/// Upon receiving this, a decoder performs no new action.
pub struct Idle;

impl Idle {
    /// Serialise the packed into the provided buffer
    pub fn serialise(&self, buf: &mut SerialiseBuffer) -> Result<usize> {
        buf[0..16].copy_from_bitslice([0xff, 0xfe].view_bits::<Msb0>()); // preamble
        buf.set(15, false); // start bit
        buf[16..24].copy_from_bitslice([0xff].view_bits::<Msb0>());
        buf.set(24, false); // data start bit
        buf[25..33].copy_from_bitslice([0x00].view_bits::<Msb0>());
        buf.set(33, false); // ecc start bit
        buf[34..42].copy_from_bitslice([0xff].view_bits::<Msb0>());
        buf.set(42, true); // stop bit

        Ok(43)
    }
}

/// Instruct all decoders to stop, either immediately or by simply
/// removing motor power ("float"). The specification allows a direction
/// field, but that is not implemented here because in situations where
/// a BroadcastStop is being sent it is unlikely that direction settings
/// will be important. (whereas a regular stop might wish to retain
/// headlight states)
pub struct BroadcastStop {
    float: bool,
}

impl BroadcastStop {
    /// Bring all locomotives to an immediate stop
    pub fn immediate() -> Self {
        Self { float: false }
    }

    /// Bring all locomotives to a gently/floating stop
    pub fn float() -> Self {
        Self { float: true }
    }

    /// Serialise the packed into the provided buffer
    pub fn serialise(&self, buf: &mut SerialiseBuffer) -> Result<usize> {
        let instr = if self.float { 0b0101_0000 } else { 0b0100_0000 };
        buf[0..16].copy_from_bitslice([0xff, 0xfe].view_bits::<Msb0>()); // preamble
        buf.set(15, false); // start bit
        buf[16..24].copy_from_bitslice([0x00].view_bits::<Msb0>());
        buf.set(24, false); // data start bit
        buf[25..33].copy_from_bitslice([instr].view_bits::<Msb0>());
        buf.set(33, false); // ecc start bit
        buf[34..42].copy_from_bitslice([instr].view_bits::<Msb0>());
        buf.set(42, true); // stop bit

        Ok(43)
    }
}

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

    fn display_serialise_buffer(buf: &SerialiseBuffer) {
        println!("{buf:?}");
        //        15              1 8        1 8        1 8        1
        //        15              16 24      25 33      34 42      43
        println!("ppppppppppppppp s aaaaaaaa s 01dvvvvv s cccccccc s");
        println!(
            "{} {} {} {} {} {} {} {}",
            buf[..15]
                .iter()
                .map(|b| if *b { "1" } else { "0" })
                .collect::<Vec<_>>()
                .join(""),
            if *buf.get(15).unwrap() { "1" } else { "0" },
            buf[16..24]
                .iter()
                .map(|b| if *b { "1" } else { "0" })
                .collect::<Vec<_>>()
                .join(""),
            if *buf.get(24).unwrap() { "1" } else { "0" },
            buf[25..33]
                .iter()
                .map(|b| if *b { "1" } else { "0" })
                .collect::<Vec<_>>()
                .join(""),
            if *buf.get(33).unwrap() { "1" } else { "0" },
            buf[34..42]
                .iter()
                .map(|b| if *b { "1" } else { "0" })
                .collect::<Vec<_>>()
                .join(""),
            if *buf.get(42).unwrap() { "1" } else { "0" },
        );
    }

    #[test]
    fn make_speed_and_direction() -> Result<()> {
        let pkt = SpeedAndDirection::builder()
            .address(35)?
            .speed(14)?
            .direction(Direction::Forward)
            .build();
        assert_eq!(pkt.address, 35);
        let expected = 0b0111_1000;
        eprintln!("Got instruction: {:08b}", pkt.instruction);
        eprintln!("Expected:        {expected:08b}");
        assert_eq!(pkt.instruction, expected);
        assert_eq!(pkt.ecc, 0x5b);

        Ok(())
    }

    #[test]
    fn serialise_speed_and_direction() -> Result<()> {
        let pkt = SpeedAndDirection::builder()
            .address(35)?
            .speed(14)?
            .direction(Direction::Forward)
            .build();
        let mut buf = SerialiseBuffer::default();
        let len = pkt.serialise(&mut buf)?;
        // instruction is:
        // 01 D S SSSS
        // 01 1 1 1101
        #[allow(clippy::unusual_byte_groupings)]
        let expected_arr = [
            0xff_u8,      // preamble
            0b1111_1110,  // preamble + start
            35,           // address
            0b0_0111_100, // start + instr[..7]
            0b0_0_010110, // instr[7] + start + ecc[..6]
            0b11_1_00000, // ecc[6..] + stop + 5 zeroes
        ];
        let mut expected = SerialiseBuffer::default();
        expected[..43]
            .copy_from_bitslice(&expected_arr.view_bits::<Msb0>()[..43]);
        println!("got:");
        display_serialise_buffer(&buf);
        println!("expected:");
        display_serialise_buffer(&expected);
        assert_eq!(len, 43);
        assert_eq!(buf[..len], expected[..43]);
        Ok(())
    }

    #[test]
    fn serialise_reset_packet() -> Result<()> {
        let pkt = Reset;
        let mut buf = SerialiseBuffer::default();
        let len = pkt.serialise(&mut buf)?;

        #[allow(clippy::unusual_byte_groupings)]
        let expected_arr = [
            0xff_u8,      // preamble
            0b1111_1110,  // preamble + start
            0x00,         // address
            0b0_0000_000, // start + instr[..7]
            0b0_0_000000, // instr[7] + start + ecc[..6]
            0b00_1_00000, // ecc[6..] + stop + 5 zeroes
        ];

        let mut expected = SerialiseBuffer::default();
        expected[..43]
            .copy_from_bitslice(&expected_arr.view_bits::<Msb0>()[..43]);
        println!("got:");
        display_serialise_buffer(&buf);
        println!("expected:");
        display_serialise_buffer(&expected);
        assert_eq!(len, 43);
        assert_eq!(buf[..len], expected[..43]);
        Ok(())
    }

    #[test]
    fn serialise_idle_packet() -> Result<()> {
        let pkt = Idle;
        let mut buf = SerialiseBuffer::default();
        let len = pkt.serialise(&mut buf)?;

        #[allow(clippy::unusual_byte_groupings)]
        let expected_arr = [
            0xff_u8,      // preamble
            0b1111_1110,  // preamble + start
            0xff,         // address
            0b0_0000_000, // start + instr[..7]
            0b0_0_111111, // instr[7] + start + ecc[..6]
            0b11_1_00000, // ecc[6..] + stop + 5 zeroes
        ];

        let mut expected = SerialiseBuffer::default();
        expected[..43]
            .copy_from_bitslice(&expected_arr.view_bits::<Msb0>()[..43]);
        println!("got:");
        display_serialise_buffer(&buf);
        println!("expected:");
        display_serialise_buffer(&expected);
        assert_eq!(len, 43);
        assert_eq!(buf[..len], expected[..43]);
        Ok(())
    }

    #[test]
    fn serialise_broadcast_stop_packet() -> Result<()> {
        let pkt = BroadcastStop::float();
        let mut buf = SerialiseBuffer::default();
        let len = pkt.serialise(&mut buf)?;

        #[allow(clippy::unusual_byte_groupings)]
        let expected_arr = [
            0xff_u8,      // preamble
            0b1111_1110,  // preamble + start
            0x00,         // address
            0b0_0101_000, // start + instr[..7]
            0b0_0_010100, // instr[7] + start + ecc[..6]
            0b00_1_00000, // ecc[6..] + stop + 5 zeroes
        ];

        let mut expected = SerialiseBuffer::default();
        expected[..43]
            .copy_from_bitslice(&expected_arr.view_bits::<Msb0>()[..43]);
        println!("got:");
        display_serialise_buffer(&buf);
        println!("expected:");
        display_serialise_buffer(&expected);
        assert_eq!(len, 43);
        assert_eq!(buf[..len], expected[..43]);
        Ok(())
    }
}