m_bus_application_layer/

data_information.rs

use super::data_information::{self};
use super::variable_user_data::DataRecordError;
use super::LongTplHeader;

#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DataInformationBlock<'a> {
    pub data_information_field: DataInformationField,
    pub data_information_field_extension: Option<DataInformationFieldExtensions<'a>>,
}

impl DataInformationBlock<'_> {
    #[must_use]
    pub fn get_size(&self) -> usize {
        let mut size = 1;
        if let Some(dife) = &self.data_information_field_extension {
            size += dife.len();
        }
        size
    }
}
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DataInformationField {
    pub data: u8,
}

impl From<data_information::DataInformationError> for DataRecordError {
    fn from(error: data_information::DataInformationError) -> Self {
        Self::DataInformationError(error)
    }
}

impl From<u8> for DataInformationField {
    fn from(data: u8) -> Self {
        Self { data }
    }
}

impl From<u8> for DataInformationFieldExtension {
    fn from(data: u8) -> Self {
        Self { data }
    }
}

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, PartialEq)]
#[repr(transparent)]
pub struct DataInformationFieldExtension {
    pub data: u8,
}

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Clone, Debug, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DataInformationFieldExtensions<'a>(&'a [u8]);
impl<'a> DataInformationFieldExtensions<'a> {
    const fn new(data: &'a [u8]) -> Self {
        Self(data)
    }
}

impl Iterator for DataInformationFieldExtensions<'_> {
    type Item = DataInformationFieldExtension;
    fn next(&mut self) -> Option<Self::Item> {
        let (head, tail) = self.0.split_first()?;
        self.0 = tail;
        Some(DataInformationFieldExtension { data: *head })
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.0.len(), Some(self.0.len()))
    }
}
impl ExactSizeIterator for DataInformationFieldExtensions<'_> {}
impl DoubleEndedIterator for DataInformationFieldExtensions<'_> {
    fn next_back(&mut self) -> Option<Self::Item> {
        let (end, start) = self.0.split_last()?;
        self.0 = start;
        Some(DataInformationFieldExtension { data: *end })
    }
}

impl<'a> TryFrom<&'a [u8]> for DataInformationBlock<'a> {
    type Error = DataInformationError;

    fn try_from(data: &'a [u8]) -> Result<Self, DataInformationError> {
        let Some((dif_byte, data)) = data.split_first() else {
            return Err(DataInformationError::NoData);
        };
        let dif = DataInformationField::from(*dif_byte);

        if !dif.has_extension() {
            return Ok(DataInformationBlock {
                data_information_field: dif,
                data_information_field_extension: None,
            });
        }

        let length = data.iter().take_while(|&&u8| u8 & 0x80 != 0).count();
        let offset = length + 1;
        if offset > MAXIMUM_DATA_INFORMATION_SIZE {
            return Err(DataInformationError::DataTooLong);
        }
        Ok(DataInformationBlock {
            data_information_field: dif,
            data_information_field_extension: Some(DataInformationFieldExtensions::new(
                data.get(..offset)
                    .ok_or(DataInformationError::DataTooShort)?,
            )),
        })
    }
}

impl DataInformationField {
    const fn has_extension(&self) -> bool {
        self.data & 0x80 != 0
    }

    pub const fn is_special_function(&self) -> bool {
        self.data & 0x0F == 0x0F
    }

    pub const fn special_function(&self) -> SpecialFunctions {
        match self.data {
            0x0F => SpecialFunctions::ManufacturerSpecific,
            0x1F => SpecialFunctions::MoreRecordsFollow,
            0x2F => SpecialFunctions::IdleFiller,
            0x7F => SpecialFunctions::GlobalReadoutRequest,
            _ => SpecialFunctions::Reserved,
        }
    }
}
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DataInformation {
    pub storage_number: u64,
    pub tariff: u64,
    pub device: u64,
    pub function_field: FunctionField,
    pub data_field_coding: DataFieldCoding,
    pub data_information_extension: Option<DataInformationExtensionField>,
    pub size: usize,
}

#[cfg(feature = "std")]
impl std::fmt::Display for DataInformation {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "{},{},{}",
            self.storage_number, self.function_field, self.data_field_coding
        )
    }
}

const MAXIMUM_DATA_INFORMATION_SIZE: usize = 11;
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DataInformationExtensionField {}

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum DataInformationError {
    NoData,
    DataTooLong,
    DataTooShort,
    InvalidValueInformation,
    Unimplemented { feature: &'static str },
}

#[cfg(feature = "std")]
impl std::fmt::Display for DataInformationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            DataInformationError::NoData => write!(f, "No data available"),
            DataInformationError::DataTooLong => write!(f, "Data too long"),
            DataInformationError::DataTooShort => write!(f, "Data too short"),
            DataInformationError::InvalidValueInformation => {
                write!(f, "Invalid value information")
            }
            DataInformationError::Unimplemented { feature } => {
                write!(f, "Unimplemented feature: {}", feature)
            }
        }
    }
}

#[cfg(feature = "std")]
impl std::error::Error for DataInformationError {}

impl TryFrom<&DataInformationBlock<'_>> for DataInformation {
    type Error = DataInformationError;

    fn try_from(
        data_information_block: &DataInformationBlock,
    ) -> Result<Self, DataInformationError> {
        let dif = data_information_block.data_information_field.data;
        let possible_difes = &data_information_block.data_information_field_extension;
        let mut storage_number = u64::from((dif & 0b0100_0000) >> 6);

        let mut extension_bit = dif & 0x80 != 0;
        let mut extension_index = 1;
        let mut tariff = 0;
        let mut device = 0;
        if let Some(difes) = possible_difes {
            let mut tariff_index = 0;
            for (device_index, dife) in difes.clone().enumerate() {
                if extension_index > MAXIMUM_DATA_INFORMATION_SIZE {
                    return Err(DataInformationError::DataTooLong);
                }
                let dife = dife.data;
                storage_number += u64::from(dife & 0x0f) << ((extension_index * 4) + 1);
                tariff |= u64::from((dife & 0x30) >> 4) << (tariff_index);
                tariff_index += 2;
                device |= u64::from((dife & 0x40) >> 6) << device_index;
                extension_bit = dife & 0x80 != 0;
                extension_index += 1;
            }
        }

        let function_field = match (dif & 0b0011_0000) >> 4 {
            0b00 => FunctionField::InstantaneousValue,
            0b01 => FunctionField::MaximumValue,
            0b10 => FunctionField::MinimumValue,
            _ => FunctionField::ValueDuringErrorState,
        };
        let data_field_coding = match dif & 0b0000_1111 {
            0b0000 => DataFieldCoding::NoData,
            0b0001 => DataFieldCoding::Integer8Bit,
            0b0010 => DataFieldCoding::Integer16Bit,
            0b0011 => DataFieldCoding::Integer24Bit,
            0b0100 => DataFieldCoding::Integer32Bit,
            0b0101 => DataFieldCoding::Real32Bit,
            0b0110 => DataFieldCoding::Integer48Bit,
            0b0111 => DataFieldCoding::Integer64Bit,
            0b1000 => DataFieldCoding::SelectionForReadout,
            0b1001 => DataFieldCoding::BCD2Digit,
            0b1010 => DataFieldCoding::BCD4Digit,
            0b1011 => DataFieldCoding::BCD6Digit,
            0b1100 => DataFieldCoding::BCD8Digit,
            0b1101 => DataFieldCoding::VariableLength,
            0b1110 => DataFieldCoding::BCDDigit12,
            0b1111 => DataFieldCoding::SpecialFunctions(
                data_information_block
                    .data_information_field
                    .special_function(),
            ),
            _ => unreachable!(), // This case should never occur due to the 4-bit width
        };

        Ok(Self {
            storage_number,
            tariff,
            device,
            function_field,
            data_field_coding,
            data_information_extension: if extension_bit {
                Some(DataInformationExtensionField {})
            } else {
                None
            },
            size: extension_index,
        })
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize), serde(into = "String"))]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct TextUnit<'a>(&'a [u8]);
impl<'a> TextUnit<'a> {
    #[must_use]
    pub const fn new(input: &'a [u8]) -> Self {
        Self(input)
    }
}

impl PartialEq<str> for TextUnit<'_> {
    fn eq(&self, other: &str) -> bool {
        self.0.iter().eq(other.as_bytes().iter().rev())
    }
}

#[cfg(feature = "std")]
impl std::fmt::Display for TextUnit<'_> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", decode_text_unit(self.0))
    }
}

#[cfg(feature = "std")]
impl From<TextUnit<'_>> for String {
    fn from(value: TextUnit<'_>) -> Self {
        decode_text_unit(value.0)
    }
}

#[cfg(feature = "std")]
fn decode_text_unit(input: &[u8]) -> String {
    let bytes: Vec<u8> = input.iter().copied().rev().collect();
    match String::from_utf8(bytes) {
        Ok(value) => value,
        Err(error) => error.into_bytes().into_iter().map(char::from).collect(),
    }
}

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, PartialEq, Clone, Copy)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum Month {
    January,
    February,
    March,
    April,
    May,
    June,
    July,
    August,
    September,
    October,
    November,
    December,
}

#[cfg(feature = "std")]
impl std::fmt::Display for Month {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Month::January => write!(f, "Jan"),
            Month::February => write!(f, "Feb"),
            Month::March => write!(f, "Mar"),
            Month::April => write!(f, "Apr"),
            Month::May => write!(f, "May"),
            Month::June => write!(f, "Jun"),
            Month::July => write!(f, "Jul"),
            Month::August => write!(f, "Aug"),
            Month::September => write!(f, "Sep"),
            Month::October => write!(f, "Oct"),
            Month::November => write!(f, "Nov"),
            Month::December => write!(f, "Dec"),
        }
    }
}

pub type Year = u16;
pub type DayOfMonth = u8;
pub type Hour = u8;
pub type Minute = u8;
pub type Second = u8;

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum SingleEveryOrInvalid<T> {
    Single(T),
    Every(),
    Invalid(),
}

#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum DataType<'a> {
    Text(TextUnit<'a>),
    Number(f64),
    LossyNumber(f64),
    Date(
        SingleEveryOrInvalid<DayOfMonth>,
        SingleEveryOrInvalid<Month>,
        SingleEveryOrInvalid<Year>,
    ),
    Time(
        SingleEveryOrInvalid<Second>,
        SingleEveryOrInvalid<Minute>,
        SingleEveryOrInvalid<Hour>,
    ),
    DateTime(
        SingleEveryOrInvalid<DayOfMonth>,
        SingleEveryOrInvalid<Month>,
        SingleEveryOrInvalid<Year>,
        SingleEveryOrInvalid<Hour>,
        SingleEveryOrInvalid<Minute>,
    ),
    DateTimeWithSeconds(
        SingleEveryOrInvalid<DayOfMonth>,
        SingleEveryOrInvalid<Month>,
        SingleEveryOrInvalid<Year>,
        SingleEveryOrInvalid<Hour>,
        SingleEveryOrInvalid<Minute>,
        SingleEveryOrInvalid<Second>,
    ),
    ManufacturerSpecific(
        #[cfg_attr(
            feature = "serde",
            serde(serialize_with = "m_bus_core::serde_hex::serialize")
        )]
        &'a [u8],
    ),
}
#[cfg_attr(feature = "serde", derive(serde::Serialize))]
#[derive(PartialEq, Debug, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct Data<'a> {
    pub value: Option<DataType<'a>>,
    pub size: usize,
}

#[cfg(feature = "std")]
impl<T: std::fmt::Display> std::fmt::Display for SingleEveryOrInvalid<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            SingleEveryOrInvalid::Single(value) => write!(f, "{}", value),
            SingleEveryOrInvalid::Every() => write!(f, "Every"),
            SingleEveryOrInvalid::Invalid() => write!(f, "Invalid"),
        }
    }
}

#[cfg(feature = "std")]
impl std::fmt::Display for Data<'_> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.value {
            Some(value) => match value {
                DataType::Number(value) => write!(f, "{}", value),
                DataType::LossyNumber(value) => write!(f, "{}", value),
                DataType::Date(day, month, year) => write!(f, "{}/{}/{}", day, month, year),
                DataType::DateTime(day, month, year, hour, minute) => {
                    write!(f, "{}/{}/{} {}:{}:00", day, month, year, hour, minute)
                }
                DataType::DateTimeWithSeconds(day, month, year, hour, minute, second) => {
                    write!(
                        f,
                        "{}/{}/{} {}:{}:{}",
                        day, month, year, hour, minute, second
                    )
                }
                DataType::Time(seconds, minutes, hours) => {
                    write!(f, "{}:{}:{}", hours, minutes, seconds)
                }
                DataType::Text(text_unit) => {
                    let text: String = (*text_unit).into();
                    write!(f, "{}", text)
                }
                DataType::ManufacturerSpecific(data) => {
                    write!(f, "Manufacturer Specific: {:?}", data)
                }
            },
            None => write!(f, "No Data"),
        }
    }
}

impl Data<'_> {
    #[must_use]
    pub const fn get_size(&self) -> usize {
        self.size
    }
}

macro_rules! parse_single_or_every {
    ($input:expr, $mask:expr, $all_value:expr, $shift:expr) => {
        if $input & $mask == $all_value {
            SingleEveryOrInvalid::Every()
        } else {
            SingleEveryOrInvalid::Single(($input & $mask) >> $shift)
        }
    };
}

macro_rules! parse_month {
    ($input:expr) => {
        match $input & 0xF {
            0x1 => SingleEveryOrInvalid::Single(Month::January),
            0x2 => SingleEveryOrInvalid::Single(Month::February),
            0x3 => SingleEveryOrInvalid::Single(Month::March),
            0x4 => SingleEveryOrInvalid::Single(Month::April),
            0x5 => SingleEveryOrInvalid::Single(Month::May),
            0x6 => SingleEveryOrInvalid::Single(Month::June),
            0x7 => SingleEveryOrInvalid::Single(Month::July),
            0x8 => SingleEveryOrInvalid::Single(Month::August),
            0x9 => SingleEveryOrInvalid::Single(Month::September),
            0xA => SingleEveryOrInvalid::Single(Month::October),
            0xB => SingleEveryOrInvalid::Single(Month::November),
            0xC => SingleEveryOrInvalid::Single(Month::December),
            _ => SingleEveryOrInvalid::Invalid(),
        }
    };
}

/// Decode the seven year bits of an EN 13757-3 type F, G or I field.
///
/// The year is split across two bytes: `$day_index` carries Y0..Y2 in bits
/// 5-7 and `$month_index` carries Y3..Y6 in bits 4-7. Their position differs
/// per type, so both indices are named by the caller.
///
/// The field holds two digits and no century, so it is read as 20xx, the same
/// convention as the libmbus-compatible XML output.
macro_rules! parse_year {
    ($input:expr, $day_index:expr, $month_index:expr) => {{
        let day_byte = u16::from($input.get($day_index).copied().unwrap_or(0) & 0xE0);
        let month_byte = u16::from($input.get($month_index).copied().unwrap_or(0) & 0xF0);
        let year = (day_byte >> 5) | (month_byte >> 1);
        if year == 0x7F {
            SingleEveryOrInvalid::Every()
        } else {
            SingleEveryOrInvalid::Single(2000 + year)
        }
    }};
}
fn bcd_to_value_internal(
    data: &[u8],
    num_digits: usize,
    sign: i32,
    lsb_order: bool,
) -> Result<Data<'_>, DataRecordError> {
    if data.len() < num_digits.div_ceil(2) {
        return Err(DataRecordError::InsufficientData);
    }

    let mut data_value = 0.0;
    let mut current_weight = 1.0;
    let mut negative = false;

    for i in 0..num_digits {
        let index = if lsb_order {
            (num_digits - i - 1) / 2
        } else {
            i / 2
        };
        let byte = data.get(index).ok_or(DataRecordError::InsufficientData)?;

        let digit = if i % 2 == 0 {
            byte & 0x0F
        } else {
            (byte >> 4) & 0x0F
        };

        // EN 13757-3: Fh in the most significant digit marks a negative value.
        // It is a sign marker, not a digit, and contributes nothing to the
        // magnitude.
        if digit == 0x0F && i == num_digits - 1 {
            negative = true;
            break;
        }

        if digit > 9 {
            return Err(DataRecordError::DataInformationError(
                DataInformationError::InvalidValueInformation,
            ));
        }

        data_value += f64::from(digit) * current_weight;
        current_weight *= 10.0;
    }

    let sign = if negative { -sign } else { sign };
    // Avoid -0.0, which would render as "-0.000000".
    let signed_value = if data_value == 0.0 {
        0.0
    } else {
        data_value * sign as f64
    };

    Ok(Data {
        value: Some(DataType::Number(signed_value)),
        size: num_digits.div_ceil(2),
    })
}

fn integer_to_value_internal(data: &[u8], byte_size: usize) -> Data<'_> {
    let mut data_value = 0i64;
    let mut shift = 0;
    for byte in data.iter().take(if byte_size > 8 { 8 } else { byte_size }) {
        data_value |= (*byte as i64) << shift;
        shift += 8;
    }

    let msb = (data_value >> (shift - 1)) & 1;
    let data_value = if byte_size < 8 && msb == 1 {
        -((data_value ^ (2i64.pow(shift) - 1)) + 1)
    } else {
        data_value
    };

    let output = if byte_size > 8 {
        DataType::LossyNumber(data_value as f64)
    } else {
        DataType::Number(data_value as f64)
    };
    Data {
        value: Some(output),
        size: byte_size,
    }
}

impl DataFieldCoding {
    /// Returns how many bytes the data field occupies, without decoding it.
    ///
    /// The length of every coding but [`DataFieldCoding::VariableLength`] is
    /// fixed by the DIF alone, so `input` is only read for the LVAR byte of a
    /// variable-length field. Returns `None` when the length cannot be
    /// determined, which is the case for a missing or reserved LVAR byte and
    /// for a reserved special function.
    ///
    /// This is what [`DataFieldCoding::parse`] would report as
    /// [`Data::get_size`] on success, so a record whose contents fail to decode
    /// can still be stepped over.
    #[must_use]
    pub fn data_size(&self, input: &[u8]) -> Option<usize> {
        match self {
            Self::NoData | Self::SelectionForReadout => Some(0),
            Self::Integer8Bit | Self::BCD2Digit => Some(1),
            Self::Integer16Bit | Self::BCD4Digit | Self::DateTypeG => Some(2),
            Self::Integer24Bit | Self::BCD6Digit => Some(3),
            Self::Integer32Bit
            | Self::Real32Bit
            | Self::BCD8Digit
            | Self::DateTimeTypeF
            | Self::DateTimeTypeJ => Some(4),
            Self::Integer48Bit | Self::BCDDigit12 | Self::DateTimeTypeI => Some(6),
            Self::Integer64Bit => Some(8),
            Self::VariableLength => match *input.first()? {
                length @ 0x00..=0xBF => Some(length as usize + 1),
                length @ 0xC0..=0xC9 => Some((length - 0xC0) as usize + 1),
                length @ 0xD0..=0xD9 => Some((length - 0xD0) as usize + 1),
                length @ 0xE0..=0xEF => Some((length - 0xE0) as usize + 1),
                length @ 0xF0..=0xF4 => Some(4 * (length - 0xEC) as usize + 1),
                0xF5 => Some(48 + 1),
                0xF6 => Some(64 + 1),
                _ => None,
            },
            Self::SpecialFunctions(code) => match code {
                SpecialFunctions::ManufacturerSpecific | SpecialFunctions::MoreRecordsFollow => {
                    Some(input.len())
                }
                SpecialFunctions::IdleFiller | SpecialFunctions::GlobalReadoutRequest => Some(0),
                SpecialFunctions::Reserved => None,
            },
        }
    }

    pub fn parse<'a>(
        &self,
        input: &'a [u8],
        fixed_data_header: Option<&'a LongTplHeader>,
    ) -> Result<Data<'a>, DataRecordError> {
        let lsb_order = fixed_data_header.map(|x| x.lsb_order).unwrap_or(false);

        macro_rules! bcd_to_value {
            ($data:expr, $num_digits:expr) => {{
                bcd_to_value_internal($data, $num_digits, 1, lsb_order)
            }};

            ($data:expr, $num_digits:expr, $sign:expr) => {{
                bcd_to_value_internal($data, $num_digits, $sign, lsb_order)
            }};
        }

        macro_rules! integer_to_value {
            ($data:expr, $byte_size:expr) => {{
                if $data.len() < $byte_size {
                    return Err(DataRecordError::InsufficientData);
                }
                Ok(integer_to_value_internal($data, $byte_size))
            }};
        }
        match self {
            Self::NoData => Ok(Data {
                value: None,
                size: 0,
            }),
            Self::Integer8Bit => integer_to_value!(input, 1),
            Self::Integer16Bit => integer_to_value!(input, 2),
            Self::Integer24Bit => integer_to_value!(input, 3),
            Self::Integer32Bit => integer_to_value!(input, 4),
            Self::Integer48Bit => integer_to_value!(input, 6),
            Self::Integer64Bit => integer_to_value!(input, 8),

            Self::Real32Bit => {
                if input.len() < 4 {
                    return Err(DataRecordError::InsufficientData);
                }
                if let Ok(x) = input
                    .get(0..4)
                    .ok_or(DataRecordError::InsufficientData)?
                    .try_into()
                {
                    let x: [u8; 4] = x;
                    Ok(Data {
                        value: Some(DataType::Number(f64::from(f32::from_le_bytes(x)))),
                        size: 4,
                    })
                } else {
                    Err(DataRecordError::InsufficientData)
                }
            }

            Self::SelectionForReadout => Ok(Data {
                value: None,
                size: 0,
            }),

            Self::BCD2Digit => bcd_to_value!(input, 2),
            Self::BCD4Digit => bcd_to_value!(input, 4),
            Self::BCD6Digit => bcd_to_value!(input, 6),
            Self::BCD8Digit => bcd_to_value!(input, 8),
            Self::BCDDigit12 => bcd_to_value!(input, 12),

            Self::VariableLength => {
                let mut length = *input.first().ok_or(DataRecordError::InsufficientData)?;
                match length {
                    0x00..=0xBF => Ok(Data {
                        value: Some(DataType::Text(TextUnit::new(
                            input
                                .get(1..(1 + length as usize))
                                .ok_or(DataRecordError::InsufficientData)?,
                        ))),
                        size: length as usize + 1,
                    }),
                    0xC0..=0xC9 => {
                        length -= 0xC0;
                        let bytes = input
                            .get(1..(1 + length as usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match bcd_to_value!(bytes, 2 * length as usize) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    0xD0..=0xD9 => {
                        length -= 0xD0;
                        let bytes = input
                            .get(1..(1 + length as usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match bcd_to_value!(bytes, 2 * length as usize, -1) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    0xE0..=0xEF => {
                        length -= 0xE0;
                        let bytes = input
                            .get(1..(1 + length as usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match integer_to_value!(bytes, length as usize) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    0xF0..=0xF4 => {
                        length -= 0xEC;
                        let bytes = input
                            .get(1..(1 + 4 * length as usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match integer_to_value!(bytes, 4 * length as usize) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    0xF5 => {
                        let bytes = input
                            .get(1..(1 + 48_usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match integer_to_value!(bytes, 48_usize) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    0xF6 => {
                        let bytes = input
                            .get(1..(1 + 64_usize))
                            .ok_or(DataRecordError::InsufficientData)?;
                        match integer_to_value!(bytes, 64_usize) {
                            Ok(data) => Ok(Data {
                                value: data.value,
                                size: data.size + 1,
                            }),
                            Err(err) => Err(err),
                        }
                    }
                    _ => Err(DataRecordError::DataInformationError(
                        DataInformationError::Unimplemented {
                            feature: "Variable length parsing for reserved length values",
                        },
                    )),
                }
            }

            Self::SpecialFunctions(code) => match code {
                SpecialFunctions::ManufacturerSpecific | SpecialFunctions::MoreRecordsFollow => {
                    Ok(Data {
                        value: Some(DataType::ManufacturerSpecific(input)),
                        size: input.len(),
                    })
                }
                SpecialFunctions::IdleFiller => Ok(Data {
                    value: None,
                    size: 0,
                }),
                SpecialFunctions::GlobalReadoutRequest => Ok(Data {
                    value: None,
                    size: 0,
                }),
                SpecialFunctions::Reserved => Err(DataRecordError::DataInformationError(
                    DataInformationError::InvalidValueInformation,
                )),
            },

            Self::DateTypeG => {
                let day = parse_single_or_every!(
                    input.first().ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0,
                    0
                );
                let month = parse_month!(input.get(1).ok_or(DataRecordError::InsufficientData)?);
                let year = parse_year!(input, 0, 1);

                Ok(Data {
                    value: Some(DataType::Date(day, month, year)),
                    size: 2,
                })
            }
            Self::DateTimeTypeF => {
                let minutes = parse_single_or_every!(
                    input.first().ok_or(DataRecordError::InsufficientData)?,
                    0x3F,
                    0x3F,
                    0
                );
                let hour = parse_single_or_every!(
                    input.get(1).ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0x1F,
                    0
                );
                let day = parse_single_or_every!(
                    input.get(2).ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0x1F,
                    0
                );
                let month = parse_month!(input.get(3).ok_or(DataRecordError::InsufficientData)?);
                let year = parse_year!(input, 2, 3);

                Ok(Data {
                    value: Some(DataType::DateTime(day, month, year, hour, minutes)),
                    size: 4,
                })
            }
            Self::DateTimeTypeJ => {
                let seconds = parse_single_or_every!(
                    input.first().ok_or(DataRecordError::InsufficientData)?,
                    0x3F,
                    0x3F,
                    0
                );
                let minutes = parse_single_or_every!(
                    input.get(1).ok_or(DataRecordError::InsufficientData)?,
                    0x3F,
                    0x3F,
                    0
                );
                let hours = parse_single_or_every!(
                    input.get(2).ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0x1F,
                    0
                );

                Ok(Data {
                    value: Some(DataType::Time(seconds, minutes, hours)),
                    size: 4,
                })
            }
            Self::DateTimeTypeI => {
                // note: more information can be extracted from the data,
                // however, because this data can be derived from the other data that is
                // that is extracted, it is not necessary to extract it.

                let seconds = parse_single_or_every!(
                    input.first().ok_or(DataRecordError::InsufficientData)?,
                    0x3F,
                    0x3F,
                    0
                );

                let minutes = parse_single_or_every!(
                    input.get(1).ok_or(DataRecordError::InsufficientData)?,
                    0x3F,
                    0x3F,
                    0
                );

                let hours = parse_single_or_every!(
                    input.get(2).ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0x1F,
                    0
                );
                let days = parse_single_or_every!(
                    input.get(3).ok_or(DataRecordError::InsufficientData)?,
                    0x1F,
                    0x1F,
                    0
                );
                let months = parse_month!(input.get(4).ok_or(DataRecordError::InsufficientData)?);
                let year = parse_year!(input, 3, 4);

                Ok(Data {
                    value: Some(DataType::DateTimeWithSeconds(
                        days, months, year, hours, minutes, seconds,
                    )),
                    size: 6,
                })
            }
        }
    }
}

impl DataInformation {
    #[must_use]
    pub const fn get_size(&self) -> usize {
        self.size
    }
}
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum FunctionField {
    InstantaneousValue,
    MaximumValue,
    MinimumValue,
    ValueDuringErrorState,
}

#[cfg(feature = "std")]
impl std::fmt::Display for FunctionField {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            FunctionField::InstantaneousValue => write!(f, "Inst"),
            FunctionField::MaximumValue => write!(f, "Max"),
            FunctionField::MinimumValue => write!(f, "Min"),
            FunctionField::ValueDuringErrorState => write!(f, "Value During Error State"),
        }
    }
}
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum SpecialFunctions {
    ManufacturerSpecific,
    MoreRecordsFollow,
    IdleFiller,
    Reserved,
    GlobalReadoutRequest,
}

#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct Value {
    pub data: f64,
    pub byte_size: usize,
}

#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Debug, Clone, Copy, PartialEq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[non_exhaustive]
pub enum DataFieldCoding {
    NoData,
    Integer8Bit,
    Integer16Bit,
    Integer24Bit,
    Integer32Bit,
    Real32Bit,
    Integer48Bit,
    Integer64Bit,
    SelectionForReadout,
    BCD2Digit,
    BCD4Digit,
    BCD6Digit,
    BCD8Digit,
    VariableLength,
    BCDDigit12,
    SpecialFunctions(SpecialFunctions),
    DateTypeG,
    DateTimeTypeF,
    DateTimeTypeJ,
    DateTimeTypeI,
}

#[cfg(feature = "std")]
impl std::fmt::Display for DataFieldCoding {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            DataFieldCoding::NoData => write!(f, "No Data"),
            DataFieldCoding::Integer8Bit => write!(f, "8-bit Integer"),
            DataFieldCoding::Integer16Bit => write!(f, "16-bit Integer"),
            DataFieldCoding::Integer24Bit => write!(f, "24-bit Integer"),
            DataFieldCoding::Integer32Bit => write!(f, "32-bit Integer"),
            DataFieldCoding::Real32Bit => write!(f, "32-bit Real"),
            DataFieldCoding::Integer48Bit => write!(f, "48-bit Integer"),
            DataFieldCoding::Integer64Bit => write!(f, "64-bit Integer"),
            DataFieldCoding::SelectionForReadout => write!(f, "Selection for Readout"),
            DataFieldCoding::BCD2Digit => write!(f, "BCD 2-digit"),
            DataFieldCoding::BCD4Digit => write!(f, "BCD 4-digit"),
            DataFieldCoding::BCD6Digit => write!(f, "BCD 6-digit"),
            DataFieldCoding::BCD8Digit => write!(f, "BCD 8-digit"),
            DataFieldCoding::VariableLength => write!(f, "Variable Length"),
            DataFieldCoding::BCDDigit12 => write!(f, "BCD 12-digit"),
            DataFieldCoding::DateTypeG => write!(f, "Date Type G"),
            DataFieldCoding::DateTimeTypeF => write!(f, "Date Time Type F"),
            DataFieldCoding::DateTimeTypeJ => write!(f, "Date Time Type J"),
            DataFieldCoding::DateTimeTypeI => write!(f, "Date Time Type I"),
            DataFieldCoding::SpecialFunctions(code) => write!(f, "Special Functions ({:?})", code),
        }
    }
}

#[cfg(test)]
mod tests {

    use super::*;
    #[test]
    fn test_data_information() {
        let data = [0x13_u8];
        let result = DataInformationBlock::try_from(data.as_slice());
        let result = DataInformation::try_from(&result.unwrap());
        assert_eq!(
            result,
            Ok(DataInformation {
                storage_number: 0,
                device: 0,
                tariff: 0,
                function_field: FunctionField::MaximumValue,
                data_field_coding: DataFieldCoding::Integer24Bit,
                data_information_extension: None,
                size: 1,
            })
        );
    }

    #[test]
    fn unextended_dif_does_not_interpret_following_bytes_as_extensions() {
        for dif in 0..=0x7f {
            let mut bytes = [0xff; MAXIMUM_DATA_INFORMATION_SIZE + 3];
            bytes[0] = dif;
            let block = DataInformationBlock::try_from(bytes.as_slice()).unwrap();
            assert_eq!(block.data_information_field.data, dif);
            assert_eq!(block.get_size(), 1);
            assert!(block.data_information_field_extension.is_none());
        }
    }

    #[test]
    fn test_complex_data_information() {
        let data = [0xc4, 0x80, 0x40];
        let result = DataInformationBlock::try_from(data.as_slice());
        let result = DataInformation::try_from(&result.unwrap());
        assert_eq!(
            result,
            Ok(DataInformation {
                storage_number: 1,
                device: 2,
                tariff: 0,
                function_field: FunctionField::InstantaneousValue,
                data_field_coding: DataFieldCoding::Integer32Bit,
                data_information_extension: None,
                size: 3,
            })
        );
    }

    #[test]
    fn reverse_text_unit() {
        let original_value = [0x6c, 0x61, 0x67, 0x69];
        let parsed = TextUnit::new(&original_value);
        assert_eq!(&parsed, "igal");
    }

    #[cfg(feature = "std")]
    #[test]
    fn text_unit_latin1_swedish_characters() {
        // "Malmö" in Latin-1 (reversed byte order per M-Bus)
        let bytes = [0xF6, 0x6D, 0x6C, 0x61, 0x4D]; // ö m l a M
        let text = TextUnit::new(&bytes);
        assert_eq!(String::from(text), "Malmö");
    }

    #[cfg(feature = "std")]
    #[test]
    fn text_unit_latin1_superscript_three() {
        // "m³/h" in Latin-1 (reversed byte order per M-Bus)
        let bytes = [0x68, 0x2F, 0xB3, 0x6D]; // h / ³ m
        let text = TextUnit::new(&bytes);
        assert_eq!(String::from(text), "m³/h");
    }

    #[cfg(feature = "std")]
    #[test]
    fn text_unit_utf8_superscript_three() {
        // "m³/h" in UTF-8 (reversed byte order per M-Bus)
        let bytes = [0x68, 0x2F, 0xB3, 0xC2, 0x6D]; // h / UTF-8(³) m
        let text = TextUnit::new(&bytes);
        assert_eq!(String::from(text), "m³/h");
    }

    #[test]
    fn test_invalid_data_information() {
        let data = [
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        ];
        let result = DataInformationBlock::try_from(data.as_slice());
        assert_eq!(result, Err(DataInformationError::DataTooLong));
    }

    #[test]
    fn test_longest_data_information_not_too_long() {
        let data = [
            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01,
        ];
        let result = DataInformationBlock::try_from(data.as_slice());
        assert_ne!(result, Err(DataInformationError::DataTooLong));
    }

    #[test]
    fn test_short_data_information() {
        let data = [0xFF];
        let result = DataInformationBlock::try_from(data.as_slice());
        assert_eq!(result, Err(DataInformationError::DataTooShort));
    }

    #[test]
    fn test_data_inforamtion1() {
        let data = [178, 1];
        let result = DataInformationBlock::try_from(data.as_slice());
        assert!(result.is_ok());
        assert_eq!(result.unwrap().get_size(), 2);
    }

    #[test]
    fn test_bcd_to_value_unsigned() {
        let data = [0x54, 0x76, 0x98];
        let result = bcd_to_value_internal(&data, 6, 1, false);
        assert_eq!(
            result.unwrap(),
            Data {
                value: Some(DataType::Number(987654.0)),
                size: 3
            }
        );
    }

    #[test]
    fn test_bcd_to_value_invalid() {
        let data = [0x5A, 0x76, 0x98];
        let result = bcd_to_value_internal(&data, 6, 1, false);
        assert!(matches!(
            result,
            Err(DataRecordError::DataInformationError(
                DataInformationError::InvalidValueInformation
            ))
        ));
    }

    #[test]
    fn test_bcd_to_value_negative_sign_nibble() {
        // EN 13757-3: Fh in the most significant digit is a sign marker.
        // SLB_CF-Compact-Integral-MK-MaXX carries -18 as `18 00 F0`.
        let data = [0x18, 0x00, 0xF0];
        let result = bcd_to_value_internal(&data, 6, 1, false);
        assert_eq!(
            result.unwrap(),
            Data {
                value: Some(DataType::Number(-18.0)),
                size: 3
            }
        );
    }

    #[test]
    fn test_bcd_to_value_negative_zero_is_positive_zero() {
        let data = [0x00, 0x00, 0xF0];
        let result = bcd_to_value_internal(&data, 6, 1, false);
        let Some(DataType::Number(value)) = result.unwrap().value else {
            panic!("expected a number");
        };
        assert!(value == 0.0 && value.is_sign_positive());
    }

    #[test]
    fn test_bcd_to_value_sign_nibble_only_in_most_significant_digit() {
        // An Fh anywhere but the top digit is still invalid BCD.
        let data = [0x18, 0xF0, 0x00];
        let result = bcd_to_value_internal(&data, 6, 1, false);
        assert!(matches!(
            result,
            Err(DataRecordError::DataInformationError(
                DataInformationError::InvalidValueInformation
            ))
        ));
    }

    #[test]
    fn test_data_size_matches_parsed_size() {
        // `data_size` is the resynchronisation path for records that fail to
        // decode, so it must not drift from what `parse` consumes.
        let payload = [0x01_u8; 80];
        let codings = [
            DataFieldCoding::NoData,
            DataFieldCoding::Integer8Bit,
            DataFieldCoding::Integer16Bit,
            DataFieldCoding::Integer24Bit,
            DataFieldCoding::Integer32Bit,
            DataFieldCoding::Real32Bit,
            DataFieldCoding::Integer48Bit,
            DataFieldCoding::Integer64Bit,
            DataFieldCoding::SelectionForReadout,
            DataFieldCoding::BCD2Digit,
            DataFieldCoding::BCD4Digit,
            DataFieldCoding::BCD6Digit,
            DataFieldCoding::BCD8Digit,
            DataFieldCoding::BCDDigit12,
            DataFieldCoding::DateTypeG,
            DataFieldCoding::DateTimeTypeF,
            DataFieldCoding::DateTimeTypeJ,
            DataFieldCoding::DateTimeTypeI,
        ];

        for coding in codings {
            let parsed = coding.parse(&payload, None).expect("coding parses");
            assert_eq!(
                coding.data_size(&payload),
                Some(parsed.get_size()),
                "data_size disagrees with parse for {coding:?}"
            );
        }

        // Variable length: the LVAR byte drives both.
        for lvar in [0x03_u8, 0xC3, 0xD3, 0xE3, 0xF0, 0xF5, 0xF6] {
            let mut input = [0x00_u8; 80];
            input[0] = lvar;
            let parsed = DataFieldCoding::VariableLength
                .parse(&input, None)
                .expect("variable length parses");
            assert_eq!(
                DataFieldCoding::VariableLength.data_size(&input),
                Some(parsed.get_size()),
                "data_size disagrees with parse for LVAR {lvar:#04X}"
            );
        }
    }

    #[test]
    fn test_date_type_g_reads_the_full_year() {
        // 8C 11: day 12, month 1, year bits 0b0001_100 = 12 -> 2012.
        assert_eq!(
            DataFieldCoding::DateTypeG.parse(&[0x8C, 0x11], None),
            Ok(Data {
                value: Some(DataType::Date(
                    SingleEveryOrInvalid::Single(12),
                    SingleEveryOrInvalid::Single(Month::January),
                    SingleEveryOrInvalid::Single(2012),
                )),
                size: 2,
            })
        );
    }

    #[test]
    fn test_date_time_type_f_reads_the_year_from_the_day_and_month_bytes() {
        // 2D 0D 0F 33: 15 March 2024, 13:45. The year bits live in the third
        // and fourth byte, not in the minute and hour bytes.
        assert_eq!(
            DataFieldCoding::DateTimeTypeF.parse(&[0x2D, 0x0D, 0x0F, 0x33], None),
            Ok(Data {
                value: Some(DataType::DateTime(
                    SingleEveryOrInvalid::Single(15),
                    SingleEveryOrInvalid::Single(Month::March),
                    SingleEveryOrInvalid::Single(2024),
                    SingleEveryOrInvalid::Single(13),
                    SingleEveryOrInvalid::Single(45),
                )),
                size: 4,
            })
        );
    }

    #[test]
    fn test_date_time_type_i_reads_the_year_from_the_day_and_month_bytes() {
        // 36 35 C0 53 39 00: 19 September 2026, 00:53:54.
        assert_eq!(
            DataFieldCoding::DateTimeTypeI.parse(&[0x36, 0x35, 0xC0, 0x53, 0x39, 0x00], None),
            Ok(Data {
                value: Some(DataType::DateTimeWithSeconds(
                    SingleEveryOrInvalid::Single(19),
                    SingleEveryOrInvalid::Single(Month::September),
                    SingleEveryOrInvalid::Single(2026),
                    SingleEveryOrInvalid::Single(0),
                    SingleEveryOrInvalid::Single(53),
                    SingleEveryOrInvalid::Single(54),
                )),
                size: 6,
            })
        );
    }

    #[test]
    fn test_date_type_g_every_year_wildcard() {
        // All seven year bits set is the "every year" wildcard, not year 2127.
        assert_eq!(
            DataFieldCoding::DateTypeG.parse(&[0xEC, 0xF1], None),
            Ok(Data {
                value: Some(DataType::Date(
                    SingleEveryOrInvalid::Single(12),
                    SingleEveryOrInvalid::Single(Month::January),
                    SingleEveryOrInvalid::Every(),
                )),
                size: 2,
            })
        );
    }

    #[test]
    fn test_integer_to_value_8_bit_positive() {
        let data = [0x7F];
        let result = integer_to_value_internal(&data, 1);
        assert_eq!(
            result,
            Data {
                value: Some(DataType::Number(127.0)),
                size: 1
            }
        );
    }

    #[test]
    fn test_integer_to_value_8_bit_negative() {
        let data = [0xFF];
        let result = integer_to_value_internal(&data, 1);
        assert_eq!(
            result,
            Data {
                value: Some(DataType::Number(-1.0)),
                size: 1
            }
        );
    }

    #[test]
    fn test_integer_to_value_64_bit_positive() {
        let data = [0xFA, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00];
        let result = integer_to_value_internal(&data, 8);
        assert_eq!(
            result,
            Data {
                value: Some(DataType::Number(250.0)),
                size: 8
            }
        );
    }

    #[test]
    fn test_integer_to_value_64_bit_negative() {
        let data = [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF];
        let result = integer_to_value_internal(&data, 8);
        assert_eq!(
            result,
            Data {
                value: Some(DataType::Number(-1.0)),
                size: 8
            }
        );
    }
}