//! # Introduction
//!
//! This is a platform agnostic Rust driver for the Sensirion SHTC3 temperature /
//! humidity sensor, based on the
//! [`embedded-hal`](https://github.com/rust-embedded/embedded-hal) traits.
//!
//! ## Supported Devices
//!
//! Tested with the following sensors:
//! - [SHTC3](https://www.sensirion.com/shtc3/)
//!
//! ## Blocking / Non-Blocking Modes
//!
//! This driver provides blocking and non-blocking calls. The blocking calls delay the execution
//! until the measurement is done and return the results. The non-blocking ones just start the
//! measurement and allow the application code to do other stuff and get the results afterwards.
//!
//! ## Clock Stretching
//!
//! While the sensor would provide measurement commands with clock stretching to indicate when the
//! measurement is done, this is not implemented and probably won't be.
//!
//! ## Usage
//!
//! ### Setup
//!
//! Instantiate a new driver instance using a [blocking I²C HAL
//! implementation](https://docs.rs/embedded-hal/0.2.*/embedded_hal/blocking/i2c/index.html)
//! and a [blocking `Delay`
//! instance](https://docs.rs/embedded-hal/0.2.*/embedded_hal/blocking/delay/index.html).
//! For example, using `linux-embedded-hal` and an SHTC3 sensor:
//!
//! ```no_run
//! use linux_embedded_hal::{Delay, I2cdev};
//! use sachy_shtc3::ShtC3;
//!
//! let dev = I2cdev::new("/dev/i2c-1").unwrap();
//! let mut sht = ShtC3::new(dev, Default::default());
//! ```
//!
//! ### Device Info
//!
//! Then, you can query information about the sensor:
//!
//! ```no_run
//! use linux_embedded_hal::{Delay, I2cdev};
//! use sachy_shtc3::ShtC3;
//! let mut sht = ShtC3::new(I2cdev::new("/dev/i2c-1").unwrap(), Default::default());
//! let device_id = sht.device_identifier().unwrap();
//! let raw_id = sht.raw_id_register().unwrap();
//! ```
//!
//! ### Measurements (Blocking)
//!
//! For measuring your environment, you can either measure just temperature,
//! just humidity, or both:
//!
//! ```no_run
//! use linux_embedded_hal::{Delay, I2cdev};
//! use sachy_shtc3::{ShtC3, PowerMode};
//!
//! let mut sht = ShtC3::new(I2cdev::new("/dev/i2c-1").unwrap(), Default::default());
//! let mut delay = Delay;
//!
//! let temperature = sht.measure_temperature(&mut delay).unwrap();
//! let humidity = sht.measure_humidity(&mut delay).unwrap();
//! let combined = sht.measure(&mut delay).unwrap();
//!
//! println!("Temperature: {} °C", temperature.as_degrees_celsius());
//! println!("Humidity: {} %RH", humidity.as_percent());
//! println!("Combined: {} °C / {} %RH",
//!          combined.temperature.as_degrees_celsius(),
//!          combined.humidity.as_percent());
//! ```
//!
//! You can also use the low power mode for less power consumption, at the cost
//! of reduced repeatability and accuracy of the sensor signals. For more
//! information, see the ["Low Power Measurement Mode" application note][low-power].
//!
//! [low-power]: https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHTC3_Low_Power_Measurement_Mode.pdf
//!
//! ```no_run
//! use linux_embedded_hal::{Delay, I2cdev};
//! use sachy_shtc3::{ShtC3, PowerMode};
//! let mut sht = ShtC3::new(I2cdev::new("/dev/i2c-1").unwrap(), PowerMode::LowPower);
//! let mut delay = Delay;
//! let measurement = sht.measure(&mut delay).unwrap();
//! ```
//!
//! ### Measurements (Non-Blocking)
//!
//! If you want to avoid blocking measurements, you can use the non-blocking
//! commands instead. You are, however, responsible for ensuring the correct
//! timing of the calls.
//!
//! ```no_run
//! use linux_embedded_hal::I2cdev;
//! use sachy_shtc3::{ShtC3, PowerMode};
//!
//! let mut sht = ShtC3::new(I2cdev::new("/dev/i2c-1").unwrap(), PowerMode::NormalMode);
//!
//! sht.start_measurement().unwrap();
//! // Wait for at least `max_measurement_duration(&sht, PowerMode::NormalMode)` µs
//! let result = sht.get_measurement_result().unwrap();
//! ```
//!
//! In non-blocking mode, if desired, you can also read the raw 16-bit
//! measurement results from the sensor by using the following two methods
//! instead:
//!
//! - [`get_raw_measurement_result`](crate::ShtC3::get_raw_measurement_result())
//! - [`get_raw_partial_measurement_result`](crate::ShtC3::get_raw_partial_measurement_result())
//!
//! The raw values are of type u16. They require a conversion formula for
//! conversion to a temperature / humidity value (see datasheet).
//!
//! Invoking any command other than
//! [`wakeup`](crate::ShtC3::wakeup()) while the sensor is in
//! sleep mode will result in an error.
//!
//! ### Soft Reset
//!
//! The SHTC3 provides a soft reset mechanism that forces the system into a
//! well-defined state without removing the power supply. If the system is in
//! its idle state (i.e. if no measurement is in progress) the soft reset
//! command can be sent. This triggers the sensor to reset all internal state
//! machines and reload calibration data from the memory.
//!
//! ```no_run
//! use linux_embedded_hal::{Delay, I2cdev};
//! use sachy_shtc3::{ShtC3, PowerMode};
//! let mut sht = ShtC3::new(I2cdev::new("/dev/i2c-1").unwrap(), PowerMode::NormalMode);
//! let mut delay = Delay;
//! sht.reset(&mut delay).unwrap();
//! ```
#![deny(unsafe_code, missing_docs)]
#![no_std]

mod crc;
mod types;

use embedded_hal::{
    delay::DelayNs as BlockingDelayNs,
    i2c::{self, I2c, SevenBitAddress},
};

use crc::crc8;
use embedded_hal_async::delay::DelayNs;
pub use types::*;

/// Whether temperature or humidity is returned first when doing a measurement.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
enum MeasurementOrder {
    TemperatureFirst,
    HumidityFirst,
}

/// Measurement power mode: Normal mode or low power mode.
///
/// The sensors provides a low power measurement mode. Using the low power mode
/// significantly shortens the measurement duration and thus minimizes the
/// energy consumption per measurement. The benefit of ultra-low power
/// consumption comes at the cost of reduced repeatability of the sensor
/// signals: while the impact on the relative humidity signal is negligible and
/// does not affect accuracy, it has an effect on temperature accuracy.
///
/// More details can be found in the ["Low Power Measurement Mode" application
/// note][an-low-power] by Sensirion.
///
/// [an-low-power]: https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHTC3_Low_Power_Measurement_Mode.pdf
#[derive(Debug, Default, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum PowerMode {
    /// Normal measurement.
    #[default]
    NormalMode,
    /// Low power measurement: Less energy consumption, but repeatability and
    /// accuracy of measurements are negatively impacted.
    LowPower,
}

/// All possible errors in this crate
#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum Error<E> {
    /// I²C bus error
    I2c(E),
    /// CRC checksum validation failed
    Crc,
}

impl<E> From<CrcError> for Error<E> {
    fn from(_value: CrcError) -> Self {
        Self::Crc
    }
}

#[derive(Debug, PartialEq, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
struct CrcError;

impl<E> From<E> for Error<E>
where
    E: i2c::Error,
{
    fn from(e: E) -> Self {
        Error::I2c(e)
    }
}

/// I²C commands sent to the sensor.
#[derive(Debug, Copy, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
enum Command {
    /// Go into sleep mode.
    Sleep,
    /// Wake up from sleep mode.
    WakeUp,
    /// Measurement commands.
    Measure {
        power_mode: PowerMode,
        order: MeasurementOrder,
    },
    /// Software reset.
    SoftwareReset,
    /// Read ID register.
    ReadIdRegister,
}

impl Command {
    fn as_bytes(self) -> [u8; 2] {
        match self {
            Command::Sleep => [0xB0, 0x98],
            Command::WakeUp => [0x35, 0x17],
            Command::Measure {
                power_mode: PowerMode::NormalMode,
                order: MeasurementOrder::TemperatureFirst,
            } => [0x78, 0x66],
            Command::Measure {
                power_mode: PowerMode::NormalMode,
                order: MeasurementOrder::HumidityFirst,
            } => [0x58, 0xE0],
            Command::Measure {
                power_mode: PowerMode::LowPower,
                order: MeasurementOrder::TemperatureFirst,
            } => [0x60, 0x9C],
            Command::Measure {
                power_mode: PowerMode::LowPower,
                order: MeasurementOrder::HumidityFirst,
            } => [0x40, 0x1A],
            Command::ReadIdRegister => [0xEF, 0xC8],
            Command::SoftwareReset => [0x80, 0x5D],
        }
    }
}

/// Driver for the SHTC3 sensor.
#[derive(Debug, Default)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct ShtC3<I2C> {
    /// The concrete I²C device implementation.
    i2c: I2C,
    /// The I²C device address.
    address: u8,
    mode: PowerMode,
}

impl<I2C> ShtC3<I2C> {
    /// Create a new instance of the driver for the SHTC3.
    #[inline]
    pub const fn new(i2c: I2C, mode: PowerMode) -> Self {
        Self {
            i2c,
            address: 0x70,
            mode,
        }
    }

    /// Get the device's wakeup delay duration in microseconds
    #[inline(always)]
    pub const fn wakeup_duration(&self) -> u32 {
        240
    }

    /// Destroy driver instance, return I²C bus instance.
    pub fn destroy(self) -> I2C {
        self.i2c
    }

    /// Return the maximum measurement duration (depending on the mode) in
    /// microseconds.
    ///
    /// Maximum measurement duration (SHTC3 datasheet 3.1):
    /// - Normal mode: 12.1 ms
    /// - Low power mode: 0.8 ms
    #[inline(always)]
    pub const fn max_measurement_duration(&self) -> u32 {
        match self.mode {
            PowerMode::NormalMode => 12100,
            PowerMode::LowPower => 800,
        }
    }

    /// Returns the reset duration for the SHTC3 in microseconds
    #[inline(always)]
    pub const fn reset_duration(&self) -> u32 {
        240_000
    }

    /// Iterate over the provided buffer and validate the CRC8 checksum.
    ///
    /// If the checksum is wrong, return `CrcError`.
    ///
    /// Note: This method will consider every third byte a checksum byte. If
    /// the buffer size is not a multiple of 3, then not all data will be
    /// validated.
    fn validate_crc(&self, buf: &[u8]) -> Result<(), CrcError> {
        let mut chunks = buf.chunks_exact(3);

        for chunk in chunks.by_ref() {
            if crc8(&chunk[..2]) != chunk[2] {
                return Err(CrcError);
            }
        }

        #[cfg(feature = "defmt")]
        if !chunks.remainder().is_empty() {
            defmt::warn!("Remaining data in buffer was not CRC8 validated");
        }

        Ok(())
    }
}

impl<I2C> ShtC3<I2C>
where
    I2C: embedded_hal_async::i2c::I2c<embedded_hal_async::i2c::SevenBitAddress>,
{
    /// Write an I²C command to the sensor.
    async fn send_command_async(&mut self, command: Command) -> Result<(), Error<I2C::Error>> {
        self.i2c
            .write(self.address, &command.as_bytes())
            .await
            .map_err(Error::I2c)
    }

    /// Read data into the provided buffer and validate the CRC8 checksum.
    ///
    /// If the checksum is wrong, return `Error::Crc`.
    ///
    /// Note: This method will consider every third byte a checksum byte. If
    /// the buffer size is not a multiple of 3, then not all data will be
    /// validated.
    async fn read_with_crc_async(&mut self, buf: &mut [u8]) -> Result<(), Error<I2C::Error>> {
        self.i2c.read(self.address, buf).await?;
        self.validate_crc(buf)?;
        Ok(())
    }

    /// Return the raw ID register.
    pub async fn raw_id_register_async(&mut self) -> Result<u16, Error<I2C::Error>> {
        // Request serial number
        self.send_command_async(Command::ReadIdRegister).await?;

        // Read id register
        let mut buf = [0; 3];
        self.read_with_crc_async(&mut buf).await?;

        Ok(u16::from_be_bytes([buf[0], buf[1]]))
    }

    /// Return the 7-bit device identifier.
    ///
    /// Should be 0x47 (71) for the SHTC3.
    pub async fn device_identifier_async(&mut self) -> Result<u8, Error<I2C::Error>> {
        let ident = self.raw_id_register_async().await?;
        let lsb = (ident & 0b0011_1111) as u8;
        let msb = ((ident & 0b0000_1000_0000_0000) >> 5) as u8;
        Ok(lsb | msb)
    }

    /// Set sensor to sleep mode.
    ///
    /// When in sleep mode, the sensor consumes around 0.3-0.6 µA. It requires
    /// a dedicated [`wakeup`](#method.wakeup) command to enable further I2C
    /// communication.
    pub async fn sleep_async(&mut self) -> Result<(), Error<I2C::Error>> {
        self.send_command_async(Command::Sleep).await
    }

    /// Trigger a soft reset. (async)
    ///
    /// The SHTC3 provides a soft reset mechanism that forces the system into a
    /// well-defined state without removing the power supply. If the system is
    /// in its idle state (i.e. if no measurement is in progress) the soft
    /// reset command can be sent. This triggers the sensor to reset all
    /// internal state machines and reload calibration data from the memory.
    pub async fn reset_async(&mut self, delay: &mut impl DelayNs) -> Result<(), Error<I2C::Error>> {
        self.send_command_async(Command::SoftwareReset).await?;
        // Table 5: 180-240 µs
        delay.delay_us(self.reset_duration()).await;
        Ok(())
    }

    /// Wake up sensor from [sleep mode](#method.sleep) and wait until it is ready. (async)
    pub async fn wakeup_async(
        &mut self,
        delay: &mut impl DelayNs,
    ) -> Result<(), Error<I2C::Error>> {
        self.send_command_async(Command::WakeUp).await?;
        delay.delay_us(self.wakeup_duration()).await;
        Ok(())
    }

    /// Run a temperature/humidity measurement and return the combined result.
    ///
    /// This is an async function call.
    pub async fn measure_async(
        &mut self,
        delay: &mut impl DelayNs,
    ) -> Result<Measurement, Error<I2C::Error>> {
        self.send_command_async(Command::Measure {
            power_mode: self.mode,
            order: MeasurementOrder::TemperatureFirst,
        })
        .await?;

        delay.delay_us(self.max_measurement_duration()).await;

        let mut buf = [0; 6];
        self.read_with_crc_async(&mut buf).await?;

        Ok(RawMeasurement {
            temperature: u16::from_be_bytes([buf[0], buf[1]]),
            humidity: u16::from_be_bytes([buf[3], buf[4]]),
        }
        .into())
    }
}

/// General blocking functions.
impl<I2C> ShtC3<I2C>
where
    I2C: I2c<SevenBitAddress>,
{
    /// Write an I²C command to the sensor.
    fn send_command(&mut self, command: Command) -> Result<(), Error<I2C::Error>> {
        self.i2c
            .write(self.address, &command.as_bytes())
            .map_err(Error::I2c)
    }

    /// Read data into the provided buffer and validate the CRC8 checksum.
    ///
    /// If the checksum is wrong, return `Error::Crc`.
    ///
    /// Note: This method will consider every third byte a checksum byte. If
    /// the buffer size is not a multiple of 3, then not all data will be
    /// validated.
    fn read_with_crc(&mut self, buf: &mut [u8]) -> Result<(), Error<I2C::Error>> {
        self.i2c.read(self.address, buf)?;
        self.validate_crc(buf)?;
        Ok(())
    }

    /// Return the raw ID register.
    pub fn raw_id_register(&mut self) -> Result<u16, Error<I2C::Error>> {
        // Request serial number
        self.send_command(Command::ReadIdRegister)?;

        // Read id register
        let mut buf = [0; 3];
        self.read_with_crc(&mut buf)?;

        Ok(u16::from_be_bytes([buf[0], buf[1]]))
    }

    /// Return the 7-bit device identifier.
    ///
    /// Should be 0x47 (71) for the SHTC3.
    pub fn device_identifier(&mut self) -> Result<u8, Error<I2C::Error>> {
        let ident = self.raw_id_register()?;
        let lsb = (ident & 0b0011_1111) as u8;
        let msb = ((ident & 0b0000_1000_0000_0000) >> 5) as u8;
        Ok(lsb | msb)
    }

    /// Trigger a soft reset. (blocking)
    ///
    /// The SHTC3 provides a soft reset mechanism that forces the system into a
    /// well-defined state without removing the power supply. If the system is
    /// in its idle state (i.e. if no measurement is in progress) the soft
    /// reset command can be sent. This triggers the sensor to reset all
    /// internal state machines and reload calibration data from the memory.
    pub fn reset(&mut self, delay: &mut impl BlockingDelayNs) -> Result<(), Error<I2C::Error>> {
        self.send_command(Command::SoftwareReset)?;
        // Table 5: 180-240 µs
        delay.delay_us(self.reset_duration());
        Ok(())
    }

    /// Trigger a soft reset.
    ///
    /// The SHTC3 provides a soft reset mechanism that forces the system into a
    /// well-defined state without removing the power supply. If the system is
    /// in its idle state (i.e. if no measurement is in progress) the soft
    /// reset command can be sent. This triggers the sensor to reset all
    /// internal state machines and reload calibration data from the memory.
    pub fn start_reset(&mut self) -> Result<(), Error<I2C::Error>> {
        self.send_command(Command::SoftwareReset)
    }

    /// Set sensor to sleep mode.
    ///
    /// When in sleep mode, the sensor consumes around 0.3-0.6 µA. It requires
    /// a dedicated [`wakeup`](#method.wakeup) command to enable further I2C
    /// communication.
    pub fn sleep(&mut self) -> Result<(), Error<I2C::Error>> {
        self.send_command(Command::Sleep)
    }

    /// Wake up sensor from [sleep mode](#method.sleep) and wait until it is ready.
    pub fn wakeup(&mut self, delay: &mut impl BlockingDelayNs) -> Result<(), Error<I2C::Error>> {
        self.start_wakeup()?;
        delay.delay_us(self.wakeup_duration());
        Ok(())
    }
}

/// Non-blocking functions for starting / reading measurements.
impl<I2C> ShtC3<I2C>
where
    I2C: I2c<SevenBitAddress>,
{
    /// Start a measurement with the specified measurement order and write the
    /// result into the provided buffer.
    ///
    /// If you just need one of the two measurements, provide a 3-byte buffer
    /// instead of a 6-byte buffer.
    fn start_measure_partial(
        &mut self,
        power_mode: PowerMode,
        order: MeasurementOrder,
    ) -> Result<(), Error<I2C::Error>> {
        // Request measurement
        self.send_command(Command::Measure { power_mode, order })
    }

    /// Start a combined temperature / humidity measurement.
    pub fn start_measurement(&mut self) -> Result<(), Error<I2C::Error>> {
        self.start_measure_partial(self.mode, MeasurementOrder::TemperatureFirst)
    }

    /// Start a temperature measurement.
    pub fn start_temperature_measurement(&mut self) -> Result<(), Error<I2C::Error>> {
        self.start_measure_partial(self.mode, MeasurementOrder::TemperatureFirst)
    }

    /// Start a humidity measurement.
    pub fn start_humidity_measurement(&mut self) -> Result<(), Error<I2C::Error>> {
        self.start_measure_partial(self.mode, MeasurementOrder::HumidityFirst)
    }

    /// Read the result of a temperature / humidity measurement.
    pub fn get_measurement_result(&mut self) -> Result<Measurement, Error<I2C::Error>> {
        let raw = self.get_raw_measurement_result()?;
        Ok(raw.into())
    }

    /// Read the result of a temperature measurement.
    pub fn get_temperature_measurement_result(&mut self) -> Result<Temperature, Error<I2C::Error>> {
        let raw = self.get_raw_partial_measurement_result()?;
        Ok(Temperature::from_raw(raw))
    }

    /// Read the result of a humidity measurement.
    pub fn get_humidity_measurement_result(&mut self) -> Result<Humidity, Error<I2C::Error>> {
        let raw = self.get_raw_partial_measurement_result()?;
        Ok(Humidity::from_raw(raw))
    }

    /// Read the raw result of a combined temperature / humidity measurement.
    pub fn get_raw_measurement_result(&mut self) -> Result<RawMeasurement, Error<I2C::Error>> {
        let mut buf = [0; 6];
        self.read_with_crc(&mut buf)?;
        Ok(RawMeasurement {
            temperature: u16::from_be_bytes([buf[0], buf[1]]),
            humidity: u16::from_be_bytes([buf[3], buf[4]]),
        })
    }

    /// Read the raw result of a partial temperature or humidity measurement.
    ///
    /// Return the raw 3-byte buffer (after validating CRC).
    pub fn get_raw_partial_measurement_result(&mut self) -> Result<u16, Error<I2C::Error>> {
        let mut buf = [0; 3];
        self.read_with_crc(&mut buf)?;
        Ok(u16::from_be_bytes([buf[0], buf[1]]))
    }

    /// Wake up sensor from [sleep mode](#method.sleep).
    pub fn start_wakeup(&mut self) -> Result<(), Error<I2C::Error>> {
        self.send_command(Command::WakeUp)
    }
}

/// Blocking functions for doing measurements.
impl<I2C> ShtC3<I2C>
where
    I2C: I2c<SevenBitAddress>,
{
    /// Wait the maximum time needed for the given measurement mode
    pub fn wait_for_measurement(&mut self, delay: &mut impl BlockingDelayNs) {
        delay.delay_us(self.max_measurement_duration());
    }

    /// Run a temperature/humidity measurement and return the combined result.
    ///
    /// This is a blocking function call.
    pub fn measure(
        &mut self,
        delay: &mut impl BlockingDelayNs,
    ) -> Result<Measurement, Error<I2C::Error>> {
        self.start_measurement()?;
        self.wait_for_measurement(delay);
        self.get_measurement_result()
    }

    /// Run a temperature measurement and return the result.
    ///
    /// This is a blocking function call.
    ///
    /// Internally, it will request a measurement in "temperature first" mode
    /// and only read the first half of the measurement response.
    pub fn measure_temperature(
        &mut self,
        delay: &mut impl BlockingDelayNs,
    ) -> Result<Temperature, Error<I2C::Error>> {
        self.start_temperature_measurement()?;
        self.wait_for_measurement(delay);
        self.get_temperature_measurement_result()
    }

    /// Run a humidity measurement and return the result.
    ///
    /// This is a blocking function call.
    ///
    /// Internally, it will request a measurement in "humidity first" mode
    /// and only read the first half of the measurement response.
    pub fn measure_humidity(
        &mut self,
        delay: &mut impl BlockingDelayNs,
    ) -> Result<Humidity, Error<I2C::Error>> {
        self.start_humidity_measurement()?;
        self.wait_for_measurement(delay);
        self.get_humidity_measurement_result()
    }
}

#[cfg(test)]
mod tests {
    extern crate alloc;

    use super::*;

    use embedded_hal::i2c::ErrorKind;
    use embedded_hal_mock::eh1::{
        delay::NoopDelay,
        i2c::{Mock as I2cMock, Transaction},
    };

    const SHT_ADDR: u8 = 0x70;

    mod core {
        use super::*;

        /// Test whether the `send_command` function propagates I²C errors.
        #[test]
        fn send_command_error() {
            let expectations =
                [Transaction::write(SHT_ADDR, alloc::vec![0xef, 0xc8])
                    .with_error(ErrorKind::Other)];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let err = sht.send_command(Command::ReadIdRegister).unwrap_err();
            assert_eq!(err, Error::I2c(ErrorKind::Other));
            sht.destroy().done();
        }

        /// Test the `validate_crc` function.
        #[test]
        fn validate_crc() {
            let mock = I2cMock::new(&[]);
            let sht = ShtC3::new(mock, PowerMode::NormalMode);

            // Not enough data
            sht.validate_crc(&[]).unwrap();
            sht.validate_crc(&[0xbe]).unwrap();
            sht.validate_crc(&[0xbe, 0xef]).unwrap();

            // Valid CRC
            sht.validate_crc(&[0xbe, 0xef, 0x92]).unwrap();

            // Invalid CRC
            match sht.validate_crc(&[0xbe, 0xef, 0x91]) {
                Err(CrcError) => {}
                Ok(_) => panic!("CRC check did not fail"),
            }

            // Valid CRC (8 bytes)
            sht.validate_crc(&[0xbe, 0xef, 0x92, 0xbe, 0xef, 0x92, 0x00, 0x00])
                .unwrap();

            // Invalid CRC (8 bytes)
            match sht.validate_crc(&[0xbe, 0xef, 0x92, 0xbe, 0xef, 0xff, 0x00, 0x00]) {
                Err(CrcError) => {}
                Ok(_) => panic!("CRC check did not fail"),
            }

            sht.destroy().done();
        }

        /// Test the `read_with_crc` function.
        #[test]
        fn read_with_crc() {
            let mut buf = [0; 3];

            // Valid CRC
            let expectations = [Transaction::read(SHT_ADDR, alloc::vec![0xbe, 0xef, 0x92])];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            sht.read_with_crc(&mut buf).unwrap();
            assert_eq!(buf, [0xbe, 0xef, 0x92]);
            sht.destroy().done();

            // Invalid CRC
            let expectations = [Transaction::read(SHT_ADDR, alloc::vec![0xbe, 0xef, 0x00])];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            match sht.read_with_crc(&mut buf) {
                Err(Error::Crc) => {}
                Err(_) => panic!("Invalid error: Must be Crc"),
                Ok(_) => panic!("CRC check did not fail"),
            }
            assert_eq!(buf, [0xbe, 0xef, 0x00]); // Buf was changed
            sht.destroy().done();
        }
    }

    mod factory_functions {
        use super::*;

        #[test]
        fn new_shtc3() {
            let mock = I2cMock::new(&[]);
            let sht = ShtC3::new(mock, PowerMode::NormalMode);
            assert_eq!(sht.address, 0x70);
            sht.destroy().done();
        }
    }

    mod device_info {
        use super::*;

        /// Test the `raw_id_register` function.
        #[test]
        fn raw_id_register() {
            let msb = 0b00001000;
            let lsb = 0b00000111;
            let crc = crc8(&[msb, lsb]);
            let expectations = [
                Transaction::write(SHT_ADDR, alloc::vec![0xef, 0xc8]),
                Transaction::read(SHT_ADDR, alloc::vec![msb, lsb, crc]),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let val = sht.raw_id_register().unwrap();
            assert_eq!(val, (msb as u16) << 8 | (lsb as u16));
            sht.destroy().done();
        }

        /// Test the `device_identifier` function.
        #[test]
        fn device_identifier() {
            let msb = 0b00001000;
            let lsb = 0b00000111;
            let crc = crc8(&[msb, lsb]);
            let expectations = [
                Transaction::write(SHT_ADDR, alloc::vec![0xef, 0xc8]),
                Transaction::read(SHT_ADDR, alloc::vec![msb, lsb, crc]),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let ident = sht.device_identifier().unwrap();
            assert_eq!(ident, 0b01000111);
            sht.destroy().done();
        }
    }

    mod measurements {
        use super::*;

        #[test]
        fn measure_normal() {
            let expectations = [
                // Expect a write command: Normal mode measurement, temperature
                // first, no clock stretching.
                Transaction::write(SHT_ADDR, alloc::vec![0x78, 0x66]),
                // Return the measurement result (using example values from the
                // datasheet, section 5.4 "Measuring and Reading the Signals")
                Transaction::read(
                    SHT_ADDR,
                    alloc::vec![
                        0b0110_0100,
                        0b1000_1011,
                        0b1100_0111,
                        0b1010_0001,
                        0b0011_0011,
                        0b0001_1100,
                    ],
                ),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let mut delay = NoopDelay;
            let measurement = sht.measure(&mut delay).unwrap();
            assert_eq!(measurement.temperature.as_millidegrees_celsius(), 23_730); // 23.7°C
            assert_eq!(measurement.humidity.as_millipercent(), 62_968); // 62.9 %RH
            sht.destroy().done();
        }

        #[test]
        fn measure_low_power() {
            let expectations = [
                // Expect a write command: Low power mode measurement, temperature
                // first, no clock stretching.
                Transaction::write(SHT_ADDR, alloc::vec![0x60, 0x9C]),
                // Return the measurement result (using example values from the
                // datasheet, section 5.4 "Measuring and Reading the Signals")
                Transaction::read(
                    SHT_ADDR,
                    alloc::vec![
                        0b0110_0100,
                        0b1000_1011,
                        0b1100_0111,
                        0b1010_0001,
                        0b0011_0011,
                        0b0001_1100,
                    ],
                ),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::LowPower);
            let mut delay = NoopDelay;
            let measurement = sht.measure(&mut delay).unwrap();
            assert_eq!(measurement.temperature.as_millidegrees_celsius(), 23_730); // 23.7°C
            assert_eq!(measurement.humidity.as_millipercent(), 62_968); // 62.9 %RH
            sht.destroy().done();
        }

        #[test]
        fn measure_temperature_only() {
            let expectations = [
                // Expect a write command: Normal mode measurement, temperature
                // first, no clock stretching.
                Transaction::write(SHT_ADDR, alloc::vec![0x78, 0x66]),
                // Return the measurement result (using example values from the
                // datasheet, section 5.4 "Measuring and Reading the Signals")
                Transaction::read(SHT_ADDR, alloc::vec![0b0110_0100, 0b1000_1011, 0b1100_0111]),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let mut delay = NoopDelay;
            let temperature = sht.measure_temperature(&mut delay).unwrap();
            assert_eq!(temperature.as_millidegrees_celsius(), 23_730); // 23.7°C
            sht.destroy().done();
        }

        #[test]
        fn measure_humidity_only() {
            let expectations = [
                // Expect a write command: Normal mode measurement, humidity
                // first, no clock stretching.
                Transaction::write(SHT_ADDR, alloc::vec![0x58, 0xE0]),
                // Return the measurement result (using example values from the
                // datasheet, section 5.4 "Measuring and Reading the Signals")
                Transaction::read(SHT_ADDR, alloc::vec![0b1010_0001, 0b0011_0011, 0b0001_1100]),
            ];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            let mut delay = NoopDelay;
            let humidity = sht.measure_humidity(&mut delay).unwrap();
            assert_eq!(humidity.as_millipercent(), 62_968); // 62.9 %RH
            sht.destroy().done();
        }

        /// Ensure that I²C write errors are handled when measuring.
        #[test]
        fn measure_write_error() {
            let expectations =
                [Transaction::write(SHT_ADDR, alloc::vec![0x60, 0x9C])
                    .with_error(ErrorKind::Other)];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::LowPower);
            let err = sht.measure(&mut NoopDelay).unwrap_err();
            assert_eq!(err, Error::I2c(ErrorKind::Other));
            sht.destroy().done();
        }
    }

    mod power_management {
        use super::*;

        /// Test the `sleep` function.
        #[test]
        fn sleep() {
            let expectations = [Transaction::write(SHT_ADDR, alloc::vec![0xB0, 0x98])];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            sht.sleep().unwrap();
            sht.destroy().done();
        }

        /// Test the `wakeup` function.
        #[test]
        fn wakeup() {
            let expectations = [Transaction::write(SHT_ADDR, alloc::vec![0x35, 0x17])];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            sht.wakeup(&mut NoopDelay).unwrap();
            sht.destroy().done();
        }

        /// Test the `reset` function.
        #[test]
        fn reset() {
            let expectations = [Transaction::write(SHT_ADDR, alloc::vec![0x80, 0x5D])];
            let mock = I2cMock::new(&expectations);
            let mut sht = ShtC3::new(mock, PowerMode::NormalMode);
            sht.reset(&mut NoopDelay).unwrap();
            sht.destroy().done();
        }
    }

    mod max_measurement_duration {
        use super::*;

        #[test]
        fn shortcut_function() {
            let c3 = ShtC3::new(I2cMock::new(&[]), PowerMode::NormalMode);

            assert_eq!(c3.max_measurement_duration(), 12100);

            let i2c = c3.destroy();

            let c3 = ShtC3::new(i2c, PowerMode::LowPower);

            assert_eq!(c3.max_measurement_duration(), 800);

            c3.destroy().done();
        }
    }
}