use {
    crate::Error,
    std::io::{Read, Write},
};

/// Represents the major and minor numbers of a Unix special Device node
#[derive(Debug, PartialEq, Eq)]
pub struct Special {
    pub major: u32,
    pub minor: u32,
}

impl Special {
    pub(crate) fn read<T: Read>(reader: &mut T) -> Result<Self, Error> {
        let mut buf = [0; 8];
        reader.read_exact(&mut buf)?;
        let major: [u8; 4] = buf[..4].try_into()?;
        let major = u32::from_le_bytes(major);
        let minor: [u8; 4] = buf[4..].try_into()?;
        let minor = u32::from_le_bytes(minor);
        Ok(Self { major, minor })
    }

    pub(crate) fn write<T: Write>(&self, writer: &mut T) -> Result<(), Error> {
        writer.write_all(&self.major.to_le_bytes())?;
        writer.write_all(&self.minor.to_le_bytes())?;
        Ok(())
    }

    #[cfg(all(target_os = "freebsd", target_arch = "x86_64"))]
    #[allow(clippy::cast_possible_truncation)]
    pub(super) fn from_rdev(rdev: u64) -> Self {
        Self {
            major: ((rdev >> 8) & 0xff) as u32,
            minor: (rdev & 0xffff_00ff) as u32,
        }
    }

    #[cfg(target_os = "linux")]
    #[allow(clippy::cast_possible_truncation)]
    pub(super) fn from_rdev(rdev: u64) -> Self {
        let mut major = 0;
        major |= (rdev & 0x0000_0000_000f_ff00) >> 8;
        major |= (rdev & 0xffff_f000_0000_0000) >> 32;
        let mut minor = 0;
        minor |= rdev & 0x0000_0000_0000_00ff;
        minor |= (rdev & 0x0000_0fff_fff0_0000) >> 12;
        Self {
            major: major as u32,
            minor: minor as u32,
        }
    }
}

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

    #[test]
    fn load_store() {
        {
            let mut fd = File::options()
                .write(true)
                .create(true)
                .truncate(true)
                .open("test/device")
                .unwrap();
            let dev = Special {
                major: 42,
                minor: 69,
            };
            dev.write(&mut fd).unwrap();
        }
        let mut fd = File::open("test/device").unwrap();
        let dev = Special::read(&mut fd).unwrap();
        assert_eq!(dev.major, 42);
        assert_eq!(dev.minor, 69);
    }
}