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

/// Optional checksumming for individual files
#[derive(Debug)]
pub enum Checksum {
    /// Md5 checksumming, fastest
    Md5([u8; 16]),
    /// Sha1 checksumming. On par with md5.
    Sha1([u8; 20]),
    /// The most thorough checksumming offered. Use this if data integrity is of
    /// utmost importance and computational overhead is of lesser importance.
    Sha256([u8; 32]),
    /// Do not use checksumming. If this option is selected it is recommended that
    /// the entire archive is downloaded in entirety and checksummed to ensure it's
    /// integrity, as was the pattern with Unix 'tar' archives and 'iso' images
    Skip,
}

impl Checksum {
    pub fn read<T: Read>(reader: &mut T) -> Result<Self, Error> {
        let mut buf = [0; 1];
        reader.read_exact(&mut buf)?;
        match buf[0] {
            0 => {
                let mut sum = [0; 16];
                reader.read_exact(&mut sum)?;
                Ok(Self::Md5(sum))
            }
            1 => {
                let mut sum = [0; 20];
                reader.read_exact(&mut sum)?;
                Ok(Self::Sha1(sum))
            }
            2 => {
                let mut sum = [0; 32];
                reader.read_exact(&mut sum)?;
                Ok(Self::Sha256(sum))
            }
            _ => Ok(Self::Skip),
        }
    }

    pub fn write<T: Write>(&self, writer: &mut T) -> Result<(), Error> {
        match self {
            Self::Md5(sum) => {
                writer.write_all(&[b'0'])?;
                writer.write_all(&sum[..])?;
            }
            Self::Sha1(sum) => {
                writer.write_all(&[b'1'])?;
                writer.write_all(&sum[..])?;
            }
            Self::Sha256(sum) => {
                writer.write_all(&[b'2'])?;
                writer.write_all(&sum[..])?;
            }
            Self::Skip => writer.write_all(&[b'3'])?,
        }
        Ok(())
    }
}