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// License: see LICENSE file at root directory of `master` branch

//! # Hash functions

use {
    alloc::{
        string::String,
        vec::Vec,
    },
    core::fmt::{self, Display, Formatter},

    crate::Keccak,

    super::bits::Bits,
};

#[cfg(feature="std")]
use {
    std::io::{Read, Write},
};

#[allow(deprecated)]
#[cfg(feature="std")]
use {
    crate::{HashReader, HashWriter},
};

#[cfg(test)]
use {
    core::convert::TryFrom,
};

/// # Hash functions
///
/// This is used to make new [`Keccak`][struct:Keccak].
///
/// [struct:Keccak]: struct.Keccak.html
#[derive(Debug, Eq, PartialEq, Hash, Clone)]
pub enum Hash {

    /// # SHA3-224
    Sha3_224,

    /// # SHA3-256
    Sha3_256,

    /// # SHA3-384
    Sha3_384,

    /// # SHA3-512
    Sha3_512,

    /// # SHAKE128
    Shake128,

    /// # SHAKE256
    Shake256,

}

impl Hash {

    /// # Name of this instance
    pub fn name(&self) -> &str {
        match self {
            Hash::Sha3_224 => "SHA3-224",
            Hash::Sha3_256 => "SHA3-256",
            Hash::Sha3_384 => "SHA3-384",
            Hash::Sha3_512 => "SHA3-512",
            Hash::Shake128 => "SHAKE128",
            Hash::Shake256 => "SHAKE256",
        }
    }

    /// # Makes new [`Keccak`][struct:Keccak] from this instance
    ///
    /// [struct:Keccak]: struct.Keccak.html
    pub fn new_keccak(&self) -> Keccak {
        Keccak::new(self.clone())
    }

    /// # Makes new [`HashWriter`][struct:HashWriter]
    ///
    /// [struct:HashWriter]: struct.HashWriter.html
    #[deprecated(note = "Beta")]
    #[allow(deprecated)]
    #[cfg(feature="std")]
    pub fn new_writer<W>(&self, writer: W) -> HashWriter<W> where W: Write {
        HashWriter::new(self.new_keccak(), writer)
    }

    /// # Makes new [`HashReader`][struct:HashReader]
    ///
    /// [struct:HashReader]: struct.HashReader.html
    #[deprecated(note = "Beta")]
    #[allow(deprecated)]
    #[cfg(feature="std")]
    pub fn new_reader<R>(&self, reader: R) -> HashReader<R> where R: Read {
        HashReader::new(self.new_keccak(), reader)
    }

    /// # Hashes input bytes
    ///
    /// This can be used for small amount of data. For large data, see [`new_keccak()`][fn:new_keccak].
    ///
    /// [fn:new_keccak]: #method.new_keccak
    pub fn hash<B>(&self, bytes: B) -> Vec<u8> where B: AsRef<[u8]> {
        let mut keccak = self.new_keccak();
        keccak.update(bytes);
        keccak.finish()
    }

    /// # Hashes input bytes and returns hash as a hexadecimal string, in lower-case
    ///
    /// This can be used for small amount of data. For large data, see [`new_keccak()`][fn:new_keccak].
    ///
    /// [fn:new_keccak]: #method.new_keccak
    pub fn hash_as_hex<B>(&self, bytes: B) -> String where B: AsRef<[u8]> {
        crate::bytes_to_hex(self.hash(bytes))
    }

    /// # Capacity
    pub (crate) const fn capacity(&self) -> usize {
        match self {
            Hash::Sha3_224 => 448,
            Hash::Sha3_256 => 512,
            Hash::Sha3_384 => 768,
            Hash::Sha3_512 => 1024,
            Hash::Shake128 => 256,
            Hash::Shake256 => 512,
        }
    }

    /// # Output bytes
    pub (crate) const fn output_bytes(&self) -> usize {
        match self {
            Hash::Sha3_224 => 28,
            Hash::Sha3_256 => 32,
            Hash::Sha3_384 => 48,
            Hash::Sha3_512 => 64,
            Hash::Shake128 => 16,
            Hash::Shake256 => 32,
        }
    }

    /// # Suffix (to be added to message)
    pub (crate) const fn suffix(&self) -> &[bool] {
        match self {
            Hash::Sha3_224 => &[false, true],
            Hash::Sha3_256 => &[false, true],
            Hash::Sha3_384 => &[false, true],
            Hash::Sha3_512 => &[false, true],
            Hash::Shake128 => &[true, true, true, true],
            Hash::Shake256 => &[true, true, true, true],
        }
    }

    /// # Rate
    pub (crate) const fn rate(&self) -> usize {
        Bits::B1600.bits() - self.capacity()
    }

}

impl Display for Hash {

    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
        f.write_str(self.name())
    }

}

#[test]
fn test_hashes() {
    for h in &[Hash::Sha3_224, Hash::Sha3_256, Hash::Sha3_384, Hash::Sha3_512, Hash::Shake128, Hash::Shake256] {
        assert!(h.capacity() < Bits::B1600.bits());
        assert_eq!(h.output_bytes().checked_mul(16).unwrap(), h.capacity());

        let capacity = h.capacity();
        assert!(capacity > 0 && capacity % 64 == 0);

        let rate = h.rate();
        assert!(rate > 0 && rate % 64 == 0);

        // For BitStr::pad()
        isize::try_from(rate).unwrap();
    }
}