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use crate::{left_encode, right_encode, CShake, Hasher, Xof};

/// The `TupleHash` extendable-output and hash functions defined in [`SP800-185`].
///
/// [`SP800-185`]: https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-185.pdf
#[derive(Clone)]
pub struct TupleHash {
    state: CShake,
    xof_started: bool,
}

impl TupleHash {
    /// Creates  new [`TupleHash`] hasher with a security level of 128 bits.
    ///
    /// [`TupleHash`]: struct.TupleHash.html
    pub fn v128(custom_string: &[u8]) -> TupleHash {
        TupleHash::new(custom_string, 128)
    }

    /// Creates  new [`TupleHash`] hasher with a security level of 256 bits.
    ///
    /// [`TupleHash`]: struct.TupleHash.html
    pub fn v256(custom_string: &[u8]) -> TupleHash {
        TupleHash::new(custom_string, 256)
    }

    fn new(custom_string: &[u8], bits: usize) -> TupleHash {
        TupleHash {
            state: CShake::new(b"TupleHash", custom_string, bits),
            xof_started: false,
        }
    }
}

impl Hasher for TupleHash {
    fn update(&mut self, input: &[u8]) {
        self.state.update(left_encode(input.len() * 8).value());
        self.state.update(input)
    }

    fn finalize(mut self, output: &mut [u8]) {
        self.state.update(right_encode(output.len() * 8).value());
        self.state.finalize(output)
    }
}

impl Xof for TupleHash {
    fn squeeze(&mut self, output: &mut [u8]) {
        if !self.xof_started {
            self.xof_started = true;
            self.state.update(right_encode(0).value());
        }

        self.state.squeeze(output)
    }
}