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// Copyright (C) 2019-2022 Aleo Systems Inc.
// This file is part of the snarkVM library.

// The snarkVM library is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// The snarkVM library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with the snarkVM library. If not, see <https://www.gnu.org/licenses/>.

///!
///! Blake2Xs function
///!
///! This implementation is based on the BLAKE2Xs specification in Section 2 of
///! <https://www.blake2.net/blake2x.pdf>
///!
mod hash_to_curve;

pub struct Blake2Xs;

impl Blake2Xs {
    /// Returns the BLAKE2Xs digest given:
    ///  - `input` is an input message as a slice of bytes,
    ///  - `XOF_DIGEST_LENGTH` is a `u16` set to the length of the final output digest in bytes,
    ///  - `PERSONALIZATION` is a `u64` representing a UTF-8 string of 8 characters.
    fn evaluate(input: &[u8], xof_digest_length: u16, persona: &[u8]) -> Vec<u8> {
        assert!(xof_digest_length > 0, "Output digest must be of non-zero length");
        assert!(persona.len() <= 8, "Personalization may be at most 8 characters");

        // Start by computing the digest of the input bytes.
        let xof_digest_length_node_offset = (xof_digest_length as u64) << 32;
        let input_digest = blake2s_simd::Params::new()
            .hash_length(32)
            .node_offset(xof_digest_length_node_offset)
            .personal(persona)
            .hash(input);

        let mut output = vec![];

        let num_rounds = xof_digest_length.saturating_add(31) / 32;
        for node_offset in 0..num_rounds {
            // Calculate the digest length for this round.
            let is_final_round = node_offset == num_rounds - 1;
            let has_remainder = xof_digest_length % 32 != 0;
            let digest_length = match is_final_round && has_remainder {
                true => (xof_digest_length % 32) as usize,
                false => 32,
            };

            // Compute the next part of the output digest.
            output.extend_from_slice(
                blake2s_simd::Params::new()
                    .hash_length(digest_length)
                    .fanout(0)
                    .max_depth(0)
                    .max_leaf_length(32)
                    .node_offset(xof_digest_length_node_offset | (node_offset as u64))
                    .inner_hash_length(32)
                    .personal(persona)
                    .hash(input_digest.as_bytes())
                    .as_bytes(),
            );
        }

        output
    }
}

#[cfg(test)]
mod tests {
    use crate::Blake2Xs;
    use serde::Deserialize;

    #[derive(Deserialize)]
    struct Case {
        hash: String,
        #[serde(rename = "in")]
        input: String,
        key: String,
        #[serde(rename = "out")]
        output: String,
    }

    #[test]
    fn test_blake2xs() {
        // Run test vector cases.
        let vectors: Vec<Case> = serde_json::from_str(include_str!("./resources/blake2-kat.json")).unwrap();
        for case in vectors.iter().filter(|v| &v.hash == "blake2xs" && v.key.is_empty()) {
            let input = hex::decode(case.input.as_bytes()).unwrap();
            let xof_digest_length = u16::try_from(case.output.len()).unwrap() / 2;
            let output = hex::encode(Blake2Xs::evaluate(&input, xof_digest_length, "".as_bytes()));
            assert_eq!(output, case.output);
        }
    }

    #[test]
    fn test_blake2s() {
        // Run test vector cases for blake2s as a sanity check for the underlying impl.
        let vectors: Vec<Case> = serde_json::from_str(include_str!("./resources/blake2-kat.json")).unwrap();
        for case in vectors.iter().filter(|v| &v.hash == "blake2s" && v.key.is_empty()) {
            let input = hex::decode(case.input.as_bytes()).unwrap();
            let output = hex::encode(blake2s_simd::Params::new().personal(&0u64.to_le_bytes()).hash(&input).as_bytes());
            assert_eq!(output, case.output);
        }
    }
}