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// SPDX-License-Identifier: CC0-1.0

//! SHA256d implementation (double SHA256).
//!

use core::ops::Index;
use core::slice::SliceIndex;
use core::str;

use crate::{sha256, FromSliceError};

crate::internal_macros::hash_type! {
    256,
    true,
    "Output of the SHA256d hash function.",
    "crate::util::json_hex_string::len_32"
}

type HashEngine = sha256::HashEngine;

fn from_engine(e: sha256::HashEngine) -> Hash {
    use crate::Hash as _;

    let sha2 = sha256::Hash::from_engine(e);
    let sha2d = sha256::Hash::hash(&sha2[..]);

    let mut ret = [0; 32];
    ret.copy_from_slice(&sha2d[..]);
    Hash(ret)
}

#[cfg(test)]
mod tests {
    #[test]
    #[cfg(feature = "alloc")]
    fn test() {
        use crate::{sha256, sha256d, Hash, HashEngine};

        #[derive(Clone)]
        struct Test {
            input: &'static str,
            output: Vec<u8>,
            output_str: &'static str,
        }

        #[rustfmt::skip]
        let tests = vec![
            // Test vector copied out of rust-bitcoin
            Test {
                input: "",
                output: vec![
                    0x5d, 0xf6, 0xe0, 0xe2, 0x76, 0x13, 0x59, 0xd3,
                    0x0a, 0x82, 0x75, 0x05, 0x8e, 0x29, 0x9f, 0xcc,
                    0x03, 0x81, 0x53, 0x45, 0x45, 0xf5, 0x5c, 0xf4,
                    0x3e, 0x41, 0x98, 0x3f, 0x5d, 0x4c, 0x94, 0x56,
                ],
                output_str: "56944c5d3f98413ef45cf54545538103cc9f298e0575820ad3591376e2e0f65d",
            },
        ];

        for test in tests {
            // Hash through high-level API, check hex encoding/decoding
            let hash = sha256d::Hash::hash(test.input.as_bytes());
            assert_eq!(hash, test.output_str.parse::<sha256d::Hash>().expect("parse hex"));
            assert_eq!(&hash[..], &test.output[..]);
            assert_eq!(&hash.to_string(), &test.output_str);

            // Hash through engine, checking that we can input byte by byte
            let mut engine = sha256d::Hash::engine();
            for ch in test.input.as_bytes() {
                engine.input(&[*ch]);
            }
            let manual_hash = sha256d::Hash::from_engine(engine);
            assert_eq!(hash, manual_hash);

            // Hash by computing a sha256 then `hash_again`ing it
            let sha2_hash = sha256::Hash::hash(test.input.as_bytes());
            let sha2d_hash = sha2_hash.hash_again();
            assert_eq!(hash, sha2d_hash);

            assert_eq!(hash.to_byte_array()[..].as_ref(), test.output.as_slice());
        }
    }

    #[cfg(feature = "serde")]
    #[test]
    fn sha256_serde() {
        use serde_test::{assert_tokens, Configure, Token};

        use crate::{sha256d, Hash};

        #[rustfmt::skip]
        static HASH_BYTES: [u8; 32] = [
            0xef, 0x53, 0x7f, 0x25, 0xc8, 0x95, 0xbf, 0xa7,
            0x82, 0x52, 0x65, 0x29, 0xa9, 0xb6, 0x3d, 0x97,
            0xaa, 0x63, 0x15, 0x64, 0xd5, 0xd7, 0x89, 0xc2,
            0xb7, 0x65, 0x44, 0x8c, 0x86, 0x35, 0xfb, 0x6c,
        ];

        let hash = sha256d::Hash::from_slice(&HASH_BYTES).expect("right number of bytes");
        assert_tokens(&hash.compact(), &[Token::BorrowedBytes(&HASH_BYTES[..])]);
        assert_tokens(
            &hash.readable(),
            &[Token::Str("6cfb35868c4465b7c289d7d5641563aa973db6a929655282a7bf95c8257f53ef")],
        );
    }
}

#[cfg(bench)]
mod benches {
    use test::Bencher;

    use crate::{sha256d, Hash, HashEngine};

    #[bench]
    pub fn sha256d_10(bh: &mut Bencher) {
        let mut engine = sha256d::Hash::engine();
        let bytes = [1u8; 10];
        bh.iter(|| {
            engine.input(&bytes);
        });
        bh.bytes = bytes.len() as u64;
    }

    #[bench]
    pub fn sha256d_1k(bh: &mut Bencher) {
        let mut engine = sha256d::Hash::engine();
        let bytes = [1u8; 1024];
        bh.iter(|| {
            engine.input(&bytes);
        });
        bh.bytes = bytes.len() as u64;
    }

    #[bench]
    pub fn sha256d_64k(bh: &mut Bencher) {
        let mut engine = sha256d::Hash::engine();
        let bytes = [1u8; 65536];
        bh.iter(|| {
            engine.input(&bytes);
        });
        bh.bytes = bytes.len() as u64;
    }
}