lexe-common 0.1.6

use std::{
    cmp::Ordering,
    fmt::{self, Display},
    str::FromStr,
};

use bitcoin::hashes::Hash as _;
use serde::{Deserialize, Serialize};

/// A Bitcoin transaction ID. Serialized as a 64-character hex string in
/// conventional (reversed) byte order, e.g.
/// `"a1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d"`.
//
// Almost exactly [`bitcoin::Txid`], but fixes the inconsistency between the
// string-serialized and unserialized orderings caused by bitcoin sha256d hash
// types being displayed in reverse hex order (thanks Satoshi!). Also provides
// an `Arbitrary` impl. When neither of these are required, it is perfectly
// fine (and equivalent) to use [`bitcoin::Txid`] directly.
//
// To ensure that we don't accidentally display a non-reversed hash to a Lexe
// user, we still display using [`bitcoin::Txid`]'s provided reverse hex impl,
// but we override the [`Ord`] implementation to be consistent with the
// user-facing lexicographic ordering.
//
// See [`bitcoin::hashes::Hash::DISPLAY_BACKWARD`] or the `hash_newtype!`
// definition of [`bitcoin::Txid`] for more info.
#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
pub struct Txid(pub bitcoin::Txid);

impl Display for Txid {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        bitcoin::Txid::fmt(&self.0, f)
    }
}

impl FromStr for Txid {
    type Err = bitcoin::hex::HexToArrayError;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        bitcoin::Txid::from_str(s).map(Self)
    }
}

impl Ord for Txid {
    fn cmp(&self, other: &Self) -> Ordering {
        // Compare the two hashes byte by byte, starting with the least
        // significant byte (i.e. in reverse order), returning as soon as we
        // find a pair of bytes that are not equal, returning Ordering::Equal if
        // all of the bytes were equal.
        self.0
            .as_raw_hash()
            .as_byte_array()
            .iter()
            .rev()
            .cmp(other.0.as_byte_array().iter().rev())
    }
}

impl PartialOrd for Txid {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

#[cfg(any(test, feature = "test-utils"))]
mod arbitrary_impl {
    use proptest::{
        arbitrary::{Arbitrary, any},
        strategy::{BoxedStrategy, Strategy},
    };

    use super::*;

    impl Arbitrary for Txid {
        type Parameters = ();
        type Strategy = BoxedStrategy<Self>;
        fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
            // Excluding .no_shrink() makes it easier to debug
            any::<[u8; 32]>()
                .prop_map(bitcoin::Txid::from_byte_array)
                .prop_map(Self)
                .boxed()
        }
    }
}

#[cfg(test)]
mod test {
    use proptest::{arbitrary::any, prop_assert_eq, proptest};

    use super::*;
    use crate::test_utils::roundtrip;

    #[test]
    fn txid_roundtrip() {
        roundtrip::fromstr_display_roundtrip_proptest::<Txid>();
        roundtrip::json_string_roundtrip_proptest::<Txid>();
        roundtrip::bcs_roundtrip_proptest::<Txid>();
    }

    #[test]
    fn txid_ordering_equivalence() {
        proptest!(|(txid1 in any::<Txid>(), txid2 in any::<Txid>())| {
            let txid1_str = txid1.to_string();
            let txid2_str = txid2.to_string();

            let unserialized_order = txid1.cmp(&txid2);
            let string_serialized_order = txid1_str.cmp(&txid2_str);

            prop_assert_eq!(unserialized_order, string_serialized_order);
        });
    }
}