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//! UUID utilities.
//!
//! This module re-exports the [`Uuid`] type from the [`uuid`] crate,
//! and provides additional utility functions.
//!
//! [`uuid`]: uuid

pub use ::uuid::Uuid;

/// Generates a new UUID from the given UUIDs `a` and `b`,
/// where the bytes are generated by a bitwise `a ^ b.rotate_right(1)`.
///
/// The generated UUID will be a `UUIDv4`
/// (meaning that the bytes should be random, not e.g. derived from the system time).
#[allow(clippy::unusual_byte_groupings)] // unusual byte grouping is meant to signal the relevant bits
pub const fn generate_composite_uuid(a: Uuid, b: Uuid) -> Uuid {
    let mut new = [0; 16];
    let mut i = 0;
    while i < new.len() {
        // rotating ensures different uuids for A<B<C>> and B<A<C>> because: A ^ (B ^ C) = B ^ (A ^ C)
        // notice that you have to rotate the second parameter: A.rr ^ (B.rr ^ C) = B.rr ^ (A.rr ^ C)
        // Solution: A ^ (B ^ C.rr).rr != B ^ (A ^ C.rr).rr
        new[i] = a.as_bytes()[i] ^ b.as_bytes()[i].rotate_right(1);

        i += 1;
    }

    // Version: the most significant 4 bits in the 6th byte: 11110000
    new[6] = new[6] & 0b0000_1111 | 0b0100_0000; // set version to v4

    // Variant: the most significant 3 bits in the 8th byte: 11100000
    new[8] = new[8] & 0b000_11111 | 0b100_00000; // set variant to rfc4122

    Uuid::from_bytes(new)
}