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//! [`PassportId`] — the passport's unique identifier.
use serde::{Deserialize, Serialize};
use uuid::Uuid;
/// Newtype wrapper for a passport's unique identifier.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(transparent)]
pub struct PassportId(pub Uuid);
impl PassportId {
#[must_use]
pub fn new() -> Self {
Self(Uuid::now_v7())
}
/// The carrier serial a passport gets when its operator attributes none:
/// the **last ten bytes** of this id as lowercase hex.
///
/// Exactly twenty characters from `[0-9a-f]`, so it fits GS1's AI 21 limit
/// and sits inside CSET 82 by construction. It is also the last twenty hex
/// digits of the id's canonical text form, which is what lets storage index
/// it with an expression over the id rather than a stored copy of it —
/// `the_default_is_the_tail_of_the_canonical_id` pins that equivalence.
///
/// # Why the last ten bytes, not the first
///
/// Passport IDs are UUIDv7, whose leading six bytes are a big-endian
/// millisecond timestamp (RFC 9562 §5.7). Taking the *first* ten bytes gave a
/// serial that sorted in creation order and whose first twelve hex characters
/// decoded directly to the passport's creation instant — so a code printed on
/// a physical battery published its creation time to the millisecond, and
/// any two codes revealed their production order and the rate between them.
///
/// Bytes 6..16 are the `rand_a` and `rand_b` fields: 74 random bits, with only
/// the 4-bit version and 2-bit variant fixed. No timestamp, no ordering, and
/// nothing to guess a neighbouring passport's serial from.
#[must_use]
pub fn default_carrier_serial(&self) -> String {
let mut serial = String::with_capacity(20);
for byte in &self.0.as_bytes()[6..] {
serial.push_str(&format!("{byte:02x}"));
}
serial
}
}
impl Default for PassportId {
fn default() -> Self {
Self::new()
}
}
impl std::fmt::Display for PassportId {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.0.fmt(f)
}
}