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use std::cell::Cell;
use std::time::{SystemTime, UNIX_EPOCH};
thread_local! {
static RNG_STATE: Cell<u64> = const { Cell::new(0) };
}
fn next_u64() -> u64 {
RNG_STATE.with(|state| {
let mut value = state.get();
if value == 0 {
let nanos = SystemTime::now()
.duration_since(UNIX_EPOCH)
.map(|duration| duration.as_nanos() as u64)
.unwrap_or(0x9e37_79b9_7f4a_7c15);
value = nanos
^ (std::process::id() as u64).rotate_left(32)
^ 0x9e37_79b9_7f4a_7c15;
}
value ^= value << 13;
value ^= value >> 7;
value ^= value << 17;
state.set(value);
value
})
}
pub fn generate_uuid() -> String {
let mut bytes = [0u8; 16];
for chunk in bytes.chunks_mut(8) {
let random = next_u64().to_le_bytes();
chunk.copy_from_slice(&random[..chunk.len()]);
}
bytes[6] = (bytes[6] & 0x0f) | 0x40;
bytes[8] = (bytes[8] & 0x3f) | 0x80;
let hex: Vec<String> = bytes.iter().map(|byte| format!("{byte:02x}")).collect();
format!(
"{}-{}-{}-{}-{}",
hex[0..4].join(""),
hex[4..6].join(""),
hex[6..8].join(""),
hex[8..10].join(""),
hex[10..16].join("")
)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn generates_uuid_shaped_unique_ids() {
let id = generate_uuid();
let parts: Vec<&str> = id.split('-').collect();
assert_eq!(parts.len(), 5);
assert_eq!(parts[0].len(), 8);
assert_eq!(parts[1].len(), 4);
assert_eq!(parts[4].len(), 12);
assert_ne!(generate_uuid(), generate_uuid());
}
}
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