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use std::time::{Duration, SystemTime};
use std::fmt;
use crate::Ulid;
/// A Ulid generator that provides monotonically increasing Ulids
pub struct Generator {
previous: Ulid,
}
impl Generator {
/// Create a new ulid generator for monotonically ordered ulids
///
/// # Example
/// ```rust
/// use ulid::Generator;
///
/// let mut gen = Generator::new();
///
/// let ulid1 = gen.generate().unwrap();
/// let ulid2 = gen.generate().unwrap();
///
/// assert!(ulid1 < ulid2);
/// ```
pub const fn new() -> Generator {
Generator {
previous: Ulid::nil(),
}
}
/// Generate a new Ulid. Each call is guaranteed to provide a Ulid with a larger value than the
/// last call. If the random bits would overflow, this method will return an error.
///
/// ```rust
/// use ulid::Generator;
/// let mut gen = Generator::new();
///
/// let ulid1 = gen.generate().unwrap();
/// let ulid2 = gen.generate().unwrap();
///
/// assert!(ulid1 < ulid2);
/// ```
pub fn generate(&mut self) -> Result<Ulid, MonotonicError> {
self.generate_from_datetime(crate::time_utils::now())
}
/// Generate a new Ulid matching the given DateTime.
/// Each call is guaranteed to provide a Ulid with a larger value than the last call.
/// If the random bits would overflow, this method will return an error.
///
/// # Example
/// ```rust
/// use ulid::Generator;
/// use std::time::SystemTime;
///
/// let dt = SystemTime::now();
/// let mut gen = Generator::new();
///
/// let ulid1 = gen.generate_from_datetime(dt).unwrap();
/// let ulid2 = gen.generate_from_datetime(dt).unwrap();
///
/// assert_eq!(ulid1.datetime(), ulid2.datetime());
/// assert!(ulid1 < ulid2);
/// ```
pub fn generate_from_datetime(&mut self, datetime: SystemTime) -> Result<Ulid, MonotonicError> {
self.generate_from_datetime_with_source(datetime, &mut rand::rng())
}
/// Generate a new monotonic increasing Ulid with the given source
/// Each call is guaranteed to provide a Ulid with a larger value than the last call.
/// If the random bits would overflow, this method will return an error.
///
/// # Example
/// ```rust
/// use ulid::Generator;
/// use ulid::Ulid;
/// use std::time::SystemTime;
/// use rand::prelude::*;
///
/// let mut rng = StdRng::from_os_rng();
/// let mut gen = Generator::new();
///
/// let ulid1 = gen.generate_with_source(&mut rng).unwrap();
/// let ulid2 = gen.generate_with_source(&mut rng).unwrap();
///
/// assert!(ulid1 < ulid2);
/// ```
pub fn generate_with_source<R>(&mut self, source: &mut R) -> Result<Ulid, MonotonicError>
where
R: rand::Rng + ?Sized,
{
self.generate_from_datetime_with_source(crate::time_utils::now(), source)
}
/// Generate a new monotonic increasing Ulid with the given source matching the given DateTime
/// Each call is guaranteed to provide a Ulid with a larger value than the last call.
/// If the random bits would overflow, this method will return an error.
///
/// # Example
/// ```rust
/// use ulid::Generator;
/// use std::time::SystemTime;
/// use rand::prelude::*;
///
/// let dt = SystemTime::now();
/// let mut rng = StdRng::from_os_rng();
/// let mut gen = Generator::new();
///
/// let ulid1 = gen.generate_from_datetime_with_source(dt, &mut rng).unwrap();
/// let ulid2 = gen.generate_from_datetime_with_source(dt, &mut rng).unwrap();
///
/// assert_eq!(ulid1.datetime(), ulid2.datetime());
/// assert!(ulid1 < ulid2);
/// ```
pub fn generate_from_datetime_with_source<R>(
&mut self,
datetime: SystemTime,
source: &mut R,
) -> Result<Ulid, MonotonicError>
where
R: rand::Rng + ?Sized,
{
let last_ms = self.previous.timestamp_ms();
// maybe time went backward, or it is the same ms.
// increment instead of generating a new random so that it is monotonic
if datetime
.duration_since(SystemTime::UNIX_EPOCH)
.unwrap_or(Duration::ZERO)
.as_millis()
<= u128::from(last_ms)
{
if let Some(next) = self.previous.increment() {
self.previous = next;
return Ok(next);
} else {
return Err(MonotonicError::Overflow);
}
}
let next = Ulid::from_datetime_with_source(datetime, source);
self.previous = next;
Ok(next)
}
}
impl Default for Generator {
fn default() -> Self {
Self::new()
}
}
/// Error while trying to generate a monotonic increment in the same millisecond
#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
pub enum MonotonicError {
/// Would overflow into the next millisecond
Overflow,
}
impl std::error::Error for MonotonicError {}
impl fmt::Display for MonotonicError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
let text = match *self {
MonotonicError::Overflow => "Ulid random bits would overflow",
};
write!(f, "{}", text)
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::time::Duration;
#[test]
fn test_order_monotonic() {
let dt = SystemTime::now();
let mut gen = Generator::new();
let ulid1 = gen.generate_from_datetime(dt).unwrap();
let ulid2 = gen.generate_from_datetime(dt).unwrap();
let ulid3 = Ulid::from_datetime(dt + Duration::from_millis(1));
assert_eq!(ulid1.0 + 1, ulid2.0);
assert!(ulid2 < ulid3);
assert!(ulid2.timestamp_ms() < ulid3.timestamp_ms())
}
#[test]
fn test_order_monotonic_with_source() {
use rand::rngs::mock::StepRng;
let mut source = StepRng::new(123, 0);
let mut gen = Generator::new();
let _has_default = Generator::default();
let ulid1 = gen.generate_with_source(&mut source).unwrap();
let ulid2 = gen.generate_with_source(&mut source).unwrap();
assert!(ulid1 < ulid2);
}
#[test]
fn can_display_things() {
println!("{}", MonotonicError::Overflow);
}
}