defernodate

A pure, synchronous Rust library for RFC 5545 recurrence expansion (RRULE + EXDATE + per-instance overrides). No I/O, no async runtime, no storage — the caller supplies ids, timestamps, and persistence.

What it does

• Parses FREQ=WEEKLY;BYDAY=MO,WE,FR-style RRULE strings.
• Expands a Series across a bounded UTC range, applying Overrides and cancellations.
• Handles DST correctly: local DTSTART + IANA timezone; expansion happens in local time, instances are indexed in UTC.
• Supports "this and future" splits via split_series, avoiding exception-list explosion on long-running series.

What it does NOT do

• Store anything. A Series, its Overrides, and any instance cache are the caller's problem. The previous 0.1.x line embedded a Redis store; 0.2.0 removed it so consumers can pick their own storage (Redis, Postgres, in-memory, etc.).
• Generate ids or timestamps. Callers pass Uuid::new_v4() and Utc::now() in at the call site, keeping the library deterministic and fully testable with fixed inputs.
• Run async. The whole public surface is synchronous.

Quick start

[dependencies]
defernodate = "0.2"

use chrono::{NaiveDate, TimeZone, Utc};
use defernodate::{build_series, expand_series, CreateSeries};
use uuid::Uuid;

fn main() -> defernodate::Result<()> {
    let series = build_series(
        CreateSeries {
            calendar_id: Uuid::new_v4(),
            title: "Standup".into(),
            dtstart_local: NaiveDate::from_ymd_opt(2026, 4, 6)
                .unwrap()
                .and_hms_opt(9, 0, 0)
                .unwrap(),
            tzid: chrono_tz::America::New_York,
            duration_secs: 900,
            rrule: Some("FREQ=WEEKLY;BYDAY=MO,WE,FR".into()),
        },
        Uuid::new_v4(),
        Utc::now(),
    );

    let start = Utc.with_ymd_and_hms(2026, 4, 1, 0, 0, 0).unwrap();
    let end = Utc.with_ymd_and_hms(2026, 5, 1, 0, 0, 0).unwrap();
    let instances = expand_series(&series, &[], start, end)?;

    for inst in instances {
        println!("{} at {}", inst.title, inst.start_utc);
    }
    Ok(())
}

Public API

• build_series(input, id, now) -> Series
• apply_update(series, expected_version, update, now) -> Result<Series>
• split_series(old, split_at, new, new_id, now) -> (Series, Series)
• expand_series(series, overrides, range_start, range_end) -> Result<Vec<Instance>>
• get_instance(series, overrides, recurrence_id) -> Option<Instance>

See CHANGELOG.md for migration notes from 0.1.x.

License

MIT.