Provides DateTime and Schedule capabilities with no external library dependencies. Works in std/no std, optional support for scale codec encoding/decoding/type info.
Functionality provided:
* conversion from unixtime (mills from epoch) to DateTime, and vice versa
* finding next occurrence for a schedule comprising:
* start DateTime
* repeat frequency (multiples of year/month/week/day/hour/minute/second/millis)
* optional end DateTime
* scale feature enabling Encode/Decode/TypeInfo support for DateTime/Schedule structs.
This library works with DateTimes and schedules within years of [1970, 4000].
Does not support timezones.
Overflow of months (>12), days (>28, >30, >31), hour (>23), minute/second (>59), millis (>999) is discouraged yet allowed, with excess added eg. 31 April ~= 1 May. Underflow of month/day (=0) causes panic. To avoid panic, validate hand crafted DateTime via Calendar::validate() or convert to unixtime via Calendar::to_unixtime_opt().
Reasoning behind these restrictions is to keep the footprint reasonably compact and performance reasonably fast, and cater for real life scenarios.
```rust use chrono_light::prelude::*;
let c = Calendar::create(); let nowinms: u64 = 1650412800000; // represents 20/04/2022 00:00:00:000 let schedule = Schedule { start: DateTime { year: 2020, month: 4, day: 30, hour: 0, minute: 0, second: 0, ms: 0 }, items: vec![(Frequency::Year, 1)], end: Some(DateTime { year: 2025, month: 4, day: 30, hour: 0, minute: 0, second: 0, ms: 0 }) }; assert!(c.validateschedule(&schedule).isok()); asserteq!(Some(10*24*60*60*1000), c.nextoccurrencems(&c.fromunixtime(nowinms), &schedule)); // triggers in 10 days ```