https://github.com/pnelson/te
Package te implements temporal expressions.
https://github.com/pnelson/te
Last synced: 6 months ago
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Package te implements temporal expressions.
- Host: GitHub
- URL: https://github.com/pnelson/te
- Owner: pnelson
- License: isc
- Created: 2016-08-31T04:34:17.000Z (almost 10 years ago)
- Default Branch: main
- Last Pushed: 2022-11-12T04:20:29.000Z (over 3 years ago)
- Last Synced: 2025-10-13T05:13:03.590Z (9 months ago)
- Language: Go
- Homepage: https://godocs.io/github.com/pnelson/te
- Size: 62.5 KB
- Stars: 0
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# te
Package te implements temporal expressions.
An expression is an implementation of the `Expression` interface. Two methods
must be implemented: `IsActive` which returns true if the expression is active
at the given time, and `Next` which returns the next active time.
A handful of expressions are included. They compute the next time within the
location of the given time. Daylight savings is respected.
To find the first day of the month:
```go
expr := te.Day(1)
next := time.Now()
for i := 0; i < 4; i++ {
next = expr.Next(next)
fmt.Println(next)
}
// 2020-09-01 00:00:00 -0400 EDT
// 2020-10-01 00:00:00 -0400 EDT
// 2020-11-01 00:00:00 -0400 EDT
// 2020-12-01 00:00:00 -0500 EST
```
To find every day at 4am:
```go
expr := te.Hour(4)
next := time.Now()
for i := 0; i < 4; i++ {
next = expr.Next(next)
fmt.Println(next)
}
// 2020-09-01 04:00:00 -0400 EDT
// 2020-09-02 04:00:00 -0400 EDT
// 2020-09-03 04:00:00 -0400 EDT
// 2020-09-04 04:00:00 -0400 EDT
```
Complex expressions can be composed from more primitive expressions. For
example, one can continuously generate `time.Time`s for every 3rd or 5th of
the month that falls on a Thursday or Friday except in February and December.
```go
expr := te.Intersect(
te.Union(
te.Day(3),
te.Day(5),
),
te.Union(
te.Weekday(time.Thursday),
te.Weekday(time.Friday),
),
te.Except(
te.Union(
te.Month(time.February),
te.Month(time.December),
),
),
)
next := time.Now()
for i := 0; i < 4; i++ {
next = expr.Next(next)
fmt.Println(next)
}
// 2020-09-03 00:00:00 -0400 EDT
// 2020-11-05 00:00:00 -0500 EST
// 2021-03-05 00:00:00 -0500 EST
// 2021-06-03 00:00:00 -0400 EDT
```
Limited expression parsing is supported:
```go
expr, err := te.Parse("Tue/Thu at 4am", time.Local)
if err != nil {
log.Fatal(err)
}
next := time.Now()
for i := 0; i < 4; i++ {
next = expr.Next(next)
fmt.Println(next)
}
// 2020-09-01 04:00:00 -0400 EDT
// 2020-09-03 04:00:00 -0400 EDT
// 2020-09-08 04:00:00 -0400 EDT
// 2020-09-10 04:00:00 -0400 EDT
```
See `parser_test.go` for more examples.
## Inspiration
This package is inspired by a paper on Recurring Events for Calendars
written by Martin Fowler. https://martinfowler.com/apsupp/recurring.pdf