/
middleware.go
109 lines (95 loc) · 2.84 KB
/
middleware.go
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// Copyright (c) 2020 - The Event Horizon authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package scheduler
import (
"context"
"time"
"github.com/gorhill/cronexpr"
eh "github.com/looplab/eventhorizon"
)
// NewMiddleware creates a new scheduler middleware that runs until the context is canceled.
func NewMiddleware(ctx context.Context) (eh.EventHandlerMiddleware, *Scheduler) {
s := &Scheduler{ctx: ctx}
return eh.EventHandlerMiddleware(func(h eh.EventHandler) eh.EventHandler {
m := &eventHandler{h, s.newChannel()}
go m.run(ctx)
return m
}), s
}
// Scheduler is a event scheduler that periodically inserts events into the event stream.
// It uses the cron syntax from https://github.com/gorhill/cronexpr.
type Scheduler struct {
ctx context.Context
eventChs []chan data
}
func (s *Scheduler) newChannel() <-chan data {
ch := make(chan data)
s.eventChs = append(s.eventChs, ch)
return ch
}
// ScheduleEvent schedules an event to be sent on regular intervals, using
// a line in the crontab format to setup the timing. The eventFunc should create
// the event to send given the triggered time as input. Cancelling the context
// will stop the triggering of more events.
func (s *Scheduler) ScheduleEvent(ctx context.Context, cronLine string, eventFunc func(time.Time) eh.Event) error {
if err := s.ctx.Err(); err != nil {
return err
}
expr, err := cronexpr.Parse(cronLine)
if err != nil {
return err
}
// Schedule until either this schedule is canceled or the full scheduler is stopped.
go func() {
for {
nextTime := expr.Next(time.Now())
select {
case <-time.After(time.Until(nextTime)):
for _, eventCh := range s.eventChs {
eventCh <- data{ctx, eventFunc(nextTime)}
}
case <-ctx.Done():
// Stop when this individual scheduling is canceled.
return
case <-s.ctx.Done():
// Stop when the full scheduler is stopped.
return
}
}
}()
return nil
}
type data struct {
ctx context.Context
event eh.Event
}
type eventHandler struct {
eh.EventHandler
eventsCh <-chan data
}
func (h *eventHandler) run(ctx context.Context) error {
for {
select {
case data := <-h.eventsCh:
if err := h.HandleEvent(data.ctx, data.event); err != nil {
return err
}
case <-ctx.Done():
if err := ctx.Err(); err != nil && err != context.Canceled {
return err
}
return nil
}
}
}