hswro-alarm-bot/filters_sync.go

package main

import (
	"log"
	"sync"

	"git.sr.ht/~michalr/go-satel"
)

type SyncFilter[MsgType any] interface {
	Then(what SyncFilter[MsgType]) SyncFilter[MsgType]
	Call(msg MsgType)
}

type SyncFilterImpl[MsgType any] struct {
	next SyncFilter[MsgType]
}

func (impl *SyncFilterImpl[MsgType]) Then(what SyncFilter[MsgType]) SyncFilter[MsgType] {
	impl.next = what
	return what
}

func (impl *SyncFilterImpl[MsgType]) CallNext(msg MsgType) {
	if impl.next != nil {
		impl.next.Call(msg)
	}
}

type CollectFromChannel[MsgType any] struct{ SyncFilterImpl[MsgType] }

func (collect *CollectFromChannel[MsgType]) Call(msg MsgType) {
	collect.CallNext(msg)
}

func (collect CollectFromChannel[MsgType]) Collect(events <-chan MsgType, wg *sync.WaitGroup, onClose func()) {
	wg.Add(1)
	go func() {
		defer wg.Done()
		defer onClose()

		for e := range events {
			collect.Call(e)
		}
	}()
}

type ThrottleSync struct {
	SyncFilterImpl[GenericMessage]

	events chan GenericMessage
}

func appendToGenericMessage(msg *GenericMessage, new *GenericMessage) *GenericMessage {
	if msg == nil {
		msg = &GenericMessage{make([]satel.BasicEventElement, 0)}
	}

throughNewMessages:
	for _, newEv := range new.Messages {
		for i, oldEv := range msg.Messages {
			if oldEv.Index == newEv.Index && oldEv.Type == newEv.Type {
				// this message was seen - update its value
				msg.Messages[i].Value = newEv.Value
				continue throughNewMessages
			}
		}
		// apparently this type of message was not yet seen, save it
		msg.Messages = append(msg.Messages, newEv)
	}
	return msg
}

func MakeThrottleSync(sleeper Sleeper, logger *log.Logger, wg *sync.WaitGroup) *ThrottleSync {
	events := make(chan GenericMessage)

	throttle := ThrottleSync{SyncFilterImpl[GenericMessage]{}, events}

	wg.Add(1)
	go func() {
		timeoutEvents := make(chan interface{})
		var currentEvent *GenericMessage = nil
	loop:
		for {
			select {
			case ev, ok := <-events:
				if !ok {
					break loop
				}
				if currentEvent == nil {
					logger.Print("Waiting for more messages to arrive before sending...")
					sleeper.Sleep(timeoutEvents)
				}
				currentEvent = appendToGenericMessage(currentEvent, &ev)
			case <-timeoutEvents:
				logger.Print("Time's up, sending all messages we've got for now.")
				throttle.CallNext(*currentEvent)
				currentEvent = nil
			}
		}

		// If anything is left to be sent, send it now
		if currentEvent != nil {
			throttle.CallNext(*currentEvent)
		}
		wg.Done()
		logger.Print("Throttling goroutine finishing")
	}()

	return &throttle
}

func (throttle *ThrottleSync) Close() { close(throttle.events) }

func (throttle *ThrottleSync) Call(msg GenericMessage) {
	throttle.events <- msg
}