hswro-alarm-bot/sender_worker.go

package main

import (
	"log"
	"strings"
	"sync"
)

type GenericMessage struct {
	chatId int64
	msg    string
}

type Sender interface {
	Send(msg GenericMessage) error
}

type Sleeper interface {
	Sleep(ch chan<- interface{})
}

func Consume(events <-chan GenericMessage) {
	go func() {
		for range events {
		}
	}()
}

func SendToTg(events <-chan GenericMessage, s Sender, wg *sync.WaitGroup, logger *log.Logger) <-chan GenericMessage {
	returnEvents := make(chan GenericMessage)

	go func() {
		wg.Add(1)
		defer wg.Done()
		for e := range events {
			returnEvents <- e
			err := s.Send(e)
			if err != nil {
				// TODO: handle it better
				panic(err)
			}
		}
		close(returnEvents)
	}()

	return returnEvents
}

func tgSenderWorker(tgEvents <-chan GenericMessage, wg *sync.WaitGroup, sleeper Sleeper, logger *log.Logger) <-chan GenericMessage {
	logger.Print("Starting")
	messagesToSend := make(map[int64]*strings.Builder)
	waitingStarted := false
	timeoutEvents := make(chan interface{})
	returnEvents := make(chan GenericMessage)

	go func() {
		wg.Add(1)
		defer wg.Done()
		defer close(returnEvents)
	loop:
		for {
			select {
			case ev, ok := <-tgEvents:
				if !ok {
					break loop
				}
				// Collect all messages to send them at once
				_, messageBuilderExists := messagesToSend[ev.chatId]
				if !messageBuilderExists {
					messagesToSend[ev.chatId] = &strings.Builder{}
				}
				messagesToSend[ev.chatId].WriteString(ev.msg)
				messagesToSend[ev.chatId].WriteRune('\n')
				if !waitingStarted {
					logger.Print("Waiting for more messages to arrive before sending...")
					waitingStarted = true
					sleeper.Sleep(timeoutEvents)
				}
			case <-timeoutEvents:
				logger.Print("Time's up, sending all messages we've got for now.")
				waitingStarted = false
				for chatId, msgBuilder := range messagesToSend {
					returnEvents <- GenericMessage{chatId, msgBuilder.String()}
					delete(messagesToSend, chatId)
				}
			}
		}

		logger.Print("Exiting")
		// If anything is left to be sent, send it now
		for chatId, msgBuilder := range messagesToSend {
			returnEvents <- GenericMessage{chatId, msgBuilder.String()}
		}
	}()

	return returnEvents
}