chat.go

package main

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"strings"

	"github.com/ably/ably-go/ably"
	"github.com/ably/ably-go/ably/proto"
	"github.com/joho/godotenv"
)

func main() {
	godotenv.Load()

	var username string

	// If no username specified, ask for one
	if len(os.Args) < 2 {
		fmt.Println("Type your username")
		reader := bufio.NewReader(os.Stdin)
		username, _ = reader.ReadString('\n')
		username = strings.Replace(username, "\n", "", -1)
	} else {
		username = os.Args[1]
	}

	// Connect to Ably using the API key and ClientID specified above
	client, err := ably.NewRealtime(
		ably.WithKey(os.Getenv("ABLY_KEY")),
		// ably.WithEchoMessages(true), // Uncomment to stop messages you send from being sent back
		ably.WithClientID(username))
	if err != nil {
		panic(err)
	}

	fmt.Println("You can now send messages!")

	// Connect to the Ably Channel with name 'chat'
	channel := client.Channels.Get("chat")

	// Enter the Presence set of the channel
	channel.Presence.Enter(context.Background(), "")

	getHistory(channel)

	subscribe(channel)

	// Start the goroutine to allow for publishing messages
	publishing(channel)
}

func getHistory(channel *ably.RealtimeChannel) {
	// Before subscribing for messages, check the channel's
	// History for any missed messages. By default a channel
	// will keep 2 minutes of history available, but this can
	// be extended to 48 hours
	page, err := channel.History(nil)
	for ; err == nil && page != nil; page, err = page.Next() {
		for _, msg := range page.Messages() {
			fmt.Printf("Previous message from %v: '%v'\n", msg.ClientID, msg.Data)
		}
	}
}

func subscribe(channel *ably.RealtimeChannel) {
	// Subscribe to messages sent on the channel
	_, err := channel.SubscribeAll(context.Background(), func(msg *ably.Message) {
		fmt.Printf("Received message from %v: '%v'\n", msg.ClientID, msg.Data)
	})
	if err != nil {
		err := fmt.Errorf("subscribing to channel: %w", err)
		fmt.Println(err)
	}

	// Subscribe to presence events (people entering and leaving) on the channel
	_, pErr := channel.Presence.SubscribeAll(context.Background(), func(msg *ably.PresenceMessage) {
		if msg.Action == proto.PresenceEnter {
			fmt.Printf("%v has entered the chat\n", msg.ClientID)
		} else if msg.Action == proto.PresenceLeave {
			fmt.Printf("%v has left the chat\n", msg.ClientID)
		}
	})
	if pErr != nil {
		err := fmt.Errorf("subscribing to presence in channel: %w", pErr)
		fmt.Println(err)
	}
}

func publishing(channel *ably.RealtimeChannel) {
	reader := bufio.NewReader(os.Stdin)

	for {
		text, _ := reader.ReadString('\n')
		text = strings.ReplaceAll(text, "\n", "")

		// Publish the message typed in to the Ably Channel
		err := channel.Publish(context.Background(), "message", text)
		// await confirmation that message was received by Ably
		if err != nil {
			err := fmt.Errorf("publishing to channel: %w", err)
			fmt.Println(err)
		}
	}
}