🐛 Ignore Old AppMention Events (#18)

This commit adds a check to the AppMention event handler, to check how
recent the message was created. If the message is greater than 2 seconds
old, it will be ignored. This will prevent the bot responding to edited,
older messages.

Previously, the bot would respond to any incoming AppMention event,
regardless of how old the message was.

Fixes #16.

internal/events/events_api.go

@@ -2,7 +2,9 @@ package events
 
 import (
 	"fmt"
+	"strconv"
 	"strings"
+	"time"
 
 	"github.com/slack-go/slack"
 	"github.com/slack-go/slack/slackevents"
@@ -55,6 +57,11 @@ func teamJoin(ev *slackevents.TeamJoinEvent, api *slack.Client) {
 }
 
 func appMention(ev *slackevents.AppMentionEvent, api *slack.Client) {
+	// If the message was created in the past, then ignore it.
+	if pastAppMention(ev) {
+		return
+	}
+
 	// If the message contains "ping", then respond with a randomly selected greeting message.
 	if strings.Contains(ev.Text, "ping") {
 		err := ping.Handler(api, ev)
@@ -68,5 +75,23 @@ func appMention(ev *slackevents.AppMentionEvent, api *slack.Client) {
 	if strings.Contains(ev.Text, "coffee") {
 		coffee.Handler(api, ev)
 	}
+}
+
+// pastAppMention checks how recently the message was created.
+// The message is considered in the past if it was created 2 seconds ago or more.
+func pastAppMention(ev *slackevents.AppMentionEvent) bool {
+
+	// Split the timestamp into seconds and nanoseconds.
+	// Only the seconds are needed.
+	tp := strings.Split(ev.TimeStamp, ".")
+
+	ct := time.Now().Unix()
+	et, err := strconv.ParseInt(tp[0], 10, 64)
+	if err != nil {
+		fmt.Printf("Error parsing event timestamp: %s", err)
+	}
+
+	td := ct - et
 
+	return td >= 2
 }