Publish Discord inbound replies on the post event bus (#19)

Inbound publishes PostCreated after saving the Discord link. Outbound skips already-linked posts so the bot does not echo. Mail uses the existing subscriber.

Reviewed-on: #19
Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/discord/bot.go

@@ -13,7 +13,6 @@ import (
 	"github.com/bwmarrin/discordgo"
 
 	"plumber/internal/events"
-	"plumber/internal/mail"
 	"plumber/internal/store"
 )
 
@@ -25,7 +24,7 @@ type Bot struct {
 	links     store.DiscordLinkStore
 	api       API
 	store     store.Store
-	mail      mail.Notifier
+	bus       events.Publisher
 	admins    map[string]string
 	botUserID string
 }
@@ -36,7 +35,7 @@ func New(channelID string, links store.DiscordLinkStore, api API) *Bot {
 }
 
 // FromEnv builds a bot when Discord env is set. Missing config is a no-op.
-func FromEnv(links store.DiscordLinkStore, bus *events.Bus, st store.Store, mailer mail.Notifier) (*Bot, error) {
+func FromEnv(links store.DiscordLinkStore, bus *events.Bus, st store.Store) (*Bot, error) {
 	token := strings.TrimSpace(os.Getenv("DISCORD_BOT_TOKEN"))
 	channelID := strings.TrimSpace(os.Getenv("DISCORD_CHANNEL_ID"))
 	if token == "" && channelID == "" {
@@ -56,12 +55,9 @@ func FromEnv(links store.DiscordLinkStore, bus *events.Bus, st store.Store, mail
 		return nil, err
 	}
 	session.Identify.Intents = discordgo.IntentsGuilds | discordgo.IntentsGuildMessages | discordgo.IntentsMessageContent
-	if mailer == nil {
-		mailer = mail.Nop{}
-	}
 	bot := New(channelID, links, &sessionAPI{session: session})
 	bot.store = st
-	bot.mail = mailer
+	bot.bus = bus
 	bot.admins = parseAdminMap(os.Getenv("DISCORD_ADMIN_MAP"))
 	session.AddHandler(bot.onMessageCreate)
 	if bus != nil {
@@ -102,6 +98,14 @@ func (b *Bot) Handle(_ context.Context, ev any) {
 }
 
 func (b *Bot) onCreated(ctx context.Context, ev events.PostEvent) {
+	_, err := b.links.GetByPostID(ctx, ev.PostID)
+	if err == nil {
+		return
+	}
+	if !errors.Is(err, sql.ErrNoRows) {
+		log.Printf("discord: load link %s: %v", ev.PostID, err)
+		return
+	}
 	if isRoot(ev) {
 		b.createRoot(ctx, ev)
 		return