Implement internal mail skill MVP

internal/pop3/pop3.go

@@ -0,0 +1,69 @@
+package pop3
+
+import (
+	"context"
+	"fmt"
+
+	gopop3 "github.com/knadh/go-pop3"
+
+	"internal-mail-skill/internal/config"
+	"internal-mail-skill/internal/model"
+)
+
+type Fetcher struct {
+	cfg config.POP3Config
+}
+
+func NewFetcher(cfg config.POP3Config) *Fetcher {
+	return &Fetcher{cfg: cfg}
+}
+
+func (f *Fetcher) Fetch(ctx context.Context) ([]model.FetchedMessage, error) {
+	if f.cfg.Host == "" {
+		return nil, fmt.Errorf("POP3_HOST is required")
+	}
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	default:
+	}
+
+	client := gopop3.New(gopop3.Opt{
+		Host:        f.cfg.Host,
+		Port:        f.cfg.Port,
+		TLSEnabled:  f.cfg.UseTLS,
+		DialTimeout: f.cfg.Timeout(),
+	})
+	conn, err := client.NewConn()
+	if err != nil {
+		return nil, fmt.Errorf("connect POP3: %w", err)
+	}
+	defer conn.Quit()
+
+	if err := conn.Auth(f.cfg.Username, f.cfg.Password); err != nil {
+		return nil, fmt.Errorf("POP3 auth: %w", err)
+	}
+	ids, err := conn.Uidl(0)
+	if err != nil {
+		return nil, fmt.Errorf("POP3 UIDL: %w", err)
+	}
+	out := make([]model.FetchedMessage, 0, len(ids))
+	for _, item := range ids {
+		select {
+		case <-ctx.Done():
+			return out, ctx.Err()
+		default:
+		}
+		raw, err := conn.RetrRaw(item.ID)
+		if err != nil {
+			out = append(out, model.FetchedMessage{ServerID: item.ID, UID: item.UID, Error: fmt.Sprintf("POP3 RETR %d: %v", item.ID, err)})
+			continue
+		}
+		out = append(out, model.FetchedMessage{
+			ServerID: item.ID,
+			UID:      item.UID,
+			Raw:      raw.Bytes(),
+		})
+	}
+	return out, nil
+}