Mail-Graveyard/backend/05-imap-target.go

package backend

import (
	"fmt"
	"strings"

	"github.com/emersion/go-imap/v2"
)

// TargetMailbox = das Ziel-Postfach (neuer Host). Der Umzug schreibt hier per
// IMAP APPEND hinein -- NICHT per SMTP. APPEND erhaelt Ordner, Flags und
// Original-Datum; SMTP wuerde alles als "neu/ungelesen" mit falschem Datum
// zustellen und die Ordnerstruktur zerstoeren.
type TargetMailbox interface {
	Folders() ([]TargetFolder, error)         // vorhandene Ziel-Ordner (fuer Rollen-Zuordnung)
	Delim() string                            // Hierarchie-Trenner des Ziels
	EnsureFolder(name string) error           // anlegen + subscriben, falls fehlt
	Append(folder string, m RawMessage) error // mit m.Flags und m.InternalDate
	Headers(folder string, limit, offset int) ([]MessageHeader, error)
	FetchOne(folder string, uid uint32) (RawMessage, error)
	DeleteUIDs(folder string, uids []uint32) error
	Close() error
}

func OpenIMAPTarget(a Account) (TargetMailbox, error) {
	c, err := dialIMAPClient(a.DstHost, a.DstPort, a.DstSecurity, a.DstInsecure)
	if err != nil {
		return nil, err
	}
	if err := c.Login(a.DstUser, a.DstPass).Wait(); err != nil {
		_ = c.Close()
		return nil, err
	}
	return &imapTarget{mailbox: &imapClientMailbox{c: c}}, nil
}

type imapTarget struct {
	mailbox *imapClientMailbox
	delim   string
}

func (t *imapTarget) Folders() ([]TargetFolder, error) {
	boxes, err := t.mailbox.listMailboxes()
	if err != nil {
		return nil, err
	}
	folders := make([]TargetFolder, 0, len(boxes))
	for _, box := range boxes {
		if t.delim == "" && box.Delim != "" {
			t.delim = box.Delim
		}
		if hasIMAPAttr(box.Attrs, `\Noselect`) {
			continue
		}
		folders = append(folders, TargetFolder{Name: box.Name, Attrs: box.Attrs})
	}
	if len(folders) == 0 {
		folders = append(folders, TargetFolder{Name: "INBOX"})
	}
	return folders, nil
}

func (t *imapTarget) Delim() string {
	if t.delim != "" {
		return t.delim
	}
	return "/"
}

func (t *imapTarget) EnsureFolder(name string) error {
	name = strings.TrimSpace(name)
	if name == "" || strings.EqualFold(name, "INBOX") {
		return nil
	}
	if err := t.ensureParentFolders(name); err != nil {
		return err
	}
	if err := t.createFolder(name); err != nil {
		return err
	}
	_ = t.mailbox.c.Subscribe(name).Wait()
	return nil
}

func (t *imapTarget) ensureParentFolders(name string) error {
	delim := t.Delim()
	if delim == "" || !strings.Contains(name, delim) {
		return nil
	}
	parts := strings.Split(name, delim)
	for i := 1; i < len(parts); i++ {
		parent := strings.Join(parts[:i], delim)
		if strings.TrimSpace(parent) == "" || strings.EqualFold(parent, "INBOX") {
			continue
		}
		if err := t.createFolder(parent); err != nil {
			return err
		}
	}
	return nil
}

func (t *imapTarget) createFolder(name string) error {
	err := t.mailbox.c.Create(name, nil).Wait()
	if err == nil || isAlreadyExistsError(err) {
		return nil
	}
	return fmt.Errorf("imap create %q failed: %w", name, err)
}

func (t *imapTarget) Append(folder string, m RawMessage) error {
	opts := &imap.AppendOptions{Flags: stringsToFlags(m.Flags), Time: m.InternalDate}
	cmd := t.mailbox.c.Append(folder, int64(len(m.Body)), opts)
	if _, err := cmd.Write(m.Body); err != nil {
		_ = cmd.Close()
		return err
	}
	if err := cmd.Close(); err != nil {
		return err
	}
	_, err := cmd.Wait()
	return err
}

func (t *imapTarget) Headers(folder string, limit, offset int) ([]MessageHeader, error) {
	return t.mailbox.fetchHeaders(folder, limit, offset)
}

func (t *imapTarget) FetchOne(folder string, uid uint32) (RawMessage, error) {
	return t.mailbox.fetchOne(folder, uid)
}

func (t *imapTarget) DeleteUIDs(folder string, uids []uint32) error {
	if len(uids) == 0 {
		return nil
	}
	if _, err := t.mailbox.c.Select(folder, nil).Wait(); err != nil {
		return err
	}
	uidSet := imap.UIDSetNum(uint32sToUIDs(uids)...)
	flags := &imap.StoreFlags{Op: imap.StoreFlagsAdd, Silent: true, Flags: []imap.Flag{imap.FlagDeleted}}
	if err := t.mailbox.c.Store(uidSet, flags, nil).Close(); err != nil {
		return err
	}
	_, err := t.mailbox.c.UIDExpunge(uidSet).Collect()
	return err
}

func (t *imapTarget) Close() error {
	return t.mailbox.Close()
}

func uint32sToUIDs(values []uint32) []imap.UID {
	out := make([]imap.UID, 0, len(values))
	for _, value := range values {
		if value != 0 {
			out = append(out, imap.UID(value))
		}
	}
	return out
}