package maildir

import (
	"bufio"
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/emersion/go-maildir"

	aercLib "git.sr.ht/~rjarry/aerc/lib"
	"git.sr.ht/~rjarry/aerc/lib/iterator"
	"git.sr.ht/~rjarry/aerc/lib/log"
	"git.sr.ht/~rjarry/aerc/lib/watchers"
	"git.sr.ht/~rjarry/aerc/lib/xdg"
	"git.sr.ht/~rjarry/aerc/models"
	"git.sr.ht/~rjarry/aerc/worker/handlers"
	"git.sr.ht/~rjarry/aerc/worker/lib"
	"git.sr.ht/~rjarry/aerc/worker/middleware"
	"git.sr.ht/~rjarry/aerc/worker/types"
)

func init() {
	handlers.RegisterWorkerFactory("maildir", NewWorker)
	handlers.RegisterWorkerFactory("maildirpp", NewMaildirppWorker)
}

var errUnsupported = fmt.Errorf("unsupported command")

// A Worker handles interfacing between aerc's UI and a group of maildirs.
type Worker struct {
	c                   *Container
	selected            *maildir.Dir
	selectedName        string
	selectedInfo        *models.DirectoryInfo
	worker              types.WorkerInteractor
	watcher             watchers.FSWatcher
	watcherDebounce     *time.Timer
	fsEvents            chan struct{}
	currentSortCriteria []*types.SortCriterion
	maildirpp           bool // whether to use Maildir++ directory layout
	capabilities        *models.Capabilities
	headers             []string
	headersExclude      []string
}

// NewWorker creates a new maildir worker with the provided worker.
func NewWorker(worker *types.Worker) (types.Backend, error) {
	watch, err := watchers.NewWatcher()
	if err != nil {
		return nil, fmt.Errorf("could not create file system watcher: %w", err)
	}
	return &Worker{
		capabilities: &models.Capabilities{
			Sort:   true,
			Thread: true,
		},
		worker:   worker,
		watcher:  watch,
		fsEvents: make(chan struct{}),
	}, nil
}

// NewMaildirppWorker creates a new Maildir++ worker with the provided worker.
func NewMaildirppWorker(worker *types.Worker) (types.Backend, error) {
	watch, err := watchers.NewWatcher()
	if err != nil {
		return nil, fmt.Errorf("could not create file system watcher: %w", err)
	}
	return &Worker{
		capabilities: &models.Capabilities{
			Sort:   true,
			Thread: true,
		},
		worker:    worker,
		watcher:   watch,
		maildirpp: true,
	}, nil
}

// Run starts the worker's message handling loop.
func (w *Worker) Run() {
	for {
		select {
		case action := <-w.worker.Actions():
			w.handleAction(action)
		case <-w.watcher.Events():
			if w.watcherDebounce != nil {
				w.watcherDebounce.Stop()
			}
			// Debounce FS changes
			w.watcherDebounce = time.AfterFunc(50*time.Millisecond, func() {
				defer log.PanicHandler()
				w.fsEvents <- struct{}{}
			})
		case <-w.fsEvents:
			w.handleFSEvent()
		}
	}
}

func (w *Worker) Capabilities() *models.Capabilities {
	return w.capabilities
}

func (w *Worker) PathSeparator() string {
	return string(os.PathSeparator)
}

func (w *Worker) handleAction(action types.WorkerMessage) {
	msg := w.worker.ProcessAction(action)
	switch msg := msg.(type) {
	// Explicitly handle all asynchronous actions. Async actions are
	// responsible for posting their own Done message
	case *types.CheckMail:
		go w.handleCheckMail(msg)
	default:
		// Default handling, will be performed synchronously
		err := w.handleMessage(msg)
		switch {
		case errors.Is(err, errUnsupported):
			w.worker.PostMessage(&types.Unsupported{
				Message: types.RespondTo(msg),
			}, nil)
		case errors.Is(err, context.Canceled):
			w.worker.PostMessage(&types.Cancelled{
				Message: types.RespondTo(msg),
			}, nil)
		case err != nil:
			w.worker.PostMessage(&types.Error{
				Message: types.RespondTo(msg),
				Error:   err,
			}, nil)
		default:
			w.done(msg)
		}
	}
}

func (w *Worker) handleFSEvent() {
	// if there's not a selected directory to rescan, ignore
	if w.selected == nil {
		return
	}
	err := w.c.SyncNewMail(*w.selected)
	if err != nil {
		w.worker.Errorf("could not move new to cur : %v", err)
		return
	}

	w.selectedInfo = w.getDirectoryInfo(w.selectedName)
	w.worker.PostMessage(&types.DirectoryInfo{
		Info:    w.selectedInfo,
		Refetch: true,
	}, nil)
}

func (w *Worker) done(msg types.WorkerMessage) {
	w.worker.PostMessage(&types.Done{Message: types.RespondTo(msg)}, nil)
}

func (w *Worker) err(msg types.WorkerMessage, err error) {
	w.worker.PostMessage(&types.Error{
		Message: types.RespondTo(msg),
		Error:   err,
	}, nil)
}

func splitMaildirFile(name string) (uniq string, flags []maildir.Flag, err error) {
	i := strings.LastIndexByte(name, ':')
	if i < 0 {
		return "", nil, &maildir.MailfileError{Name: name}
	}
	info := name[i+1:]
	uniq = name[:i]
	if len(info) < 2 {
		return "", nil, &maildir.FlagError{Info: info, Experimental: false}
	}
	if info[1] != ',' || info[0] != '2' {
		return "", nil, &maildir.FlagError{Info: info, Experimental: false}
	}
	if info[0] == '1' {
		return "", nil, &maildir.FlagError{Info: info, Experimental: true}
	}
	flags = []maildir.Flag(info[2:])
	sort.Slice(flags, func(i, j int) bool { return info[i] < info[j] })
	return uniq, flags, nil
}

func dirFiles(name string) ([]string, error) {
	dir, err := os.Open(filepath.Join(name, "cur"))
	if err != nil {
		return nil, err
	}
	defer dir.Close()
	return dir.Readdirnames(-1)
}

func (w *Worker) getDirectoryInfo(name string) *models.DirectoryInfo {
	dirInfo := &models.DirectoryInfo{
		Name: name,
		// total messages
		Exists: 0,
		// new messages since mailbox was last opened
		Recent: 0,
		// total unread
		Unseen: 0,
	}

	dir := w.c.Store.Dir(name)
	var keyFlags map[string][]maildir.Flag
	files, err := dirFiles(string(dir))
	if err == nil {
		keyFlags = make(map[string][]maildir.Flag, len(files))
		for _, v := range files {
			key, flags, err := splitMaildirFile(v)
			if err != nil {
				w.worker.Errorf("%q: error parsing flags (%q): %v", v, key, err)
				continue
			}
			keyFlags[key] = flags
		}
	} else {
		w.worker.Tracef("disabled flags cache: %q: %v", dir, err)
	}

	uids, err := w.c.UIDs(dir)
	if err != nil && len(uids) == 0 {
		w.worker.Errorf("could not get uids: %v", err)
		return dirInfo
	}

	dirInfo.Exists = len(uids)
	for _, uid := range uids {
		message, err := w.c.Message(dir, uid)
		if err != nil {
			w.worker.Errorf("could not get message: %v", err)
			continue
		}
		var flags []maildir.Flag
		if keyFlags != nil {
			ok := false
			flags, ok = keyFlags[message.key]
			if !ok {
				w.worker.Tracef("message (key=%q uid=%d) not found in map cache",
					message.key, message.uid)
				flags, err = message.Flags()
				if err != nil {
					w.worker.Errorf("could not get flags: %v", err)
					continue
				}
			}
		} else {
			flags, err = message.Flags()
			if err != nil {
				w.worker.Errorf("could not get flags: %v", err)
				continue
			}
		}
		seen := false
		for _, flag := range flags {
			if flag == maildir.FlagSeen {
				seen = true
				break
			}
		}
		if !seen {
			dirInfo.Unseen++
		}
		if w.c.IsRecent(uid) {
			dirInfo.Recent++
		}
	}
	return dirInfo
}

func (w *Worker) handleMessage(msg types.WorkerMessage) error {
	switch msg := msg.(type) {
	case *types.Unsupported:
		// No-op
	case *types.Configure:
		return w.handleConfigure(msg)
	case *types.Connect:
		return w.handleConnect(msg)
	case *types.ListDirectories:
		return w.handleListDirectories(msg)
	case *types.OpenDirectory:
		return w.handleOpenDirectory(msg)
	case *types.FetchDirectoryContents:
		return w.handleFetchDirectoryContents(msg)
	case *types.FetchDirectoryThreaded:
		return w.handleFetchDirectoryThreaded(msg)
	case *types.CreateDirectory:
		return w.handleCreateDirectory(msg)
	case *types.RemoveDirectory:
		return w.handleRemoveDirectory(msg)
	case *types.FetchMessageHeaders:
		return w.handleFetchMessageHeaders(msg)
	case *types.FetchMessageBodyPart:
		return w.handleFetchMessageBodyPart(msg)
	case *types.FetchFullMessages:
		return w.handleFetchFullMessages(msg)
	case *types.DeleteMessages:
		return w.handleDeleteMessages(msg)
	case *types.FlagMessages:
		return w.handleFlagMessages(msg)
	case *types.AnsweredMessages:
		return w.handleAnsweredMessages(msg)
	case *types.CopyMessages:
		return w.handleCopyMessages(msg)
	case *types.MoveMessages:
		return w.handleMoveMessages(msg)
	case *types.AppendMessage:
		return w.handleAppendMessage(msg)
	case *types.SearchDirectory:
		return w.handleSearchDirectory(msg)
	}
	return errUnsupported
}

func (w *Worker) handleConfigure(msg *types.Configure) error {
	u, err := url.Parse(msg.Config.Source)
	if err != nil {
		w.worker.Errorf("error configuring maildir worker: %v", err)
		return err
	}
	dir := u.Path
	if u.Host == "~" {
		home, err := os.UserHomeDir()
		if err != nil {
			return fmt.Errorf("could not resolve home directory: %w", err)
		}
		dir = filepath.Join(home, u.Path)
	}
	if len(dir) == 0 {
		return fmt.Errorf("could not resolve maildir from URL '%s'", msg.Config.Source)
	}
	c, err := NewContainer(dir, w.maildirpp)
	if err != nil {
		w.worker.Errorf("could not configure maildir: %s", dir)
		return err
	}
	w.c = c
	err = w.watcher.Configure(dir)
	if err != nil {
		return err
	}
	w.headers = msg.Config.Headers
	w.headersExclude = msg.Config.HeadersExclude
	w.worker.Debugf("configured base maildir: %s", dir)

	if name, ok := msg.Config.Params["folder-map"]; ok {
		file := xdg.ExpandHome(name)
		f, err := os.Open(file)
		if err != nil {
			return err
		}
		defer f.Close()
		fmap, order, err := lib.ParseFolderMap(bufio.NewReader(f))
		if err != nil {
			return err
		}
		w.worker = middleware.NewFolderMapper(w.worker, fmap, order)
	}

	return nil
}

func (w *Worker) handleConnect(msg *types.Connect) error {
	return nil
}

func (w *Worker) handleListDirectories(msg *types.ListDirectories) error {
	// TODO If handleConfigure has returned error, w.c is nil.
	// It could be better if we skip directory listing completely
	// when configure fails.
	if w.c == nil {
		return errors.New("Incorrect maildir directory")
	}
	dirs, err := w.c.Store.FolderMap()
	if err != nil {
		w.worker.Errorf("failed listing directories: %v", err)
		return err
	}
	for name := range dirs {
		w.worker.PostMessage(&types.Directory{
			Message: types.RespondTo(msg),
			Dir: &models.Directory{
				Name: name,
			},
		}, nil)

		w.worker.PostMessage(&types.DirectoryInfo{
			Info: w.getDirectoryInfo(name),
		}, nil)
	}
	return nil
}

func (w *Worker) handleOpenDirectory(msg *types.OpenDirectory) error {
	w.worker.Debugf("opening %s", msg.Directory)

	// open the directory
	dir, err := w.c.OpenDirectory(msg.Directory)
	if err != nil {
		return err
	}

	// remove existing watch paths
	if w.selected != nil {
		prevDir := filepath.Join(string(*w.selected), "new")
		if err := w.watcher.Remove(prevDir); err != nil {
			return fmt.Errorf("could not unwatch previous directory: %w", err)
		}
		prevDir = filepath.Join(string(*w.selected), "cur")
		if err := w.watcher.Remove(prevDir); err != nil {
			return fmt.Errorf("could not unwatch previous directory: %w", err)
		}
	}

	w.selected = &dir
	w.selectedName = msg.Directory

	// add watch paths
	newDir := filepath.Join(string(*w.selected), "new")
	if err := w.watcher.Add(newDir); err != nil {
		return fmt.Errorf("could not add watch to directory: %w", err)
	}
	newDir = filepath.Join(string(*w.selected), "cur")
	if err := w.watcher.Add(newDir); err != nil {
		return fmt.Errorf("could not add watch to directory: %w", err)
	}

	if err := dir.Clean(); err != nil {
		return fmt.Errorf("could not clean directory: %w", err)
	}

	info := &types.DirectoryInfo{
		Info: w.getDirectoryInfo(msg.Directory),
	}
	w.selectedInfo = info.Info
	w.worker.PostMessage(info, nil)
	return nil
}

func (w *Worker) handleFetchDirectoryContents(
	msg *types.FetchDirectoryContents,
) error {
	var (
		uids []uint32
		err  error
	)
	if msg.Filter != nil {
		uids, err = w.search(msg.Context, msg.Filter)
		if err != nil {
			return err
		}
	} else {
		uids, err = w.c.UIDs(*w.selected)
		if err != nil && len(uids) == 0 {
			w.worker.Errorf("failed scanning uids: %v", err)
			return err
		}

		if err != nil {
			w.worker.PostMessage(&types.Error{
				Error: fmt.Errorf("could not get all uids for %s: %w", *w.selected, err),
			}, nil)
		}
	}
	sortedUids, err := w.sort(msg.Context, uids, msg.SortCriteria)
	if err != nil {
		w.worker.Errorf("failed sorting directory: %v", err)
		return err
	}
	w.currentSortCriteria = msg.SortCriteria
	w.worker.PostMessage(&types.DirectoryContents{
		Message: types.RespondTo(msg),
		Uids:    sortedUids,
	}, nil)
	return nil
}

func (w *Worker) sort(ctx context.Context, uids []uint32, criteria []*types.SortCriterion) ([]uint32, error) {
	if len(criteria) == 0 {
		// At least sort by uid, parallel searching can create random
		// order
		sort.Slice(uids, func(i int, j int) bool {
			return uids[i] < uids[j]
		})
		return uids, nil
	}
	var msgInfos []*models.MessageInfo
	mu := sync.Mutex{}
	wg := sync.WaitGroup{}
	// Hard limit at 2x CPU cores
	max := runtime.NumCPU() * 2
	limit := make(chan struct{}, max)
	for _, uid := range uids {
		select {
		case <-ctx.Done():
			return nil, context.Canceled
		default:
			limit <- struct{}{}
			wg.Add(1)
			go func(uid uint32) {
				defer log.PanicHandler()
				defer wg.Done()
				info, err := w.msgHeadersFromUid(uid)
				if err != nil {
					w.worker.Errorf("could not get message info: %v", err)
					<-limit
					return
				}
				mu.Lock()
				msgInfos = append(msgInfos, info)
				mu.Unlock()
				<-limit
			}(uid)
		}
	}

	wg.Wait()
	sortedUids, err := lib.Sort(msgInfos, criteria)
	if err != nil {
		w.worker.Errorf("could not sort the messages: %v", err)
		return nil, err
	}
	return sortedUids, nil
}

func (w *Worker) handleFetchDirectoryThreaded(
	msg *types.FetchDirectoryThreaded,
) error {
	var (
		uids []uint32
		err  error
	)
	if msg.Filter != nil {
		uids, err = w.search(msg.Context, msg.Filter)
		if err != nil {
			return err
		}
	} else {
		uids, err = w.c.UIDs(*w.selected)
		if err != nil {
			w.worker.Errorf("failed scanning uids: %v", err)
			return err
		}
	}
	threads, err := w.threads(msg.Context, uids, msg.SortCriteria)
	if err != nil {
		w.worker.Errorf("failed sorting directory: %v", err)
		return err
	}
	w.currentSortCriteria = msg.SortCriteria
	w.worker.PostMessage(&types.DirectoryThreaded{
		Message: types.RespondTo(msg),
		Threads: threads,
	}, nil)
	return nil
}

func (w *Worker) threads(ctx context.Context, uids []uint32,
	criteria []*types.SortCriterion,
) ([]*types.Thread, error) {
	builder := aercLib.NewThreadBuilder(iterator.NewFactory(false))
	msgInfos := make([]*models.MessageInfo, 0, len(uids))
	mu := sync.Mutex{}
	wg := sync.WaitGroup{}
	max := runtime.NumCPU() * 2
	limit := make(chan struct{}, max)
	for _, uid := range uids {
		select {
		case <-ctx.Done():
			return nil, context.Canceled
		default:
			limit <- struct{}{}
			wg.Add(1)
			go func(uid uint32) {
				defer log.PanicHandler()
				defer wg.Done()
				info, err := w.msgHeadersFromUid(uid)
				if err != nil {
					w.worker.Errorf("could not get message info: %v", err)
					<-limit
					return
				}
				mu.Lock()
				builder.Update(info)
				msgInfos = append(msgInfos, info)
				mu.Unlock()
				<-limit
			}(uid)
		}
	}
	wg.Wait()
	var err error
	switch {
	case len(criteria) == 0:
		sort.Slice(uids, func(i int, j int) bool {
			return uids[i] < uids[j]
		})
	default:
		uids, err = lib.Sort(msgInfos, criteria)
		if err != nil {
			w.worker.Errorf("could not sort the messages: %v", err)
			return nil, err
		}
	}
	threads := builder.Threads(uids, false, false)
	return threads, nil
}

func (w *Worker) handleCreateDirectory(msg *types.CreateDirectory) error {
	dir := w.c.Store.Dir(msg.Directory)
	if err := dir.Init(); err != nil {
		w.worker.Errorf("could not create directory %s: %v",
			msg.Directory, err)
		return err
	}
	return nil
}

func (w *Worker) handleRemoveDirectory(msg *types.RemoveDirectory) error {
	dir := w.c.Store.Dir(msg.Directory)
	if err := os.RemoveAll(string(dir)); err != nil {
		w.worker.Errorf("could not remove directory %s: %v",
			msg.Directory, err)
		return err
	}
	return nil
}

func (w *Worker) handleFetchMessageHeaders(
	msg *types.FetchMessageHeaders,
) error {
	for _, uid := range msg.Uids {
		info, err := w.msgInfoFromUid(uid)
		if err != nil {
			w.worker.Errorf("could not get message info: %v", err)
			log.Errorf("could not get message info: %v", err)
			w.worker.PostMessage(&types.MessageInfo{
				Info: &models.MessageInfo{
					Envelope: &models.Envelope{},
					Flags:    models.SeenFlag,
					Uid:      uid,
					Error:    err,
				},
				Message: types.RespondTo(msg),
			}, nil)
			continue
		}
		switch {
		case len(w.headersExclude) > 0:
			info.RFC822Headers = lib.LimitHeaders(info.RFC822Headers, w.headersExclude, true)
		case len(w.headers) > 0:
			info.RFC822Headers = lib.LimitHeaders(info.RFC822Headers, w.headers, false)
		}
		w.worker.PostMessage(&types.MessageInfo{
			Message: types.RespondTo(msg),
			Info:    info,
		}, nil)
		w.c.ClearRecentFlag(uid)
	}
	return nil
}

func (w *Worker) handleFetchMessageBodyPart(
	msg *types.FetchMessageBodyPart,
) error {
	// get reader
	m, err := w.c.Message(*w.selected, msg.Uid)
	if err != nil {
		w.worker.Errorf("could not get message %d: %v", msg.Uid, err)
		return err
	}
	r, err := m.NewBodyPartReader(msg.Part)
	if err != nil {
		w.worker.Errorf(
			"could not get body part reader for message=%d, parts=%#v: %w",
			msg.Uid, msg.Part, err)
		return err
	}
	w.worker.PostMessage(&types.MessageBodyPart{
		Message: types.RespondTo(msg),
		Part: &models.MessageBodyPart{
			Reader: r,
			Uid:    msg.Uid,
		},
	}, nil)

	return nil
}

func (w *Worker) handleFetchFullMessages(msg *types.FetchFullMessages) error {
	for _, uid := range msg.Uids {
		m, err := w.c.Message(*w.selected, uid)
		if err != nil {
			w.worker.Errorf("could not get message %d: %v", uid, err)
			return err
		}
		r, err := m.NewReader()
		if err != nil {
			w.worker.Errorf("could not get message reader: %v", err)
			return err
		}
		defer r.Close()
		b, err := io.ReadAll(r)
		if err != nil {
			return err
		}
		w.worker.PostMessage(&types.FullMessage{
			Message: types.RespondTo(msg),
			Content: &models.FullMessage{
				Uid:    uid,
				Reader: bytes.NewReader(b),
			},
		}, nil)
	}
	w.worker.PostMessage(&types.Done{
		Message: types.RespondTo(msg),
	}, nil)
	return nil
}

func (w *Worker) handleDeleteMessages(msg *types.DeleteMessages) error {
	deleted, err := w.c.DeleteAll(*w.selected, msg.Uids)
	if len(deleted) > 0 {
		w.worker.PostMessage(&types.MessagesDeleted{
			Message: types.RespondTo(msg),
			Uids:    deleted,
		}, nil)
	}
	if err != nil {
		w.worker.Errorf("failed removing messages: %v", err)
		return err
	}
	return nil
}

func (w *Worker) handleAnsweredMessages(msg *types.AnsweredMessages) error {
	for _, uid := range msg.Uids {
		m, err := w.c.Message(*w.selected, uid)
		if err != nil {
			w.worker.Errorf("could not get message: %v", err)
			w.err(msg, err)
			continue
		}
		if err := m.MarkReplied(msg.Answered); err != nil {
			w.worker.Errorf("could not mark message as answered: %v", err)
			w.err(msg, err)
			continue
		}
		info, err := m.MessageInfo()
		if err != nil {
			w.worker.Errorf("could not get message info: %v", err)
			w.err(msg, err)
			continue
		}

		w.worker.PostMessage(&types.MessageInfo{
			Message: types.RespondTo(msg),
			Info:    info,
		}, nil)

		w.worker.PostMessage(&types.DirectoryInfo{
			Info: w.getDirectoryInfo(w.selectedName),
		}, nil)
	}
	return nil
}

func (w *Worker) handleFlagMessages(msg *types.FlagMessages) error {
	for _, uid := range msg.Uids {
		m, err := w.c.Message(*w.selected, uid)
		if err != nil {
			w.worker.Errorf("could not get message: %v", err)
			w.err(msg, err)
			continue
		}
		flag := lib.FlagToMaildir[msg.Flags]
		if err := m.SetOneFlag(flag, msg.Enable); err != nil {
			w.worker.Errorf("could change flag %v to %v on message: %v", flag, msg.Enable, err)
			w.err(msg, err)
			continue
		}
		info, err := m.MessageInfo()
		if err != nil {
			w.worker.Errorf("could not get message info: %v", err)
			w.err(msg, err)
			continue
		}

		w.worker.PostMessage(&types.MessageInfo{
			Message: types.RespondTo(msg),
			Info:    info,
		}, nil)
	}

	w.worker.PostMessage(&types.DirectoryInfo{
		Info: w.getDirectoryInfo(w.selectedName),
	}, nil)

	return nil
}

func (w *Worker) handleCopyMessages(msg *types.CopyMessages) error {
	dest := w.c.Store.Dir(msg.Destination)
	err := w.c.CopyAll(dest, *w.selected, msg.Uids)
	if err != nil {
		return err
	}
	w.worker.PostMessage(&types.MessagesCopied{
		Message:     types.RespondTo(msg),
		Destination: msg.Destination,
		Uids:        msg.Uids,
	}, nil)
	return nil
}

func (w *Worker) handleMoveMessages(msg *types.MoveMessages) error {
	dest := w.c.Store.Dir(msg.Destination)
	moved, err := w.c.MoveAll(dest, *w.selected, msg.Uids)
	w.worker.PostMessage(&types.MessagesMoved{
		Message:     types.RespondTo(msg),
		Destination: msg.Destination,
		Uids:        moved,
	}, nil)
	w.worker.PostMessage(&types.MessagesDeleted{
		Message: types.RespondTo(msg),
		Uids:    moved,
	}, nil)
	return err
}

func (w *Worker) handleAppendMessage(msg *types.AppendMessage) error {
	// since we are the "master" maildir process, we can modify the maildir directly
	dest := w.c.Store.Dir(msg.Destination)
	_, writer, err := dest.Create(lib.ToMaildirFlags(msg.Flags))
	if err != nil {
		return fmt.Errorf("could not create message at %s: %w",
			msg.Destination, err)
	}
	defer writer.Close()
	if _, err := io.Copy(writer, msg.Reader); err != nil {
		return fmt.Errorf(
			"could not write message to destination: %w", err)
	}
	w.worker.PostMessage(&types.Done{
		Message: types.RespondTo(msg),
	}, nil)
	w.worker.PostMessage(&types.DirectoryInfo{
		Info: w.getDirectoryInfo(msg.Destination),
	}, nil)
	return nil
}

func (w *Worker) handleSearchDirectory(msg *types.SearchDirectory) error {
	w.worker.Tracef("Searching with criteria: %#v", msg.Criteria)
	uids, err := w.search(msg.Context, msg.Criteria)
	if err != nil {
		return err
	}
	w.worker.PostMessage(&types.SearchResults{
		Message: types.RespondTo(msg),
		Uids:    uids,
	}, nil)
	return nil
}

func (w *Worker) msgInfoFromUid(uid uint32) (*models.MessageInfo, error) {
	m, err := w.c.Message(*w.selected, uid)
	if err != nil {
		return nil, err
	}
	info, err := m.MessageInfo()
	if err != nil {
		return nil, err
	}
	name, err := m.dir.Filename(m.key)
	if err != nil {
		return nil, err
	}
	info.Filenames = []string{name}
	if w.c.IsRecent(uid) {
		info.Flags |= models.RecentFlag
	}
	return info, nil
}

func (w *Worker) msgHeadersFromUid(uid uint32) (*models.MessageInfo, error) {
	m, err := w.c.Message(*w.selected, uid)
	if err != nil {
		return nil, err
	}
	info, err := m.MessageHeaders()
	if err != nil {
		return nil, err
	}
	return info, nil
}

func (w *Worker) handleCheckMail(msg *types.CheckMail) {
	defer log.PanicHandler()
	if msg.Command == "" {
		w.err(msg, fmt.Errorf("checkmail: no command specified"))
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), msg.Timeout)
	defer cancel()
	cmd := exec.CommandContext(ctx, "sh", "-c", msg.Command)
	ch := make(chan error)
	go func() {
		defer log.PanicHandler()

		_, err := cmd.Output()
		if err != nil {
			var exitError *exec.ExitError
			if errors.As(err, &exitError) {
				err = fmt.Errorf("%w\n%s", err, string(exitError.Stderr))
			}
		}
		ch <- err
	}()
	select {
	case <-ctx.Done():
		w.err(msg, fmt.Errorf("checkmail: timed out"))
	case err := <-ch:
		if err != nil {
			w.err(msg, fmt.Errorf("checkmail: error running command: %w", err))
		} else {
			dirs, err := w.c.Store.FolderMap()
			if err != nil {
				w.err(msg, fmt.Errorf("failed listing directories: %w", err))
			}
			for name, dir := range dirs {
				err := w.c.SyncNewMail(dir)
				if err != nil {
					w.err(msg, fmt.Errorf("could not sync new mail: %w", err))
				}
				dirInfo := w.getDirectoryInfo(name)
				w.worker.PostMessage(&types.DirectoryInfo{
					Info: dirInfo,
				}, nil)
			}
			w.done(msg)
		}
	}
}