3 files changed, 78 insertions, 0 deletions
diff --git a/worker/maildir/container.go b/worker/maildir/container.go
index 85e892a..a7acfb7 100644
--- a/worker/maildir/container.go
+++ b/worker/maildir/container.go
@@ -10,6 +10,7 @@ import (
 	"github.com/emersion/go-maildir"
 
 	"git.sr.ht/~sircmpwn/aerc/lib/uidstore"
+	"git.sr.ht/~sircmpwn/aerc/worker/types"
 )
 
 // A Container is a directory which contains other directories which adhere to
@@ -123,3 +124,48 @@ func (c *Container) copyMessage(
 	_, err := src.Copy(dest, key)
 	return err
 }
+
+func (c *Container) ScanThreads(d maildir.Dir) ([]*types.Thread, error) {
+	uids, err := c.UIDs(d)
+	if err != nil {
+		return nil, err
+	}
+
+	// a map from message-id to the Thread that represents it
+	threads := make(map[string]*types.Thread)
+
+	for _, uid := range uids {
+		m, err := c.Message(d, uid)
+		if err != nil {
+			return nil, err
+		}
+		hs, err := m.Headers()
+		if err != nil {
+			return nil, err
+		}
+		msgID, err := hs.Text("message-id")
+		if err != nil {
+			return nil, err
+		}
+		irt, err := hs.Text("in-reply-to")
+		if err != nil {
+			return nil, err
+		}
+
+		t := &types.Thread{Uid: uid}
+		threads[msgID] = t
+
+		if p, ok := threads[irt]; ok {
+			p.Children = append(p.Children, t)
+			t.Parent = p
+		}
+	}
+
+	var threadSlice []*types.Thread
+	for _, t := range threads {
+		if t.Parent == nil {
+			threadSlice = append(threadSlice, t)
+		}
+	}
+	return threadSlice, nil
+}
diff --git a/worker/maildir/message.go b/worker/maildir/message.go
index dc5646b..283a3cd 100644
--- a/worker/maildir/message.go
+++ b/worker/maildir/message.go
@@ -1,6 +1,7 @@
 package maildir
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"io"
@@ -8,6 +9,7 @@ import (
 
 	"github.com/emersion/go-maildir"
 	"github.com/emersion/go-message"
+	"github.com/emersion/go-message/textproto"
 
 	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/worker/lib"
@@ -119,3 +121,18 @@ func translateFlags(maildirFlags []maildir.Flag) []models.Flag {
 func (m Message) UID() uint32 {
 	return m.uid
 }
+
+func (m Message) Headers() (*message.Header, error) {
+	f, err := m.dir.Open(m.key)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	br := bufio.NewReader(f)
+	h, err := textproto.ReadHeader(br)
+	if err != nil {
+		return nil, err
+	}
+	mh := message.Header{h}
+	return &mh, nil
+}
diff --git a/worker/maildir/worker.go b/worker/maildir/worker.go
index 1df4e09..7bd7cbd 100644
--- a/worker/maildir/worker.go
+++ b/worker/maildir/worker.go
@@ -170,6 +170,8 @@ func (w *Worker) handleMessage(msg types.WorkerMessage) error {
 		return w.handleOpenDirectory(msg)
 	case *types.FetchDirectoryContents:
 		return w.handleFetchDirectoryContents(msg)
+	case *types.FetchDirectoryThreaded:
+		return w.handleDirectoryThreaded(msg)
 	case *types.CreateDirectory:
 		return w.handleCreateDirectory(msg)
 	case *types.FetchMessageHeaders:
@@ -291,6 +293,19 @@ func (w *Worker) handleFetchDirectoryContents(
 	return nil
 }
 
+func (w *Worker) handleDirectoryThreaded(msg *types.FetchDirectoryThreaded) error {
+	threads, err := w.c.ScanThreads(*w.selected)
+	if err != nil {
+		w.worker.Logger.Printf("error scanning threads: %v", err)
+		return err
+	}
+	w.worker.PostMessage(&types.DirectoryThreaded{
+		Message: types.RespondTo(msg),
+		Threads: threads,
+	}, nil)
+	return nil
+}
+
 func (w *Worker) sort(uids []uint32, criteria []*types.SortCriterion) ([]uint32, error) {
 	if len(criteria) == 0 {
 		return uids, nil