1 files changed, 114 insertions, 0 deletions
diff --git a/lib/mailstuff/thread.go b/lib/mailstuff/thread.go
new file mode 100644
index 0000000..2cdf9a4
--- /dev/null
+++ b/lib/mailstuff/thread.go
@@ -0,0 +1,114 @@
+package mailstuff
+
+import (
+	"fmt"
+	"net/mail"
+	"regexp"
+	"strings"
+)
+
+type Set[T comparable] map[T]struct{}
+
+func (s Set[T]) Insert(val T) {
+	s[val] = struct{}{}
+}
+
+func mapHas[K comparable, V any](m map[K]V, k K) bool {
+	_, ok := m[k]
+	return ok
+}
+
+func (s Set[T]) Has(val T) bool {
+	return mapHas(s, val)
+}
+
+func (s Set[T]) PickOne() T {
+	for v := range s {
+		return v
+	}
+	var zero T
+	return zero
+}
+
+type MessageID string
+
+type ThreadedMessage struct {
+	*mail.Message
+	Parent   *ThreadedMessage
+	Children Set[*ThreadedMessage]
+}
+
+var reReplyID = regexp.MustCompile("<[^> \t\r\n]+>")
+
+func rfc2822parse(msg *mail.Message) *jwzMessage {
+	// TODO: This is bad, and needs a real implementation.
+	ret := &jwzMessage{
+		Subject: msg.Header.Get("Subject"),
+		ID:      jwzID(msg.Header.Get("Message-ID")),
+	}
+	refIDs := strings.Fields(msg.Header.Get("References"))
+	strings.Fields(msg.Header.Get("References"))
+	if replyID := reReplyID.FindString(msg.Header.Get("In-Reply-To")); replyID != "" {
+		refIDs = append(refIDs, replyID)
+	}
+	ret.References = make([]jwzID, len(refIDs))
+	for i := range refIDs {
+		ret.References[i] = jwzID(refIDs[i])
+	}
+	return ret
+}
+
+func ThreadMessages(msgs []*mail.Message) (Set[*ThreadedMessage], map[MessageID]*ThreadedMessage) {
+	jwzMsgs := make(map[jwzID]*jwzMessage, len(msgs))
+	retMsgs := make(map[jwzID]*ThreadedMessage, len(msgs))
+	bogusCnt := 0
+	for _, msg := range msgs {
+		jwzMsg := rfc2822parse(msg)
+
+		// RFC 5256:
+		//
+		//	If a message does not contain a Message-ID header
+		//	line, or the Message-ID header line does not
+		//	contain a valid Message ID, then assign a unique
+		//	Message ID to this message.
+		//
+		//	If two or more messages have the same Message ID,
+		//	then only use that Message ID in the first (lowest
+		//	sequence number) message, and assign a unique
+		//	Message ID to each of the subsequent messages with
+		//	a duplicate of that Message ID.
+		for jwzMsg.ID == "" || mapHas(jwzMsgs, jwzMsg.ID) {
+			jwzMsg.ID = jwzID(fmt.Sprintf("bogus.%d", bogusCnt))
+			bogusCnt++
+		}
+
+		jwzMsgs[jwzMsg.ID] = jwzMsg
+		retMsgs[jwzMsg.ID] = &ThreadedMessage{
+			Message: msg,
+		}
+	}
+
+	jwzThreads := jwzThreadMessages(jwzMsgs)
+
+	var convertMessage func(*jwzContainer) *ThreadedMessage
+	convertMessage = func(in *jwzContainer) *ThreadedMessage {
+		var out *ThreadedMessage
+		if in.Message == nil {
+			out = new(ThreadedMessage)
+		} else {
+			out = retMsgs[in.Message.ID]
+		}
+		out.Children = make(Set[*ThreadedMessage], len(in.Children))
+		for inChild := range in.Children {
+			outChild := convertMessage(inChild)
+			out.Children.Insert(outChild)
+			outChild.Parent = out
+		}
+		return out
+	}
+	retThreads := make(Set[*ThreadedMessage], len(jwzThreads))
+	for inThread := range jwzThreads {
+		retThreads.Insert(convertMessage(inThread))
+	}
+	return retThreads, retMsgs
+}