Correctly handle LISTMESSAGES and STATUS commands using SeqNum instead of UID

internal/imap/uidlist/entry.go

@@ -7,8 +7,10 @@ import (
 )
 
 type Entry struct {
-	UID               uint64
-	Extra             map[string][]string
+	UID    uint64
+	SeqNum uint64
+	Extra  map[string][]string
+
 	LastKnownFilename string
 }
 

internal/imap/uidlist/uidlist.go

@@ -83,6 +83,12 @@ func handleFile(filename string, flags int) (*List, error) {
 	}, nil
 }
 
+func (l *List) NextUID() uint64 {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	return l.header.NextUID
+}
 func (l *List) UIDValidity() uint64 {
 	return l.header.UIDValidity
 }
@@ -95,11 +101,35 @@ func (l *List) Entries() []Entry {
 	l.mutex.Lock()
 	defer l.mutex.Unlock()
 
-	// FIXME: use copy() ?
 	return l.entries
 }
 
-func (l *List) EntriesInRange(start, end uint64) []Entry {
+func (l *List) EntriesInRangeBySeqNum(start, end uint64) []Entry {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	// IMAP SeqNums are indexed from 1. So 0 should be invalid, right?
+	if start == 0 {
+		return nil
+	}
+
+	start--
+	if int(start) > len(l.entries) {
+		return nil
+	}
+
+	if end == 0 {
+		return l.entries[start:]
+	}
+
+	if int(end) > len(l.entries) {
+		end = uint64(len(l.entries))
+	}
+
+	return l.entries[start:end]
+}
+
+func (l *List) EntriesInRangeByUID(start, end uint64) []Entry {
 	l.mutex.Lock()
 	defer l.mutex.Unlock()
 
@@ -124,6 +154,13 @@ func (l *List) Entry(key string) *Entry {
 	return nil
 }
 
+func (l *List) Count() uint64 {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+
+	return uint64(len(l.entries))
+}
+
 func (l *List) Append(filenames ...string) error {
 	l.mutex.Lock()
 	defer l.mutex.Unlock()