pipe: fix ordering by message id for long patch series

Git send-email Message-Id headers have the following format:

   DATETIME.PID-NUM-COMMITTER

Unfortunately, when there are more than 9 patches, the patch number
(NUM) is not zero-padded which makes ascii sorting invalid, e.g.:

   1 10 11 12 2 3 4 5 6 7 8 9

Instead of:

   1 2 3 4 5 6 7 8 9 10 11 12

We need the patches to be ordered correctly to pipe them to git am.

Make sure to pad the patch number with zero characters to allow series
of up to 999 patches.

Only re-order messages before piping them if all the Message-Id headers
look like git-send-email headers.

Link: https://github.com/git/git/blob/v2.36.0/git-send-email.perl#L1197
Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Koni Marti <koni.marti@gmail.com>

commands/msg/pipe.go

@@ -5,7 +5,9 @@ import (
 	"fmt"
 	"io"
 	"os/exec"
+	"regexp"
 	"sort"
+	"strconv"
 	"time"
 
 	"git.sr.ht/~rjarry/aerc/commands"
@@ -164,16 +166,28 @@ func (Pipe) Execute(aerc *widgets.Aerc, args []string) error {
 				}
 			}
 
-			// Sort all messages by increasing Message-Id header.
-			// This will ensure that patch series are applied in order.
-			sort.Slice(messages, func(i, j int) bool {
-				infoi := store.Messages[messages[i].Content.Uid]
-				infoj := store.Messages[messages[j].Content.Uid]
-				if infoi == nil || infoj == nil {
-					return false
+			is_git_patches := true
+			for _, msg := range messages {
+				info := store.Messages[msg.Content.Uid]
+				if info == nil || !gitMessageIdRe.MatchString(info.Envelope.MessageId) {
+					is_git_patches = false
+					break
 				}
-				return infoi.Envelope.MessageId < infoj.Envelope.MessageId
-			})
+			}
+			if is_git_patches {
+				// Sort all messages by increasing Message-Id header.
+				// This will ensure that patch series are applied in order.
+				sort.Slice(messages, func(i, j int) bool {
+					infoi := store.Messages[messages[i].Content.Uid]
+					infoj := store.Messages[messages[j].Content.Uid]
+					if infoi == nil || infoj == nil {
+						return false
+					}
+					msgidi := padGitMessageId(infoi.Envelope.MessageId)
+					msgidj := padGitMessageId(infoj.Envelope.MessageId)
+					return msgidi < msgidj
+				})
+			}
 
 			reader := newMessagesReader(messages, len(messages) > 1)
 			if background {
@@ -219,3 +233,20 @@ func newMessagesReader(messages []*types.FullMessage, useMbox bool) io.Reader {
 	}()
 	return pr
 }
+
+var gitMessageIdRe = regexp.MustCompile(`^(\d+\.\d+)-(\d+)-(.+)$`)
+
+// Git send-email Message-Id headers have the following format:
+//    DATETIME.PID-NUM-COMMITTER
+// Return a copy of the message id with NUM zero-padded to three characters.
+func padGitMessageId(msgId string) string {
+	matches := gitMessageIdRe.FindStringSubmatch(msgId)
+	if matches == nil {
+		return msgId
+	}
+	number, err := strconv.Atoi(matches[2])
+	if err != nil {
+		return msgId
+	}
+	return fmt.Sprintf("%s-%03d-%s", matches[1], number, matches[3])
+}