piem-am: Order attached patches by file name prefix

When extracting patches from attachments, piem-gnus-am-ready-mbox and
piem-notmuch-am-ready-mbox construct the mbox messages in the same
order as the attachments.  This depends on the sender attaching the
patches in ascending order.

Be a bit more helpful in situations where the sender attaches the
patches out of order by reordering patches according to the NNNN-
prefix that git-format-patch adds to the start of the patch file name.
This approach won't be able to reliably sort patches that aren't
generated by git-format-patch, but that's outside of any use case that
piem is intended to support.

Suggested-by: Ihor Radchenko <yantar92@gmail.com>
Link: https://inbox.kyleam.com/piem/87mtdj9dzt.fsf@localhost
Message-Id: <878rp2pyx1.fsf@kyleam.com>

3 files changed, 36 insertions, 18 deletions

diff --git a/piem-gnus.el b/piem-gnus.el
index c62a2e6..4011fa2 100644
--- a/piem-gnus.el
+++ b/piem-gnus.el
@@ -91,17 +91,24 @@
 
 (defun piem-gnus-am-ready-mbox ()
   "Return a function that inserts an am-ready mbox.
+
 If the buffer has any MIME parts that look like a patch, use
-those parts' contents (in order) as the mbox.  Otherwise, use the
-message itself if it looks like a patch."
+those parts' contents as the mbox, ordering the patches based on
+the number at the start of the file name.  If none of the file
+names start with a number, retain the original order of the
+attachments.
+
+If no MIME parts look like a patch, use the message itself if it
+looks like a patch."
   (when (derived-mode-p 'gnus-article-mode 'gnus-summary-mode)
     (cond
      (gnus-article-mime-handles
       (when-let ((patches (delq nil (mapcar #'piem-am-extract-attached-patch
                                             gnus-article-mime-handles))))
+        (setq patches (sort patches (lambda (x y) (< (car x) (car y)))))
         (cons (lambda ()
                 (dolist (patch patches)
-                  (insert patch)))
+                  (insert (cdr patch))))
               "mbox")))
      (gnus-article-buffer
       (when-let ((patch (with-current-buffer gnus-article-buffer
diff --git a/piem-notmuch.el b/piem-notmuch.el
index 41f2793..493b724 100644
--- a/piem-notmuch.el
+++ b/piem-notmuch.el
@@ -85,9 +85,15 @@ have surrounding brackets."
 
 (defun piem-notmuch-am-ready-mbox ()
   "Return a function that inserts an am-ready mbox.
+
 If the buffer has any MIME parts that look like a patch, use
-those parts' contents (in order) as the mbox.  Otherwise, use the
-message itself if it looks like a patch."
+those parts' contents as the mbox, ordering the patches based on
+the number at the start of the file name.  If none of the file
+names start with a number, retain the original order of the
+attachments.
+
+If no MIME parts look like a patch, use the message itself if it
+looks like a patch."
   (when (derived-mode-p 'notmuch-show-mode)
     (let* ((handle (piem-notmuch--with-current-message
                      (mm-dissect-buffer)))
@@ -106,10 +112,11 @@ message itself if it looks like a patch."
              (push patch patches)))
          handle)
         (when patches
-          (setq patches (nreverse patches))
+          (setq patches (sort (nreverse patches)
+                              (lambda (x y) (< (car x) (car y)))))
           (cons (lambda ()
                   (dolist (patch patches)
-                    (insert patch)))
+                    (insert (cdr patch))))
                 "mbox"))))))
 
 (defun piem-notmuch-extract-patch-am-ready-mbox ()
diff --git a/piem.el b/piem.el
index 47944e4..63c358a 100644
--- a/piem.el
+++ b/piem.el
@@ -817,17 +817,21 @@ message for MID, not the entire thread."
 ;;;; Patch handling
 
 (defun piem-am-extract-attached-patch (handle)
-  "Return content for HANDLE if it looks like a patch."
-  (and (listp handle)
-       (let ((type (mm-handle-media-type handle))
-             (filename (mm-handle-filename handle)))
-         (or (member type '("text/x-diff" "text/x-patch"))
-             (and filename
-                  (equal type "text/plain")
-                  (string-suffix-p ".patch" filename t))))
-       (with-temp-buffer
-         (mm-display-inline handle)
-         (buffer-substring-no-properties (point-min) (point-max)))))
+  "Get the content for HANDLE if it looks like a patch.
+The return value is of the form (N . CONTENT), where N is the
+number at the start of the file name."
+  (when (listp handle)
+    (let ((type (mm-handle-media-type handle))
+          (filename (mm-handle-filename handle)))
+      (and (or (member type '("text/x-diff" "text/x-patch"))
+               (and filename
+                    (equal type "text/plain")
+                    (string-suffix-p ".patch" filename t)))
+           (with-temp-buffer
+             (mm-display-inline handle)
+             (cons
+              (string-to-number filename)
+              (buffer-substring-no-properties (point-min) (point-max))))))))
 
 (defun piem-extract-mbox-info (&optional buffer)
   "Collect information from message in BUFFER.