From d55b7895a8829d4fd120295bfb6134b51bf87fe4 Mon Sep 17 00:00:00 2001
From: Kyle Meyer <kyle@kyleam.com>
Date: Sun, 10 May 2020 23:41:59 -0400
Subject: piem: Extract "inbox from headers" logic from -notmuch

This will be used in the upcoming piem-gnus.el as well.
---
 piem-notmuch.el | 25 +++----------------------
 piem.el         | 27 +++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 22 deletions(-)

diff --git a/piem-notmuch.el b/piem-notmuch.el
index ed5bd4b..96b8a05 100644
--- a/piem-notmuch.el
+++ b/piem-notmuch.el
@@ -26,7 +26,6 @@
 
 ;;; Code:
 
-(require 'message)
 (require 'notmuch)
 (require 'piem)
 (require 'subr-x)
@@ -49,27 +48,9 @@
 
 (defun piem-notmuch-get-inbox ()
   "Return inbox name from a `notmuch-show-mode' buffer."
-  (pcase-let ((`(,listid ,to ,cc)
-               (when (derived-mode-p 'notmuch-show-mode)
-                 (piem-notmuch--with-current-message
-                  (message-narrow-to-headers)
-                  (list (message-fetch-field "list-id")
-                        (message-fetch-field "to")
-                        (message-fetch-field "cc"))))))
-    (catch 'hit
-      (dolist (inbox piem-inboxes)
-        (let* ((info (cdr inbox))
-               (p-listid (plist-get info :listid)))
-          (when (and listid
-                     p-listid
-                     (string-match-p (concat "<" (regexp-quote p-listid) ">")
-                                     listid))
-            (throw 'hit (car inbox)))
-          (when-let ((addr (plist-get info :address))
-                     (to (mapconcat #'identity (list to cc)
-                                    " ")))
-            (when (string-match-p (regexp-quote addr) to)
-              (throw 'hit (car inbox)))))))))
+  (when (derived-mode-p 'notmuch-show-mode)
+    (piem-notmuch--with-current-message
+     (piem-inbox-by-header-match))))
 
 (defun piem-notmuch-get-mid ()
   "Return the message ID of a `notmuch-show-mode' buffer."
diff --git a/piem.el b/piem.el
index 979f944..63d9443 100644
--- a/piem.el
+++ b/piem.el
@@ -26,6 +26,7 @@
 
 ;;; Code:
 
+(require 'message)
 (require 'subr-x)
 
 (defgroup piem ()
@@ -90,6 +91,32 @@ should return a function that takes no arguments and inserts the
 mbox's contents in the current buffer."
   :type 'hook)
 
+(defun piem-inbox-by-header-match ()
+  "Return inbox based on matching message headers.
+This should be called from a buffer containing a message and is
+intended to be used by libraries implementing a function for
+`piem-get-mid-functions'."
+  (pcase-let ((`(,listid ,to ,cc)
+               (save-restriction
+                 (message-narrow-to-headers)
+                 (list (message-fetch-field "list-id")
+                       (message-fetch-field "to")
+                       (message-fetch-field "cc")))))
+    (catch 'hit
+      (dolist (inbox piem-inboxes)
+        (let* ((info (cdr inbox))
+               (p-listid (plist-get info :listid)))
+          (when (and listid
+                     p-listid
+                     (string-match-p (concat "<" (regexp-quote p-listid) ">")
+                                     listid))
+            (throw 'hit (car inbox)))
+          (when-let ((addr (plist-get info :address))
+                     (to (mapconcat #'identity (list to cc)
+                                    " ")))
+            (when (string-match-p (regexp-quote addr) to)
+              (throw 'hit (car inbox)))))))))
+
 ;;;###autoload
 (defun piem-inbox ()
   "Return the current buffer's inbox."
-- 
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