Add a barely useful interface to b4-am

Aside from switching the 'b4 am' process to an asynchronous one, the
am-ready commands may not need a lot of work.  The more interesting
variant, piem-b4-am-from-mid, can find an associated code repository
and am the patch, but there's a lot that needs to be fleshed out.

4 files changed, 217 insertions, 2 deletions

diff --git a/.gitignore b/.gitignore
index f02607a..8171c92 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 *.elc
 *.info
+config.mk
diff --git a/Makefile b/Makefile
index 8b04a53..50c87d2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,12 @@
 
-BATCH = emacs -Q --batch
+-include config.mk
 
-all: piem.elc piem.info
+TRANSIENT_DIR ?= /dev/null
+
+LOAD_PATH = -L . -L $(TRANSIENT_DIR)
+BATCH = emacs -Q --batch $(LOAD_PATH)
+
+all: piem.elc piem-b4.elc piem.info
 
 .PHONY: clean
 clean:
diff --git a/piem-b4.el b/piem-b4.el
new file mode 100644
index 0000000..957994e
--- /dev/null
+++ b/piem-b4.el
@@ -0,0 +1,205 @@
+;;; piem-b4.el --- Emacs interface to the b4 tool  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2020  Kyle Meyer
+
+;; Author: Kyle Meyer <kyle@kyleam.com>
+;; Keywords: vc, tools
+;; Version: 0.0.0
+;; Package-Requires: ((emacs "26.3") (transient "0.2.0"))
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'piem)
+(require 'subr-x)
+(require 'transient)
+
+
+;;; Options
+
+(defgroup piem-b4 nil
+  "Control the b4 tool from Emacs."
+  :link '(info-link "(piem)b4 integration")
+  :group 'piem)
+
+(defcustom piem-b4-b4-executable "b4"
+  "Which b4 executable to use."
+  :type 'string)
+
+(defcustom piem-b4-git-executable
+  (or (and (boundp 'magit-git-executable) magit-git-executable)
+      "git")
+  "Which git executable to use."
+  :type 'string)
+
+(defcustom piem-b4-use-magit (featurep 'magit)
+  "Whether to use Magit where possible."
+  :type 'boolean)
+
+
+;;; Internals
+
+(define-error 'piem-b4-error "b4 error")
+
+(defconst piem-b4-output-buffer "*piem-b4-output*")
+
+;; TODO: Use an asynchronous process.
+(defun piem-b4--call-b4 (&rest args)
+  (unless piem-b4-b4-executable
+    (user-error "piem-b4-b4-executable must be non-nil"))
+  (let ((temp-buffer-show-function (lambda (_))))
+    (with-output-to-temp-buffer piem-b4-output-buffer
+      (unless (= 0 (apply #'call-process piem-b4-b4-executable
+                          nil standard-output nil
+                          (remq nil args)))
+        (display-buffer piem-b4-output-buffer)
+        (signal 'piem-b4-error
+                (list (format "b4 call in %s failed" default-directory)))))))
+
+;; In many cases, we don't really need b4 to download the mbox for us,
+;; as we already have our own mbox to URL mapping.  Perhaps we should
+;; default to using that, but it should still be an option to use b4
+;; so that we honor its customization/URL resolution.
+(defun piem-b4--get-mbox-file (mid coderepo args)
+  (let* ((mbox-name (format "%s.mbx" mid))
+         (outdir (file-name-as-directory
+                  (make-temp-file "piem-b4-" t)))
+         (mbox-am (concat outdir mbox-name))
+         (mbox-thread (concat mbox-am "-thread"))
+         (custom-p nil))
+    (when-let ((fn (run-hook-with-args-until-success
+                    'piem-mid-to-thread-functions mid)))
+      (with-temp-file mbox-thread
+        (funcall fn)
+        (unless (= (point-max) 1)
+          (setq custom-p t))))
+    ;; Move to the coderepo so that we pick up any b4 configuration
+    ;; from there.
+    (let ((default-directory coderepo))
+      (apply #'piem-b4--call-b4 "am"
+             (and custom-p
+                  (concat "--use-local-mbox=" mbox-thread))
+             (concat "--outdir=" outdir)
+             (concat "--mbox-name=" mbox-name)
+             (append args (list mid))))
+    (unless (file-exists-p mbox-am)
+      (error "Expected mbox file does not exist: %s" mbox-am))
+    mbox-am))
+
+
+;;; Commands
+
+;;;###autoload
+(defun piem-b4-am-ready-from-mbox (mbox &optional args)
+  (interactive (list (read-file-name "mbox: ")
+                     (transient-args 'piem-b4-am)))
+  (apply #'piem-b4--call-b4 "am"
+         (cons (concat "--use-local-mbox=" mbox) args))
+  (display-buffer piem-b4-output-buffer))
+
+;;;###autoload
+(defun piem-b4-am-ready-from-mid (mid &optional args)
+  (interactive (list (read-string "Message ID: " nil nil (piem-mid))
+                     (transient-args 'piem-b4-am)))
+  (apply #'piem-b4--call-b4 "am" (append args (list mid)))
+  (display-buffer piem-b4-output-buffer))
+
+;;;###autoload
+(defun piem-b4-am-from-mid (mid &optional args)
+  (interactive (list (or (piem-mid)
+                         (read-string "Message ID: "))
+                     (transient-args 'piem-b4-am)))
+  (when-let ((badopt (cl-some
+                      (lambda (arg)
+                        (and (string-match
+                              (rx string-start
+                                  (group (or "--outdir" "--mbox-name")) "=")
+                              arg)
+                             (match-string 1 arg)))
+                      args)))
+    (user-error "%s is incompatible with this command" badopt))
+  (let* ((coderepo (or (piem-inbox-coderepo)
+                       (and (fboundp 'projectile-relevant-known-projects)
+                            (completing-read
+                             "Project: "
+                             (projectile-relevant-known-projects)))
+                       (and piem-b4-use-magit
+                            (fboundp 'magit-read-repository)
+                            (magit-read-repository))
+                       (read-directory-name "Git repository: ")))
+         (mbox-file (piem-b4--get-mbox-file mid coderepo args))
+         (default-directory coderepo))
+    ;; TODO: From the mbox file (1) search for base commit and (2)
+    ;; gather information to suggest default branch name.
+
+    ;; TODO: Add branch call.  Without base, will need to ask branch
+    ;; name and starting point.  Detached head could be signaled with
+    ;; empty string.
+
+    ;; TODO: Optionally do more through Magit.
+    (call-process piem-b4-git-executable
+                  mbox-file nil nil "am" "--scissors")
+    (if (and piem-b4-use-magit
+             (fboundp 'magit-status-setup-buffer))
+        (magit-status-setup-buffer)
+      (dired "."))))
+
+(define-infix-argument piem-b4-am:--outdir ()
+  :description "Output directory"
+  :class 'transient-option
+  :shortarg "-o"
+  :argument "--outdir="
+  :reader #'transient-read-existing-directory)
+
+(define-infix-argument piem-b4-am:--mbox-name ()
+  :description "Base file name for mbox"
+  :class 'transient-option
+  :shortarg "-n"
+  :argument "--mbox-name="
+  :reader #'read-string)
+
+(define-infix-argument piem-b4-am:--use-version ()
+  :description "Desired version of patch series"
+  :class 'transient-option
+  :shortarg "-v"
+  :argument "--use-version="
+  :reader #'transient-read-number-N+)
+
+;;;###autoload (autoload 'piem-b4-am "b4" nil t)
+(define-transient-command piem-b4-am ()
+  "Filter mbox to patches and feed to git-am"
+  ["General options"
+   ("-c" "Check newer versions" "--check-newer-revisions")
+   ("-C" "Don't use local cache" "--no-cache")
+   ("-s" "Add my signed-off-by" "--add-my-sob")
+   ("-S" "Apply trailers without checking email addresses" "--sloppy-trailers")
+   ("-t" "Apply cover letter trailers" "--apply-cover-trailers")
+   ("-T" "Do not add trailers" "--no-add-trailers")
+   (piem-b4-am:--use-version)]
+  ["Options for creating am-ready mboxes"
+   (piem-b4-am:--outdir)
+   (piem-b4-am:--mbox-name)]
+  ["Actions"
+   [("a" "Message ID -> mbox -> git-am" piem-b4-am-from-mid)]
+   [("b" "Local mbox -> am-ready mbox" piem-b4-am-ready-from-mbox)
+    ("i" "Message ID -> am-ready mbox" piem-b4-am-ready-from-mid)]])
+
+;;; piem-b4.el ends here
+(provide 'piem-b4)
diff --git a/piem.texi b/piem.texi
index 15b0e2e..137a7cb 100644
--- a/piem.texi
+++ b/piem.texi
@@ -45,6 +45,7 @@ This manual is for piem version @value{VERSION}.
 
 @menu
 * Overview::
+* b4 interface::
 * Related tools::
 * Contributing::
 
@@ -64,6 +65,9 @@ Indices
 @node public-inbox
 @section public-inbox
 
+@node b4 interface
+@chapter b4 interface
+
 @node Related tools
 @chapter Related tools