;;; piem.el --- Emacs tools for working with public-inbox  -*- lexical-binding: t; -*-

;; Copyright (C) 2020-2021  all contributors <piem@inbox.kyleam.com>

;; Author: Kyle Meyer <kyle@kyleam.com>
;; Keywords: vc, tools
;; Version: 0.1.0
;; Package-Requires: ((emacs "26.3") (transient "0.3.0"))
;; Homepage: https://git.kyleam.com/piem/about/

;; 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:

;; This library provides functionality for working with public-inbox
;; archives [1] within Emacs (e.g., applying a patch series to the
;; associated Git repository or downloading an mbox for the thread and
;; injecting it into a local Maildir directory).  The user option
;; `piem-inboxes' defines a set of public-inbox archives.  For most
;; the functions here to do something useful, the current buffer needs
;; to be linked to an inbox in that list, which requires enabling the
;; minor mode provided by at least one integration library (such as
;; `piem-gnus', `piem-eww', or `piem-notmuch').
;;
;; [1] https://public-inbox.org/README

;;; Code:

(require 'browse-url)
(require 'cl-lib)
(require 'mail-extr)
(require 'message)
(require 'mm-decode)
(require 'piem-maildir)
(require 'rfc2047)
(require 'subr-x)
(require 'transient)
(require 'url)

(defvar url-http-end-of-headers)
(defvar url-http-response-status)

\f
;;;; Options

(defgroup piem ()
  "Emacs tools for working with public-inbox archives."
  :link '(info-link "(piem)Top")
  :group 'tools)

;; TODO: These intentionally follow public-inbox's configuration
;; names.  Eventually reading values from there as well should be
;; supported.
;;
;; TODO: Decide how to deal with inboxes that map to more than one
;; coderepos.  This is important to support for people that want to
;; use a catchall inbox for small projects which they don't think
;; (yet) need a dedicated address.
(defcustom piem-inboxes nil
  "List of public-inbox-archived projects.

Elements have the form (NAME . INFO), where INFO is a property
list that supports the following properties:

  :address
  :listid
      The email address and List-ID for the inbox.
  :coderepo
      Local path of the code repository associated with the inbox.
  :url
      A URL hosting HTTPS archives.  This value must end with a slash.

Here's an example for the public-inbox project itself:

    (\"public-inbox\"
     :coderepo \"~/src/public-inbox/\"
     :address \"meta@public-inbox.org\"
     :listid \"meta.public-inbox.org\"
     :url \"https://public-inbox.org/meta/\")"
  :type '(alist :key-type string
                :value-type
                (plist :value-type string)))

(defcustom piem-get-inbox-functions nil
  "Functions tried to get the inbox of the current buffer.
Each function should accept no arguments and return the name of
the inbox associated with the current buffer or nil."
  :type 'hook)

(defcustom piem-get-mid-functions nil
  "Functions tried to get the message ID of the current buffer.
Each function should accept no arguments and return the
message ID associated with the current buffer or nil."
  :type 'hook)

(defcustom piem-mid-to-thread-functions nil
  "Functions tried to create an mbox from a message ID.
Each function should accept one argument, the message ID.  If the
function knows how to create an mbox for the message ID, it
should return a function that takes no arguments and inserts the
mbox's contents (in mboxrd format) in the current buffer."
  :type 'hook)

(defcustom piem-am-ready-mbox-functions nil
  "Functions tried to get an mbox to be fed to `git am'.
The functions are called with no arguments.  If a function knows
how to create an mbox, it should return a function that takes no
arguments and inserts the mbox's contents in the current buffer.
The return value can also be (FUNCTION . FORMAT), where FORMAT is
either \"mbox\" or \"mboxrd\" and maps to the --patch-format
value passed to `git am'.  If unspecified, \"mboxrd\" is used."
  :type 'hook)

(defcustom piem-add-message-id-header nil
  "Whether to add Message-Id header to non-mail patches.
If this value is non-nil and a patch returned by a function in
`piem-am-ready-mbox-functions' looks like a patch that was
attached rather than sent inline, add a Message-Id header with
the return value of `piem-mid'."
  :type 'boolean)

(defcustom piem-git-executable
  (or (and (boundp 'magit-git-executable) magit-git-executable)
      "git")
  "Which git executable to use."
  :type 'string)

(defcustom piem-use-magit (featurep 'magit)
  "Whether to use Magit where possible."
  :type 'boolean)

(defcustom piem-default-branch-function
  #'piem-name-branch-who-what-v
  "Function that generates the default branch on completion.

The function is called with one argument, a plist that contains
the following information about the patch series:

  :date
  :from
  :subject
      The date, sender, and subject of the cover letter, if any, or of
      the first patch otherwise.
  :base-commit
      The reported base commit of the patch, if any."
  :type 'function)

(defcustom piem-am-create-worktree nil
  "Whether to create a dedicated worktree for applying patches."
  :type 'boolean)

(defcustom piem-am-read-worktree-function #'piem-am-read-worktree
  "Function that reads a to-be-created worktree from the user.
This function is called with two arguments, the directory of the
code repository that the worktree will be created from and the
name of the branch that will be created.  The branch may be nil
if the caller requested a detached HEAD."
  :type 'function)

(defcustom piem-maildir-directory nil
  "Inject public-inbox threads into this directory.
If non-nil, this must be an existing Maildir directory."
  :type 'string)

(defcustom piem-mail-injection-skipif-predicate nil
  "Predicate to decide whether to skip injecting a message.

The function is called with the message ID (no surrounding
brackets) within a buffer that is narrowed to the message.  The
function does not need to worry about saving point.  A non-nil
return value signals that `piem-inject-thread-into-maildir'
should skip the message.

Notmuch users can use `piem-notmuch-known-mid-p' as the predicate
to skip messages that are already in the Notmuch database."
  :type 'function)

(defcustom piem-after-mail-injection-functions nil
  "Functions called after writing messages to `piem-maildir-directory'.
Functions should accept one argument, the message ID given to
`piem-inject-thread-into-maildir'."
  :type 'hook)

(defcustom piem-browse-url-browser-function nil
  "Overriding value for `browse-url-browser-function'.

public-inbox's HTTP interface is well suited for browsers like
w3m and EWW, allowing you to stay in Emacs rather than launch an
external browser.  However, assuming you have `browse-url'
configured to usually go through an external browser, sending
public-inbox URLs through, say, EWW would require you to
configure `browse-url-browser-function' with a regular expression
for each inbox URL that you want to be handled by
`eww-browse-url'.

Instead, you can simply set this option to `eww-browse-url' (or
anything else `browse-url-browser-function' accepts), and piem
will use it when calling `browse-url'.

When this option is nil, piem calls `browse-url' without
overriding the value of `browse-url-browser-function'."
  :type (append
         '(choice
           (const :tag "Don't override `browse-url-browser-function'" nil))
         (cdr (get 'browse-url-browser-function 'custom-type))))

\f
;;;; Subprocess handling

(defvar piem-process-mode-font-lock-keywords
  `((,(rx line-start
          ";;; " (or "process" "directory" "time")
          ":" (one-or-more not-newline)
          line-end)
      (0 font-lock-comment-face t))
    (,(rx line-start
          "Process " (one-or-more not-newline) " finished"
          line-end)
     (0 font-lock-comment-face))))

(defconst piem-process-output-buffer "*piem-process-output*")

(define-derived-mode piem-process-mode nil "piem-process"
  "Major mode for displaying processes created by piem."
  :group 'piem
  (setq buffer-read-only t)
  (setq-local window-point-insertion-type t)
  (setq-local font-lock-defaults
              '(piem-process-mode-font-lock-keywords)))

(define-error 'piem-process-error "piem process error")

(defvar-local piem--buffer-process nil)

(defun piem--process-go (dir program program-args fn)
  (setq dir (or dir default-directory))
  (let ((buffer (get-buffer-create piem-process-output-buffer)))
    (with-current-buffer buffer
      (when (and piem--buffer-process
                 (process-live-p piem--buffer-process))
        (user-error "Buffer %s already has an active process: %s"
                    (current-buffer) piem--buffer-process))
      (unless (derived-mode-p 'piem-process-mode)
        (piem-process-mode))
      (setq default-directory (file-name-as-directory dir))
      (goto-char (point-max))
      (display-buffer buffer)
      (let ((inhibit-read-only t))
        (insert (format "
%s
;;; process: %S
;;; directory:  %s
;;; time: %s
"
                        (char-to-string 12) ; form feed
                        (cons program program-args)
                        default-directory
                        (format-time-string "%FT%T%z")))
        (funcall fn)))))

(defun piem-process-start (dir program &rest program-args)
  (setq program-args (remq nil program-args))
  (piem--process-go
   dir program program-args
   (lambda ()
     (setq piem--buffer-process
          (apply #'start-process
                 (file-name-nondirectory program)
                 (current-buffer)
                 program program-args)))))

(defun piem-process-call (dir program &rest program-args)
  (setq program-args (remq nil program-args))
  (piem--process-go
   dir program program-args
   (lambda ()
     (unless (= 0 (apply #'call-process program nil t nil program-args))
       (signal 'piem-process-error
               (list (format "%s call in %s failed"
                             program default-directory)))))))

(defun piem-process-call-with-buffer-input
    (dir buffer program &rest program-args)
  (setq program-args (remq nil program-args))
  (piem--process-go
   dir program program-args
   (lambda ()
     (let ((outdir default-directory)
           (outbuf (current-buffer)))
       (with-current-buffer buffer
         (let ((default-directory outdir))
           (unless (= 0 (apply #'call-process-region nil nil
                               program nil outbuf nil program-args))
             (signal 'piem-process-error
                     (list (format "%s call in %s failed"
                                   program default-directory))))))))))

\f
;;;; Extractors

(defun piem--ensure-trailing-slash (s)
  (if (string-suffix-p "/" s) s (concat s "/")))

(defun piem-message-link-re (url &optional mid)
  "Return a regular expression matching a public-inbox url.
URL should be the top-level url for the inbox.  If MID is
non-nil, make the match specific for that message."
  (rx-to-string
   `(and ,(piem--ensure-trailing-slash url)
         (group ,(or (and mid (piem-escape-mid mid))
                     '(one-or-more (not (any "/" "\n")))))
         "/" (group (zero-or-one
                     (or "raw"
                         "t.mbox.gz"
                         (and (or "t" "T") "/#"
                              (one-or-more (not (any "/" "\n")))))))
         string-end)))

(defun piem--message-fetch-decoded-fields (headers)
  (save-excursion
    (save-restriction
      (message-narrow-to-head)
      (mapcar (lambda (header)
                (when-let ((val (message-fetch-field header)))
                  (rfc2047-decode-string val)))
              headers))))

(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)
               (piem--message-fetch-decoded-fields '("list-id" "to" "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)))))))))

(defun piem-inbox ()
  "Return the current buffer's inbox."
  (run-hook-with-args-until-success 'piem-get-inbox-functions))

(defun piem-inbox-get (key &optional inbox)
  "Get info KEY for INBOX's entry in `piem-inboxes'.
If INBOX is nil, use the inbox returned by `piem-inbox'."
  (when-let ((p (or inbox (piem-inbox))))
    (plist-get (cdr (assoc p piem-inboxes)) key)))

(defun piem-inbox-coderepo (&optional inbox)
  "Return the code repository of current buffer's inbox."
  (when-let ((repo (piem-inbox-get :coderepo inbox)))
    (expand-file-name repo)))

(defun piem-inbox-by-url-match (url)
  "Return inbox based on matching URL against `:url'."
  (setq url (piem--ensure-trailing-slash url))
  (catch 'hit
    (dolist (inbox piem-inboxes)
      (when-let ((info (cdr inbox))
                 (p-url (plist-get info :url)))
        (setq p-url (piem--ensure-trailing-slash p-url))
        (when (string-match-p (regexp-quote p-url) url)
          (throw 'hit (car inbox)))))))

(defun piem-inbox-coderepo-maybe-read ()
  "Like `piem-inbox-coderepo', but fall back to reading the repo."
  (let ((inbox
         (or (piem-inbox-coderepo)
             (and (bound-and-true-p projectile-known-projects)
                  (expand-file-name
                   (completing-read
                    "Project: "
                    projectile-known-projects nil t nil nil
                    (when-let ((current (and (fboundp 'projectile-project-root)
                                             (projectile-project-root))))
                      (abbreviate-file-name current)))))
             (and (bound-and-true-p project-list-file)
                  (file-exists-p project-list-file)
                  (fboundp 'project-prompt-project-dir)
                  (expand-file-name
                   (project-prompt-project-dir)))
             (and piem-use-magit
                  (fboundp 'magit-read-repository)
                  (magit-read-repository))
             (read-directory-name "Git repository: "))))
    (if (equal inbox "")
        (user-error "No inbox specified")
      inbox)))

(defun piem-mid ()
  "Return the current buffer's message ID."
  (run-hook-with-args-until-success 'piem-get-mid-functions))

(defun piem--insert-message-id-header (mid)
  ;; Be strict about case because this is coming from
  ;; git-format-patch.
  (let ((case-fold-search nil))
    (while (re-search-forward
            (rx line-start
                "From " (>= 40 hex-digit) " Mon Sep 17 00:00:00 2001"
                line-end)
            nil t)
      (catch 'has-message-id
        (let ((header-count 0))
          (while (and (= (forward-line) 0)
                      (not (looking-at-p
                            (rx line-start (zero-or-one space) line-end))))
            (cond
             ((looking-at-p
               (rx line-start
                   "Message-Id: <" (one-or-more not-newline) ">"
                   line-end))
              (throw 'has-message-id nil))
             ((looking-at-p
               (rx line-start (or "From" "Date" "Subject") ": "
                   not-newline))
              (cl-incf header-count))))
          (when (= header-count 3)
            ;; Found all the expected headers before hitting a
            ;; blank line.  Assume we're in a header.
            (insert (format "Message-Id: <%s>\n" mid))))))))

(defun piem-am-ready-mbox ()
  "Generate a buffer containing an am-ready mbox.
The return value is (BUFFER . FORMAT), where FORMAT is either
\"mbox\" or \"mboxrd\".  Callers are responsible for killing the
buffer."
  (when-let ((res (run-hook-with-args-until-success
                   'piem-am-ready-mbox-functions)))
    (pcase-let ((buffer (generate-new-buffer " *piem am-ready mbox*"))
                (`(,fn . ,format)
                 (if (member (cdr-safe res) '("mbox" "mboxrd"))
                     res
                   (cons res "mboxrd")))
                (mid (and piem-add-message-id-header (piem-mid)))
                (has-content nil))
      (with-current-buffer buffer
        (funcall fn)
        (setq has-content (< 1 (point-max)))
        (when (and has-content mid)
          (goto-char (point-min))
          (piem--insert-message-id-header mid)))
      (if has-content
          (cons buffer format)
        (kill-buffer buffer)
        nil))))

\f
;;;; Link handling

(defconst piem--unreserved-chars
  (append url-unreserved-chars
          ;; These extra characters follow what's used by
          ;; public-inbox's mid_escape().
          (list ?! ?$ ?& ?' ?\( ?\) ?* ?+ ?, ?= ?: ?\; ?@)))

(defun piem-escape-mid (mid)
  "Escape MID for use in path part of a public-inbox URL."
  (url-hexify-string mid piem--unreserved-chars))

(defun piem-mid-url (mid &optional inbox)
  "Return a public-inbox URL for MID.
The URL is determined by INBOX's entry in `piem-inboxes'.  If
INBOX is nil, use the inbox returned by `piem-inbox'."
  (concat
   (piem--ensure-trailing-slash
    (or (piem-inbox-get :url inbox)
        (user-error "Couldn't find URL for %s"
                    (or inbox "current buffer"))))
   (piem-escape-mid mid)))

;;;###autoload
(defun piem-copy-mid-url (&optional browse)
  "Copy public-inbox URL for the current buffer's message.
With prefix argument BROWSE, call `browse-url' on the URL
afterwards.  If `piem-browse-url-browser-function' is non-nil, it
is used as the value of `browse-url-browser-function'."
  (interactive "P")
  (let ((url (piem-mid-url
              (or (piem-mid)
                  (user-error "No message ID found for the current buffer"))
              (piem-inbox))))
    (prog1
        (kill-new (message "%s" url))
      (when browse
        (let ((browse-url-browser-function
               (or piem-browse-url-browser-function
                   browse-url-browser-function)))
          (browse-url url))))))

\f
;;;; Download helpers

(defvar piem--has-gunzip)
(defun piem-check-gunzip ()
  "Return non-nil if gunzip is available."
  (unless (boundp 'piem--has-gunzip)
    (setq piem--has-gunzip (executable-find "gunzip")))
  piem--has-gunzip)

(defun piem--url-remove-header ()
  (goto-char (1+ url-http-end-of-headers))
  (delete-region (point-min) (point)))

(defun piem--url-decompress ()
  (unless (= 0 (call-process-region nil nil "gunzip" nil t))
    (error "Decompressing t.mbox.gz failed"))
  (delete-region (point) (point-max))
  (goto-char (point-min)))

(defun piem-download-and-decompress (url)
  "Retrieve gzipped content at URL and decompress it.
A buffer with the decompressed content is returned."
  (unless (piem-check-gunzip)
    (user-error "gunzip executable not found"))
  (when-let ((buffer (url-retrieve-synchronously url 'silent)))
    (with-current-buffer buffer
      (if (/= url-http-response-status 200)
          (progn (kill-buffer buffer)
                 (error "Download of %s failed" url))
        (piem--url-remove-header)
        (piem--url-decompress))
      buffer)))

\f
;;;; Maildir injection

(defun piem--write-mbox-to-maildir ()
  (let ((n-added 0)
        (n-skipped 0))
    (while (and (not (eobp))
                (re-search-forward "^From mboxrd@z" nil t))
      (let* ((beg (line-beginning-position 2))
             (end (or (and (re-search-forward "^From mboxrd@z" nil t)
                           (progn (goto-char (line-beginning-position 0))
                                  (point-marker)))
                      (point-max-marker)))
             (basename (piem-maildir-make-uniq-maildir-id))
             (tmpfile (concat piem-maildir-directory "/tmp/" basename)))
        (goto-char beg)
        (if (and (functionp piem-mail-injection-skipif-predicate)
                 (save-excursion
                   (save-restriction
                     (narrow-to-region beg end)
                     (funcall piem-mail-injection-skipif-predicate
                              (replace-regexp-in-string
                               "\\`<\\(.*\\)>\\'" "\\1"
                               (or (save-restriction
                                     (save-excursion
                                       (message-narrow-to-head-1)
                                       (message-fetch-field "message-id" t)))
                                   (error "Message lacks message-ID")))))))
            (cl-incf n-skipped)
          (let ((case-fold-search nil))
            (while (re-search-forward
                    (rx line-start ">" (group (zero-or-more ">") "From "))
                    end t)
              (replace-match "\\1" t)))
          (write-region beg end tmpfile nil nil nil 'excl)
          (piem-maildir-move-tmp-to-new piem-maildir-directory
                                        basename)
          (delete-file tmpfile)
          (cl-incf n-added))
        (goto-char end)))
    (cons n-added n-skipped)))

;;;###autoload
(defun piem-inject-thread-into-maildir (mid &optional message-only)
  "Inject thread containing MID into `piem-maildir-directory'.

If prefix argument MESSAGE-ONLY is non-nil, inject just the
message for MID, not the entire thread.

This function depends on :url being configured for entries in
`piem-inboxes'."
  (interactive
   (list (or (piem-mid)
             (user-error "No message ID found for the current buffer"))
         current-prefix-arg))
  (cond
   ((not piem-maildir-directory)
    (user-error "`piem-maildir-directory' is not configured"))
   ((not (piem-maildir-dir-is-maildir-p piem-maildir-directory))
    (user-error
     "`piem-maildir-directory' does not look like a Maildir directory"))
   ((not (or message-only (piem-check-gunzip)))
    (user-error "gunzip executable not found")))
  (when-let ((url (concat (piem-mid-url mid)
                          (if message-only "/raw" "/t.mbox.gz")))
             (buffer (url-retrieve-synchronously url 'silent)))
    (unwind-protect
        (with-current-buffer buffer
          (if (/= url-http-response-status 200)
              (error "Download of %s failed" url)
            (piem--url-remove-header)
            (unless message-only
              (piem--url-decompress))
            (pcase-let ((`(,added-count . ,skipped-count)
                         (piem--write-mbox-to-maildir)))
              (message "Added %d message%s%s for %s to %s"
                       added-count
                       (if (= added-count 1) "" "s")
                       (if (> skipped-count 0)
                           (format " (skipping %d)" skipped-count)
                         "")
                       mid
                       (abbreviate-file-name piem-maildir-directory)))
            (run-hook-with-args 'piem-after-mail-injection-functions mid)))
      (kill-buffer buffer))))

\f
;;;; 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)))))

(defun piem-extract-mbox-info (&optional buffer)
  "Collect information from message in BUFFER.
If BUFFER is nil, the current buffer is used.  Any message after
the first will be ignored."
  (with-current-buffer (or buffer (current-buffer))
    (let ((info (cl-mapcan #'list '(:date :from :subject)
                           (piem--message-fetch-decoded-fields
                            '("date" "from" "subject")))))
      (when (re-search-forward (rx line-start "base-commit: "
                                   (group (>= 40 hex-digit))
                                   line-end)
                               nil t)
        (plist-put info :base-commit (match-string 1)))
      info)))

(defvar piem-patch-subject-re
  (rx (zero-or-more space) "["
      (zero-or-more (not (any "]" "\n")))
      "PATCH"
      (zero-or-more (not (any "]" "\n")))
      "]" (one-or-more space)))

(defun piem--shorten-subject (subject)
  (let ((words
         (mapcar #'downcase
                 (split-string
                  (thread-last subject
                    (replace-regexp-in-string
                     (rx (any "'\""))
                     "")
                    (replace-regexp-in-string
                     piem-patch-subject-re ""))
                  "\\W+" t)))
        (ignore-these (list "a" "an" "the"))
        (num-words 0)
        (num-chars 0)
        kept)
    (catch 'stop
      (dolist (word words)
        (when (not (member word ignore-these))
          (cl-incf num-words)
          (cl-incf num-chars (length word))
          (push word kept)
          (when (or (> num-words 5)
                    (> num-chars 20))
            (throw 'stop nil)))))
    (mapconcat #'identity (reverse kept) "-")))

(defun piem-name-branch-who-what-v (info)
  "Construct a branch name like \"km/b4-short-subj__v3\".

In the above example, \"k\" and \"m\" are the first letters of
the first and second \"words\" in the \"From:\" field.
\"b4-short-subj\" is a stripped down, truncated variant of
\"Subject:\".  And \"v3\" is the version of the patch series, as
indicated in the subject.

INFO is a plist with properties documented
in `piem-default-branch-function'."
  (when-let ((from (plist-get info :from))
             (sender (let ((mail-extr-ignore-single-names nil)
                           (mail-extr-ignore-realname-equals-mailbox-name nil))
                       (car (mail-extract-address-components from))))
             (subject (plist-get info :subject)))
    (let* ((subnames (split-string sender))
           (initials (mapconcat
                      (lambda (subname)
                        (and subname
                             (downcase (substring subname nil 1))))
                      (list (car subnames) (cadr subnames))
                      ""))
           (version (and (string-match
                          (rx "[" (zero-or-more (not (any "[" "\n")))
                              "PATCH "
                              (zero-or-one (group "v" (one-or-more digit))))
                          subject)
                         (match-string 1 subject))))
      (concat initials "/"
              (piem--shorten-subject subject)
              (and version (concat "__" version))))))

(defvar piem-am-args (list "--scissors" "--3way"))

(defun piem-am-read-worktree (coderepo branch)
  "Read a worktree to create for applying patches.
This function is intended to be used as a value of
`piem-am-read-worktree-function'.  The worktree directory is
completed from the parent directory of CODEREPO.  If BRANCH is
non-nil, it is used to construct the default completion value."
  (let ((fname (directory-file-name coderepo)))
    (read-directory-name
     "Create worktree: "
     (file-name-directory fname) nil nil
     (and branch
          (concat (file-name-nondirectory fname) "-"
                  (replace-regexp-in-string "/" "-" branch))))))

;;;###autoload
(defun piem-am (mbox &optional format info coderepo toggle-worktree)
  "Feed an am-ready mbox to `git am'.

MBOX is a buffer whose contents are an am-ready mbox (obtained
via `piem-am-ready-mbox' when called interactively).  FORMAT
controls the value passed as the --patch-format option of `git
am'.  \"mbox\" and \"mboxrd\" are valid values, and \"mboxrd\" is
the default.

INFO is a plist that with information to help choose a default
branch name or starting point (see `piem-default-branch-function'
for a list of possible properties).

CODEREPO, if given, indicates the code repository to operate
within.  If not specified, the default directory is used.

When prefix argument TOGGLE-WORKTREE is non-nil, invert the
meaning of `piem-am-create-worktree'.  With the default value,
this triggers the creation of a new worktree."
  (interactive
   (pcase-let ((`(,mbox . ,format)
                (or (piem-am-ready-mbox)
                    (user-error
                     "Could not find am-ready mbox for current buffer"))))
     ;; We're responsible for cleaning up the buffer created by
     ;; `piem-am-ready-mbox'; sneak in an indication to let the
     ;; downstream code know.
     (list (cons :interactive mbox)
           format
           (piem-extract-mbox-info mbox)
           (piem-inbox-coderepo-maybe-read)
           current-prefix-arg)))
  (setq format (or format "mboxrd"))
  (let* ((default-directory (or coderepo default-directory))
         (am-directory default-directory)
         (use-worktree (xor piem-am-create-worktree toggle-worktree))
         (interactivep (eq (car-safe mbox) :interactive)))
    (when interactivep
      (setq mbox (cdr mbox)))
    (let ((new-branch
           (let ((b (read-string "New branch (empty for detached): "
                                 (funcall piem-default-branch-function info))))
             (and (not (string-empty-p b)) b)))
          (base (completing-read
                 "Base commit: "
                 (let ((cands (and piem-use-magit
                                   (fboundp 'magit-list-local-branch-names)
                                   (magit-list-local-branch-names)))
                       (base (plist-get info :base-commit)))
                   (if base (cons base cands) cands)))))
      (when use-worktree
        (setq am-directory
              (expand-file-name
               (funcall piem-am-read-worktree-function
                        default-directory new-branch)))
        (when (file-exists-p am-directory)
          (user-error "Worktree directory already exists")))
      (apply #'piem-process-call nil piem-git-executable
             (append (if use-worktree
                         (list "worktree" "add")
                       (list "checkout"))
                     (if new-branch (list "-b" new-branch) (list "--detach"))
                     (and use-worktree (list am-directory))
                     (and (not (string-blank-p base))
                          (list base)))))
    (let ((args (cons (concat "--patch-format=" format)
                      piem-am-args)))
      (if (bufferp mbox)
          (unwind-protect
              (apply #'piem-process-call-with-buffer-input
                     am-directory mbox piem-git-executable "am" args)
            (when interactivep
              (kill-buffer mbox)))
        (apply #'piem-process-call am-directory piem-git-executable "am"
               (append args (list mbox)))))
    (if (and piem-use-magit
             (fboundp 'magit-status-setup-buffer))
        (magit-status-setup-buffer am-directory)
      (dired am-directory))))

\f
;;;; Dispatch

;;;###autoload (autoload 'piem-dispatch "piem" nil t)
(transient-define-prefix piem-dispatch ()
  "Invoke a piem command."
  [[("a" "apply patch" piem-am)
    ("b" "call b4-am" piem-b4-am)]
   [("i" "inject thread into maildir" piem-inject-thread-into-maildir)
    ("l" "copy public-inbox link" piem-copy-mid-url)]])

\f

(defun piem-please ()
  "How I wish I could intersect my emails, feeds, and repos")

;;; piem.el ends here
(provide 'piem)