;;; piem.el --- Emacs tools for working with public-index  -*- 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"))

;; 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 'message)
(require 'piem-maildir)
(require 'rfc2047)
(require 'subr-x)
(require 'url)

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

\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.

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

(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)

\f
;;;; Subprocess handling

(defvar piem-process-mode-font-lock-keywords
  `((,(rx line-start
          ";;; " (or "process" "directory") ":" (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 "\n%s\n;;; process: %S\n;;; directory:  %s\n"
                        (char-to-string 12) ; form feed
                        (cons program program-args)
                        default-directory))
        (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

(defvar piem-link-re
  (rx "/" (group (one-or-more (not (any "/" "\n"))))
      "/" (group (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)
  "Regular expression matching public-inbox HTTP link.
The first group is the inbox, the second is the message ID, and
the rest is any trailing endpoint.")

(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-head)
                 (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)))))))))

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

(defun piem-inbox-coderepo ()
  "Return the code repository of current buffer's inbox."
  (when-let ((p (piem-inbox))
             (repo (plist-get (cdr (assoc p piem-inboxes)) :coderepo)))
    (expand-file-name repo)))

(defun piem-inbox-url ()
  "Return the URL of current buffer's inbox."
  (when-let ((p (piem-inbox)))
    (plist-get (cdr (assoc p piem-inboxes)) :url)))

(defun piem-inbox-coderepo-maybe-read ()
  "Like `piem-inbox-coderepo', but fall back to reading the repo."
  (or (piem-inbox-coderepo)
      (and (fboundp 'projectile-relevant-known-projects)
           (completing-read
            "Project: "
            (projectile-relevant-known-projects)))
      (and piem-use-magit
           (fboundp 'magit-read-repository)
           (magit-read-repository))
      (read-directory-name "Git repository: ")))

(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
;;;; Maildir injection

(defun piem--write-mbox-to-maildir ()
  (let ((n-messages 0))
    (while (and (not (eobp))
                (search-forward "From mboxrd@z" nil t))
      (let* ((beg (line-beginning-position 2))
             (end (or (and (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)
        ;; TODO: Consider supporting a caller-specified predicate that
        ;; could be used, for example, to skip messages already in
        ;; their local mail.
        (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-messages)
        (goto-char end)))
    n-messages))

(defun piem--inject-thread-callback (status mid message-only)
  (let ((buffer (current-buffer)))
    (unwind-protect
        (let ((error-status (plist-get status :error)))
          (if error-status
              (signal (car error-status) (cdr error-status))
            (goto-char (1+ url-http-end-of-headers))
            (delete-region (point-min) (point))
            (unless message-only
              (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))
            (let ((message-count (piem--write-mbox-to-maildir)))
              (message "%d message(s) for %s moved to %s"
                       message-count mid piem-maildir-directory))
            (run-hook-with-args 'piem-after-mail-injection-functions mid)))
      (and (buffer-live-p buffer)
           (kill-buffer buffer)))))

(defvar piem--has-gunzip)

;;;###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))
  (unless (or message-only (boundp 'piem--has-gunzip))
    (setq piem--has-gunzip (executable-find "gunzip")))
  (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--has-gunzip))
    (user-error "gunzip executable not found")))
  (url-retrieve (concat (or (piem-inbox-url)
                            (user-error
                             "Could not find inbox URL for current buffer"))
                        mid
                        (if message-only "/raw" "/t.mbox.gz"))
                #'piem--inject-thread-callback
                (list mid message-only)))

\f
;;;; Patch handling

(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 (save-excursion
                  (save-restriction
                    (message-narrow-to-head)
                    (list :date (message-fetch-field "date")
                          :from (when-let ((from (message-fetch-field "from")))
                                  (rfc2047-decode-string from))
                          :subject (message-fetch-field "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 (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"))

;;;###autoload
(defun piem-am (mbox &optional format info coderepo)
  "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).

If CODEREPO is given, switch to this directory before calling
`git am'."
  (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))))
  (setq format (or format "mboxrd"))
  (let ((default-directory (or coderepo default-directory))
        (interactivep (eq (car-safe mbox) :interactive)))
    (when interactivep
      (setq mbox (cdr mbox)))
    (let ((new-branch (read-string
                       "New branch (empty for detached): "
                       (funcall piem-default-branch-function info)))
          (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)))))
      (apply #'piem-process-call nil piem-git-executable "checkout"
             (append (if (string-empty-p new-branch)
                         (list "--detach")
                       (list "-b" new-branch))
                     (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
                     nil mbox piem-git-executable "am" args)
            (when interactivep
              (kill-buffer mbox)))
        (apply #'piem-process-call nil piem-git-executable "am"
               (append args (list mbox)))))
    (if (and piem-use-magit
             (fboundp 'magit-status-setup-buffer))
        (magit-status-setup-buffer)
      (dired "."))))

\f

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

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