;;; mu4e-headers.el -- part of mu4e, the mu mail user agent -*- lexical-binding: t -*-

;; Copyright (C) 2011-2020 Dirk-Jan C. Binnema

;; Author: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
;; Maintainer: Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>

;; This file is not part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; In this file are function related mu4e-headers-mode, to creating the list of
;; one-line descriptions of emails, aka 'headers' (not to be confused with
;; headers like 'To:' or 'Subject:')

;;; Code:

(require 'cl-lib)
(require 'fringe)
(require 'hl-line)

(require 'mule-util) ;; seems _some_ people need this for truncate-string-ellipsis

(require 'mu4e-utils)    ;; utility functions
(require 'mu4e-proc)
(require 'mu4e-vars)
(require 'mu4e-mark)
(require 'mu4e-compose)
(require 'mu4e-actions)
(require 'mu4e-message)

(eval-when-compile (require 'mu4e-view))

(declare-function mu4e-view       "mu4e-view")
(declare-function mu4e~main-view  "mu4e-main")

;;; Options

(defgroup mu4e-headers nil
  "Settings for the headers view."
  :group 'mu4e)

(defcustom mu4e-headers-fields
  '( (:human-date    .   12)
     (:flags         .    6)
     (:mailing-list  .   10)
     (:from          .   22)
     (:subject       .   nil))
  "A list of header fields to show in the headers buffer.
Each element has the form (HEADER . WIDTH), where HEADER is one of
the available headers (see `mu4e-header-info') and WIDTH is the
respective width in characters.  A width of `nil' means
'unrestricted', and this is best reserved for the rightmost (last)
field. Note that emacs may become very slow with excessively long
lines (1000s of characters), so if you regularly get such messages,
you want to avoid fields with `nil' altogether."
  :type `(repeat (cons (choice ,@(mapcar (lambda (h)
                                           (list 'const :tag
                                                 (plist-get (cdr h) :help)
                                                 (car h)))
                                         mu4e-header-info))
                       (choice (integer :tag "width")
                               (const :tag "unrestricted width" nil))))
  :group 'mu4e-headers)

(defcustom mu4e-headers-date-format "%x"
  "Date format to use in the headers view.
In the format of `format-time-string'."
  :type  'string
  :group 'mu4e-headers)

(defcustom mu4e-headers-time-format "%X"
  "Time format to use in the headers view.
In the format of `format-time-string'."
  :type  'string
  :group 'mu4e-headers)

(defcustom mu4e-headers-long-date-format "%c"
  "Date format to use in the headers view tooltip.
In the format of `format-time-string'."
  :type  'string
  :group 'mu4e-headers)

(defcustom mu4e-headers-visible-lines 10
  "Number of lines to display in the header view when using the
horizontal split-view. This includes the header-line at the top,
and the mode-line."
  :type 'integer
  :group 'mu4e-headers)

(defcustom mu4e-headers-visible-columns 30
  "Number of columns to display for the header view when using the
vertical split-view."
  :type 'integer
  :group 'mu4e-headers)

(defcustom mu4e-headers-auto-update t
  "Whether to automatically update the current headers buffer if an
indexing operation showed changes."
  :type 'boolean
  :group 'mu4e-headers)

(defcustom mu4e-headers-results-limit 500
  "Maximum number of results to show; this affects performance
quite a bit, especially when `mu4e-headers-include-related' is
non-nil. Set to -1 for no limits, and you temporarily (for one
query) ignore the limit by pressing a C-u before invoking the
search.

Note that there are a few complications when
`mu4e-headers-include-related' is enabled: mu perform *two*
queries; the first one with this limit set, and then a second
(unlimited) query for all messages that are related to the first
matches. We then limit this second result as well, favoring the
messages that were found in the first set (the \"leaders\").
"
  :type '(choice (const :tag "Unlimited" -1)
                 (integer :tag "Limit"))
  :group 'mu4e-headers)

(make-obsolete-variable 'mu4e-search-results-limit
                        'mu4e-headers-results-limit "0.9.9.5-dev6")

(defcustom mu4e-headers-advance-after-mark t
  "With this option set to non-nil, automatically advance to the
next mail after marking a message in header view."
  :type 'boolean
  :group 'mu4e-headers)


(defvar mu4e-headers-hide-predicate nil
  "Predicate function applied to headers before they are shown;
if function is nil or evaluates to nil, show the header,
otherwise don't. function takes one parameter MSG, which is the
message plist for the message to be hidden or not.

Example that hides all 'trashed' messages:
  (setq mu4e-headers-hide-predicate
     (lambda (msg)
       (member 'trashed (mu4e-message-field msg :flags))))

Note that this is merely a display filter.")

(defcustom mu4e-headers-visible-flags
  '(draft flagged new passed replied seen trashed attach encrypted signed unread)
  "An ordered list of flags to show in the headers buffer. Each
element is a symbol in the list (DRAFT FLAGGED NEW PASSED
REPLIED SEEN TRASHED ATTACH ENCRYPTED SIGNED UNREAD)."
  :type '(set
          (const :tag "Draft" draft)
          (const :tag "Flagged" flagged)
          (const :tag "New" new)
          (const :tag "Passed" passed)
          (const :tag "Replied" replied)
          (const :tag "Seen" seen)
          (const :tag "Trashed" trashed)
          (const :tag "Attach" attach)
          (const :tag "Encrypted" encrypted)
          (const :tag "Signed" signed)
          (const :tag "Unread" unread))
  :group 'mu4e-headers)

(defcustom mu4e-headers-found-hook nil
  "Hook run just *after* all of the headers for the last search
query have been received and are displayed."
  :type 'hook
  :group 'mu4e-headers)

(defcustom mu4e-headers-search-bookmark-hook nil
  "Hook run just after we invoke a bookmarked search. This
function receives the query as its parameter, before any
rewriting as per `mu4e-query-rewrite-function' has taken place.

The reason to use this instead of `mu4e-headers-search-hook' is
if you only want to execute a hook when a search is entered via a
bookmark, e.g. if you'd like to treat the bookmarks as a custom
folder and change the options for the search, e.g.
`mu4e-headers-show-threads', `mu4e-headers-include-related',
`mu4e-headers-skip-duplicates` or `mu4e-headers-results-limit'.
"
  :type 'hook
  :group 'mu4e-headers)

(defcustom mu4e-headers-search-hook nil
  "Hook run just before executing a new search operation. This
function receives the query as its parameter, before any
rewriting as per `mu4e-query-rewrite-function' has taken place

This is a more general hook facility than the
`mu4e-headers-search-bookmark-hook'. It gets called on every
executed search, not just those that are invoked via bookmarks,
but also manually invoked searches."
  :type 'hook
  :group 'mu4e-headers)

;;; Public variables

(defvar mu4e-headers-sort-field :date
  "Field to sort the headers by. Must be a symbol,
one of: `:date', `:subject', `:size', `:prio', `:from', `:to.',
`:list'")

(defvar mu4e-headers-sort-direction 'descending
  "Direction to sort by; a symbol either `descending' (sorting
  Z->A) or `ascending' (sorting A->Z).")

;;;; Fancy marks

;; marks for headers of the form; each is a cons-cell (basic . fancy)
;; each of which is basic ascii char and something fancy, respectively
(defvar mu4e-headers-draft-mark     '("D" . "⚒") "Draft.")
(defvar mu4e-headers-flagged-mark   '("F" . "✚") "Flagged.")
(defvar mu4e-headers-new-mark       '("N" . "✱") "New.")
(defvar mu4e-headers-passed-mark    '("P" . "❯") "Passed (fwd).")
(defvar mu4e-headers-replied-mark   '("R" . "❮") "Replied.")
(defvar mu4e-headers-seen-mark      '("S" . "✔") "Seen.")
(defvar mu4e-headers-trashed-mark   '("T" . "⏚") "Trashed.")
(defvar mu4e-headers-attach-mark    '("a" . "⚓") "W/ attachments.")
(defvar mu4e-headers-encrypted-mark '("x" . "⚴") "Encrypted.")
(defvar mu4e-headers-signed-mark    '("s" . "☡") "Signed.")
(defvar mu4e-headers-unread-mark    '("u" . "⎕") "Unread.")

;;;; Graph drawing

(defvar mu4e-headers-thread-child-prefix '("├>" . "┣▶ ")
  "Prefix for messages in sub threads that do have a following sibling.")

(defvar mu4e-headers-thread-last-child-prefix '("└>" . "┗▶ ")
  "Prefix for messages in sub threads that do not have a following sibling.")

(defvar mu4e-headers-thread-connection-prefix '("│" . "┃ ")
  "Prefix to connect sibling messages that do not follow each other.

This prefix should have the same length as `mu4e-headers-thread-blank-prefix'.")

(defvar mu4e-headers-thread-blank-prefix '(" " . "  ")
  "Prefix to separate non connected messages.

This prefix should have the same length as `mu4e-headers-thread-connection-prefix'.")

(defvar mu4e-headers-thread-orphan-prefix '("┬>" . "┳▶ ")
  "Prefix for orphan messages with siblings.")

(defvar mu4e-headers-thread-single-orphan-prefix '("─>" . "━▶ ")
  "Prefix for orphan messages with no siblings.")

(defvar mu4e-headers-thread-duplicate-prefix '("=" . "≡ ")
  "Prefix for duplicate messages.")

;;;; Various

(defvar mu4e-headers-actions
  '( ("capture message"  . mu4e-action-capture-message)
     ("show this thread" . mu4e-action-show-thread))
  "List of actions to perform on messages in the headers list.
The actions are cons-cells of the form (NAME . FUNC) where:
* NAME is the name of the action (e.g. \"Count lines\")
* FUNC is a function which receives a message plist as an argument.

The first character of NAME is used as the shortcut.")

(defvar mu4e-headers-custom-markers
  '(("Older than"
     (lambda (msg date) (time-less-p (mu4e-msg-field msg :date) date))
     (lambda () (mu4e-get-time-date "Match messages before: ")))
    ("Newer than"
     (lambda (msg date) (time-less-p date (mu4e-msg-field msg :date)))
     (lambda () (mu4e-get-time-date "Match messages after: ")))
    ("Bigger than"
     (lambda (msg bytes) (> (mu4e-msg-field msg :size) (* 1024 bytes)))
     (lambda () (read-number "Match messages bigger than (Kbytes): "))))
  "List of custom markers -- functions to mark message that match
some custom function. Each of the list members has the following format:
  (NAME PREDICATE-FUNC PARAM-FUNC)
* NAME is the name of the predicate function, and the first character
is the shortcut (so keep those unique).
* PREDICATE-FUNC is a function that takes two parameters, MSG
and (optionally) PARAM, and should return non-nil when there's a
match.
* PARAM-FUNC is function that is evaluated once, and its value is then passed to
PREDICATE-FUNC as PARAM. This is useful for getting user-input.")

(defvar mu4e-headers-show-threads t
  "Whether to show threads in the headers list.")

(defvar mu4e-headers-full-search nil
  "Whether to show all results.
If this is nil show results up to `mu4e-headers-results-limit')")

;;; Internal variables/constants

;; docid cookies
(defconst mu4e~headers-docid-pre "\376"
  "Each header starts (invisibly) with the `mu4e~headers-docid-pre',
followed by the docid, followed by `mu4e~headers-docid-post'.")
(defconst mu4e~headers-docid-post "\377"
  "Each header starts (invisibly) with the `mu4e~headers-docid-pre',
followed by the docid, followed by `mu4e~headers-docid-post'.")

(defvar mu4e~headers-view-win nil
  "The view window connected to this headers view.")

(defvar mu4e~headers-sort-field-choices
  '( ("date"    . :date)
     ("from"    . :from)
     ("list"    . :list)
     ("maildir" . :maildir)
     ("prio"    . :prio)
     ("zsize"   . :size)
     ("subject" . :subject)
     ("to"      . :to))
  "List of cells describing the various sort-options.
In the format needed for `mu4e-read-option'.")

;;; Clear

(defun mu4e~headers-clear (&optional msg)
  "Clear the header buffer and related data structures."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (let ((inhibit-read-only t))
      (with-current-buffer (mu4e-get-headers-buffer)
        (mu4e~mark-clear)
        (erase-buffer)
        (when msg
          (goto-char (point-min))
          (insert (propertize msg 'face 'mu4e-system-face 'intangible t)))))))

;;; Handler functions

;; next are a bunch of handler functions; those will be called from mu4e~proc in
;; response to output from the server process

(defun mu4e~headers-view-handler (msg)
  "Handler function for displaying a message."
  (mu4e-view msg))

(defun mu4e~headers-view-this-message-p (docid)
  "Is DOCID currently being viewed?"
  (when (buffer-live-p (mu4e-get-view-buffer))
    (with-current-buffer (mu4e-get-view-buffer)
      (eq docid (plist-get mu4e~view-message :docid)))))

(defun mu4e~headers-update-handler (msg is-move maybe-view)
  "Update handler, will be called when a message has been updated
in the database. This function will update the current list of
headers."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (with-current-buffer (mu4e-get-headers-buffer)
      (let* ((docid (mu4e-message-field msg :docid))
             (initial-message-at-point (mu4e~headers-docid-at-point))
             (initial-column (current-column))
             (point (mu4e~headers-docid-pos docid)))

        (when point ;; is the message present in this list?

          ;; if it's marked, unmark it now
          (when (mu4e-mark-docid-marked-p docid)
            (mu4e-mark-set 'unmark))

          ;; re-use the thread info from the old one; this is needed because
          ;; *update* messages don't have thread info by themselves (unlike
          ;; search results)
          ;; since we still have the search results, re-use
          ;; those
          (plist-put msg :thread
                     (mu4e~headers-field-for-docid docid :thread))

          ;; first, remove the old one (otherwise, we'd have two headers with
          ;; the same docid...
          (mu4e~headers-remove-header docid t)

          ;; if we're actually viewing this message (in mu4e-view mode), we
          ;; update it; that way, the flags can be updated, as well as the path
          ;; (which is useful for viewing the raw message)
          (when (and maybe-view (mu4e~headers-view-this-message-p docid))
            (mu4e-view msg))
          ;; now, if this update was about *moving* a message, we don't show it
          ;; anymore (of course, we cannot be sure if the message really no
          ;; longer matches the query, but this seem a good heuristic.  if it
          ;; was only a flag-change, show the message with its updated flags.
          (unless is-move
            (mu4e~headers-header-handler msg point))

          (if (and initial-message-at-point
                   (mu4e~headers-goto-docid initial-message-at-point))
              (progn
                (move-to-column initial-column)
                (mu4e~headers-highlight initial-message-at-point))
            ;; attempt to highlight the corresponding line and make it visible
            (mu4e~headers-highlight docid))
          (run-hooks 'mu4e-message-changed-hook))))))

(defun mu4e~headers-remove-handler (docid &optional skip-hook)
  "Remove handler, will be called when a message with DOCID has
been removed from the database. This function will hide the removed
message from the current list of headers. If the message is not
present, don't do anything.

If SKIP-HOOK is absent or nil, `mu4e-message-changed-hook' will be invoked."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (mu4e~headers-remove-header docid t))
  ;; if we were viewing this message, close it now.
  (when (and (mu4e~headers-view-this-message-p docid)
             (buffer-live-p (mu4e-get-view-buffer)))
    (unless (eq mu4e-split-view 'single-window)
      (mapc #'delete-window (get-buffer-window-list
                             (mu4e-get-view-buffer) nil t)))
    (kill-buffer (mu4e-get-view-buffer)))
  (unless skip-hook
    (run-hooks 'mu4e-message-changed-hook)))


;;; Misc

(defun mu4e~headers-contact-str (contacts)
  "Turn the list of contacts CONTACTS (with elements (NAME . EMAIL)
into a string."
  (mapconcat
   (lambda (ct)
     (let ((name (car ct)) (email (cdr ct)))
       (or name email "?"))) contacts ", "))

(defun mu4e~headers-thread-prefix-map (type)
  "Return the thread prefix based on the symbol TYPE."
  (let ((get-prefix
         (lambda (cell)
           (if mu4e-use-fancy-chars (cdr cell) (car cell)))))
    (cl-case type
      ('child         (funcall get-prefix mu4e-headers-thread-child-prefix))
      ('last-child    (funcall get-prefix mu4e-headers-thread-last-child-prefix))
      ('connection    (funcall get-prefix mu4e-headers-thread-connection-prefix))
      ('blank         (funcall get-prefix mu4e-headers-thread-blank-prefix))
      ('orphan        (funcall get-prefix mu4e-headers-thread-orphan-prefix))
      ('single-orphan (funcall get-prefix mu4e-headers-thread-single-orphan-prefix))
      ('duplicate     (funcall get-prefix mu4e-headers-thread-duplicate-prefix))
      (t              "?"))))

;; headers in the buffer are prefixed by an invisible string with the docid
;; followed by an EOT ('end-of-transmission', \004, ^D) non-printable ascii
;; character. this string also has a text-property with the docid. the former
;; is used for quickly finding a certain header, the latter for retrieving the
;; docid at point without string matching etc.

(defun mu4e~headers-docid-pos (docid)
  "Return the pos of the beginning of the line with the header with
docid DOCID, or nil if it cannot be found."
  (let ((pos))
    (save-excursion
      (setq pos (mu4e~headers-goto-docid docid)))
    pos))

(defun mu4e~headers-docid-cookie (docid)
  "Create an invisible string containing DOCID; this is to be used
at the beginning of lines to identify headers."
  (propertize (format "%s%d%s"
                      mu4e~headers-docid-pre docid mu4e~headers-docid-post)
              'docid docid 'invisible t));;

(defun mu4e~headers-docid-at-point (&optional point)
  "Get the docid for the header at POINT, or at current (point) if
nil. Returns the docid, or nil if there is none."
  (save-excursion
    (when point
      (goto-char point))
    (get-text-property (line-beginning-position) 'docid)))


(defun mu4e~headers-goto-docid (docid &optional to-mark)
  "Go to the beginning of the line with the header with docid
DOCID, or nil if it cannot be found. If the optional TO-MARK is
non-nil, go to the point directly *after* the docid-cookie instead
of the beginning of the line."
  (let ((oldpoint (point)) (newpoint))
    (goto-char (point-min))
    (setq newpoint
          (search-forward (mu4e~headers-docid-cookie docid) nil t))
    (unless to-mark
      (if (null newpoint)
          (goto-char oldpoint) ;; not found; restore old pos
        (progn
          (beginning-of-line) ;; found, move to beginning of line
          (setq newpoint (point)))))
    newpoint)) ;; return the point, or nil if not found

(defun mu4e~headers-field-for-docid (docid field)
  "Get FIELD (a symbol, see `mu4e-headers-names') for the message
with DOCID which must be present in the headers buffer."
  (save-excursion
    (when (mu4e~headers-goto-docid docid)
      (mu4e-message-field (mu4e-message-at-point) field))))


;; In order to print a thread tree with all the message connections,
;; it's necessary to keep track of all sub levels that still have
;; following messages. For each level, mu4e~headers-thread-state keeps
;; the value t for a connection or nil otherwise.
(defvar-local mu4e~headers-thread-state '())

(defun mu4e~headers-thread-prefix (thread)
  "Calculate the thread prefix based on thread info THREAD."
  (when thread
    (let ((prefix       "")
          (level        (plist-get thread :level))
          (has-child    (plist-get thread :has-child))
          (empty-parent (plist-get thread :empty-parent))
          (first-child  (plist-get thread :first-child))
          (last-child   (plist-get thread :last-child))
          (duplicate    (plist-get thread :duplicate)))
      ;; Do not prefix root messages.
      (if (= level 0)
          (setq mu4e~headers-thread-state '()))
      (if (> level 0)
          (let* ((length (length mu4e~headers-thread-state))
                 (padding (make-list (max 0 (- level length)) nil)))
            ;; Trim and pad the state to ensure a message will
            ;; always be shown with the correct indentation, even if
            ;; a broken thread is returned. It's trimmed to level-1
            ;; because the current level has always an connection
            ;; and it used a special formatting.
            (setq mu4e~headers-thread-state
                  (cl-subseq (append mu4e~headers-thread-state padding)
                             0 (- level 1)))
            ;; Prepare the thread prefix.
            (setq prefix
                  (concat
                   ;; Current mu4e~headers-thread-state, composed by
                   ;; connections or blanks.
                   (mapconcat
                    (lambda (s)
                      (mu4e~headers-thread-prefix-map
                       (if s 'connection 'blank)))
                    mu4e~headers-thread-state "")
                   ;; Current entry.
                   (mu4e~headers-thread-prefix-map
                    (if (and empty-parent first-child)
                        (if last-child 'single-orphan 'orphan)
                      (if last-child 'last-child 'child)))))))
      ;; If a new sub-thread will follow (has-child) and the current
      ;; one is still not done (not last-child), then a new
      ;; connection needs to be added to the tree-state.  It's not
      ;; necessary to a blank (nil), because padding will handle
      ;; that.
      (if (and has-child (not last-child))
          (setq mu4e~headers-thread-state
                (append mu4e~headers-thread-state '(t))))
      ;; Return the thread prefix.
      (format "%s%s"
              prefix
              (if duplicate
                  (mu4e~headers-thread-prefix-map 'duplicate) "")))))

(defun mu4e~headers-flags-str (flags)
  "Get a display string for the flags.
Note that `mu4e-flags-to-string' is for internal use only; this
function is for display. (This difference is significant, since
internally, the Maildir spec determines what the flags look like,
while our display may be different)."
  (let ((str "")
        (get-prefix
         (lambda (cell)  (if mu4e-use-fancy-chars (cdr cell) (car cell)))))
    (dolist (flag mu4e-headers-visible-flags)
      (when (member flag flags)
        (setq str
              (concat str
                      (cl-case flag
                        ('draft     (funcall get-prefix mu4e-headers-draft-mark))
                        ('flagged   (funcall get-prefix mu4e-headers-flagged-mark))
                        ('new       (funcall get-prefix mu4e-headers-new-mark))
                        ('passed    (funcall get-prefix mu4e-headers-passed-mark))
                        ('replied   (funcall get-prefix mu4e-headers-replied-mark))
                        ('seen      (funcall get-prefix mu4e-headers-seen-mark))
                        ('trashed   (funcall get-prefix mu4e-headers-trashed-mark))
                        ('attach    (funcall get-prefix mu4e-headers-attach-mark))
                        ('encrypted (funcall get-prefix mu4e-headers-encrypted-mark))
                        ('signed    (funcall get-prefix mu4e-headers-signed-mark))
                        ('unread    (funcall get-prefix mu4e-headers-unread-mark)))))))
    str))

;;; Special headers

(defconst mu4e-headers-from-or-to-prefix '("" . "To ")
  "Prefix for the :from-or-to field.
It's a cons cell with the car element being the From: prefix, the
cdr element the To: prefix.")

(defun mu4e~headers-from-or-to (msg)
  "When the from address for message MSG is one of the the user's addresses,
\(as per `mu4e-personal-addresses'), show the To address;
otherwise ; show the from address; prefixed with the appropriate
`mu4e-headers-from-or-to-prefix'."
  (let ((addr (cdr-safe (car-safe (mu4e-message-field msg :from)))))
    (if (mu4e-user-mail-address-p addr)
        (concat (cdr mu4e-headers-from-or-to-prefix)
                (mu4e~headers-contact-str (mu4e-message-field msg :to)))
      (concat (car mu4e-headers-from-or-to-prefix)
              (mu4e~headers-contact-str (mu4e-message-field msg :from))))))

(defun mu4e~headers-human-date (msg)
  "Show a 'human' date.
If the date is today, show the time, otherwise, show the
date. The formats used for date and time are
`mu4e-headers-date-format' and `mu4e-headers-time-format'."
  (let ((date (mu4e-msg-field msg :date)))
    (if (equal date '(0 0 0))
        "None"
      (let ((day1 (decode-time date))
            (day2 (decode-time (current-time))))
        (if (and
             (eq (nth 3 day1) (nth 3 day2))     ;; day
             (eq (nth 4 day1) (nth 4 day2))     ;; month
             (eq (nth 5 day1) (nth 5 day2)))    ;; year
            (format-time-string mu4e-headers-time-format date)
          (format-time-string mu4e-headers-date-format date))))))

(defun mu4e~headers-thread-subject (msg)
  "Get the subject if it is the first one in a thread; otherwise,
return the thread-prefix without the subject-text. In other words,
show the subject of a thread only once, similar to e.g. 'mutt'."
  (let* ((tinfo  (mu4e-message-field msg :thread))
         (subj (mu4e-msg-field msg :subject)))
    (concat ;; prefix subject with a thread indicator
     (mu4e~headers-thread-prefix tinfo)
     (if (or (not tinfo) (zerop (plist-get tinfo :level))
             (plist-get tinfo :empty-parent))
         (truncate-string-to-width subj 600) ""))))

(defun mu4e~headers-mailing-list (list)
  "Get some identifier for the mailing list."
  (if list
      (propertize (mu4e-get-mailing-list-shortname list) 'help-echo list)
    ""))

(defun mu4e~headers-custom-field (msg field)
  "Show some custom header field, or raise an error if it is not
found."
  (let* ((item (or (assoc field mu4e-header-info-custom)
                   (mu4e-error "field %S not found" field)))
         (func (or (plist-get (cdr-safe item) :function)
                   (mu4e-error "no :function defined for field %S %S"
                               field (cdr item)))))
    (funcall func msg)))

(defun mu4e~headers-field-apply-basic-properties (msg field val _width)
  (cl-case field
    (:subject
     (concat ;; prefix subject with a thread indicator
      (mu4e~headers-thread-prefix (mu4e-message-field msg :thread))
      ;;  "["(plist-get (mu4e-message-field msg :thread) :path) "] "
      ;; work-around: emacs' display gets really slow when lines are too long;
      ;; so limit subject length to 600
      (truncate-string-to-width val 600)))
    (:thread-subject (mu4e~headers-thread-subject msg))
    ((:maildir :path :message-id) val)
    ((:to :from :cc :bcc) (mu4e~headers-contact-str val))
    ;; if we (ie. `user-mail-address' is the 'From', show
    ;; 'To', otherwise show From
    (:from-or-to (mu4e~headers-from-or-to msg))
    (:date (format-time-string mu4e-headers-date-format val))
    (:mailing-list (mu4e~headers-mailing-list val))
    (:human-date (propertize (mu4e~headers-human-date msg)
                             'help-echo (format-time-string
                                         mu4e-headers-long-date-format
                                         (mu4e-msg-field msg :date))))
    (:flags (propertize (mu4e~headers-flags-str val)
                        'help-echo (format "%S" val)))
    (:tags (propertize (mapconcat 'identity val ", ")))
    (:size (mu4e-display-size val))
    (t (mu4e~headers-custom-field msg field))))

(defun mu4e~headers-field-truncate-to-width (_msg _field val width)
  "Truncate VAL to WIDTH."
  (if width
      (truncate-string-to-width val width 0 ?\s truncate-string-ellipsis)
    val))

(defvar mu4e~headers-field-handler-functions
  '(mu4e~headers-field-apply-basic-properties
    mu4e~headers-field-truncate-to-width))

(defun mu4e~headers-field-handler (f-w msg)
  "Create a description of the field of MSG described by F-W."
  (let* ((field (car f-w))
         (width (cdr f-w))
         (val (mu4e-message-field msg (car f-w))))
    (dolist (func mu4e~headers-field-handler-functions)
      (setq val (funcall func msg field val width)))
    val))

(defvar mu4e~headers-line-handler-functions
  '(mu4e~headers-line-apply-flag-face))

(defun mu4e~headers-line-apply-flag-face (msg line)
  "Adjust LINE's face property based on FLAGS."
  (let* ((flags (mu4e-message-field msg :flags))
         (face (cond
                ((memq 'trashed flags) 'mu4e-trashed-face)
                ((memq 'draft flags)   'mu4e-draft-face)
                ((or (memq 'unread flags) (memq 'new flags))
                 'mu4e-unread-face)
                ((memq 'flagged flags) 'mu4e-flagged-face)
                ((memq 'replied flags) 'mu4e-replied-face)
                ((memq 'passed flags)  'mu4e-forwarded-face)
                (t                     'mu4e-header-face))))
    ;; hmmm, this only works with emacs 24.4+
    (when (fboundp 'add-face-text-property)
      (add-face-text-property 0 (length line) face t line))
    line))

(defun mu4e~headers-line-handler (msg line)
  (dolist (func mu4e~headers-line-handler-functions)
    (setq line (funcall func msg line)))
  line)

;; note: this function is very performance-sensitive
(defun mu4e~headers-header-handler (msg &optional point)
  "Create a one line description of MSG in this buffer, at POINT,
if provided, or at the end of the buffer otherwise."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (with-current-buffer (mu4e-get-headers-buffer)
      (let ((line (mu4e~message-header-description msg)))
        (when line
          (mu4e~headers-add-header line (mu4e-message-field msg :docid)
                                   point msg))))))

(defun mu4e~message-header-description (msg)
  "Return a propertized description of MSG suitable for
displaying in the header view."
  (unless (and mu4e-headers-hide-predicate
               (funcall mu4e-headers-hide-predicate msg))
    (let ((line (mapconcat
                 (lambda (f-w) (mu4e~headers-field-handler f-w msg))
                 mu4e-headers-fields " ")))
      (mu4e~headers-line-handler msg line))))

(defconst mu4e~searching      "Searching...")
(defconst mu4e~no-matches     "No matching messages found")
(defconst mu4e~end-of-results "End of search results")

(defvar mu4e~headers-view-target nil
  "Whether to automatically view (open) the target message (as
  per `mu4e~headers-msgid-target').")

(defvar mu4e~headers-msgid-target nil
  "Message-id to jump to after the search has finished.")


(defun mu4e~headers-found-handler (count)
  "Create a one line description of the number of headers found
after the end of the search results."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (with-current-buffer (mu4e-get-headers-buffer)
      (save-excursion
        (goto-char (point-max))
        (let ((inhibit-read-only t)
              (str (if (zerop count) mu4e~no-matches mu4e~end-of-results)))
          (insert (propertize str 'face 'mu4e-system-face 'intangible t))
          (unless (zerop count)
            (mu4e-message "Found %d matching message%s"
                          count (if (= 1 count) "" "s")))))
      ;; if we need to jump to some specific message, do so now
      (goto-char (point-min))
      (when mu4e~headers-msgid-target
        (if (eq (current-buffer) (window-buffer))
            (mu4e-headers-goto-message-id mu4e~headers-msgid-target)
          (let* ((pos (mu4e-headers-goto-message-id mu4e~headers-msgid-target)))
            (when pos
              (set-window-point (get-buffer-window) pos)))))
      (when (and mu4e~headers-view-target (mu4e-message-at-point 'noerror))
        ;; view the message at point when there is one.
        (mu4e-headers-view-message))
      (setq mu4e~headers-view-target nil
            mu4e~headers-msgid-target nil)
      (when (mu4e~headers-docid-at-point)
        (mu4e~headers-highlight (mu4e~headers-docid-at-point))))

    ;; run-hooks
    (run-hooks 'mu4e-headers-found-hook)))


;;; Marking

(defmacro mu4e~headers-defun-mark-for (mark)
  "Define a function mu4e~headers-mark-MARK."
  (let ((funcname (intern (format "mu4e-headers-mark-for-%s" mark)))
        (docstring (format "Mark header at point with %s." mark)))
    `(progn
       (defun ,funcname () ,docstring
              (interactive)
              (mu4e-headers-mark-and-next ',mark))
       (put ',funcname 'definition-name ',mark))))

(mu4e~headers-defun-mark-for refile)
(mu4e~headers-defun-mark-for something)
(mu4e~headers-defun-mark-for delete)
(mu4e~headers-defun-mark-for trash)
(mu4e~headers-defun-mark-for flag)
(mu4e~headers-defun-mark-for move)
(mu4e~headers-defun-mark-for read)
(mu4e~headers-defun-mark-for unflag)
(mu4e~headers-defun-mark-for untrash)
(mu4e~headers-defun-mark-for unmark)
(mu4e~headers-defun-mark-for unread)
(mu4e~headers-defun-mark-for action)

;;; Headers-mode and mode-map

(defvar mu4e-headers-mode-map nil
  "Keymap for *mu4e-headers* buffers.")
(unless mu4e-headers-mode-map
  (setq mu4e-headers-mode-map
        (let ((map (make-sparse-keymap)))

          (define-key map  (kbd "C-S-u")   'mu4e-update-mail-and-index)
          ;; for terminal users
          (define-key map  (kbd "C-c C-u") 'mu4e-update-mail-and-index)

          (define-key map "s" 'mu4e-headers-search)
          (define-key map "S" 'mu4e-headers-search-edit)

          (define-key map "/" 'mu4e-headers-search-narrow)

          (define-key map "j" 'mu4e~headers-jump-to-maildir)

          (define-key map (kbd "<M-left>")  'mu4e-headers-query-prev)
          (define-key map (kbd "\\")        'mu4e-headers-query-prev)
          (define-key map (kbd "<M-right>") 'mu4e-headers-query-next)

          (define-key map "b" 'mu4e-headers-search-bookmark)
          (define-key map "B" 'mu4e-headers-search-bookmark-edit)

          (define-key map "O" 'mu4e-headers-change-sorting)
          (define-key map "P" 'mu4e-headers-toggle-threading)
          (define-key map "Q" 'mu4e-headers-toggle-full-search)
          (define-key map "W" 'mu4e-headers-toggle-include-related)
          (define-key map "V" 'mu4e-headers-toggle-skip-duplicates)

          (define-key map "q" 'mu4e~headers-quit-buffer)
          (define-key map "g" 'mu4e-headers-rerun-search) ;; for compatibility

          (define-key map "%" 'mu4e-headers-mark-pattern)
          (define-key map "t" 'mu4e-headers-mark-subthread)
          (define-key map "T" 'mu4e-headers-mark-thread)

          ;; navigation between messages
          (define-key map "p" 'mu4e-headers-prev)
          (define-key map "n" 'mu4e-headers-next)
          (define-key map (kbd "<M-up>") 'mu4e-headers-prev)
          (define-key map (kbd "<M-down>") 'mu4e-headers-next)

          (define-key map (kbd "[") 'mu4e-headers-prev-unread)
          (define-key map (kbd "]") 'mu4e-headers-next-unread)

          ;; change the number of headers
          (define-key map (kbd "C-+") 'mu4e-headers-split-view-grow)
          (define-key map (kbd "C--") 'mu4e-headers-split-view-shrink)
          (define-key map (kbd "<C-kp-add>") 'mu4e-headers-split-view-grow)
          (define-key map (kbd "<C-kp-subtract>") 'mu4e-headers-split-view-shrink)

          (define-key map ";" 'mu4e-context-switch)

          ;; switching to view mode (if it's visible)
          (define-key map "y" 'mu4e-select-other-view)

          ;; marking/unmarking ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
          (define-key map (kbd "<backspace>")  'mu4e-headers-mark-for-trash)
          (define-key map (kbd "d")            'mu4e-headers-mark-for-trash)
          (define-key map (kbd "<delete>")     'mu4e-headers-mark-for-delete)
          (define-key map (kbd "<deletechar>") 'mu4e-headers-mark-for-delete)
          (define-key map (kbd "D")            'mu4e-headers-mark-for-delete)
          (define-key map (kbd "m")            'mu4e-headers-mark-for-move)
          (define-key map (kbd "r")            'mu4e-headers-mark-for-refile)

          (define-key map (kbd "?")            'mu4e-headers-mark-for-unread)
          (define-key map (kbd "!")            'mu4e-headers-mark-for-read)
          (define-key map (kbd "A")            'mu4e-headers-mark-for-action)

          (define-key map (kbd "u")            'mu4e-headers-mark-for-unmark)
          (define-key map (kbd "+")            'mu4e-headers-mark-for-flag)
          (define-key map (kbd "-")            'mu4e-headers-mark-for-unflag)
          (define-key map (kbd "=")            'mu4e-headers-mark-for-untrash)
          (define-key map (kbd "&")            'mu4e-headers-mark-custom)

          (define-key map (kbd "*")              'mu4e-headers-mark-for-something)
          (define-key map (kbd "<kp-multiply>")  'mu4e-headers-mark-for-something)
          (define-key map (kbd "<insertchar>")   'mu4e-headers-mark-for-something)
          (define-key map (kbd "<insert>")       'mu4e-headers-mark-for-something)

          (define-key map (kbd "#")   'mu4e-mark-resolve-deferred-marks)

          (define-key map "U" 'mu4e-mark-unmark-all)
          (define-key map "x" 'mu4e-mark-execute-all)

          (define-key map "a" 'mu4e-headers-action)

          ;; message composition
          (define-key map "R" 'mu4e-compose-reply)
          (define-key map "F" 'mu4e-compose-forward)
          (define-key map "C" 'mu4e-compose-new)
          (define-key map "E" 'mu4e-compose-edit)

          (define-key map (kbd "RET") 'mu4e-headers-view-message)
          (define-key map [mouse-2]   'mu4e-headers-view-message)

          (define-key map "$" 'mu4e-show-log)
          (define-key map "H" 'mu4e-display-manual)

          ;; menu
          ;;(define-key map [menu-bar] (make-sparse-keymap))
          (let ((menumap (make-sparse-keymap)))
            (define-key map [menu-bar headers] (cons "Mu4e" menumap))

            (define-key menumap [mu4e~headers-quit-buffer]
              '("Quit view" . mu4e~headers-quit-buffer))
            (define-key menumap [display-help] '("Help" . mu4e-display-manual))

            (define-key menumap [sepa0] '("--"))

            (define-key menumap [toggle-include-related]
              '(menu-item "Toggle related messages"
                          mu4e-headers-toggle-include-related
                          :button (:toggle .
                                           (and (boundp 'mu4e-headers-include-related)
                                                mu4e-headers-include-related))))
            (define-key menumap [toggle-threading]
              '(menu-item "Toggle threading" mu4e-headers-toggle-threading
                          :button (:toggle .
                                           (and (boundp 'mu4e-headers-show-threads)
                                                mu4e-headers-show-threads))))

            (define-key menumap [sepa1] '("--"))

            (define-key menumap [execute-marks]  '("Execute marks"
                                                   . mu4e-mark-execute-all))
            (define-key menumap [unmark-all]  '("Unmark all" . mu4e-mark-unmark-all))
            (define-key menumap [unmark]
              '("Unmark" . mu4e-headers-mark-for-unmark))

            (define-key menumap [mark-pattern]  '("Mark pattern" .
                                                  mu4e-headers-mark-pattern))
            (define-key menumap [mark-as-read]  '("Mark as read" .
                                                  mu4e-headers-mark-for-read))
            (define-key menumap [mark-as-unread]
              '("Mark as unread" .  mu4e-headers-mark-for-unread))

            (define-key menumap [mark-delete]
              '("Mark for deletion" . mu4e-headers-mark-for-delete))
            (define-key menumap [mark-untrash]
              '("Mark for untrash" .  mu4e-headers-mark-for-untrash))
            (define-key menumap [mark-trash]
              '("Mark for trash" .  mu4e-headers-mark-for-trash))
            (define-key menumap [mark-move]
              '("Mark for move" . mu4e-headers-mark-for-move))
            (define-key menumap [sepa2] '("--"))

            (define-key menumap [resend]  '("Resend" . mu4e-compose-resend))
            (define-key menumap [forward]  '("Forward" . mu4e-compose-forward))
            (define-key menumap [reply]  '("Reply" . mu4e-compose-reply))
            (define-key menumap [compose-new]  '("Compose new" . mu4e-compose-new))

            (define-key menumap [sepa3] '("--"))

            (define-key menumap [query-next]
              '("Next query" . mu4e-headers-query-next))
            (define-key menumap [query-prev]  '("Previous query" .
                                                mu4e-headers-query-prev))
            (define-key menumap [narrow-search] '("Narrow search" .
                                                  mu4e-headers-search-narrow))
            (define-key menumap [bookmark]  '("Search bookmark" .
                                              mu4e-headers-search-bookmark))
            (define-key menumap [jump]  '("Jump to maildir" .
                                          mu4e~headers-jump-to-maildir))
            (define-key menumap [refresh]  '("Refresh" . mu4e-headers-rerun-search))
            (define-key menumap [search]  '("Search" . mu4e-headers-search))

            (define-key menumap [sepa4] '("--"))

            (define-key menumap [view]  '("View" . mu4e-headers-view-message))
            (define-key menumap [next]  '("Next" . mu4e-headers-next))
            (define-key menumap [previous]  '("Previous" . mu4e-headers-prev))
            (define-key menumap [sepa5] '("--")))
          map)))
(fset 'mu4e-headers-mode-map mu4e-headers-mode-map)

(defun mu4e~header-line-format ()
  "Get the format for the header line."
  (let ((uparrow   (if mu4e-use-fancy-chars " ▲" " ^"))
        (downarrow (if mu4e-use-fancy-chars " ▼" " V")))
    (cons
     (make-string
      (+ mu4e~mark-fringe-len (floor (fringe-columns 'left t))) ?\s)
     (mapcar
      (lambda (item)
        (let* ((field (car item)) (width (cdr item))
               (info (cdr (assoc field
                                 (append mu4e-header-info mu4e-header-info-custom))))
               (require-full (plist-get info :require-full))
               (sortable (plist-get info :sortable))
               ;; if sortable, it is either t (when field is sortable itself)
               ;; or a symbol (if another field is used for sorting)
               (sortfield (when sortable (if (booleanp sortable) field sortable)))
               (help (plist-get info :help))
               ;; triangle to mark the sorted-by column
               (arrow
                (when (and sortable (eq sortfield mu4e-headers-sort-field))
                  (if (eq mu4e-headers-sort-direction 'descending) downarrow uparrow)))
               (name (concat (plist-get info :shortname) arrow))
               (map (make-sparse-keymap)))
          (when require-full
            (mu4e-error "Field %S is not supported in mu4e-headers-mode" field))
          (when sortable
            (define-key map [header-line mouse-1]
              (lambda (&optional e)
                ;; getting the field, inspired by `tabulated-list-col-sort'
                (interactive "e")
                (let* ((obj (posn-object (event-start e)))
                       (field
                        (and obj (get-text-property 0 'field (car obj)))))
                  ;; "t": if we're already sorted by field, the sort-order is
                  ;; changed
                  (mu4e-headers-change-sorting field t)))))
          (concat
           (propertize
            (if width
                (truncate-string-to-width name width 0 ?\s truncate-string-ellipsis)
              name)
            'face (when arrow 'bold)
            'help-echo help
            'mouse-face (when sortable 'highlight)
            'keymap (when sortable map)
            'field field) " ")))
      mu4e-headers-fields))))


(defvar mu4e-headers-mode-abbrev-table nil)

(defun mu4e~headers-maybe-auto-update ()
  "Update the current headers buffer after indexing has brought
some changes, `mu4e-headers-auto-update' is non-nil and there is
no user-interaction ongoing."
  (when (and mu4e-headers-auto-update       ;; must be set
             (zerop (mu4e-mark-marks-num))     ;; non active marks
             (not (active-minibuffer-window))) ;; no user input only
    ;; rerun search if there's a live window with search results;
    ;; otherwise we'd trigger a headers view from out of nowhere.
    (when (and (buffer-live-p (mu4e-get-headers-buffer))
               (window-live-p (get-buffer-window (mu4e-get-headers-buffer) t)))
      (mu4e-headers-rerun-search))))

(define-derived-mode mu4e-headers-mode special-mode
  "mu4e:headers"
  "Major mode for displaying mu4e search results.
\\{mu4e-headers-mode-map}."
  (use-local-map mu4e-headers-mode-map)
  (make-local-variable 'mu4e~headers-proc)
  (make-local-variable 'mu4e~highlighted-docid)
  (set (make-local-variable 'hl-line-face) 'mu4e-header-highlight-face)

  (mu4e-context-in-modeline)

  ;; maybe update the current headers upon indexing changes
  (add-hook 'mu4e-index-updated-hook 'mu4e~headers-maybe-auto-update)
  (add-hook 'mu4e-index-updated-hook
            (lambda() (run-hooks 'mu4e-message-changed-hook)) t)
  (setq
   truncate-lines t
   buffer-undo-list t ;; don't record undo information
   overwrite-mode nil
   header-line-format (mu4e~header-line-format))

  (mu4e~mark-initialize) ;; initialize the marking subsystem
  (hl-line-mode 1))

;;; Highlighting

(defvar mu4e~highlighted-docid nil
  "The highlighted docid")

(defun mu4e~headers-highlight (docid)
  "Highlight the header with DOCID, or do nothing if it's not found.
Also, unhighlight any previously highlighted headers."
  (with-current-buffer (mu4e-get-headers-buffer)
    (save-excursion
      ;; first, unhighlight the previously highlighted docid, if any
      (when (and docid mu4e~highlighted-docid
                 (mu4e~headers-goto-docid mu4e~highlighted-docid))
        (hl-line-unhighlight))
      ;; now, highlight the new one
      (when (mu4e~headers-goto-docid docid)
        (hl-line-highlight)))
    (setq mu4e~highlighted-docid docid)))

;;; Misc 2

(defun mu4e~headers-select-window ()
  "When there is a visible window for the headers buffer, make sure
to select it. This is needed when adding new headers, otherwise
adding a lot of new headers looks really choppy."
  (let ((win (get-buffer-window (mu4e-get-headers-buffer))))
    (when win (select-window win))))

(defun mu4e-headers-goto-message-id (msgid)
  "Go to the next message with message-id MSGID. Return the
message plist, or nil if not found."
  (mu4e-headers-find-if
   (lambda (msg)
     (let ((this-msgid (mu4e-message-field msg :message-id)))
       (when (and this-msgid (string= msgid this-msgid))
         msg)))))

;;; Marking 2

(defun mu4e~headers-mark (docid mark)
  "(Visually) mark the header for DOCID with character MARK."
  (with-current-buffer (mu4e-get-headers-buffer)
    (let ((inhibit-read-only t) (oldpoint (point)))
      (unless (mu4e~headers-goto-docid docid)
        (mu4e-error "Cannot find message with docid %S" docid))
      ;; now, we're at the beginning of the header, looking at
      ;; <docid>\004
      ;; (which is invisible). jump past that…
      (unless (re-search-forward mu4e~headers-docid-post nil t)
        (mu4e-error "Cannot find the `mu4e~headers-docid-post' separator"))

      ;; clear old marks, and add the new ones.
      (let ((msg (get-text-property (point) 'msg)))
        (delete-char mu4e~mark-fringe-len)
        (insert (propertize
                 (format mu4e~mark-fringe-format mark)
                 'face 'mu4e-header-marks-face
                 'docid docid
                 'msg msg)))
      (goto-char oldpoint))))

(defun mu4e~headers-add-header (str docid point &optional msg)
  "Add header STR with DOCID to the buffer at POINT if non-nil, or
at (point-max) otherwise. If MSG is not nil, add it as the
text-property `msg'."
  (when (buffer-live-p (mu4e-get-headers-buffer))
    (with-current-buffer (mu4e-get-headers-buffer)
      (let ((inhibit-read-only t))
        (save-excursion
          (goto-char (if point point (point-max)))
          (insert
           (propertize
            (concat
             (mu4e~headers-docid-cookie docid)
             mu4e~mark-fringe
             str "\n")
            'docid docid 'msg msg)))))))

(defun mu4e~headers-remove-header (docid &optional ignore-missing)
  "Remove header with DOCID at point.
When IGNORE-MISSING is non-nill, don't raise an error when the
docid is not found."
  (with-current-buffer (mu4e-get-headers-buffer)
    (if (mu4e~headers-goto-docid docid)
        (let ((inhibit-read-only t))
          (delete-region (line-beginning-position) (line-beginning-position 2)))
      (unless ignore-missing
        (mu4e-error "Cannot find message with docid %S" docid)))))

;;; Queries & searching

(defcustom mu4e-query-rewrite-function 'identity
  "Function that takes a search expression string, and returns a
  possibly changed search expression string.

This function is applied on the search expression just before
searching, and allows users to modify the query.

For instance, we could change and of workmail into
\"maildir:/long-path-to-work-related-emails\", by setting the function

(setq mu4e-query-rewrite-function
  (lambda(expr)
     (replace-regexp-in-string \"workmail\"
                   \"maildir:/long-path-to-work-related-emails\" expr)))

It is good to remember that the replacement does not understand
anything about the query, it just does text replacement."
  :type 'function
  :group 'mu4e)

(defun mu4e~headers-search-execute (expr ignore-history)
  "Search in the mu database for EXPR, and switch to the output
buffer for the results. If IGNORE-HISTORY is true, do *not* update
the query history stack."
  ;; note: we don't want to update the history if this query comes from
  ;; `mu4e~headers-query-next' or `mu4e~headers-query-prev'.
  ;;(mu4e-hide-other-mu4e-buffers)
  (let* ((buf (get-buffer-create mu4e~headers-buffer-name))
         (inhibit-read-only t)
         (rewritten-expr (funcall mu4e-query-rewrite-function expr))
         (maxnum (unless mu4e-headers-full-search mu4e-headers-results-limit)))
    (with-current-buffer buf
      (mu4e-headers-mode)
      (unless ignore-history
        ;; save the old present query to the history list
        (when mu4e~headers-last-query
          (mu4e~headers-push-query mu4e~headers-last-query 'past)))
      (setq
       mode-name "mu4e-headers"
       mu4e~headers-last-query rewritten-expr)
      (make-local-variable 'global-mode-string)
      (add-to-list 'global-mode-string
                   '(:eval
                     (concat
                      (propertize
                       (mu4e~quote-for-modeline mu4e~headers-last-query)
                       'face 'mu4e-modeline-face)
                      " "
                      (if (and mu4e-display-update-status-in-modeline
                               (buffer-live-p mu4e~update-buffer)
                               (process-live-p (get-buffer-process
                                                mu4e~update-buffer)))
                          (propertize " (updating)" 'face 'mu4e-modeline-face)
                        "")))))

    ;; when the buffer is already visible, select it; otherwise,
    ;; switch to it.
    (unless (get-buffer-window buf 0)
      (switch-to-buffer buf))
    (run-hook-with-args 'mu4e-headers-search-hook expr)
    (mu4e~headers-clear mu4e~searching)
    (mu4e~proc-find
     rewritten-expr
     mu4e-headers-show-threads
     mu4e-headers-sort-field
     mu4e-headers-sort-direction
     maxnum
     mu4e-headers-skip-duplicates
     mu4e-headers-include-related)))

(defun mu4e~headers-redraw-get-view-window ()
  "Close all windows, redraw the headers buffer based on the value
of `mu4e-split-view', and return a window for the message view."
  (if (eq mu4e-split-view 'single-window)
      (or (and (buffer-live-p (mu4e-get-view-buffer))
               (get-buffer-window (mu4e-get-view-buffer)))
          (selected-window))
    (mu4e-hide-other-mu4e-buffers)
    (unless (buffer-live-p (mu4e-get-headers-buffer))
      (mu4e-error "No headers buffer available"))
    (switch-to-buffer (mu4e-get-headers-buffer))
    ;; kill the existing view buffer
    (when (buffer-live-p (mu4e-get-view-buffer))
      (kill-buffer (mu4e-get-view-buffer)))
    ;; get a new view window
    (setq mu4e~headers-view-win
          (let* ((new-win-func
                  (cond
                   ((eq mu4e-split-view 'horizontal) ;; split horizontally
                    '(split-window-vertically mu4e-headers-visible-lines))
                   ((eq mu4e-split-view 'vertical) ;; split vertically
                    '(split-window-horizontally mu4e-headers-visible-columns)))))
            (cond ((with-demoted-errors "Unable to split window: %S"
                     (eval new-win-func)))
                  (t ;; no splitting; just use the currently selected one
                   (selected-window)))))))

;;; Search-based marking

(defun mu4e-headers-for-each (func)
  "Call FUNC for each header, moving point to the header.
FUNC receives one argument, the message s-expression for the
corresponding header."
  (save-excursion
    (goto-char (point-min))
    (while (search-forward mu4e~headers-docid-pre nil t)
      ;; not really sure why we need to jump to bol; we do need to, otherwise we
      ;; miss lines sometimes...
      (let ((msg (get-text-property (line-beginning-position) 'msg)))
        (when msg
          (funcall func msg))))))

(defun mu4e-headers-find-if (func &optional backward)
  "Move to the next header for which FUNC returns non-`nil',
starting from the current position. FUNC receives one argument, the
message s-expression for the corresponding header. If BACKWARD is
non-`nil', search backwards. Returns the new position, or `nil' if
nothing was found. If you want to exclude matches for the current
message, you can use `mu4e-headers-find-if-next'."
  (let ((pos)
        (search-func (if backward 'search-backward 'search-forward)))
    (save-excursion
      (while (and (null pos)
                  (funcall search-func mu4e~headers-docid-pre nil t))
        ;; not really sure why we need to jump to bol; we do need to, otherwise
        ;; we miss lines sometimes...
        (let ((msg (get-text-property (line-beginning-position) 'msg)))
          (when (and msg (funcall func msg))
            (setq pos (point))))))
    (when pos
      (goto-char pos))))

(defun mu4e-headers-find-if-next (func &optional backwards)
  "Like `mu4e-headers-find-if', but do not match the current header.
Move to the next or (if BACKWARDS is non-`nil') header for which FUNC
returns non-`nil', starting from the current position."
  (let ((pos))
    (save-excursion
      (if backwards
          (beginning-of-line)
        (end-of-line))
      (setq pos (mu4e-headers-find-if func backwards)))
    (when pos (goto-char pos))))

(defvar mu4e~headers-regexp-hist nil
  "History list of regexps used.")

(defun mu4e-headers-mark-for-each-if (markpair mark-pred &optional param)
  "Mark all headers for which predicate function MARK-PRED returns
non-nil with MARKPAIR. MARK-PRED is function that receives two
arguments, MSG (the message at point) and PARAM (a user-specified
parameter). MARKPAIR is a cell (MARK . TARGET); see
`mu4e-mark-at-point' for details about marks."
  (mu4e-headers-for-each
   (lambda (msg)
     (when (funcall mark-pred msg param)
       (mu4e-mark-at-point (car markpair) (cdr markpair))))))

(defun mu4e-headers-mark-pattern ()
  "Ask user for a kind of mark (move, delete etc.), a field to
match and a regular expression to match with. Then, mark all
matching messages with that mark."
  (interactive)
  (let ((markpair (mu4e~mark-get-markpair "Mark matched messages with: " t))
        (field (mu4e-read-option "Field to match: "
                                 '( ("subject" . :subject)
                                    ("from"    . :from)
                                    ("to"      . :to)
                                    ("cc"      . :cc)
                                    ("bcc"     . :bcc)
                                    ("list"    . :mailing-list))))
        (pattern (read-string
                  (mu4e-format "Regexp:")
                  nil 'mu4e~headers-regexp-hist)))
    (mu4e-headers-mark-for-each-if
     markpair
     (lambda (msg _param)
       (let* ((value (mu4e-msg-field msg field)))
         (if (member field '(:to :from :cc :bcc :reply-to))
             (cl-find-if (lambda (contact)
                           (let ((name (car contact)) (email (cdr contact)))
                             (or (and name (string-match pattern name))
                                 (and email (string-match pattern email))))) value)
           (string-match pattern (or value ""))))))))

(defun mu4e-headers-mark-custom ()
  "Mark messages based on a user-provided predicate function."
  (interactive)
  (let* ((pred (mu4e-read-option "Match function: "
                                 mu4e-headers-custom-markers))
         (param (when (cdr pred) (eval (cdr pred))))
         (markpair (mu4e~mark-get-markpair "Mark matched messages with: " t)))
    (mu4e-headers-mark-for-each-if markpair (car pred) param)))

(defun mu4e~headers-get-thread-info (msg what)
  "Get WHAT (a symbol, either path or thread-id) for MSG."
  (let* ((thread (or (mu4e-message-field msg :thread)
                     (mu4e-error "No thread info found")))
         (path  (or (plist-get thread :path)
                    (mu4e-error "No threadpath found"))))
    (cl-case what
      (path path)
      (thread-id
       (save-match-data
         ;; the thread id is the first segment of the thread path
         (when (string-match "^\\([[:xdigit:]]+\\):?" path)
           (match-string 1 path))))
      (otherwise (mu4e-error "Not supported")))))

(defun mu4e-headers-mark-thread-using-markpair (markpair &optional subthread)
  "Mark the thread at point using the given markpair. If SUBTHREAD is
non-nil, marking is limited to the message at point and its
descendants."
  (let* ((mark (car markpair))
         (allowed-marks (mapcar 'car mu4e-marks)))
    (unless (memq mark allowed-marks)
      (mu4e-error "The mark (%s) has to be one of: %s"
                  mark allowed-marks)))
  ;; note: the thread id is shared by all messages in a thread
  (let* ((msg (mu4e-message-at-point))
         (thread-id (mu4e~headers-get-thread-info msg 'thread-id))
         (path      (mu4e~headers-get-thread-info msg 'path))
         (last-marked-point))
    (mu4e-headers-for-each
     (lambda (mymsg)
       (let ((my-thread-id (mu4e~headers-get-thread-info mymsg 'thread-id)))
         (if subthread
             ;; subthread matching; mymsg's thread path should have path as its
             ;; prefix
             (when (string-match (concat "^" path)
                                 (mu4e~headers-get-thread-info mymsg 'path))
               (mu4e-mark-at-point (car markpair) (cdr markpair))
               (setq last-marked-point (point)))
           ;; nope; not looking for the subthread; looking for the whole thread
           (when (string= thread-id my-thread-id)
             (mu4e-mark-at-point (car markpair) (cdr markpair))
             (setq last-marked-point (point)))))))
    (when last-marked-point
      (goto-char last-marked-point)
      (mu4e-headers-next))))

(defun mu4e-headers-mark-thread (&optional subthread markpair)
  "Like `mu4e-headers-mark-thread-using-markpair' but prompt for the markpair."
  (interactive
   (let* ((subthread current-prefix-arg))
     (list current-prefix-arg
           ;; FIXME: e.g., for refiling we should evaluate this
           ;; for each line separately
           (mu4e~mark-get-markpair
            (if subthread "Mark subthread with: " "Mark whole thread with: ")
            t))))
  (mu4e-headers-mark-thread-using-markpair markpair subthread))

(defun mu4e-headers-mark-subthread (&optional markpair)
  "Like `mu4e-mark-thread', but only for a sub-thread."
  (interactive)
  (if markpair (mu4e-headers-mark-thread t markpair)
    (let ((current-prefix-arg t))
      (call-interactively 'mu4e-headers-mark-thread))))


;;; The query past / present / future

(defvar mu4e~headers-query-past nil
  "Stack of queries before the present one.")
(defvar mu4e~headers-query-future nil
  "Stack of queries after the present one.")
(defvar mu4e~headers-query-stack-size 20
  "Maximum size for the query stacks.")

(defun mu4e~headers-push-query (query where)
  "Push QUERY to one of the query stacks.
WHERE is a symbol telling us where to push; it's a symbol, either
'future or 'past. Functional also removes duplicates, limits the
stack size."
  (let ((stack
         (cl-case where
           (past   mu4e~headers-query-past)
           (future mu4e~headers-query-future))))
    ;; only add if not the same item
    (unless (and stack (string= (car stack) query))
      (push query stack)
      ;; limit the stack to `mu4e~headers-query-stack-size' elements
      (when (> (length stack) mu4e~headers-query-stack-size)
        (setq stack (cl-subseq stack 0 mu4e~headers-query-stack-size)))
      ;; remove all duplicates of the new element
      (cl-remove-if (lambda (elm) (string= elm (car stack))) (cdr stack))
      ;; update the stacks
      (cl-case where
        (past   (setq mu4e~headers-query-past   stack))
        (future (setq mu4e~headers-query-future stack))))))

(defun mu4e~headers-pop-query (whence)
  "Pop a query from the stack.
WHENCE is a symbol telling us where to get it from, either `future'
or `past'."
  (cl-case whence
    (past
     (unless mu4e~headers-query-past
       (mu4e-warn "No more previous queries"))
     (pop mu4e~headers-query-past))
    (future
     (unless mu4e~headers-query-future
       (mu4e-warn "No more next queries"))
     (pop mu4e~headers-query-future))))


;;; Interactive functions

(defvar mu4e~headers-search-hist nil
  "History list of searches.")

(defun mu4e-headers-search (&optional expr prompt edit
                                      ignore-history msgid show)
  "Search in the mu database for EXPR, and switch to the output
buffer for the results. This is an interactive function which ask
user for EXPR. PROMPT, if non-nil, is the prompt used by this
function (default is \"Search for:\"). If EDIT is non-nil,
instead of executing the query for EXPR, let the user edit the
query before executing it. If IGNORE-HISTORY is true, do *not*
update the query history stack. If MSGID is non-nil, attempt to
move point to the first message with that message-id after
searching. If SHOW is non-nil, show the message with MSGID."
  ;; note: we don't want to update the history if this query comes from
  ;; `mu4e~headers-query-next' or `mu4e~headers-query-prev'."
  (interactive)
  (let* ((prompt (mu4e-format (or prompt "Search for: ")))
         (expr
          (if edit
              (read-string prompt expr)
            (or expr
                (read-string prompt nil 'mu4e~headers-search-hist)))))
    (mu4e-mark-handle-when-leaving)
    (mu4e~headers-search-execute expr ignore-history)
    (setq mu4e~headers-msgid-target msgid
          mu4e~headers-view-target show)))

(defun mu4e-headers-search-edit ()
  "Edit the last search expression."
  (interactive)
  (mu4e-headers-search mu4e~headers-last-query nil t))

(defun mu4e-headers-search-bookmark (&optional expr edit)
  "Search using some bookmarked query EXPR.
If EDIT is non-nil, let the user edit the bookmark before starting
the search."
  (interactive)
  (let ((expr
         (or expr
             (mu4e-ask-bookmark (if edit "Select bookmark: " "Bookmark: ")))))
    (run-hook-with-args 'mu4e-headers-search-bookmark-hook expr)
    (mu4e-headers-search expr (when edit "Edit bookmark: ") edit)))

(defun mu4e-headers-search-bookmark-edit ()
  "Edit an existing bookmark before executing it."
  (interactive)
  (mu4e-headers-search-bookmark nil t))

(defun mu4e-headers-search-narrow (filter )
  "Narrow the last search by appending search expression FILTER to
the last search expression. Note that you can go back to previous
query (effectively, 'widen' it), with `mu4e-headers-query-prev'."
  (interactive
   (let ((filter
          (read-string (mu4e-format "Narrow down to: ")
                       nil 'mu4e~headers-search-hist nil t)))
     (list filter)))
  (unless mu4e~headers-last-query
    (mu4e-warn "There's nothing to filter"))
  (mu4e-headers-search
   (format "(%s) AND (%s)" mu4e~headers-last-query filter)))

(defun mu4e-headers-change-sorting (&optional field dir)
  "Change the sorting/threading parameters.
FIELD is the field to sort by; DIR is a symbol: either 'ascending,
'descending, 't (meaning: if FIELD is the same as the current
sortfield, change the sort-order) or nil (ask the user)."
  (interactive)
  (let* ((field
          (or field
              (mu4e-read-option "Sortfield: " mu4e~headers-sort-field-choices)))
         ;; note: 'sortable' is either a boolean (meaning: if non-nil, this is
         ;; sortable field), _or_ another field (meaning: sort by this other field).
         (sortable (plist-get (cdr (assoc field mu4e-header-info)) :sortable))
         ;; error check
         (sortable
          (if sortable
              sortable
            (mu4e-error "Not a sortable field")))
         (sortfield (if (booleanp sortable) field sortable))
         (dir
          (cl-case dir
            ((ascending descending) dir)
            ;; change the sort order if field = curfield
            (t
             (if (eq sortfield mu4e-headers-sort-field)
                 (if (eq mu4e-headers-sort-direction 'ascending)
                     'descending 'ascending)
               'descending))
            (mu4e-read-option "Direction: "
                              '(("ascending" . 'ascending) ("descending" . 'descending))))))
    (setq
     mu4e-headers-sort-field sortfield
     mu4e-headers-sort-direction dir)
    (mu4e-message "Sorting by %s (%s)"
                  (symbol-name sortfield)
                  (symbol-name mu4e-headers-sort-direction))
    (mu4e-headers-rerun-search)))

(defun mu4e~headers-toggle (name togglevar dont-refresh)
  "Toggle variable TOGGLEVAR for feature NAME. Unless DONT-REFRESH is non-nil,
re-run the last search."
  (set togglevar (not (symbol-value togglevar)))
  (mu4e-message "%s turned %s%s"
                name
                (if (symbol-value togglevar) "on" "off")
                (if dont-refresh
                    " (press 'g' to refresh)" ""))
  (unless dont-refresh
    (mu4e-headers-rerun-search)))

(defun mu4e-headers-toggle-threading (&optional dont-refresh)
  "Toggle `mu4e-headers-show-threads'. With prefix-argument, do
_not_ refresh the last search with the new setting for threading."
  (interactive "P")
  (mu4e~headers-toggle "Threading" 'mu4e-headers-show-threads dont-refresh))

(defun mu4e-headers-toggle-full-search (&optional dont-refresh)
  "Toggle `mu4e-headers-full-search'. With prefix-argument, do
_not_ refresh the last search with the new setting for threading."
  (interactive "P")
  (mu4e~headers-toggle "Full-search"
                       'mu4e-headers-full-search dont-refresh))

(defun mu4e-headers-toggle-include-related (&optional dont-refresh)
  "Toggle `mu4e-headers-include-related'. With prefix-argument, do
_not_ refresh the last search with the new setting for threading."
  (interactive "P")
  (mu4e~headers-toggle "Include-related"
                       'mu4e-headers-include-related dont-refresh))

(defun mu4e-headers-toggle-skip-duplicates (&optional dont-refresh)
  "Toggle `mu4e-headers-skip-duplicates'. With prefix-argument, do
_not_ refresh the last search with the new setting for threading."
  (interactive "P")
  (mu4e~headers-toggle "Skip-duplicates"
                       'mu4e-headers-skip-duplicates dont-refresh))

(defvar mu4e~headers-loading-buf nil
  "A buffer for loading a message view.")

(defun mu4e~decrypt-p (msg)
  "Should we decrypt this message?"
  (unless mu4e-view-use-gnus ;; we don't decrypt in the gnus-view case
    (and (member 'encrypted (mu4e-message-field msg :flags))
         (if (eq mu4e-decryption-policy 'ask)
             (yes-or-no-p (mu4e-format "Decrypt message?"))
           mu4e-decryption-policy))))

(defun mu4e-headers-view-message ()
  "View message at point                                    .
If there's an existing window for the view, re-use that one . If
not, create a new one, depending on the value of
`mu4e-split-view': if it's a symbol `horizontal' or `vertical',
split the window accordingly; if it is nil, replace the current
window                                                      . "
  (interactive)
  (unless (eq major-mode 'mu4e-headers-mode)
    (mu4e-error "Must be in mu4e-headers-mode (%S)" major-mode))
  (let* ((msg (mu4e-message-at-point))
         (docid (or (mu4e-message-field msg :docid)
                    (mu4e-warn "No message at point")))
         (decrypt (mu4e~decrypt-p msg))
         (verify  (not mu4e-view-use-gnus))
         (viewwin (mu4e~headers-redraw-get-view-window)))
    (unless (window-live-p viewwin)
      (mu4e-error "Cannot get a message view"))
    (select-window viewwin)

    ;; show some 'loading...' buffer
    (unless (buffer-live-p mu4e~headers-loading-buf)
      (setq mu4e~headers-loading-buf (get-buffer-create " *mu4e-loading*"))
      (with-current-buffer mu4e~headers-loading-buf
        (mu4e-loading-mode)))

    (switch-to-buffer mu4e~headers-loading-buf)
    ;; Note, ideally in the 'gnus' case, we don't need to call the server to get
    ;; the body etc., we only need the path which we already have.
    ;;
    ;; However, for now we still need the body for e.g. view-in-browser so let's
    ;; not yet do that.

    ;; (if mu4e-view-use-gnus
    ;;     (mu4e-view msg)
    ;;   (mu4e~proc-view docid mu4e-view-show-images decrypt))
    (mu4e~proc-view docid mu4e-view-show-images decrypt verify)))

(defun mu4e-headers-rerun-search ()
  "Rerun the search for the last search expression."
  (interactive)
  ;; if possible, try to return to the same message
  (let* ((msg (mu4e-message-at-point t))
         (msgid (and msg (mu4e-message-field msg :message-id))))
    (mu4e-headers-search mu4e~headers-last-query nil nil t msgid)))

(defun mu4e~headers-query-navigate (whence)
  "Execute the previous query from the query stacks.
WHENCE determines where the query is taken from and is a symbol,
either `future' or `past'."
  (let ((query (mu4e~headers-pop-query whence))
        (where (if (eq whence 'future) 'past 'future)))
    (when query
      (mu4e~headers-push-query mu4e~headers-last-query where)
      (mu4e-headers-search query nil nil t))))

(defun mu4e-headers-query-next ()
  "Execute the previous query from the query stacks."
  (interactive)
  (mu4e~headers-query-navigate 'future))

(defun mu4e-headers-query-prev ()
  "Execute the previous query from the query stacks."
  (interactive)
  (mu4e~headers-query-navigate 'past))

;; forget the past so we don't repeat it :/
(defun mu4e-headers-forget-queries ()
  "Forget all the complete query history."
  (interactive)
  (setq ;; note: don't forget the present one
   mu4e~headers-query-past nil
   mu4e~headers-query-future nil)
  (mu4e-message "Query history cleared"))

(defun mu4e~headers-move (lines)
  "Move point LINES lines forward (if LINES is positive) or
backward (if LINES is negative). If this succeeds, return the new
docid. Otherwise, return nil."
  (unless (eq major-mode 'mu4e-headers-mode)
    (mu4e-error "Must be in mu4e-headers-mode (%S)" major-mode))
  (let* ((_succeeded (zerop (forward-line lines)))
         (docid (mu4e~headers-docid-at-point)))
    ;; move point, even if this function is called when this window is not
    ;; visible
    (when docid
      ;; update all windows showing the headers buffer
      (walk-windows
       (lambda (win)
         (when (eq (window-buffer win) (mu4e-get-headers-buffer))
           (set-window-point win (point))))
       nil t)
      (if (eq mu4e-split-view 'single-window)
          (when (eq (window-buffer) (mu4e-get-view-buffer))
            (mu4e-headers-view-message))
        ;; update message view if it was already showing
        (when (and mu4e-split-view (window-live-p mu4e~headers-view-win))
          (mu4e-headers-view-message)))
      ;; attempt to highlight the new line, display the message
      (mu4e~headers-highlight docid)
      docid)))

(defun mu4e-headers-next (&optional n)
  "Move point to the next message header.
If this succeeds, return the new docid. Otherwise, return nil.
Optionally, takes an integer N (prefix argument), to the Nth next
header."
  (interactive "P")
  (mu4e~headers-move (or n 1)))

(defun mu4e-headers-prev (&optional n)
  "Move point to the previous message header.
If this succeeds, return the new docid. Otherwise, return nil.
Optionally, takes an integer N (prefix argument), to the Nth
previous header."
  (interactive "P")
  (mu4e~headers-move (- (or n 1))))

(defun mu4e~headers-prev-or-next-unread (backwards)
  "Move point to the next message that is unread (and
untrashed). If BACKWARDS is non-`nil', move backwards."
  (interactive)
  (or (mu4e-headers-find-if-next
       (lambda (msg)
         (let ((flags (mu4e-message-field msg :flags)))
           (and (member 'unread flags) (not (member 'trashed flags)))))
       backwards)
      (mu4e-message (format "No %s unread message found"
                            (if backwards "previous" "next")))))

(defun mu4e-headers-prev-unread ()
  "Move point to the previous message that is unread (and
untrashed)."
  (interactive)
  (mu4e~headers-prev-or-next-unread t))

(defun mu4e-headers-next-unread ()
  "Move point to the next message that is unread (and
untrashed)."
  (interactive)
  (mu4e~headers-prev-or-next-unread nil))

(defun mu4e~headers-jump-to-maildir (maildir)
  "Show the messages in maildir (user is prompted to ask what
maildir)."
  (interactive
   (let ((maildir (mu4e-ask-maildir "Jump to maildir: ")))
     (list maildir)))
  (when maildir
    (mu4e-mark-handle-when-leaving)
    (mu4e-headers-search (format "maildir:\"%s\"" maildir))))

(defun mu4e-headers-split-view-grow (&optional n)
  "In split-view, grow the headers window.
In horizontal split-view, increase the number of lines shown by N.
In vertical split-view, increase the number of columns shown by N.
If N is negative shrink the headers window.  When not in split-view
do nothing."
  (interactive "P")
  (let ((n (or n 1))
        (hwin (get-buffer-window (mu4e-get-headers-buffer))))
    (when (and (buffer-live-p (mu4e-get-view-buffer)) (window-live-p hwin))
      (let ((n (or n 1)))
        (cl-case mu4e-split-view
          ;; emacs has weird ideas about what horizontal, vertical means...
          (horizontal
           (window-resize hwin n nil)
           (cl-incf mu4e-headers-visible-lines n))
          (vertical
           (window-resize hwin n t)
           (cl-incf mu4e-headers-visible-columns n)))))))

(defun mu4e-headers-split-view-shrink (&optional n)
  "In split-view, shrink the headers window.
In horizontal split-view, decrease the number of lines shown by N.
In vertical split-view, decrease the number of columns shown by N.
If N is negative grow the headers window.  When not in split-view
do nothing."
  (interactive "P")
  (mu4e-headers-split-view-grow (- (or n 1))))

(defun mu4e-headers-action (&optional actionfunc)
  "Ask user what to do with message-at-point, then do it.
The actions are specified in `mu4e-headers-actions'. Optionally,
pass ACTIONFUNC, which is a function that takes a msg-plist
argument."
  (interactive)
  (let ((msg (mu4e-message-at-point))
        (afunc (or actionfunc (mu4e-read-option "Action: " mu4e-headers-actions))))
    (funcall afunc msg)))

(defun mu4e-headers-mark-and-next (mark)
  "Set mark MARK on the message at point or on all messages in the
region if there is a region, then move to the next message."
  (interactive)
  (mu4e-mark-set mark)
  (when mu4e-headers-advance-after-mark (mu4e-headers-next)))

(defun mu4e~headers-quit-buffer ()
  "Quit the mu4e-headers buffer.
This is a rather complex function, to ensure we don't disturb
other windows."
  (interactive)
  (if (eq mu4e-split-view 'single-window)
      (progn (mu4e-mark-handle-when-leaving)
             (kill-buffer))
    (unless (eq major-mode 'mu4e-headers-mode)
      (mu4e-error "Must be in mu4e-headers-mode (%S)" major-mode))
    (mu4e-mark-handle-when-leaving)
    (let ((curbuf (current-buffer))
          (curwin (selected-window)))
      (walk-windows
       (lambda (win)
         (with-selected-window win
           ;; if we the view window connected to this one, kill it
           (when (and (not (one-window-p win)) (eq mu4e~headers-view-win win))
             (delete-window win)
             (setq mu4e~headers-view-win nil)))
         ;; and kill any _other_ (non-selected) window that shows the current
         ;; buffer
         (when (and
                (eq curbuf (window-buffer win)) ;; does win show curbuf?
                (not (eq curwin win))             ;; it's not the curwin?
                (not (one-window-p)))           ;; and not the last one?
           (delete-window win))))  ;; delete it!
      ;; now, all *other* windows should be gone. kill ourselves, and return
      ;; to the main view
      (kill-buffer)
      (mu4e~main-view 'refresh))))

;;; _
(provide 'mu4e-headers)
;;; mu4e-headers.el ends here
