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+;;; gnosis-string-edit.el --- gnosis edit strings  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2023-2024  Thanos Apollo
+
+;; Author: Thanos Apollo <[email protected]>
+;; Keywords: extensions
+;; URL: https://git.thanosapollo.org/gnosis
+;; Version: 0.0.1
+
+;; Package-Requires: ((emacs "27.2") (compat "29.1.4.2"))
+
+;; 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:
+
+;; A slightly modified version of string-edit.el.  Gnosis comes with a
+;; modified version string-edit.el to make gnosis available to users
+;; of Emacs versions < 29.
+
+;; Code:
+
+(require 'cl-lib)
+
+(defface gnosis-string-edit-prompt
+  '((t (:inherit font-lock-comment-face)))
+  "Face used on `gnosis-string-edit' help text."
+  :group 'text)
+
+(defvar gnosis-string-edit--success-callback)
+(defvar gnosis-string-edit--abort-callback)
+
+(defun gnosis-string-edit-ensure-empty-lines (&optional lines)
+  "Ensure that there are LINES number of empty lines before point.
+If LINES is nil or omitted, ensure that there is a single empty
+line before point.
+
+If called interactively, LINES is given by the prefix argument.
+
+If there are more than LINES empty lines before point, the number
+of empty lines is reduced to LINES.
+
+If point is not at the beginning of a line, a newline character
+is inserted before adjusting the number of empty lines."
+  (interactive "p")
+  (unless (bolp)
+    (insert "\n"))
+  (let ((lines (or lines 1))
+        (start (save-excursion
+                 (if (re-search-backward "[^\n]" nil t)
+                     (+ (point) 2)
+                   (point-min)))))
+    (cond
+     ((> (- (point) start) lines)
+      (delete-region (point) (- (point) (- (point) start lines))))
+     ((< (- (point) start) lines)
+      (insert (make-string (- lines (- (point) start)) ?\n))))))
+
+;;;###autoload
+(cl-defun gnosis-string-edit (prompt string success-callback
+                              &key abort-callback)
+  "Switch to a new buffer to edit STRING.
+When the user finishes editing (with \\<gnosis-string-edit-mode-map>\\[gnosis-string-edit-done]), SUCCESS-CALLBACK
+is called with the resulting string.
+
+If the user aborts (with \\<gnosis-string-edit-mode-map>\\[gnosis-string-edit-abort]), ABORT-CALLBACK (if any) is
+called with no parameters.
+
+PROMPT will be inserted at the start of the buffer, but won't be
+included in the resulting string.  If PROMPT is nil, no help text
+will be inserted.
+
+Also see `read-string-from-buffer'."
+  (with-current-buffer (generate-new-buffer "*edit string*")
+    (when prompt
+      (let ((inhibit-read-only t))
+        (insert prompt)
+        (gnosis-string-edit-ensure-empty-lines 0)
+        (add-text-properties (point-min) (point)
+                             (list 'intangible t
+                                   'face 'gnosis-string-edit-prompt
+                                   'read-only t))
+        (insert (propertize (make-separator-line) 'rear-nonsticky t))
+        (add-text-properties (point-min) (point)
+                             (list 'gnosis-string-edit--prompt t))))
+    (let ((start (point)))
+      (insert string)
+      (goto-char start))
+
+    ;; Use `fit-window-to-buffer' after the buffer is filled with text.
+    (pop-to-buffer (current-buffer)
+                   '(display-buffer-below-selected
+                     (window-height . (lambda (window)
+                                        (fit-window-to-buffer window nil 10)))))
+
+    (set-buffer-modified-p nil)
+    (setq buffer-undo-list nil)
+    (gnosis-string-edit-mode)
+    (setq-local gnosis-string-edit--success-callback success-callback)
+    (when abort-callback
+      (setq-local gnosis-string-edit--abort-callback abort-callback))
+    (setq-local header-line-format
+                (substitute-command-keys
+                 "Type \\<gnosis-string-edit-mode-map>\\[gnosis-string-edit-done] when you've finished editing or \\[gnosis-string-edit-abort] to abort"))
+    (message "%s" (substitute-command-keys
+                   "Type \\<gnosis-string-edit-mode-map>\\[gnosis-string-edit-done] when you've finished editing"))))
+
+(defvar-keymap gnosis-string-edit-mode-map
+  "C-c C-c" #'gnosis-string-edit-done
+  "C-c C-k" #'gnosis-string-edit-abort)
+
+(define-derived-mode gnosis-string-edit-mode text-mode "String"
+  "Mode for editing strings."
+  :interactive nil)
+
+(defun gnosis-string-edit-done ()
+  "Finish editing the string and call the callback function.
+This will kill the current buffer."
+  (interactive)
+  (goto-char (point-min))
+  ;; Skip past the help text.
+  (text-property-search-forward 'gnosis-string-edit--prompt)
+  (let ((string (buffer-substring (point) (point-max)))
+        (callback gnosis-string-edit--success-callback))
+    (quit-window 'kill)
+    (funcall callback string)))
+
+(defun gnosis-string-edit-abort ()
+  "Abort editing the current string."
+  (interactive)
+  (let ((callback gnosis-string-edit--abort-callback))
+    (quit-window 'kill)
+    (when callback
+      (funcall callback))))
+
+(provide 'gnosis-string-edit)
+
+;;; gnosis-string-edit.el ends here
+