;;; dirtrack.el --- Directory Tracking by watching the prompt  -*- lexical-binding: t -*-

;; Copyright (C) 1996, 2001-2025 Free Software Foundation, Inc.

;; Author: Peter Breton <pbreton@cs.umb.edu>
;; Created: Sun Nov 17 1996
;; Keywords: processes

;; This file is 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Shell directory tracking by watching the prompt.
;;
;; This is yet another attempt at a directory-tracking package for
;; Emacs shell-mode.  However, this package makes one strong
;; assumption: that you can customize your shell's prompt to contain
;; the current working directory.  Most shells do support this,
;; including almost every type of Bourne and C shell on Unix, the
;; native shells on Windows 9X (COMMAND.COM) and modern MS-Windows
;; systems (cmd.exe), and most 3rd party MS-Windows shells.  If you
;; cannot do this, or do not wish to, this package will be useless to
;; you.
;;
;; Installation:
;;
;; 1) Set your shell's prompt to contain the current working directory.
;; You may need to consult your shell's documentation to find out how to
;; do this.
;;
;; Note that directory tracking is done by matching regular expressions,
;; therefore it is *VERY IMPORTANT* for your prompt to be easily
;; distinguishable from other output.  If your prompt regexp is too general,
;; you will see error messages from the dirtrack filter as it attempts to cd
;; to non-existent directories.
;;
;; 2) Set the variable `dirtrack-list' to an appropriate value.  This
;; should be a list of two elements: the first is a regular expression
;; which matches your prompt up to and including the pathname part.
;; The second is a number which tells which regular expression group to
;; match to extract only the pathname.  If you use a multi-line prompt,
;; add t as a third element.  Note that some of the functions in
;; 'comint.el' assume a single-line prompt (eg, comint-bol).
;;
;; Determining this information may take some experimentation.  Using
;; `dirtrack-debug-mode' may help; it causes the directory-tracking
;; filter to log messages to the buffer `dirtrack-debug-buffer'.
;;
;; 3) Activate `dirtrack-mode'.  You may wish to turn ordinary shell
;; tracking off by calling `shell-dirtrack-mode'.
;;
;; Examples:
;;
;; 1) On MS-Windows, my prompt is set to emacs$S$P$G.
;; 'dirtrack-list' is set to (list "^emacs \\([a-zA-Z]:.*\\)>" 1)
;;
;; 2) On Solaris running bash, my prompt is set like this:
;;    PS1="\w\012emacs@\h(\!) [\t]% "
;;    'dirtrack-list' is set to (list "^\\([/~].*\\)\nemacs@[^%]+% *" 1 t)
;;
;; I'd appreciate other examples from people who use this package.
;;
;; Here's one from Stephen Eglen:
;;
;;   Running under tcsh:
;;   (setq-default dirtrack-list '("^%E \\([^ ]+\\)" 1))
;;
;;   It might be worth mentioning in your file that Emacs sources start up
;;   files of the form: ~/.emacs_<SHELL> where <SHELL> is the name of the
;;   shell.  So for example, I have the following in ~/.emacs_tcsh:
;;
;;   set prompt = "%%E %~ %h% "
;;
;;   This produces a prompt of the form:
;;   %E /var/spool 10%
;;
;;   This saves me from having to use the %E prefix in other non-emacs
;;   shells.
;;
;; A final note:
;;
;;   I run LOTS of shell buffers through Emacs, sometimes as different users
;;   (e.g., when logged in as myself, I'll run a root shell in the same Emacs).
;;   If you do this, and the shell prompt contains a ~, Emacs will interpret
;;   this relative to the user which owns the Emacs process, not the user
;;   who owns the shell buffer.  This may cause dirtrack to behave strangely
;;   (typically it reports that it is unable to cd to a directory
;;   with a ~ in it).
;;
;;   The same behavior can occur if you use dirtrack with remote filesystems
;;   (using telnet, ssh, etc.) as Emacs will be checking the local
;;   filesystem, not the remote one.  This problem is not specific to dirtrack,
;;   but also affects file completion, etc.

;;; Code:

(eval-when-compile
  (require 'comint)
  (require 'shell))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Customization Variables
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defgroup dirtrack nil
  "Directory tracking by watching the prompt."
  :prefix "dirtrack-"
  :group 'shell)

(defcustom dirtrack-list (list "^emacs \\([a-zA-Z]:.*\\)>" 1)
  "List for directory tracking.
First item is a regexp that describes where to find the path in a prompt.
Second is a number, the regexp group to match."
  :type  '(sexp (regexp  :tag "Prompt Expression")
		(integer :tag "Regexp Group"))
  :version "24.1")

(make-variable-buffer-local 'dirtrack-list)

(defcustom dirtrack-debug nil
  "If non-nil, the function `dirtrack' will report debugging info."
  :type  'boolean)

(defcustom dirtrack-debug-buffer "*Directory Tracking Log*"
  "Buffer in which to write directory tracking debug information."
  :type  'string)

(defcustom dirtrack-directory-function
  (if (memq system-type '(ms-dos windows-nt cygwin))
      'dirtrack-windows-directory-function
    'file-name-as-directory)
  "Function to apply to the prompt directory for comparison purposes."
  :type  'function)

(defcustom dirtrack-canonicalize-function
  (if (memq system-type '(ms-dos windows-nt cygwin))
      'downcase 'identity)
  "Function to apply to the default directory for comparison purposes."
  :type  'function)

(defcustom dirtrack-directory-change-hook nil
  "Hook that is called when a directory change is made."
  :type 'hook)


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


(defun dirtrack-windows-directory-function (dir)
  "Return a canonical directory for comparison purposes.
Such a directory is all lowercase, has forward-slashes as delimiters,
and ends with a forward slash."
  (file-name-as-directory (downcase (subst-char-in-string ?\\ ?/ dir))))

(defun dirtrack-cygwin-directory-function (dir)
  "Return a canonical directory taken from a Cygwin path for comparison purposes."
  (if (string-match "/cygdrive/\\([A-Z]\\)\\(.*\\)" dir)
      (concat (match-string 1 dir) ":" (match-string 2 dir))
    dir))


;;;###autoload
(define-minor-mode dirtrack-mode
  "Toggle directory tracking in shell buffers (Dirtrack mode).

This method requires that your shell prompt contain the current
working directory at all times, and that you set the variable
`dirtrack-list' to match the prompt.

This is an alternative to `shell-dirtrack-mode', which works by
tracking `cd' and similar commands which change the shell working
directory."
  :lighter nil
  (if dirtrack-mode
      (add-hook 'comint-preoutput-filter-functions 'dirtrack nil t)
    (remove-hook 'comint-preoutput-filter-functions 'dirtrack t)))


(define-minor-mode dirtrack-debug-mode
  "Toggle Dirtrack debugging."
  :lighter nil
  (if dirtrack-debug-mode
      (display-buffer (get-buffer-create dirtrack-debug-buffer))))

(defun dirtrack-debug-message (msg1 msg2)
  "Insert strings at the end of `dirtrack-debug-buffer'."
  (when dirtrack-debug-mode
    (with-current-buffer (get-buffer-create dirtrack-debug-buffer)
      (goto-char (point-max))
      (insert (substitute-command-keys msg1) msg2 "\n"))))

(declare-function shell-prefixed-directory-name "shell" (dir))
(declare-function shell-process-cd "shell" (arg))

;;;###autoload
(defun dirtrack (input)
  "Determine the current directory from the process output for a prompt.
This filter function is used by `dirtrack-mode'.  It looks for
the prompt specified by `dirtrack-list', and calls
`shell-process-cd' if the directory seems to have changed away
from `default-directory'."
  (when (and dirtrack-mode
	     (not (eq (point) (point-min)))) ; there must be output
    (save-excursion ; What's this for? -- cyd
      (if (not (string-match (nth 0 dirtrack-list) input))
	  ;; No match
	  (dirtrack-debug-message
	   "Input failed to match `dirtrack-list': " input)
	(let ((prompt-path (match-string (nth 1 dirtrack-list) input))
	      temp)
	  (cond
	   ;; Don't do anything for empty string
	   ((string-equal prompt-path "")
	    (dirtrack-debug-message "Prompt match gives empty string: " input))
	   ;; If the prompt contains an absolute file name, call
	   ;; `shell-process-cd' if the directory has changed.
	   ((file-name-absolute-p prompt-path)
	    ;; Transform prompts into canonical forms
	    (let ((orig-prompt-path (funcall dirtrack-directory-function
					     prompt-path))
		  (current-dir      (funcall dirtrack-canonicalize-function
					     default-directory)))
	      (setq prompt-path (shell-prefixed-directory-name orig-prompt-path))
	      ;; Compare them
	      (if (or (string-equal current-dir prompt-path)
		      (string-equal (expand-file-name current-dir)
				    (expand-file-name prompt-path)))
		  (dirtrack-debug-message "Not changing directory: " current-dir)
		;; It's possible that Emacs thinks the directory
		;; doesn't exist (e.g. rlogin buffers)
		(if (file-accessible-directory-p prompt-path)
		    ;; `shell-process-cd' adds the prefix, so we need
		    ;; to give it the original (un-prefixed) path.
		    (progn
		      (shell-process-cd orig-prompt-path)
		      (run-hooks 'dirtrack-directory-change-hook)
		      (dirtrack-debug-message "Changing directory to "
					      prompt-path))
		  (dirtrack-debug-message "Not changing to non-existent directory: "
					  prompt-path)))))
	   ;; If the file name is non-absolute, try and see if it
	   ;; seems to be up or down from where we were.
	   ((string-match "\\`\\(.*\\)\\(?:/.*\\)?\n\\(.*/\\)\\1\\(?:/.*\\)?\\'"
			  (setq temp
				(concat prompt-path "\n" default-directory)))
	    (shell-process-cd (concat (match-string 2 temp)
				      prompt-path))
	    (run-hooks 'dirtrack-directory-change-hook)))))))
  input)

(provide 'dirtrack)

;;; dirtrack.el ends here
