;;; esh-var.el --- handling of variables  -*- lexical-binding:t -*-

;; Copyright (C) 1999-2021 Free Software Foundation, Inc.

;; Author: John Wiegley <johnw@gnu.org>

;; 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:

;; These are the possible variable interpolation syntaxes.  Also keep
;; in mind that if an argument looks like a number, it will be
;; converted to a number.  This is not significant when invoking
;; external commands, but it's important when calling Lisp functions.
;;
;;   $VARIABLE
;;
;; Interval the value of an environment variable, or a Lisp variable
;;
;;   $ALSO-VAR
;;
;; "-" is a valid part of a variable name.
;;
;;   $<MYVAR>-TOO
;;
;; Only "MYVAR" is part of the variable name in this case.
;;
;;   $#VARIABLE
;;
;; Returns the length of the value of VARIABLE.  This could also be
;; done using the `length' Lisp function.
;;
;;   $(lisp)
;;
;; Returns result of lisp evaluation.  Note: Used alone like this, it
;; is identical to just saying (lisp); but with the variable expansion
;; form, the result may be interpolated a larger string, such as
;; '$(lisp)/other'.
;;
;;   ${command}
;;
;; Returns the value of an eshell subcommand.  See the note above
;; regarding Lisp evaluations.
;;
;;   $ANYVAR[10]
;;
;; Return the 10th element of ANYVAR.  If ANYVAR's value is a string,
;; it will be split in order to make it a list.  The splitting will
;; occur at whitespace.
;;
;;   $ANYVAR[: 10]
;;
;; As above, except that splitting occurs at the colon now.
;;
;;   $ANYVAR[: 10 20]
;;
;; As above, but instead of returning just a string, it now returns a
;; list of two strings.  If the result is being interpolated into a
;; larger string, this list will be flattened into one big string,
;; with each element separated by a space.
;;
;;   $ANYVAR["\\\\" 10]
;;
;; Separate on backslash characters.  Actually, the first argument --
;; if it doesn't have the form of a number, or a plain variable name
;; -- can be any regular expression.  So to split on numbers, use
;; '$ANYVAR["[0-9]+" 10 20]'.
;;
;;   $ANYVAR[hello]
;;
;; Calls `assoc' on ANYVAR with 'hello', expecting it to be an alist.
;;
;;   $#ANYVAR[hello]
;;
;; Returns the length of the cdr of the element of ANYVAR who car is
;; equal to "hello".
;;
;; There are also a few special variables defined by Eshell.  '$$' is
;; the value of the last command (t or nil, in the case of an external
;; command).  This makes it possible to chain results:
;;
;;   /tmp $ echo /var/spool/mail/johnw
;;   /var/spool/mail/johnw
;;   /tmp $ dirname $$
;;   /var/spool/mail/
;;   /tmp $ cd $$
;;   /var/spool/mail $
;;
;; '$_' refers to the last argument of the last command.  And $?
;; contains the exit code of the last command (0 or 1 for Lisp
;; functions, based on successful completion).

;;; Code:

(require 'esh-util)
(require 'esh-cmd)
(require 'esh-opt)
(require 'esh-module)
(require 'esh-arg)
(require 'esh-io)

(require 'pcomplete)
(require 'ring)

(defgroup eshell-var nil
  "Variable interpolation is introduced whenever the `$' character
appears unquoted in any argument (except when that argument is
surrounded by single quotes).  It may be used to interpolate a
variable value, a subcommand, or even the result of a Lisp form."
  :tag "Variable handling"
  :group 'eshell)

;;; User Variables:

(defcustom eshell-var-load-hook nil
  "A list of functions to call when loading `eshell-var'."
  :version "24.1"			; removed eshell-var-initialize
  :type 'hook)

(defcustom eshell-prefer-lisp-variables nil
  "If non-nil, prefer Lisp variables to environment variables."
  :type 'boolean)

(defcustom eshell-complete-export-definition t
  "If non-nil, completing names for `export' shows current definition."
  :type 'boolean)

(defcustom eshell-modify-global-environment nil
  "If non-nil, using `export' changes Emacs's global environment."
  :type 'boolean)

(defcustom eshell-variable-name-regexp "[A-Za-z0-9_-]+"
  "A regexp identifying what constitutes a variable name reference.
Note that this only applies for `$NAME'.  If the syntax `$<NAME>' is
used, then NAME can contain any character, including angle brackets,
if they are quoted with a backslash."
  :type 'regexp)

(defcustom eshell-variable-aliases-list
  `(;; for eshell.el
    ("COLUMNS" ,(lambda (_indices) (window-width)) t)
    ("LINES" ,(lambda (_indices) (window-height)) t)

    ;; for eshell-cmd.el
    ("_" ,(lambda (indices)
	    (if (not indices)
	        (car (last eshell-last-arguments))
	      (eshell-apply-indices eshell-last-arguments
				    indices))))
    ("?" eshell-last-command-status)
    ("$" eshell-last-command-result)
    ("0" eshell-command-name)
    ("1" ,(lambda (_indices) (nth 0 eshell-command-arguments)))
    ("2" ,(lambda (_indices) (nth 1 eshell-command-arguments)))
    ("3" ,(lambda (_indices) (nth 2 eshell-command-arguments)))
    ("4" ,(lambda (_indices) (nth 3 eshell-command-arguments)))
    ("5" ,(lambda (_indices) (nth 4 eshell-command-arguments)))
    ("6" ,(lambda (_indices) (nth 5 eshell-command-arguments)))
    ("7" ,(lambda (_indices) (nth 6 eshell-command-arguments)))
    ("8" ,(lambda (_indices) (nth 7 eshell-command-arguments)))
    ("9" ,(lambda (_indices) (nth 8 eshell-command-arguments)))
    ("*" ,(lambda (indices)
	    (if (not indices)
	        eshell-command-arguments
	      (eshell-apply-indices eshell-command-arguments
				    indices)))))
  "This list provides aliasing for variable references.
Each member defines the name of a variable, and a Lisp value used to
compute the string value that will be returned when the variable is
accessed via the syntax `$NAME'.

If the value is a function, call that function with two arguments: the
list of the indices that was used in the reference, and whether the
user is requesting the length of the ultimate element.  For example, a
reference of `$NAME[10][20]' would result in the function for alias
`NAME' being called (assuming it were aliased to a function), and the
arguments passed to this function would be the list '(10 20)', and
nil.

If the value is a string, return the value for the variable with that
name in the current environment.  If no variable with that name exists
in the environment, but if a symbol with that same name exists and has
a value bound to it, return its value instead.  You can prioritize
symbol values over environment values by setting
`eshell-prefer-lisp-variables' to t.

If the value is a symbol, return the value bound to it.

If the value has any other type, signal an error.

Additionally, each member may specify if it should be copied to the
environment of created subprocesses."
  :type '(repeat (list string sexp
		       (choice (const :tag "Copy to environment" t)
			       (const :tag "Use only in Eshell" nil)))))

(put 'eshell-variable-aliases-list 'risky-local-variable t)

(defvar eshell-var-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "C-c M-v") #'eshell-insert-envvar)
    map))

;;; Functions:

(define-minor-mode eshell-var-mode
  "Minor mode for the esh-var module.

\\{eshell-var-mode-map}"
  :keymap eshell-var-mode-map)

(defun eshell-var-initialize ()     ;Called from `eshell-mode' via intern-soft!
  "Initialize the variable handle code."
  ;; Break the association with our parent's environment.  Otherwise,
  ;; changing a variable will affect all of Emacs.
  (unless eshell-modify-global-environment
    (setq-local process-environment (eshell-copy-environment)))

  (setq-local eshell-special-chars-inside-quoting
       (append eshell-special-chars-inside-quoting '(?$)))
  (setq-local eshell-special-chars-outside-quoting
       (append eshell-special-chars-outside-quoting '(?$)))

  (add-hook 'eshell-parse-argument-hook #'eshell-interpolate-variable t t)

  (add-hook 'eshell-prepare-command-hook
	    #'eshell-handle-local-variables nil t)

  (when (eshell-using-module 'eshell-cmpl)
    (add-hook 'pcomplete-try-first-hook
	      #'eshell-complete-variable-reference nil t)
    (add-hook 'pcomplete-try-first-hook
	      #'eshell-complete-variable-assignment nil t)))

(defun eshell-handle-local-variables ()
  "Allow for the syntax `VAR=val <command> <args>'."
  ;; strip off any null commands, which can only happen if a variable
  ;; evaluates to nil, such as "$var x", where `var' is nil.  The
  ;; command name in that case becomes `x', for compatibility with
  ;; most regular shells (the difference is that they do an
  ;; interpolation pass before the argument parsing pass, but Eshell
  ;; does both at the same time).
  (while (and (not eshell-last-command-name)
	      eshell-last-arguments)
    (setq eshell-last-command-name (car eshell-last-arguments)
	  eshell-last-arguments (cdr eshell-last-arguments)))
  (let ((setvar "\\`\\([A-Za-z_][A-Za-z0-9_]*\\)=\\(.*\\)\\'")
	(command (eshell-stringify eshell-last-command-name))
	(args eshell-last-arguments))
    ;; local variable settings (such as 'CFLAGS=-O2 make') are handled
    ;; by making the whole command into a subcommand, and calling
    ;; setenv immediately before the command is invoked.  This means
    ;; that 'BLAH=x cd blah' won't work exactly as expected, but that
    ;; is by no means a typical use of local environment variables.
    (if (and command (string-match setvar command))
	(throw
	 'eshell-replace-command
	 (list
	  'eshell-as-subcommand
	  (append
	   (list 'progn)
	   (let ((l (list t)))
	     (while (string-match setvar command)
	       (nconc
		l (list
		   (list 'setenv (match-string 1 command)
			 (match-string 2 command)
			 (= (length (match-string 2 command)) 0))))
	       (setq command (eshell-stringify (car args))
		     args (cdr args)))
	     (cdr l))
	   (list (list 'eshell-named-command
		       command (list 'quote args)))))))))

(defun eshell-interpolate-variable ()
  "Parse a variable interpolation.
This function is explicit for adding to `eshell-parse-argument-hook'."
  (when (and (eq (char-after) ?$)
	     (/= (1+ (point)) (point-max)))
    (forward-char)
    (list 'eshell-escape-arg
	  (eshell-parse-variable))))

(defun eshell/define (var-alias definition)
  "Define a VAR-ALIAS using DEFINITION."
  (if (not definition)
      (setq eshell-variable-aliases-list
	    (delq (assoc var-alias eshell-variable-aliases-list)
		  eshell-variable-aliases-list))
    (let ((def (assoc var-alias eshell-variable-aliases-list))
	  (alias-def
	   (list var-alias
		 (list 'quote (if (= (length definition) 1)
				  (car definition)
				definition)))))
      (if def
	  (setq eshell-variable-aliases-list
		(delq (assoc var-alias eshell-variable-aliases-list)
		      eshell-variable-aliases-list)))
      (setq eshell-variable-aliases-list
	    (cons alias-def
		  eshell-variable-aliases-list))))
  nil)

(defun eshell/export (&rest sets)
  "This alias allows the `export' command to act as bash users expect."
  (while sets
    (if (and (stringp (car sets))
	     (string-match "^\\([^=]+\\)=\\(.*\\)" (car sets)))
	(setenv (match-string 1 (car sets))
		(match-string 2 (car sets))))
    (setq sets (cdr sets))))

(defun pcomplete/eshell-mode/export ()
  "Completion function for Eshell's `export'."
  (while (pcomplete-here
	  (if eshell-complete-export-definition
	      process-environment
	    (eshell-envvar-names)))))

(defun eshell/unset (&rest args)
  "Unset an environment variable."
  (while args
    (if (stringp (car args))
	(setenv (car args) nil t))
    (setq args (cdr args))))

(defun pcomplete/eshell-mode/unset ()
  "Completion function for Eshell's `unset'."
  (while (pcomplete-here (eshell-envvar-names))))

(defun eshell/setq (&rest args)
  "Allow command-ish use of `setq'."
  (let (last-value)
    (while args
      (let ((sym (intern (car args)))
	    (val (cadr args)))
	(setq last-value (set sym val)
	      args (cddr args))))
    last-value))

(defun pcomplete/eshell-mode/setq ()
  "Completion function for Eshell's `setq'."
  (while (and (pcomplete-here (all-completions pcomplete-stub
					       obarray #'boundp))
	      (pcomplete-here))))

;; FIXME the real "env" command does more than this, it runs a program
;; in a modified environment.
(defun eshell/env (&rest args)
  "Implementation of `env' in Lisp."
  (eshell-init-print-buffer)
  (eshell-eval-using-options
   "env" args
   '((?h "help" nil nil "show this usage screen")
     :external "env"
     :usage "<no arguments>")
   (dolist (setting (sort (eshell-environment-variables) 'string-lessp))
     (eshell-buffered-print setting "\n"))
   (eshell-flush)))

(defun eshell-insert-envvar (envvar-name)
  "Insert ENVVAR-NAME into the current buffer at point."
  (interactive
   (list (read-envvar-name "Name of environment variable: " t)))
  (insert-and-inherit "$" envvar-name))

(defun eshell-envvar-names (&optional environment)
  "Return a list of currently visible environment variable names."
  (mapcar (lambda (x)
            (substring x 0 (string-search "=" x)))
	  (or environment process-environment)))

(defun eshell-environment-variables ()
  "Return a `process-environment', fully updated.
This involves setting any variable aliases which affect the
environment, as specified in `eshell-variable-aliases-list'."
  (let ((process-environment (eshell-copy-environment)))
    (dolist (var-alias eshell-variable-aliases-list)
      (if (nth 2 var-alias)
	  (setenv (car var-alias)
		  (eshell-stringify
		   (or (eshell-get-variable (car var-alias)) "")))))
    process-environment))

(defun eshell-parse-variable ()
  "Parse the next variable reference at point.
The variable name could refer to either an environment variable, or a
Lisp variable.  The priority order depends on the setting of
`eshell-prefer-lisp-variables'.

Its purpose is to call `eshell-parse-variable-ref', and then to
process any indices that come after the variable reference."
  (let* ((get-len (when (eq (char-after) ?#)
		    (forward-char) t))
	 value indices)
    (setq value (eshell-parse-variable-ref)
	  indices (and (not (eobp))
		       (eq (char-after) ?\[)
		       (eshell-parse-indices))
          ;; This is an expression that will be evaluated by `eshell-do-eval',
          ;; which only support let-binding of dynamically-scoped vars
	  value `(let ((indices ',indices)) ,value))
    (if get-len
	`(length ,value)
      value)))

(defun eshell-parse-variable-ref ()
  "Eval a variable reference.
Returns a Lisp form which, if evaluated, will return the value of the
variable.

Possible options are:

  NAME          an environment or Lisp variable value
  <LONG-NAME>   disambiguates the length of the name
  {COMMAND}     result of command is variable's value
  (LISP-FORM)   result of Lisp form is variable's value"
  (cond
   ((eq (char-after) ?{)
    (let ((end (eshell-find-delimiter ?\{ ?\})))
      (if (not end)
          (throw 'eshell-incomplete ?\{)
        (prog1
            `(eshell-convert
              (eshell-command-to-value
               (eshell-as-subcommand
                ,(eshell-parse-command (cons (1+ (point)) end)))))
          (goto-char (1+ end))))))
   ((memq (char-after) '(?\' ?\"))
    (let ((name (if (eq (char-after) ?\')
                    (eshell-parse-literal-quote)
                  (eshell-parse-double-quote))))
      (if name
	  `(eshell-get-variable ,(eval name) indices))))
   ((eq (char-after) ?\<)
    (let ((end (eshell-find-delimiter ?\< ?\>)))
      (if (not end)
          (throw 'eshell-incomplete ?\<)
        (let* ((temp (make-temp-file temporary-file-directory))
               (cmd (concat (buffer-substring (1+ (point)) end)
                            " > " temp)))
          (prog1
              `(let ((eshell-current-handles
                      (eshell-create-handles ,temp 'overwrite)))
                 (progn
                   (eshell-as-subcommand ,(eshell-parse-command cmd))
                   (ignore
                    (nconc eshell-this-command-hook
                           (list (lambda ()
                                   (delete-file ,temp)))))
                   (quote ,temp)))
            (goto-char (1+ end)))))))
   ((eq (char-after) ?\()
    (condition-case nil
        `(eshell-command-to-value
          (eshell-lisp-command
           ',(read (current-buffer))))
      (end-of-file
       (throw 'eshell-incomplete ?\())))
   ((assoc (char-to-string (char-after))
           eshell-variable-aliases-list)
    (forward-char)
    `(eshell-get-variable ,(char-to-string (char-before)) indices))
   ((looking-at eshell-variable-name-regexp)
    (prog1
        `(eshell-get-variable ,(match-string 0) indices)
      (goto-char (match-end 0))))
   (t
    (error "Invalid variable reference"))))

(defvar eshell-glob-function)

(defun eshell-parse-indices ()
  "Parse and return a list of list of indices."
  (let (indices)
    (while (eq (char-after) ?\[)
      (let ((end (eshell-find-delimiter ?\[ ?\])))
	(if (not end)
	    (throw 'eshell-incomplete ?\[)
	  (forward-char)
	  (let (eshell-glob-function)
	    (setq indices (cons (eshell-parse-arguments (point) end)
				indices)))
	  (goto-char (1+ end)))))
    (nreverse indices)))

(defun eshell-get-variable (name &optional indices)
  "Get the value for the variable NAME."
  (let* ((alias (assoc name eshell-variable-aliases-list))
	 (var (if alias
		  (cadr alias)
		name)))
    (if (and alias (functionp var))
	(funcall var indices)
      (eshell-apply-indices
       (cond
	((stringp var)
	 (let ((sym (intern-soft var)))
	   (if (and sym (boundp sym)
		    (or eshell-prefer-lisp-variables
			(memq sym eshell--local-vars) ; bug#15372
			(not (getenv var))))
	       (symbol-value sym)
	     (getenv var))))
	((symbolp var)
	 (symbol-value var))
	(t
	 (error "Unknown variable `%s'" (eshell-stringify var))))
       indices))))

(defun eshell-apply-indices (value indices)
  "Apply to VALUE all of the given INDICES, returning the sub-result.
The format of INDICES is:

  ((INT-OR-NAME-OR-OTHER INT-OR-NAME INT-OR-NAME ...)
   ...)

Each member of INDICES represents a level of nesting.  If the first
member of a sublist is not an integer or name, and the value it's
reference is a string, that will be used as the regexp with which is
to divide the string into sub-parts.  The default is whitespace.
Otherwise, each INT-OR-NAME refers to an element of the list value.
Integers imply a direct index, and names, an associate lookup using
`assoc'.

For example, to retrieve the second element of a user's record in
'/etc/passwd', the variable reference would look like:

  ${grep johnw /etc/passwd}[: 2]"
  (while indices
    (let ((refs (car indices)))
      (when (stringp value)
	(let (separator)
	  (if (not (or (not (stringp (caar indices)))
		       (string-match
			(concat "^" eshell-variable-name-regexp "$")
			(caar indices))))
	      (setq separator (caar indices)
		    refs (cdr refs)))
	  (setq value
		(mapcar #'eshell-convert
			(split-string value separator)))))
      (cond
       ((< (length refs) 0)
	(error "Invalid array variable index: %s"
	       (eshell-stringify refs)))
       ((= (length refs) 1)
	(setq value (eshell-index-value value (car refs))))
       (t
	(let ((new-value (list t)))
	  (while refs
	    (nconc new-value
		   (list (eshell-index-value value
					     (car refs))))
	    (setq refs (cdr refs)))
	  (setq value (cdr new-value))))))
    (setq indices (cdr indices)))
  value)

(defun eshell-index-value (value index)
  "Reference VALUE using the given INDEX."
  (when (and (stringp index) (get-text-property 0 'number index))
    (setq index (string-to-number index)))
  (if (stringp index)
      (cdr (assoc index value))
    (cond
     ((ring-p value)
      (if (> index (ring-length value))
	  (error "Index exceeds length of ring")
	(ring-ref value index)))
     ((listp value)
      (if (> index (length value))
	  (error "Index exceeds length of list")
	(nth index value)))
     ((vectorp value)
      (if (> index (length value))
	  (error "Index exceeds length of vector")
	(aref value index)))
     (t
      (error "Invalid data type for indexing")))))

;;;_* Variable name completion

(defun eshell-complete-variable-reference ()
  "If there is a variable reference, complete it."
  (let ((arg (pcomplete-actual-arg)) index)
    (when (setq index
		(string-match
		 (concat "\\$\\(" eshell-variable-name-regexp
			 "\\)?\\'") arg))
      (setq pcomplete-stub (substring arg (1+ index)))
      (throw 'pcomplete-completions (eshell-variables-list)))))

(defun eshell-variables-list ()
  "Generate list of applicable variables."
  (let ((argname pcomplete-stub)
	completions)
    (dolist (alias eshell-variable-aliases-list)
      (if (string-match (concat "^" argname) (car alias))
	  (setq completions (cons (car alias) completions))))
    (sort
     (append
      (mapcar
       (lambda (varname)
         (let ((value (eshell-get-variable varname)))
           (if (and value
                    (stringp value)
                    (file-directory-p value))
               (concat varname "/")
             varname)))
       (eshell-envvar-names (eshell-environment-variables)))
      (all-completions argname obarray 'boundp)
      completions)
     'string-lessp)))

(defun eshell-complete-variable-assignment ()
  "If there is a variable assignment, allow completion of entries."
  (let ((arg (pcomplete-actual-arg)) pos)
    (when (string-match (concat "\\`" eshell-variable-name-regexp "=") arg)
      (setq pos (match-end 0))
      (if (string-match "\\(:\\)[^:]*\\'" arg)
	  (setq pos (match-end 1)))
      (setq pcomplete-stub (substring arg pos))
      (throw 'pcomplete-completions (pcomplete-entries)))))

(provide 'esh-var)
;;; esh-var.el ends here