;;; esh-opt.el --- command options processing  -*- lexical-binding:t -*-

;; Copyright (C) 1999-2020 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:

;;; Code:


;; Unused.
;; (defgroup eshell-opt nil
;;   "The options processing code handles command argument parsing for
;; Eshell commands implemented in Lisp."
;;   :tag "Command options processing"
;;   :group 'eshell)

;;; User Functions:

;; Macro expansion of eshell-eval-using-options refers to eshell-stringify-list
;; defined in esh-util.
(require 'esh-util)

(defmacro eshell-eval-using-options (name macro-args options &rest body-forms)
  "Process NAME's MACRO-ARGS using a set of command line OPTIONS.
After doing so, stores settings in local symbols as declared by OPTIONS;
then evaluates BODY-FORMS -- assuming all was OK.

OPTIONS is a list, beginning with one or more elements of the form:
\(SHORT LONG VALUE SYMBOL HELP-STRING)
Each of these elements represents a particular command-line switch.

SHORT is either nil, or a character that can be used as a switch -SHORT.
LONG is either nil, or a string that can be used as a switch --LONG.
At least one of SHORT and LONG must be non-nil.
VALUE is the value associated with the option.  It can be either:
  t   - the option needs a value to be specified after the switch;
  nil - the option is given the value t;
  anything else - specifies the actual value for the option.
SYMBOL is either nil, or the name of the Lisp symbol that will be bound
to VALUE.  A nil SYMBOL calls `eshell-show-usage', and so is appropriate
for a \"--help\" type option.
HELP-STRING is a documentation string for the option.

Any remaining elements of OPTIONS are :KEYWORD arguments.  Some take
arguments, some do not.  The recognized :KEYWORDS are:

:external STRING
  STRING is an external command to run if there are unknown switches.

:usage STRING
  STRING is the initial part of the command's documentation string.
  It appears before the options are listed.

:post-usage STRING
  STRING is an optional trailing part of the command's documentation string.
  It appears after the options, but before the final part of the
  documentation about the associated external command (if there is one).

:show-usage
  If present, then show the usage message if the command is called with no
  arguments.

:preserve-args
  If present, do not pass MACRO-ARGS through `flatten-tree'
and `eshell-stringify-list'.

:parse-leading-options-only
  If present, do not parse dash or switch arguments after the first
positional argument.  Instead, treat them as positional arguments themselves.

For example, OPTIONS might look like:

   ((?C  nil         nil multi-column    \"multi-column display\")
    (nil \"help\"      nil nil             \"show this usage display\")
    (?r  \"reverse\"   nil reverse-list    \"reverse order while sorting\")
    :external \"ls\"
    :usage \"[OPTION]... [FILE]...
  List information about the FILEs (the current directory by default).
  Sort entries alphabetically across.\")

`eshell-eval-using-options' returns the value of the last form in
BODY-FORMS.  If instead an external command is run (because of
an unknown option), the tag `eshell-external' will be thrown with
the new process for its value.

Lastly, any remaining arguments will be available in the locally
let-bound variable `args'."
  (declare (debug (form form sexp body)))
  `(let* ((temp-args
           ,(if (memq ':preserve-args (cadr options))
                macro-args
              (list 'eshell-stringify-list
                    (list 'flatten-tree macro-args))))
          (processed-args (eshell--do-opts ,name ,options temp-args))
          ,@(delete-dups
             (delq nil (mapcar (lambda (opt)
                                 (and (listp opt) (nth 3 opt)
                                      `(,(nth 3 opt) (pop processed-args))))
                               ;; `options' is of the form (quote OPTS).
                               (cadr options))))
          (args processed-args))
     ;; Silence unused lexical variable warning if body does not use `args'.
     (ignore args)
     ,@body-forms))

;;; Internal Functions:

;; Documented part of the interface; see eshell-eval-using-options.
(defvar eshell--args)

(defun eshell--do-opts (name options args)
  "Helper function for `eshell-eval-using-options'.
This code doesn't really need to be macro expanded everywhere."
  (require 'esh-ext)
  (declare-function eshell-external-command "esh-ext" (command args))
  (let ((ext-command
         (catch 'eshell-ext-command
           (let ((usage-msg
                  (catch 'eshell-usage
                    (if (and (= (length args) 0)
                             (memq ':show-usage options))
                        (eshell-show-usage name options)
                      (setq args (eshell--process-args name args options))
                      nil))))
             (when usage-msg
               (error "%s" usage-msg))))))
    (if ext-command
        (throw 'eshell-external
               (eshell-external-command ext-command args))
      args)))

(defun eshell-show-usage (name options)
  "Display the usage message for NAME, using OPTIONS."
  (require 'esh-ext)
  (declare-function eshell-search-path "esh-ext" (name))
  (let ((usage (format "usage: %s %s\n\n" name
		       (cadr (memq ':usage options))))
	(extcmd (memq ':external options))
	(post-usage (memq ':post-usage options))
	had-option)
    (while options
      (when (listp (car options))
	(let ((opt (car options)))
	  (setq had-option t)
	  (cond ((and (nth 0 opt)
		      (nth 1 opt))
		 (setq usage
		       (concat usage
			       (format "    %-20s %s\n"
				       (format "-%c, --%s" (nth 0 opt)
					       (nth 1 opt))
				       (nth 4 opt)))))
		((nth 0 opt)
		 (setq usage
		       (concat usage
			       (format "    %-20s %s\n"
				       (format "-%c" (nth 0 opt))
				       (nth 4 opt)))))
		((nth 1 opt)
		 (setq usage
		       (concat usage
			       (format "    %-20s %s\n"
				       (format "    --%s" (nth 1 opt))
				       (nth 4 opt)))))
		(t (setq had-option nil)))))
      (setq options (cdr options)))
    (if post-usage
	(setq usage (concat usage (and had-option "\n")
			    (cadr post-usage))))
    (when extcmd
      (setq extcmd (eshell-search-path (cadr extcmd)))
      (if extcmd
	  (setq usage
		(concat usage
			(format-message "
This command is implemented in Lisp.  If an unrecognized option is
passed to this command, the external version `%s'
will be called instead." extcmd)))))
    (throw 'eshell-usage usage)))

(defun eshell--set-option (name ai opt options opt-vals)
  "Using NAME's remaining args (index AI), set the OPT within OPTIONS.
If the option consumes an argument for its value, the argument list
will be modified."
  (if (not (nth 3 opt))
      (eshell-show-usage name options)
    (setcdr (assq (nth 3 opt) opt-vals)
            (if (eq (nth 2 opt) t)
                (if (> ai (length eshell--args))
                    (error "%s: missing option argument" name)
                  (pop (nthcdr ai eshell--args)))
              (or (nth 2 opt) t)))))

(defun eshell--process-option (name switch kind ai options opt-vals)
  "For NAME, process SWITCH (of type KIND), from args at index AI.
The SWITCH will be looked up in the set of OPTIONS.

SWITCH should be either a string or character.  KIND should be the
integer 0 if it's a character, or 1 if it's a string.

The SWITCH is then be matched against OPTIONS.  If no matching handler
is found, and an :external command is defined (and available), it will
be called; otherwise, an error will be triggered to say that the
switch is unrecognized."
  (let* ((opts options)
	 found)
    (while opts
      (if (and (listp (car opts))
               (nth kind (car opts))
               (equal switch (nth kind (car opts))))
	  (progn
	    (eshell--set-option name ai (car opts) options opt-vals)
	    (setq found t opts nil))
	(setq opts (cdr opts))))
    (unless found
      (let ((extcmd (memq ':external options)))
	(when extcmd
	  (setq extcmd (eshell-search-path (cadr extcmd)))
	  (if extcmd
	      (throw 'eshell-ext-command extcmd)
            (error (if (characterp switch) "%s: unrecognized option -%c"
                     "%s: unrecognized option --%s")
                   name switch)))))))

(defun eshell--process-args (name args options)
  "Process the given ARGS using OPTIONS."
  (let* ((seen ())
         (opt-vals (delq nil (mapcar (lambda (opt)
                                       (when (listp opt)
                                         (let ((sym (nth 3 opt)))
                                           (when (and sym (not (memq sym seen)))
					     (push sym seen)
                                             (list sym)))))
				     options)))
         (ai 0) arg
         (eshell--args args)
         (pos-argument-found nil))
    (while (and (< ai (length eshell--args))
                ;; Abort if we saw the first pos argument and option is set
                (not (and pos-argument-found
                          (memq :parse-leading-options-only options))))
      (setq arg (nth ai eshell--args))
      (if (not (and (stringp arg)
		    (string-match "^-\\(-\\)?\\(.*\\)" arg)))
          ;; Positional argument found, skip
	  (setq ai (1+ ai)
                pos-argument-found t)
        ;; dash or switch argument found, parse
	(let* ((dash (match-string 1 arg))
	       (switch (match-string 2 arg)))
	  (pop (nthcdr ai eshell--args))
	  (if dash
	      (if (> (length switch) 0)
		  (eshell--process-option name switch 1 ai options opt-vals)
		(setq ai (length eshell--args)))
	    (let ((len (length switch))
		  (index 0))
	      (while (< index len)
		(eshell--process-option name (aref switch index)
                                        0 ai options opt-vals)
		(setq index (1+ index))))))))
    (nconc (mapcar #'cdr opt-vals) eshell--args)))

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