;;; guix-external.el --- External programs  -*- lexical-binding: t -*-

;; Copyright © 2015 Alex Kost <alezost@gmail.com>

;; This file is part of GNU Guix.

;; GNU Guix 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 Guix 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 <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This file provides auxiliary code for running external programs.

;;; Code:

(defgroup guix-external nil
  "Settings for external programs."
  :group 'guix)

(defcustom guix-dot-program (executable-find "dot")
  "Name of the 'dot' executable."
  :type 'string
  :group 'guix-external)

(defcustom guix-dot-default-arguments
  '("-Tpng")
  "Default arguments for 'dot' program."
  :type '(repeat string)
  :group 'guix-external)

(defcustom guix-dot-file-name-function #'guix-png-file-name
  "Function used to define a file name of a temporary 'dot' file.
The function is called without arguments."
  :type '(choice (function-item guix-png-file-name)
                 (function :tag "Other function"))
  :group 'guix-external)

(defun guix-dot-arguments (output-file &rest args)
  "Return a list of dot arguments for writing a graph into OUTPUT-FILE.
If ARGS is nil, use `guix-dot-default-arguments'."
  (or guix-dot-program
      (error (concat "Couldn't find 'dot'.\n"
                     "Set guix-dot-program to a proper value")))
  (apply #'list
         guix-dot-program
         (concat "-o" output-file)
         (or args guix-dot-default-arguments)))

(defun guix-dot-file-name ()
  "Call `guix-dot-file-name-function'."
  (funcall guix-dot-file-name-function))

(defun guix-png-file-name ()
  "Return '.png' file name in the `temporary-file-directory'."
  (concat (make-temp-name
           (concat (file-name-as-directory temporary-file-directory)
                   "guix-emacs-graph-"))
          ".png"))

(provide 'guix-external)

;;; guix-external.el ends here
