;;; epg-config.el --- configuration of the EasyPG Library

;; Copyright (C) 2006-2016 Free Software Foundation, Inc.

;; Author: Daiki Ueno <ueno@unixuser.org>
;; Keywords: PGP, GnuPG
;; Package: epg

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

;;; Code:

(eval-when-compile (require 'cl-lib))

(defconst epg-package-name "epg"
  "Name of this package.")

(defconst epg-version-number "1.0.0"
  "Version number of this package.")

(defconst epg-bug-report-address "ueno@unixuser.org"
  "Report bugs to this address.")

(defgroup epg ()
  "Interface to the GNU Privacy Guard (GnuPG)."
  :tag "EasyPG"
  :version "23.1"
  :group 'data
  :group 'external)

(defcustom epg-gpg-program (if (executable-find "gpg2")
                               "gpg2"
                             "gpg")
  "The `gpg' executable."
  :version "25.1"
  :group 'epg
  :type 'string)

(defcustom epg-gpgsm-program "gpgsm"
  "The `gpgsm' executable."
  :group 'epg
  :type 'string)

(defcustom epg-gpgconf-program "gpgconf"
  "The `gpgconf' executable."
  :version "25.1"
  :group 'epg
  :type 'string)

(defcustom epg-gpg-home-directory nil
  "The directory which contains the configuration files of `epg-gpg-program'."
  :group 'epg
  :type '(choice (const :tag "Default" nil) directory))

(defcustom epg-passphrase-coding-system nil
  "Coding system to use with messages from `epg-gpg-program'."
  :group 'epg
  :type 'symbol)

(defcustom epg-debug nil
  "If non-nil, debug output goes to the \" *epg-debug*\" buffer.
Note that the buffer name starts with a space."
  :group 'epg
  :type 'boolean)

(defconst epg-gpg-minimum-version "1.4.3")

(defconst epg-config--program-alist
  '((OpenPGP
     epg-gpg-program
     epg-config--make-gpg-configuration
     ("gpg2" . "2.1.6") ("gpg" . "1.4.3"))
    (CMS
     epg-gpgsm-program
     epg-config--make-gpgsm-configuration
     ("gpgsm" . "2.0.4")))
  "Alist used to obtain the usable configuration of executables.
The first element of each entry is protocol symbol, which is
either `OpenPGP' or `CMS'.  The second element is a symbol where
the executable name is remembered.  The third element is a
function which constructs a configuration object (actually a
plist).  The rest of the entry is an alist mapping executable
names to the minimum required version suitable for the use with
Emacs.")

(defvar epg--configurations nil)

;;;###autoload
(defun epg-find-configuration (protocol &optional force)
  "Find or create a usable configuration to handle PROTOCOL.
This function first looks at the existing configuration found by
the previous invocation of this function, unless FORCE is non-nil.

Then it walks through `epg-config--program-alist'.  If
`epg-gpg-program' or `epg-gpgsm-program' is already set with
custom, use it.  Otherwise, it tries the programs listed in the
entry until the version requirement is met."
  (let ((entry (assq protocol epg-config--program-alist)))
    (unless entry
      (error "Unknown protocol %S" protocol))
    (cl-destructuring-bind (symbol constructor . alist)
        (cdr entry)
      (or (and (not force) (alist-get protocol epg--configurations))
          ;; If the executable value is already set with M-x
          ;; customize, use it without checking.
          (if (get symbol 'saved-value)
              (let ((configuration (funcall constructor (symbol-value symbol))))
                (push (cons protocol configuration) epg--configurations)
                configuration)
            (catch 'found
              (dolist (program-version alist)
                (let ((executable (executable-find (car program-version))))
                  (when executable
                    (let ((configuration
                           (funcall constructor executable)))
                      (when (ignore-errors
                              (epg-check-configuration configuration
                                                       (cdr program-version))
                              t)
                        (push (cons protocol configuration) epg--configurations)
                        (throw 'found configuration))))))))))))

;; Create an `epg-configuration' object for `gpg', using PROGRAM.
(defun epg-config--make-gpg-configuration (program)
  (let (config groups type args)
    (with-temp-buffer
      (apply #'call-process program nil (list t nil) nil
	     (append (if epg-gpg-home-directory
			 (list "--homedir" epg-gpg-home-directory))
		     '("--with-colons" "--list-config")))
      (goto-char (point-min))
      (while (re-search-forward "^cfg:\\([^:]+\\):\\(.*\\)" nil t)
	(setq type (intern (match-string 1))
	      args (match-string 2))
	(cond
	 ((eq type 'group)
	  (if (string-match "\\`\\([^:]+\\):" args)
		  (setq groups
			(cons (cons (downcase (match-string 1 args))
				    (delete "" (split-string
						(substring args
							   (match-end 0))
						";")))
			      groups))
	    (if epg-debug
		(message "Invalid group configuration: %S" args))))
	 ((memq type '(pubkey cipher digest compress))
	  (if (string-match "\\`\\([0-9]+\\)\\(;[0-9]+\\)*" args)
	      (setq config
		    (cons (cons type
				(mapcar #'string-to-number
					(delete "" (split-string args ";"))))
			  config))
	    (if epg-debug
		(message "Invalid %S algorithm configuration: %S"
			 type args))))
	 (t
	  (setq config (cons (cons type args) config))))))
    (push (cons 'program program) config)
    (if groups
	(cons (cons 'groups groups) config)
      config)))

;; Create an `epg-configuration' object for `gpgsm', using PROGRAM.
(defun epg-config--make-gpgsm-configuration (program)
  (with-temp-buffer
    (call-process program nil (list t nil) nil "--version")
    (goto-char (point-min))
    (when (looking-at "\\S-+ (")
      (goto-char (match-end 0))
      (backward-char)
      (forward-sexp)
      (skip-syntax-forward "-" (point-at-eol))
      (list (cons 'program program)
            (cons 'version (buffer-substring (point) (point-at-eol)))))))

;;;###autoload
(defun epg-configuration ()
  "Return a list of internal configuration parameters of `epg-gpg-program'."
  (declare (obsolete epg-find-configuration "25.1"))
  (epg-config--make-gpg-configuration epg-gpg-program))

(defun epg-config--parse-version (string)
  (let ((index 0)
	version)
    (while (eq index (string-match "\\([0-9]+\\)\\.?" string index))
      (setq version (cons (string-to-number (match-string 1 string))
			  version)
	    index (match-end 0)))
    (nreverse version)))

(defun epg-config--compare-version (v1 v2)
  (while (and v1 v2 (= (car v1) (car v2)))
    (setq v1 (cdr v1) v2 (cdr v2)))
  (- (or (car v1) 0) (or (car v2) 0)))

;;;###autoload
(defun epg-check-configuration (config &optional minimum-version)
  "Verify that a sufficient version of GnuPG is installed."
  (let ((entry (assq 'version config))
	version)
    (unless (and entry
		 (stringp (cdr entry)))
      (error "Undetermined version: %S" entry))
    (setq version (epg-config--parse-version (cdr entry))
	  minimum-version (epg-config--parse-version
			   (or minimum-version
			       epg-gpg-minimum-version)))
    (unless (>= (epg-config--compare-version version minimum-version) 0)
      (error "Unsupported version: %s" (cdr entry)))))

;;;###autoload
(defun epg-expand-group (config group)
  "Look at CONFIG and try to expand GROUP."
  (let ((entry (assq 'groups config)))
    (if (and entry
	     (setq entry (assoc (downcase group) (cdr entry))))
	(cdr entry))))

(provide 'epg-config)

;;; epg-config.el ends here