Add: emms-tracktag wrapper for the audiotools program

http://audiotools.sourceforge.net/ provides a tool `tracktag`
which handles writing tags for several different audio formats,
including Opus. this patch provides a very basic wrapper to interface
between EMMS track info and tracktag metadata. It also configures
emms-tag-editor.el to use it for writing tags to Opus files.

Add: test.sh and test/test-all.el

Basic setup to run ert tests from the terminal using Emacs in batch
mode. This should load up only ERT, the tests in the test/ directory
and their dependencies.

Add: opus extension to emms-libtag-known-extensions

libtag works as a reader for opus files, this just ads the opus
extension to the regexp list.

1 files changed, 71 insertions, 0 deletions

diff --git a/emms-tracktag.el b/emms-tracktag.el
new file mode 100644
index 0000000..0b8b660
--- /dev/null
+++ b/emms-tracktag.el
@@ -0,0 +1,71 @@
+;;; emms-tracktag.el --- EMMS interface for audiotools tracktag  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2021  Grant Shoshin Shangreaux
+
+;; Author: Grant Shoshin Shangreaux <grant@churls.world>
+;; Keywords:
+
+;; This program 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.
+
+;; This program 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 <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Provides a wrapper for audiotools tracktag executable
+;; http://audiotools.sourceforge.net/tracktag.html
+;; Given an EMMS TRACK structure, it will map the emms-info fields onto
+;; arguments for tracktag. Then it calls the tracktag process to write the
+;; info as metadata tags on the track's associated file.
+
+;;; Code:
+
+(require 'emms)
+
+(defvar emms-info-tracktag--info-fields
+  '((info-album . album)
+    (info-artist . artist)
+    (info-composer . composer)
+    (info-performer . performer)
+    (info-year . year)
+    (info-date . year)
+    (info-tracknumber . number)
+    (info-discnumber . album-number)
+    (info-note . comment)
+    (info-title . name))
+  "An alist mapping info-* fields to tracktag fields.")
+
+(defun emms-tracktag--map-track-info (track)
+  (seq-filter (lambda (cell) (cdr cell))
+              (mapcar (lambda (pair)
+                        (cons (cdr pair) (emms-track-get track (car pair))))
+                      emms-info-tracktag--info-fields)))
+
+(defun emms-tracktag--build-args (track)
+  (flatten-list
+   (append (mapcar (lambda (pair)
+                     (let ((tag (car pair)) (value (cdr pair)))
+                       (when value
+                         (if (string-equal value "") (concat "--remove-" (format "%s" tag))
+                           (concat "--" (format "%s" tag) "=" value)))))
+                   (emms-tracktag--map-track-info track))
+           (list (emms-track-name track)))))
+
+(defun emms-tracktag-file (track)
+  (apply #'call-process
+   "tracktag" nil
+   (get-buffer-create emms-tag-editor-log-buffer)
+   nil
+   "-Vdebug"
+   (emms-tracktag--build-args track)))
+
+(provide 'emms-tracktag)
+;;; emms-tracktag.el ends here