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.

6 files changed, 185 insertions, 2 deletions

diff --git a/emms-info-libtag.el b/emms-info-libtag.el
index fb9c5dd..9425a38 100644
--- a/emms-info-libtag.el
+++ b/emms-info-libtag.el
@@ -74,7 +74,7 @@
   :type '(string))
 
 (defcustom emms-info-libtag-known-extensions
-  (regexp-opt '("mp3" "mp4" "m4a" "ogg" "flac" "spx" "wma"))
+  (regexp-opt '("mp3" "mp4" "m4a" "ogg" "flac" "spx" "wma" "opus"))
   "Regexp of known extensions compatible with `emms-info-libtag-program-name'.
 
 Case is irrelevant."
diff --git a/emms-tag-editor.el b/emms-tag-editor.el
index 5b6e447..45c90f7 100644
--- a/emms-tag-editor.el
+++ b/emms-tag-editor.el
@@ -37,6 +37,7 @@
 (require 'emms-info-mp3info)
 (require 'emms-playlist-mode)
 (require 'emms-mark)
+(require 'emms-tracktag)
 (require 'format-spec)
 (require 'subr-x)
 
@@ -138,7 +139,8 @@ See also `emms-tag-editor-default-parser'.")
       (info-performer   . "--TOPE")
       (info-date        . "--TDAT")))
     ("ogg" . emms-tag-editor-tag-ogg)
-    ("flac" . emms-tag-editor-tag-flac))
+    ("flac" . emms-tag-editor-tag-flac)
+    ("opus" . emms-tracktag-file))
   "An alist used when committing changes to tags in files.
 If the external program sets tags by command line options
 one-by-one, then the list should like:
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
diff --git a/test.sh b/test.sh
new file mode 100755
index 0000000..50547b1
--- /dev/null
+++ b/test.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+emacs -Q --batch --directory="." -l ert -l test/test-all.el -f ert-run-tests-batch-and-exit
diff --git a/test/emms-tracktag-test.el b/test/emms-tracktag-test.el
new file mode 100644
index 0000000..9b66d5e
--- /dev/null
+++ b/test/emms-tracktag-test.el
@@ -0,0 +1,101 @@
+;; emms-tracktag-test.el --- Unit tests for emms-tracktag module  -*- 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:
+
+;; Tests for emms-tracktag.el
+
+;;; Code:
+
+(require 'emms)
+(require 'emms-tracktag)
+
+(ert-deftest emms-tracktag--map-track-info-test ()
+  "Ensure mapping of emms info to tracktag fields is correct."
+  (let ((track '(*track*
+                 (type . file) (name . "foo")
+                 (info-album . "The Sounds of the Sounds of Science")
+                 (info-artist . "Yo La Tengo")
+                 (info-title . "Sea Urchins")
+                 (info-date . "2020")
+                 (info-tracknumber . "1")))
+        (track2 '(*track*
+                  (info-composer . "Ira Kaplan, Georgia Hubley, James Mcnew")
+                  (info-performer . "Yo La Tengo")
+                  (info-year . "2002")
+                  (info-discnumber . "1")
+                  (info-note . "new soundtrack to an old film"))))
+    (should (seq-set-equal-p
+             '((album . "The Sounds of the Sounds of Science")
+               (artist . "Yo La Tengo")
+               (name . "Sea Urchins")
+               (year . "2020")
+               (number . "1"))
+             (emms-tracktag--map-track-info track)))
+    (should (seq-set-equal-p
+             '((composer . "Ira Kaplan, Georgia Hubley, James Mcnew")
+               (performer . "Yo La Tengo")
+               (year . "2002")
+               (album-number . "1")
+               (comment . "new soundtrack to an old film"))
+             (emms-tracktag--map-track-info track2)))))
+
+(ert-deftest emms-tracktag--build-args-test ()
+  "Ensure args for tracktag are properly formed."
+  (let ((track '(*track*
+                 (type . file) (name . "foo.flac")
+                 (info-album . "The Sounds of the Sounds of Science")
+                 (info-artist . "Yo La Tengo")
+                 (info-title . "Sea Urchins")
+                 (info-date . "2020")
+                 (info-tracknumber . "1")
+                 (info-composer . "Ira Kaplan, Georgia Hubley, James Mcnew")
+                 (info-performer . "Yo La Tengo")
+                 (info-discnumber . "1")
+                 (info-note . "new soundtrack to an old film"))))
+    (should (seq-set-equal-p
+             '("--album=The Sounds of the Sounds of Science"
+               "--artist=Yo La Tengo"
+               "--name=Sea Urchins"
+               "--year=2020"
+               "--number=1"
+               "--composer=Ira Kaplan, Georgia Hubley, James Mcnew"
+               "--performer=Yo La Tengo"
+               "--album-number=1"
+               "--comment=new soundtrack to an old film"
+               "foo.flac")
+             (emms-tracktag--build-args track)))
+    (let ((track-with-empty-strings (copy-alist track)))
+      (setcdr (assq 'info-title track-with-empty-strings) "")
+      (setcdr (assq 'info-note track-with-empty-strings) "")
+      (should (seq-set-equal-p
+               '("--album=The Sounds of the Sounds of Science"
+                 "--artist=Yo La Tengo"
+                 "--year=2020"
+                 "--number=1"
+                 "--composer=Ira Kaplan, Georgia Hubley, James Mcnew"
+                 "--performer=Yo La Tengo"
+                 "--album-number=1"
+                 "--remove-comment"
+                 "--remove-name"
+                 "foo.flac")
+               (emms-tracktag--build-args track-with-empty-strings))))))
+
+;;; emms-tracktag-test.el ends here
diff --git a/test/test-all.el b/test/test-all.el
new file mode 100644
index 0000000..36f00c7
--- /dev/null
+++ b/test/test-all.el
@@ -0,0 +1,6 @@
+;; maybe not needed, but ensures tests run against the latest changes
+(byte-recompile-directory ".")
+
+(mapc #'load
+      (mapcar (lambda (f) (file-truename (concat "test/" f)))
+              (seq-filter (lambda (f) (string-match "[^.#]+\\test.el$" f)) (directory-files (file-truename "./test")))))