Give Windows devices an identifier, and ask ffmpeg for them once

Three things about the dshow backend, all of them found by reading rather
than by running, so all three want checking on a real Windows machine.

The device listing is parsed in both of the shapes ffmpeg has printed it in:
newer builds mark every device `(audio)` or `(video)`, older ones print a
heading and no marks, and only the first was read. Each pattern is anchored at
both ends now, so the error lines the command ends with, which quote the device
name it was told to look for, are no longer read as a device of that name.

What is stored for a device is the alternative name under it rather than the
friendly one. A laptop with a headset plugged in has two microphones called the
same thing, and `audio=Microphone` reaches the first of them whichever one was
picked; the alternative name is unique. The friendly name stays what is shown,
which is what the (id, description) pair in these lists has always been for.

An unset microphone meant "the first one listed", and the listing costs an
ffmpeg of its own, so every press of the key paid for a process before the
recording started. The last listing is remembered instead, and opening Settings
or running `dikte devices` takes a fresh one.

And a fourth thing, which is about what the interface says rather than what it
does: whether the far side of a meeting can be captured at all is now an entry
in `audio.Sound` instead of being read off an empty device list. The two are not
the same answer. An empty list on Linux means pactl is not installed, which a
user can go and fix; False on Windows means there is no such device and no
driver that would add one. The Meeting tab says so under the empty box, and
starting a meeting says it instead of sending somebody to Settings to pick from
a list that will never have anything in it.

tests/test_audio.py

@@ -822,6 +822,42 @@ class MacRecordingCommand(OnMacOS, DikteTest):
         self.assertFalse(recorder.active)
 
 
+class NoFarSideToRecord(DikteTest):
+    """Two different answers, and the table is what tells them apart.
+
+    A sound system that records the far side has a device this machine could
+    not pick out, and Settings is where to choose one. A sound system that does
+    not had nothing to offer there in the first place, and "pick one" would
+    send somebody to an empty box and an installation that cannot help.
+    """
+
+    def failure(self, meetings):
+        recorder = audio.MeetingRecorder()
+        failures = []
+        recorder.failed.connect(failures.append)
+        with only_these_tools("ffmpeg"), \
+                mock.patch.object(audio, "default_monitor", return_value=""), \
+                mock.patch.object(audio, "sound",
+                                  return_value=audio.PULSE._replace(
+                                      meetings=meetings)):
+            recorder.start(str(self.path("meeting.wav")))
+        self.assertFalse(recorder.active)
+        return failures[0]
+
+    def test_a_system_that_records_the_far_side_sends_you_to_settings(self):
+        self.assertIn("Settings", self.failure(True))
+
+    def test_a_system_that_does_not_says_that_instead(self):
+        message = self.failure(False)
+        self.assertIn("nothing that records what the speakers", message)
+        self.assertNotIn("Settings", message)
+
+    def test_the_three_sound_systems_each_answer_the_question(self):
+        self.assertTrue(audio.PULSE.meetings)
+        self.assertTrue(audio.COREAUDIO.meetings)
+        self.assertFalse(audio.DSHOW.meetings)
+
+
 class OnWindows:
     """A test that runs as if the machine ran Windows."""
 
@@ -837,51 +873,108 @@ class WindowsDevices(OnWindows, DikteTest):
     whatever alphabet the machine speaks, so the listing here does too.
     """
 
+    MIC = "@device_cm_{33D9A762}\\wave_{B1C2}"
     LISTING = (
         '[dshow @ 0000020c] "Integrated Camera" (video)\n'
         '[dshow @ 0000020c]   Alternative name "@device_pnp_\\...."\n'
         '[dshow @ 0000020c] "Mikrofon Dizisi (Intel Smart Sound)" (audio)\n'
-        '[dshow @ 0000020c]   Alternative name "@device_cm_{33D9A762}...."\n'
+        f'[dshow @ 0000020c]   Alternative name "{MIC}"\n'
         '[dshow @ 0000020c] "Kulaklık (Soundcore Life Q30)" (audio)\n'
+        '[dshow @ 0000020c] Could not find audio only device with name '
+        '"dummy" among source devices of type audio.\n'
         "dummy: Immediate exit requested\n"
     ).encode("utf-8")
 
+    def setUp(self):
+        super().setUp()
+        # The listing is remembered between calls, so that a dictation does not
+        # run ffmpeg of its own. It cannot be remembered between tests.
+        audio._DSHOW_SEEN.clear()
+        self.addCleanup(audio._DSHOW_SEEN.clear)
+
     @contextlib.contextmanager
     def listing(self, stderr=None, tools=("ffmpeg",)):
         completed = FakeCompleted(
             returncode=1, stderr=self.LISTING if stderr is None else stderr)
         with only_these_tools(*tools), \
-                mock.patch.object(subprocess, "run", return_value=completed):
-            yield
+                mock.patch.object(subprocess, "run",
+                                  return_value=completed) as run:
+            yield run
 
     def test_windows_records_through_dshow(self):
         self.assertIs(audio.sound(), audio.DSHOW)
 
-    def test_the_audio_lines_are_the_only_ones_read(self):
+    def test_the_audio_devices_are_the_only_ones_read(self):
         with self.listing():
             self.assertEqual(audio.list_sources(), [
-                ("Mikrofon Dizisi (Intel Smart Sound)",
-                 "Mikrofon Dizisi (Intel Smart Sound)"),
+                (self.MIC, "Mikrofon Dizisi (Intel Smart Sound)"),
                 ("Kulaklık (Soundcore Life Q30)",
                  "Kulaklık (Soundcore Life Q30)"),
             ])
 
+    def test_the_device_ffmpeg_could_not_open_is_not_one_of_them(self):
+        """The command ends by quoting the name it was sent to look for."""
+        with self.listing():
+            self.assertNotIn("dummy", [name for _, name in audio.list_sources()])
+
+    def test_a_listing_from_an_ffmpeg_that_marks_nothing(self):
+        """Older builds print a heading instead of an (audio) on every line."""
+        listing = (
+            '[dshow @ 0] DirectShow video devices\n'
+            '[dshow @ 0]  "Integrated Camera"\n'
+            '[dshow @ 0]     Alternative name "@device_pnp_\\..."\n'
+            '[dshow @ 0] DirectShow audio devices\n'
+            '[dshow @ 0]  "Microphone (Realtek Audio)"\n'
+            '[dshow @ 0]     Alternative name "@device_cm_{ABCD}"\n'
+        ).encode("utf-8")
+        with self.listing(stderr=listing):
+            self.assertEqual(audio.list_sources(),
+                             [("@device_cm_{ABCD}", "Microphone (Realtek Audio)")])
+
+    def test_two_devices_called_the_same_thing_stay_apart(self):
+        """The normal state of a laptop with a headset plugged into it."""
+        listing = (
+            '[dshow @ 0] "Microphone" (audio)\n'
+            '[dshow @ 0]   Alternative name "@device_cm_{ONE}"\n'
+            '[dshow @ 0] "Microphone" (audio)\n'
+            '[dshow @ 0]   Alternative name "@device_cm_{TWO}"\n'
+        ).encode("utf-8")
+        with self.listing(stderr=listing):
+            sources = audio.list_sources()
+        self.assertEqual([identifier for identifier, _ in sources],
+                         ["@device_cm_{ONE}", "@device_cm_{TWO}"])
+        self.assertEqual({name for _, name in sources}, {"Microphone"})
+
     def test_no_ffmpeg_installed(self):
         with only_these_tools():
             self.assertEqual(audio.list_sources(), [])
             self.assertEqual(audio.recording_command(), [])
 
-    def test_the_name_is_what_the_recorder_is_given_back(self):
+    def test_the_identifier_is_what_the_recorder_is_given_back(self):
         with self.listing():
-            cmd = audio.recording_command("Kulaklık (Soundcore Life Q30)")
+            cmd = audio.recording_command(self.MIC)
         self.assertEqual(cmd[cmd.index("-f") + 1], "dshow")
-        self.assertIn("audio=Kulaklık (Soundcore Life Q30)", cmd)
+        self.assertIn(f"audio={self.MIC}", cmd)
 
     def test_no_microphone_named_means_the_first_one_listed(self):
         """dshow has no default device for an empty target to mean."""
         with self.listing():
-            self.assertIn("audio=Mikrofon Dizisi (Intel Smart Sound)",
-                          audio.recording_command())
+            self.assertIn(f"audio={self.MIC}", audio.recording_command())
+
+    def test_a_dictation_does_not_run_a_listing_of_its_own(self):
+        """Two hundred milliseconds of ffmpeg in front of every key press."""
+        with self.listing() as run:
+            audio.list_sources()
+            audio.recording_command()
+            audio.recording_command()
+        self.assertEqual(run.call_count, 1)
+
+    def test_opening_the_device_list_asks_again(self):
+        """Which is what somebody who has just plugged one in does."""
+        with self.listing() as run:
+            audio.list_sources()
+            audio.list_sources()
+        self.assertEqual(run.call_count, 2)
 
     def test_a_machine_with_no_microphone_at_all(self):
         with self.listing(stderr=b'[dshow @ 0] "Integrated Camera" (video)\n'):
@@ -899,6 +992,15 @@ class WindowsDevices(OnWindows, DikteTest):
             self.assertEqual(audio.default_monitor(), "")
             self.assertEqual(audio.meeting_commands("mic", "sys"), [])
 
+    def test_a_meeting_says_what_is_wrong_rather_than_where_to_look(self):
+        recorder = audio.MeetingRecorder()
+        failures = []
+        recorder.failed.connect(failures.append)
+        with self.listing():
+            recorder.start(str(self.path("meeting.wav")))
+        self.assertIn("nothing that records what the speakers", failures[0])
+        self.assertFalse(recorder.active)
+
 
 if __name__ == "__main__":
     unittest.main()