HeadphoneKeyEventBluetooth: Initial thought with MPRemoteCommandCenter

Turns out that `MPRemoteCommandCenter` seems to work for the 'play'
button, but it has no interface for volume buttons. I remember
discovering the volume button problem when I last looked into it several
months ago, but since forgot.

This was an attempt at replicating the method in:
https://github.com/russellhancox/btrcd/blob/c3e375f/btrcd/AppDelegate.m
by setting up an `MPRemoteCommandCenter` and calling
`addTargetWithHandler:` on each button to invoke a custom handler.

Committing this for reference. In order to get volume button
functionality, we'll have to dive into lower level Bluetooth events with
AVRCP. Seems that newer headphones might even use something newer than
AVRCP, so I wonder if we'll have to use multiple Bluetooth remote
control profiles.

A bit of a pain, as there doesn't seem to be a pre-built interface for
us to do this, but I'm learning more about interacting with IOBluetooth.
Also, `MPRemoteCommandCenter` is an OS X 10.12 Sierra API, so if there's
something we can use that's available on earlier OSes, that's a plus.

4 files changed, 34 insertions, 1 deletions

diff --git a/DomeKey/HeadphoneKey.h b/DomeKey/HeadphoneKey.h
index 6670ff5..d5e9e76 100644
--- a/DomeKey/HeadphoneKey.h
+++ b/DomeKey/HeadphoneKey.h
@@ -51,6 +51,7 @@
 
 #import "HeadphoneKeyEventDelegate.h"
 #import "HeadphoneKeyEventWired.h"
+#import "HeadphoneKeyEventBluetooth.h"
 #import "Mappings.h"
 #import "Sounds.h"
 #import "dome_key_map.h"
@@ -60,6 +61,7 @@ static const Milliseconds TIMEOUT_DEFAULT = 500;
 
 @interface HeadphoneKey : NSObject <HeadphoneKeyEventDelegate> {
     HeadphoneKeyEventWired *_wired_headphone_event;
+    HeadphoneKeyEventBluetooth *_bluetooth_headphone_event;
     NSMutableArray *_key_buffer;
     Mappings *_mappings;
     Milliseconds _timeout;
diff --git a/DomeKey/HeadphoneKey.m b/DomeKey/HeadphoneKey.m
index 3aa79ce..beba94d 100644
--- a/DomeKey/HeadphoneKey.m
+++ b/DomeKey/HeadphoneKey.m
@@ -60,6 +60,8 @@ static BOOL _play_audio;
     if (self) {
         _wired_headphone_event = [[HeadphoneKeyEventWired alloc]
             initWithDelegate:self];
+        _bluetooth_headphone_event = [[HeadphoneKeyEventBluetooth alloc]
+            initWithDelegate:self];
 
         _key_buffer = [[NSMutableArray alloc] initWithCapacity:5];
 
diff --git a/DomeKey/HeadphoneKeyEventBluetooth.h b/DomeKey/HeadphoneKeyEventBluetooth.h
index 00577c3..86e0ce7 100644
--- a/DomeKey/HeadphoneKeyEventBluetooth.h
+++ b/DomeKey/HeadphoneKeyEventBluetooth.h
@@ -8,6 +8,13 @@
 
 #import <Foundation/Foundation.h>
 
-@interface HeadphoneKeyEventBluetooth : NSObject
+#import "HeadphoneKeyEventDelegate.h"
+#import "dome_key_map.h"
+
+@interface HeadphoneKeyEventBluetooth : NSObject {
+    id <HeadphoneKeyEventDelegate> _delegate;
+}
+
+- (instancetype)initWithDelegate:(id <HeadphoneKeyEventDelegate>)delegate;
 
 @end
diff --git a/DomeKey/HeadphoneKeyEventBluetooth.m b/DomeKey/HeadphoneKeyEventBluetooth.m
index 3c02486..52e22db 100644
--- a/DomeKey/HeadphoneKeyEventBluetooth.m
+++ b/DomeKey/HeadphoneKeyEventBluetooth.m
@@ -10,4 +10,26 @@
 
 @implementation HeadphoneKeyEventBluetooth
 
+- (instancetype)initWithDelegate:(id <HeadphoneKeyEventDelegate>)delegate
+{
+    self = [self init];
+    if (self) {
+        _delegate = delegate;
+
+        MPRemoteCommandCenter *cc = [MPRemoteCommandCenter sharedCommandCenter];
+        [cc playCommand];
+        [cc pauseCommand];
+        [cc stopCommand];
+        [cc togglePlayPauseCommand];
+        // [cc nextTrackCommand];
+        // [cc seekForwardCommand];
+        // [cc previousTrackCommand];
+        // [cc seekBackwardCommand];
+    }
+    return self;
+}
+
+MPRemoteCommandHandler key_pressed(HeadphoneButton button) {
+}
+
 @end