Implement camera direction toggle

// FREEBIE

Signal/src/ViewControllers/CallViewController.swift

@@ -856,10 +856,13 @@ class CallViewController: OWSViewController, CallObserver, CallServiceObserver,
     }
 
     func didPressFlipCamera(sender: UIButton) {
-        let wantsRearFacingCamera = sender.isSelected
-        Logger.info("\(TAG) in \(#function) with wantsRearFacingCamera: \(wantsRearFacingCamera)")
+        // toggle value
+        sender.isSelected = !sender.isSelected
 
-//        callUIAdapter.updateCamera(call: call, wantsRearFacingCamera: wantsRearFacingCamera)
+        let useBackCamera = sender.isSelected
+        Logger.info("\(TAG) in \(#function) with useBackCamera: \(useBackCamera)")
+
+        callUIAdapter.setCameraSource(call: call, useBackCamera: useBackCamera)
     }
 
     /**

Signal/src/call/CallService.swift

@@ -1164,6 +1164,22 @@ protocol CallServiceObserver: class {
         self.setHasLocalVideo(hasLocalVideo: true)
     }
 
+    func setCameraSource(call: SignalCall, useBackCamera: Bool) {
+        SwiftAssertIsOnMainThread(#function)
+
+        guard call == self.call else {
+            owsFail("\(logTag) in \(#function) for non-current call.")
+            return
+        }
+
+        guard let peerConnectionClient = self.peerConnectionClient else {
+            owsFail("\(logTag) in \(#function) peerConnectionClient was unexpectedly nil")
+            return
+        }
+
+        peerConnectionClient.setCameraSource(useBackCamera: useBackCamera)
+    }
+
     /**
      * Local client received a message on the WebRTC data channel. 
      *

Signal/src/call/PeerConnectionClient.swift

@@ -120,6 +120,8 @@ class PeerConnectionClient: NSObject, RTCPeerConnectionDelegate, RTCDataChannelD
     private var videoCaptureSession: AVCaptureSession?
     private var videoSender: RTCRtpSender?
     private var localVideoTrack: RTCVideoTrack?
+    private var localVideoSource: RTCAVFoundationVideoSource?
+
     // RTCVideoTrack is fragile and prone to throwing exceptions and/or
     // causing deadlock in its destructor.  Therefore we take great care
     // with this property.
@@ -203,6 +205,8 @@ class PeerConnectionClient: NSObject, RTCPeerConnectionDelegate, RTCDataChannelD
 
         // TODO: Revisit the cameraConstraints.
         let videoSource = factory.avFoundationVideoSource(with: cameraConstraints)
+        self.localVideoSource = videoSource
+
         self.videoCaptureSession = videoSource.captureSession
         videoSource.useBackCamera = false
 
@@ -220,6 +224,21 @@ class PeerConnectionClient: NSObject, RTCPeerConnectionDelegate, RTCDataChannelD
         self.videoSender = videoSender
     }
 
+    public func setCameraSource(useBackCamera: Bool) {
+        guard let localVideoSource = self.localVideoSource else {
+            owsFail("\(logTag) in \(#function) localVideoSource was unexpectedly nil")
+            return
+        }
+
+        // certain devices, e.g. 16GB iPod touch don't have a back camera
+        guard localVideoSource.canUseBackCamera else {
+            owsFail("\(logTag) in \(#function) canUseBackCamera was unexpectedly false")
+            return
+        }
+
+        localVideoSource.useBackCamera = useBackCamera
+    }
+
     public func setLocalVideoEnabled(enabled: Bool) {
         SwiftAssertIsOnMainThread(#function)
 

Signal/src/call/UserInterface/CallUIAdapter.swift

@@ -87,11 +87,14 @@ extension CallUIAdaptee {
     private let adaptee: CallUIAdaptee
     private let contactsManager: OWSContactsManager
     internal let audioService: CallAudioService
+    internal let callService: CallService
 
     required init(callService: CallService, contactsManager: OWSContactsManager, notificationsAdapter: CallNotificationsAdapter) {
         SwiftAssertIsOnMainThread(#function)
 
         self.contactsManager = contactsManager
+        self.callService = callService
+
         if Platform.isSimulator {
             // CallKit doesn't seem entirely supported in simulator.
             // e.g. you can't receive calls in the call screen.
@@ -247,6 +250,12 @@ extension CallUIAdaptee {
         call.audioSource = audioSource
     }
 
+    internal func setCameraSource(call: SignalCall, useBackCamera: Bool) {
+        SwiftAssertIsOnMainThread(#function)
+
+        callService.setCameraSource(call: call, useBackCamera: useBackCamera)
+    }
+
     // CallKit handles ringing state on it's own. But for non-call kit we trigger ringing start/stop manually.
     internal var hasManualRinger: Bool {
         SwiftAssertIsOnMainThread(#function)