Device group support

[defagos]

As a Google Cast owner of several devices I need to be able to individually control volume/muted for paired devices.

Acceptance criteria

• An API for listing multizone devices is available.
• An API for controlling volume/muted for multizone devices is available.
• Changes are not possible for devices which do not support them.
• APIs for easy SwiftUI binding to controls are available.
• The standard Castor device management UI displays paired devices as well as individual volume/muted controls.

Design hints

The Google Cast SDK API introduces separate GCKMultizoneDevice objects, whose volume/muted values are controlled via GCKCastSession. Multizone devices are not nested within GCKDevice objects, they are rather retrieved using a GCKCastDeviceStatusListener attached to the session once connected to a device, and lost afterwards. Note that GCKDevice and GCKMultizoneDevice are different objets, not sharing a common ancestor. They have a few similar APIs but the comparison stops here.

For this reason the following API seems reasonable:

• CastDeviceManager, resp. CastMultizoneDeviceManager, are introduced to provide volume/muted control APIs (volume and range, muted flag). These are ObservableObjects which can be bound to UI elements.
• Two recipes MultizoneVolumeRecipe and MultizoneMutedRecipe are added to perform sync of volume/muted for a multizone device. CastDeviceManager is rewritten to use existing similar recipes (currently in Cast) and CastMultizoneDeviceManager is implemented similarly.
• A CastMultizoneDevice type is added, wrapping a GCKMultizoneDevice. This type is similar to CastDevice with only limited API relevant to multizone devices.
• A MultizoneDevicesRecipe is created to sync the multizone devices. A multizoneDevices property is added to sync the array of multizone devices.
• Volume and muted APIs are removed from Cast. Instead two methods deviceManager(for:) with similar signatures are added to retrieve a manager for a device or multizone device.

Tasks

• Add new multizone device type.
• Add new recipes:
  • Multizone devices.
  • Multizone volume.
  • Multizone muted.
• Implement device managers:
  • Refactor existing current device management.
  • Add multizone device manager.
• Synchronize multizone devices in Cast.
• Replace volume/muted APIs in Cast with device manager creation APIs.
• Find if there is a way to have common CastMuteButton and CastMuteIcon without code duplication.
• Update existing volume slider to use the new API.
• Display secondary sliders for multizone devices (if > 1).
• Ensure correct behavior when part of the paired devices are disconnected.

[github-actions]

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