@startuml
skinparam BackgroundColor F0F0F0
== Vol Change - from BT ==
BT ->  EVM: Vol Change request (same key symualtion)
EVM -> App: Vol Change request process Audio
== Vol Up/Down - to BT ==
EVM ->  App: process Up/Down key (popup)
        App -> Audio: request Vol Up/Down (finally)
        hnote over Audio
            Software codec applies gain
        endhnote
        EVM <- Audio: Notify sound change
        EVM -> App: show sound change
== BT device registration - audio ==
BT ->   EVM: Event: BTA2DPOn (connection established)
EVM -> Audio: Event: BTA2DPOn
hnote over Audio
            Audio notified about new BT A2DP device
        endhnote
BT <- Audio: BluetoothStreamRequestMessage (requesting metadata & queue handles)
BT -> Audio: BluetoothStreamRequestMessageResult (metadata & queue handles)
hnote over Audio
            BT A2DP setup done,
            ready to playback
        endhnote
== BT device registration - COM:WIP ==
BT -> EVM: notify new device
hnote over EVM
    do whatever whoever wants with COM port
    same as with audio device (open handles...)
endhnote
== BT device - close ==
BT -> EVM: Event: BTA2DPOff
EVM -> Audio: Event: BTA2DPOff
      EVM <- Audio: Inform that bt audio ended (?)
      EVM -> App: Show bt change (?)
hnote over BT
    BT closes handles to streams ( i.e. pipes)
    and closes it's device handling
    don't pass callback : pass handle
endhnote
@enduml