ApuOperation = object
  updates*: array[ChannelId, ChannelUpdate]
  sweep*: Option[uint8]
  volume*: Option[uint8]

ChannelAction = enum
  caNone,                   ## No action, do not update channel
  caUpdate,                 ## Update the channel by writing its registers
  caCut,                    ## Note stopped, turn DAC off
  caShutdown                 ## Channel was unlocked, zero the channel's registers

ChannelState = object
  envelope*: uint16
  timbre*: uint8
  panning*: uint8
  frequency*: uint16

ChannelUpdate = object
  case action*: ChannelAction
  of caNone:
      nil

  of caUpdate:
      flags*: UpdateFlags
      state*: ChannelState
      trigger*: bool

  of caCut:
      nil

  of caShutdown:
      nil

  

EngineFrame = object
  halted*: bool              ## Indicates if the song has halted
  startedNewRow*: bool       ## Indicates if this frame is the first of a new row being stepped.
  startedNewPattern*: bool   ## Indicates if this frame is the first step of a new pattern.
  speed*: uint8              ## Current playback speed, in Q4.4 format.
  time*: int                 ## time index of the frame
  order*: int                ## Current pattern index
  row*: int                  ## Current row index
  

GlobalState = object
  patternCommand*: PatternCommand
  patternCommandParam*: uint8
  panning*: array[ChannelId, uint8]
  speed*: uint8
  sweep*: Option[uint8]
  volume*: Option[uint8]
  halt*: bool

UpdateFlag = enum
  ufTimbre, ufEnvelope, ufPanning, ufFrequency

UpdateFlags = set[UpdateFlag]

ufAll = {ufTimbre..ufFrequency}

func init(_: typedesc[ChannelState]): ChannelState

func init(T: typedesc[GlobalState]): GlobalState