@startuml Settings_Popup
    participant TD                  as TD
    participant OS                  as OS
    participant Script              as Script
    participant SW                  as SW
    participant UI                  as UI
    actor       USER                as US

    'Possible actions and interaction types
    ' External on CANBus
    ' TD -> SW: MSG: Message
    ' SW -> TD: MSG: Message

    ' Internal to the application
    ' XX -> YY: CMD: Command
    ' XX -> XX: ACT: Action

    ' External on OS/FS
    ' SW -> Script: ACT: Command
    ' Script -> OS: CMD: Command
    ' Script -> SW: MSG: Message
    ' OS -> Script: MSG: Message

    ' US -> UI: User actions are:
    '   ASK: Display a <message>
    '   ENT: User enters a value or string
    '   TCH: User touches a button (RadioButton, CheckBox, ...)
    '   SCL: User scrolls a flip-able area

    == Navigate to popup ==
    US -> UI: TCH: Press settings headerbar icon button
    UI -> UI: ACT: Settings Popup is displayed

    == Brightness ==
    US -> UI: SCL: Brightness Slider
    UI -> SW: ACT: Request Brightness Update \
                \n\tonReleased: send slider value
    SW -> Script: ACT: brightness.sh ( )
    activate Script
        Script -> OS: CMD: set BRIGHTNESS SYSFS with updated brightness value
        OS -> Script: MSG: Current or updated brightness value
        Script -> SW: MSG: \
            \n - echo $BRIGHTNESS_VALUE \
            \n - exit #
    deactivate Script
    alt successful ( exit == 0 )
        SW -> UI: ACT: Send current brightness value set in BRIGHTNESS SYSFS
        UI -> UI: ACT:                              \
            \n - Brightness value text updated      \
            \n - Current slider position verified   
    else failed
        SW -> UI: ACT: Script Error
        UI -> UI: ACT: Undefined brightness value\n\tSlider Reverts or previous position
        UI -> US: ACT: Notify user
    end

    == Alarm Volume ==
    US -> UI: SCL: Alarm Volume Slider
    UI -> SW: ACT: Request Volume Adjustment \
                \n\tonReleased: send slider value

    SW -> TD: MSG: [xB: #1]     \
                \n\tRequest:    \
                \n\t(U32) volume

    TD -> SW: MSG: [xC: #1]             \
                \n\tResponse:           \
                \n\t(BOOL)  accepted    \
                \n\t(U32)   RR

    alt successful ( exit == 0 )
        SW -> UI: ACT: Send accepted volume value 
        UI -> UI: ACT: Update Volume Text and slider position
    else failed
        SW -> UI: ACT: Send error message
        UI -> US: ACT: Notify user
    end
@enduml