@startuml

Title ElectricUI Protocol

participant "Host" as Host
participant "Target" as Target

== Device Discovery ==

Host -> Target: Board ID request
hnote over Target
    { DataLen(0), Type(8), Int(1), Offset(0), IdLen(1), Resp(1), Acknum(0), Id('i') }
endhnote
|||
Target --> Host: Board ID response
hnote over Host
    { DataLen(2), Type(8), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('i'), Data(0xBEEF) }
endhnote
|||
Host -> Target: Message "name" request
hnote over Target
    { DataLen(0), Type(0), Int(0), Offset(0), IdLen(4), Resp(1), Acknum(0), Id('name') }
endhnote
|||
Target --> Host: Message "name" response
hnote over Host
    { DataLen(8), Type(4), Int(0), Offset(0), IdLen(4), Resp(0), Acknum(0), Id('name'), Data('my-board') }
endhnote

== Handshake ==

Host -> Target: Announce writable IDs request
hnote over Target
    { DataLen(0), Type(0), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('t') }
endhnote
|||
Target --> Host: Delimit writable ID response(s)
hnote over Host
    { DataLen(34), Type(1), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('u'), Data(...) }
endhnote
|||
Target --> Host: End of writable IDs response
hnote over Host
    { DataLen(1), Type(6), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('v'), Data(num_ids) }
endhnote
|||
Host -> Target: Send writable variables request
hnote over Target
    { DataLen(0), Type(0), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('w') }
endhnote
|||
Target --> Host: Writable variables response(s)
hnote over Host
    { DataLen(1), Type(6), Int(0), Offset(0), IdLen(9), Resp(0), Acknum(0), Id('led_blink'), Data(0) }
endhnote

== Repetition: Heartbeat ==

Host -> Target: Heartbeat request
hnote over Target
    { DataLen(1), Type(6), Int(1), Offset(0), IdLen(1), Resp(1), Acknum(0), Id('h'), Data(2) }
endhnote
|||
Target --> Host: Heartbeat response
hnote right #FFAAAA: Must respond with the request's heartbeat value (u8)
hnote over Host
    { DataLen(1), Type(6), Int(1), Offset(0), IdLen(1), Resp(0), Acknum(0), Id('h'), Data(2) }
endhnote

== Repetition: Query ==

Host -> Target: Query request
hnote over Target
    { DataLen(0), Type(6), Int(0), Offset(0), IdLen(9), Resp(1), Acknum(0), Id('led_state') }
endhnote
|||
Target --> Host: Query response
hnote over Host
    { DataLen(1), Type(6), Int(0), Offset(0), IdLen(9), Resp(0), Acknum(0), Id('led_state'), Data(1) }
endhnote

== Repetition: Action ==

Host -> Target: Action request (callback event or data)
hnote over Target
    { DataLen(2), Type(8), Int(0), Offset(0), IdLen(8), Resp(1), Acknum(1), Id('lit_time'), Data(22) }
endhnote
hnote right #aqua: Set's variable named 'lit_time' = 22
|||
Target --> Host: Action response
hnote over Host
    { DataLen(2), Type(8), Int(0), Offset(0), IdLen(8), Resp(0), Acknum(0), Id('lit_time'), Data(22) }
endhnote

@enduml