@startuml
skinparam NoteTextAlignment left
skinparam Padding 2
skinparam ParticipantPadding 40
skinparam LifelineStrategy solid
autonumber

participant "FHIR Server\nREST API"     as S
participant "Client"                    as C
participant "FHIR Server\nWebsocket Endpoint" as E

group Subscription Negotiation
  C->S: Create Subscription\n""channel.type: websocket""
  return Success\n""Subscription.status: active""
end

group Websocket Subscription Processing
else Client binds via initial token
  C->S: FHIR Operation:\n"".../Subscription/example/$get-ws-binding-token""
  return FHIR Parameters:\n""        token: token-abc""\n""   expiration: some-future-date-time""\n""websocket-url: wss://example.org/fhirR4ws""

  C->E: Connect\n""wss://example.org/fhirR4ws""

  C->E: ""bind-with-token token-abc""
  return Bundle:\n""            Bundle.type: history""\n""SubscriptionStatus.type: handshake""

else Sever sends heartbeat
    E->C: Bundle:\n""            Bundle.type: history""\n""SubscriptionStatus.type: heartbeat""
    ...
else Server sends event-notification
    E->C: Bundle:\n""            Bundle.type: history""\n""SubscriptionStatus.type: event-notification""
    ...
else Token is expiring soon
    C->S: FHIR Operation:\n"".../Subscription/example/$get-ws-binding-token""
    return FHIR Parameters:\n""        token: token-def""\n""   expiration: another-future-date-time""\n""websocket-url: wss://example.org/fhirR4ws""

    C o->o E: Client checks the url and establishes\na new connection if necessary

    C->E: ""bind-with-token: token-def""
    return Bundle:\n""            Bundle.type: history""\n""SubscriptionStatus.type: handshake""
    ...
else Either system may end a session
  C x-x E: Disconnect
end

deactivate E

@enduml