@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 "Client FHIR Server\nREST Endpoint" as E

group Subscription Negotiation
  C->S: Create Subscription\n""channel.type: message""
  return Success\n""Subscription.status: requested""

  S->>E: POST ""$process-message"" (handshake)\n""Bundle:""\n""  Bundle.type: message""\n""  entry[1]: Bundle: subscription-notification""\n""    SubscriptionStatus.type: handshake""
  return Success, e.g.:\n""200: OK""

  note right of S
    Server updates Subscription:
    ""Subscription.status: active""
  end note

end

group FHIR Messaging Subscription Processing
else Server sends heartbeat
  S->>E: POST ""$process-message"" (heartbeat)\n""Bundle:""\n""  Bundle.type: message""\n""  entry[1]: Bundle: subscription-notification""\n""    SubscriptionStatus.type: heartbeat""
  return Success, e.g.:\n""200: OK""
  ...
else Server sends event-notification
  S->>E: POST ""$process-message"" (event-notification)\n""Bundle:""\n""  Bundle.type: message""\n""  entry[1]: Bundle: subscription-notification""\n""    SubscriptionStatus.type: event-notification""
  return Success, e.g.:\n""200: OK""
  ...
end

@enduml