@startuml
skinparam NoteTextAlignment left
skinparam Padding 2
skinparam ParticipantPadding 50
skinparam LifelineStrategy solid
autonumber

participant "FHIR Server\nREST API"     as S
participant "Client"                    as C
participant "Client Endpoint\n(HTTP/S)" as E

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

  S->>E: HTTP POST - Handshake\n""Bundle:""\n""            Bundle.type: history""\n""SubscriptionStatus.type: handshake""
  return HTTP Success, e.g.:\n""200: OK""

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

group REST Subscription Processing
else Server sends heartbeat
  S->>E: HTTP POST - Heartbeat\n""Bundle:""\n""            Bundle.type: history""\n""SubscriptionStatus.type: heartbeat""
  return HTTP Success, e.g.:\n""200: OK""
  ...
else Server sends event-notification
  S->>E: HTTP POST - Notification\n""Bundle:""\n""            Bundle.type: history""\n""SubscriptionStatus.type: event-notification""
  return HTTP Success, e.g.:\n""200: OK""
  ...
end

@enduml