Batch/Include tags for fhir subscriptions

README.md

Here's my take on handling batched notifications and included resources in id-only notifications.

1. Whenever you batch multiple events in a notification you NEED to include a "focus" in the header, since you could for instance have the same resource show up multiple times in the header.
2. Whenever you have _include resources in the bundle, you need to tag that entry saying that (in addition to maybe being the focus based on "focus") you are including it for a specific event. IE, rather than tagging what resoure this was included from, you tag the event ID (which has 1 focus resource we now know this was included for).

I have 4 examples attached showing different notification use cases: Simple -> Encounter1 Include -> Encounter2 includes Encounter1 Batch -> Encounter1, Encounter2, Encounter1 Batch and Include -> Encounter 2 includes Encounter1, Encounter1

I haven't explored how this will work with full resource payloads. That combined with include makes this pretty complex.

batch.json

{
    "resourceType": "Bundle",
    "id": "notification-id-only",
    "meta": {
      "profile": [
        "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-subscription-notification"
      ]
    },
    "type": "history",
    "timestamp": "2020-05-29T11:44:13.1882432-05:00",
    "entry": [
      {
        "fullUrl": "urn:uuid:b21e4fae-ce73-45cb-8e37-1e203362b2ae",
        "resource": {
          "resourceType": "SubscriptionStatus",
          "id": "b21e4fae-ce73-45cb-8e37-1e203362b2ae",
          "status": "active",
          "type": "event-notification",
          "eventsSinceSubscriptionStart": "310",
          "eventsInNotification": 3,
          "subscription": {
            "reference": "https://example.org/fhir/r4/Subscription/admission"
          },
          "topic": "http://example.org/fhir/r4/SubscriptionTopic/admission",
          "focus": [
            "https://example.org/fhir/r4/Encounter/Encounter1",
            "https://example.org/fhir/r4/Encounter/Encounter2",
            "https://example.org/fhir/r4/Encounter/Encounter1"
          ]
        }
      },
      {
        "fullUrl": "https://example.org/fhir/r4/Patient/Encounter1"
      },
      {
        "fullUrl": "https://example.org/fhir/r4/Encounter/Encounter2"
      }
    ]
  }

batchAndInclude.json

{
    "resourceType": "Bundle",
    "id": "notification-id-only",
    "meta": {
      "profile": [
        "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-subscription-notification"
      ]
    },
    "type": "history",
    "timestamp": "2020-05-29T11:44:13.1882432-05:00",
    "entry": [
      {
        "fullUrl": "urn:uuid:b21e4fae-ce73-45cb-8e37-1e203362b2ae",
        "resource": {
          "resourceType": "SubscriptionStatus",
          "id": "b21e4fae-ce73-45cb-8e37-1e203362b2ae",
          "status": "active",
          "type": "event-notification",
          "eventsSinceSubscriptionStart": "310",
          "eventsInNotification": 1,
          "subscription": {
            "reference": "https://example.org/fhir/r4/Subscription/admission"
          },
          "topic": "http://example.org/fhir/r4/SubscriptionTopic/admission",
          "focus": [
              "https://example.org/fhir/r4/Encounter/Encounter2",
              "https://example.org/fhir/r4/Encounter/Encounter1"
            ]
        }
      },
      {
        "fullUrl": "https://example.org/fhir/r4/Encounter/Encounter2"
      },
      {
        "extension": {
            "url": "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-include-event-key",
            "valueString": "310"
        },
        "fullUrl": "https://example.org/fhir/r4/Patient/Encounter1"
      }
    ]
  }

include.json

{
    "resourceType": "Bundle",
    "id": "notification-id-only",
    "meta": {
      "profile": [
        "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-subscription-notification"
      ]
    },
    "type": "history",
    "timestamp": "2020-05-29T11:44:13.1882432-05:00",
    "entry": [
      {
        "fullUrl": "urn:uuid:b21e4fae-ce73-45cb-8e37-1e203362b2ae",
        "resource": {
          "resourceType": "SubscriptionStatus",
          "id": "b21e4fae-ce73-45cb-8e37-1e203362b2ae",
          "status": "active",
          "type": "event-notification",
          "eventsSinceSubscriptionStart": "310",
          "eventsInNotification": 1,
          "subscription": {
            "reference": "https://example.org/fhir/r4/Subscription/admission"
          },
          "topic": "http://example.org/fhir/r4/SubscriptionTopic/admission"
        }
      },
      {
        "fullUrl": "https://example.org/fhir/r4/Encounter/Encounter2"
      },
      {
        "extension": {
            "url": "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-include-event-key",
            "valueString": "310"
        },
        "fullUrl": "https://example.org/fhir/r4/Patient/Encounter1"
      }
    ]
  }

simple.json

{
    "resourceType": "Bundle",
    "id": "notification-id-only",
    "meta": {
      "profile": [
        "http://hl7.org/fhir/uv/subscriptions-backport/StructureDefinition/backport-subscription-notification"
      ]
    },
    "type": "history",
    "timestamp": "2020-05-29T11:44:13.1882432-05:00",
    "entry": [
      {
        "fullUrl": "urn:uuid:b21e4fae-ce73-45cb-8e37-1e203362b2ae",
        "resource": {
          "resourceType": "SubscriptionStatus",
          "id": "b21e4fae-ce73-45cb-8e37-1e203362b2ae",
          "status": "active",
          "type": "event-notification",
          "eventsSinceSubscriptionStart": "310",
          "eventsInNotification": 1,
          "subscription": {
            "reference": "https://example.org/fhir/r4/Subscription/admission"
          },
          "topic": "http://example.org/fhir/r4/SubscriptionTopic/admission"
        }
      },
      {
        "fullUrl": "https://example.org/fhir/r4/Encounter/Encounter1"
      }  
    ]
  }