Design delta API

Created by: eseliger

Do the GraphQL schema design for the delta API.

Idea for a delta API

diff --git a/cmd/frontend/graphqlbackend/schema.graphql b/cmd/frontend/graphqlbackend/schema.graphql
index ec24543057..de99c386c6 100755
--- a/cmd/frontend/graphqlbackend/schema.graphql
+++ b/cmd/frontend/graphqlbackend/schema.graphql
@@ -683,6 +683,78 @@ enum ChangesetSpecType {
     BRANCH
 }
 
+"""
+Description of the current changeset state vs the changeset spec desired state.
+"""
+type ChangesetSpecDelta {
+    """
+    When run, the title of the changeset will be updated.
+    """
+    titleChanged: Boolean!
+    """
+    When run, the body of the changeset will be updated.
+    """
+    bodyChanged: Boolean!
+    """
+    When run, the changeset will be published as a draft.
+    """
+    draftChanged: Boolean!
+    """
+    When run, the target branch of the changeset will be updated.
+    """
+    baseRefChanged: Boolean!
+    """
+    When run, a new commit will be created on the branch of the changeset.
+    """
+    diffChanged: Boolean!
+    """
+    When run, a new commit will be created on the branch of the changeset.
+    """
+    commitMessageChanged: Boolean!
+    """
+    When run, a new commit in the name of the specified author will be created on the branch of the changeset.
+    """
+    authorNameChanged: Boolean!
+    """
+    When run, a new commit in the name of the specified author will be created on the branch of the changeset.
+    """
+    authorEmailChanged: Boolean!
+}
+
+"""
+This enum declares all operations supported by the reconciler.
+"""
+enum ChangesetSpecOperation {
+    """
+    Update the existing changeset on the codehost. This may include pushing a new commit, which will become clearer when we have the PUSH operation.
+    """
+    UPDATE
+    """
+    Move the existing changeset out of being a draft.
+    """
+    UNDRAFT
+    """
+    Publish a changeset to the codehost.
+    """
+    PUBLISH
+    """
+    Publish a changeset to the codehost as a draft changeset. (Only on supported code hosts).
+    """
+    PUBLISH_DRAFT
+    """
+    Sync the changeset with the current state on the codehost.
+    """
+    SYNC
+    """
+    Close the changeset on the codehost.
+    """
+    CLOSE
+    """
+    Reopen the changeset on the codehost.
+    """
+    REOPEN
+}
+
 """
 A changeset spec is an immutable description of the desired state of a changeset in a campaign. To
 create a changeset spec, use the createChangesetSpec mutation.
@@ -698,6 +770,21 @@ interface ChangesetSpec {
     spec never expires (and this field is null) if its campaign spec has been applied.
     """
     expiresAt: DateTime
+
+    """
+    The operations to take to achieve the desired state of this changeset spec.
+    """
+    operations: [ChangesetSpecOperation!]!
+
+    """
+    The delta between the current changeset state and what this changeset spec envisions the changeset to look like.
+    """
+    delta: ChangesetSpecDelta!
+
+    """
+    The changeset that this changeset spec will modify. Empty if the changeset spec creates a new changeset.
+    """
+    changeset: Changeset
 }
 
 """
@@ -727,6 +814,21 @@ type HiddenChangesetSpec implements ChangesetSpec & Node {
     spec never expires (and this field is null) if its campaign spec has been applied.
     """
     expiresAt: DateTime
+
+    """
+    The operations to take to achieve the desired state of this changeset spec.
+    """
+    operations: [ChangesetSpecOperation!]!
+
+    """
+    The delta between the current changeset state and what this changeset spec envisions the changeset to look like.
+    """
+    delta: ChangesetSpecDelta!
+
+    """
+    The changeset that this changeset spec will modify. Empty if the changeset spec creates a new changeset.
+    """
+    changeset: Changeset
 }
 
 """
@@ -761,6 +863,21 @@ type VisibleChangesetSpec implements ChangesetSpec & Node {
     spec never expires (and this field is null) if its campaign spec has been applied.
     """
     expiresAt: DateTime
+
+    """
+    The operations to take to achieve the desired state of this changeset spec.
+    """
+    operations: [ChangesetSpecOperation!]!
+
+    """
+    The delta between the current changeset state and what this changeset spec envisions the changeset to look like.
+    """
+    delta: ChangesetSpecDelta!
+
+    """
+    The changeset that this changeset spec will modify. Empty if the changeset spec creates a new changeset.
+    """
+    changeset: Changeset
 }
 
 """