Draft: Resolve #3511366 "Poc content type template config entity type"

Closes #3511366

config/schema/experience_builder.schema.yml

@@ -397,6 +397,127 @@ field.field_settings.component_tree:
   constraints:
     FullyValidatable: ~
 
+experience_builder.content_type_template.*.*.*:
+  type: config_entity
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    id:
+      # This ID intentionally does not use `type: machine_name`, because it is a composite ID that is better validated
+      # using the `StringParts` constraint than the `RegEx` constraint.
+      type: string
+      label: 'ID'
+      constraints:
+        StringParts:
+          separator: .
+          reservedCharacters:
+            - ':'
+          reservedCharactersSubstitute: .
+          parts:
+            - '%parent.content_entity_type_id'
+            - '%parent.content_entity_type_bundle'
+            - '%parent.content_entity_type_view_mode'
+        Length:
+          # @see \Drupal\Core\Config\Entity\ConfigEntityStorage::MAX_ID_LENGTH
+          max: 166
+    content_entity_type_id:
+      type: string
+      label: 'Content Entity Type ID'
+      constraints:
+        PluginExists:
+          manager: entity_type.manager
+          interface: Drupal\Core\Entity\ContentEntityInterface
+    content_entity_type_bundle:
+      type: string
+      label: 'Bundle'
+      constraints:
+        EntityBundleExists: '%parent.target_entity_type_id'
+    content_entity_type_view_mode:
+      type: string
+      label: 'View mode'
+      constraints:
+        # @todo Definitely require the corresponding EntityViewMode config entity to exist. This would require adding support for dynamic values to be specified in the `prefix` option for \Drupal\Core\Config\Plugin\Validation\Constraint\ConfigExistsConstraintValidator, or for XB to subclass it. The latter is the only pragmatic choice that avoids being blocked on core. Note that core's \Drupal\Core\Validation\Plugin\Validation\Constraint\EntityBundleExistsConstraintValidator already supports this.
+        ConfigExists:
+          # @see \Drupal\Core\Entity\Entity\EntityViewMode
+          prefix: core.entity_view_mode.[%parent.content_entity_type_id]
+    # A single component tree.
+    component_tree:
+      constraints:
+        ComponentTreeMeetRequirements:
+          # Both StaticPropSource and DynamicPropSources may be used, because this can rely on an entity of a particular
+          # type and bundle to be present everywhere it is inserted/used.
+          inputs:
+            absence:
+              - adapter
+              - url-preview
+            # In fact, it MUST use DynamicPropSources, otherwise it would not be a template for a content entity type:
+            # it would be presenting static data.
+            presence:
+              - dynamic
+          tree:
+            absence:
+              # Components implementing either of these 2 interfaces are only
+              # allowed to live at the PageRegion level.
+              # @see \Drupal\experience_builder\Entity\PageRegion
+              # @see `type: experience_builder.page_region.*`
+              - Drupal\Core\Block\TitleBlockPluginInterface
+              - Drupal\Core\Block\MessagesBlockPluginInterface
+            presence: ~
+      type: experience_builder.component_tree
+      label: 'The component tree to present an entity of this content entity type in this view mode.'
+
+# Content type templates for the `default` view mode are special: they're the only ones that are allowed
+# to have exposed slots. For example:
+# exposed_slots:
+#   profile_bio:
+#     label: 'Profile Bio!'
+#     component_uuid: 28bcab26-e434-4ad4-9eaf-0520bdb32fcc
+#     slot_name: column_two
+#   intro:
+#     label: 'Intro'
+#     component_uuid: 98bcab26-e434-4ad4-9eaf-0520bdb32fcc
+#     slot_name: body
+experience_builder.content_type_template.*.*.default:
+  type: experience_builder.content_type_template.*.*.*
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    exposed_slots:
+      type: sequence
+      label: 'Exposed slots'
+      # Note: this is a sequence ordered by key, because the keys must be the machine names assigned to the
+      # exposed slots. These machine names are essentially "aliases" for a particular slot of a particular
+      # component instance in the template's tree.
+      # @todo Validate that the exposed slots' machine names are, well, valid machine names.
+      orderby: key
+      sequence:
+        # Note: if this sequence is empty, no Content Type Slots are exposed to the Content Creator by the Site Builder
+        # that crafted this Content Type Template. Consequentially, there would be NOTHING for the end user to do, other
+        # than entering values in the content entity form under the "Page Data" tab.
+        type: mapping
+        mapping:
+          # The UUID of a component instance that contains the slot which we are exposing. This CANNOT be
+          # \Drupal\experience_builder\Plugin\DataType\ComponentTreeStructure::ROOT_UUID, because that would mean the
+          # entire template was being overridden by an individual content entity, which is what our special
+          # landing page content entity type is meant for.
+          # @todo Validate that this component exists in the template's tree, and that the slot we're exposing is
+          #    empty in that instance.
+          component_uuid:
+            type: uuid
+            label: 'UUID of the component instance which contains the slot being exposed'
+            constraints: {}
+          # The name of the slot that is being exposed. For example, if the component that contains
+          # this exposed slot is a `two_column` SDC, this could be `column_one`.
+          # @todo Validate that this slot is actually defined by the component.
+          slot_name:
+            type: string
+            constraints: {}
+          # A human-readable name for the exposed slot.
+          label:
+            type: required_label
+            label: 'Exposed slot label'
+          # @todo In the future, we may define per-slot restrictions here for product requirement `17. Restrict nested components`
+
 experience_builder.pattern.*:
   type: config_entity
   constraints: