Graph clean-up

- Renamed ObjectGraph to GraphProtocol
- Added small Graph structure
- Changed topological sort to use all nodes and edges of a graph
- Removed Mutable Graph
- Removed neighbourhood selector

Sources/PoieticCore/Constraints/Constraint+Node.swift

@@ -6,7 +6,8 @@
 //
 
 public final class UniqueNeighbourRequirement: ConstraintRequirement {
-    public let selector: NeighborhoodSelector
+    public let predicate: Predicate
+    public let direction: EdgeDirection
     public let isRequired: Bool
 
     /// Creates a constraint for unique neighbour.
@@ -21,8 +22,9 @@ public final class UniqueNeighbourRequirement: ConstraintRequirement {
     ///       matching node
     ///     - required: Wether the unique neighbour is required.
     ///
-    public init(_ selector: NeighborhoodSelector, required: Bool=false) {
-        self.selector = selector
+    public init(_ predicate: Predicate, direction: EdgeDirection = .outgoing, required: Bool=false) {
+        self.predicate = predicate
+        self.direction = direction
         self.isRequired = required
     }
 
@@ -32,7 +34,9 @@ public final class UniqueNeighbourRequirement: ConstraintRequirement {
             guard $0.structure.type == .node else {
                 return false
             }
-            let hood = frame.hood($0.id, selector: self.selector)
+            let hood = frame.hood($0.id, direction: direction) { edge in
+                predicate.match(frame: frame, object: edge.snapshot)
+            }
             let count = hood.edges.count
 
             return count > 1 || (count == 0 && isRequired)

Sources/PoieticCore/Constraints/Constraint.swift

@@ -52,10 +52,8 @@ public struct ConstraintViolation: Error, CustomDebugStringConvertible {
 ///     name: "one_parameter_for_graphical_function",
 ///     match: IsTypePredicate(ObjectType.GraphicalFunction),
 ///     requirement: UniqueNeighbourRequirement(
-///         NeighborhoodSelector(
-///             predicate: IsTypePredicate(ObjectType.Parameter),
-///             direction: .incoming
-///         ),
+///         IsTypePredicate(ObjectType.Parameter),
+///         direction: .incoming,
 ///         required: false
 ///     )
 /// )

Sources/PoieticCore/Design/Frame.swift

@@ -10,7 +10,7 @@
 /// Fame Base is a protocol for all version frame types: ``TransientFrame`` and
 /// ``StableFrame``
 ///
-public protocol Frame: ObjectGraph where Node == Snapshot, Edge == EdgeSnapshot {
+public protocol Frame: GraphProtocol where Node == Snapshot, Edge == EdgeSnapshot {
     associatedtype Snapshot: ObjectSnapshot
     /// Design to which the frame belongs.
     var design: Design { get }
@@ -303,22 +303,6 @@ extension Frame {
     public func top() -> [Snapshot] {
         self.filter { $0.parent == nil }
     }
-
-    public func hood(_ nodeID: ObjectID, selector: NeighborhoodSelector) -> Neighborhood<Self> {
-        let edges: [Edge]
-        switch selector.direction {
-        case .incoming: edges = incoming(nodeID)
-        case .outgoing: edges = outgoing(nodeID)
-        }
-        let filtered: [Edge] = edges.filter {
-            selector.predicate.match(frame: self, object: $0.snapshot)
-        }
-
-        return Neighborhood(graph: self,
-                            nodeID: nodeID,
-                            direction: selector.direction,
-                            edges: filtered)
-    }
 }
 
 

Sources/PoieticCore/Design/ObjectSnapshot.swift

@@ -246,3 +246,30 @@ extension ObjectSnapshot {
         return Array(refs)
     }
 }
+
+// MARK: - Graph Protocol
+
+// TODO: Find a more descriptive name.
+/// Wrapper of an object snapshot presented as an edge.
+///
+public struct EdgeSnapshot: EdgeProtocol {
+    public typealias NodeID = ObjectID
+    public let snapshot: any ObjectSnapshot
+    public let origin: ObjectID
+    public let target: ObjectID
+
+    public init?(_ snapshot: any ObjectSnapshot) {
+        guard case let .edge(origin, target) = snapshot.structure else {
+            return nil
+        }
+
+        self.snapshot = snapshot
+        self.origin = origin
+        self.target = target
+    }
+
+    public var id: ObjectID { snapshot.id }
+    public var type: ObjectType { snapshot.type }
+    public var name: String? { snapshot.name }
+}
+

Sources/PoieticCore/Design/StableFrame.swift

@@ -84,8 +84,7 @@ public final class StableFrame: Frame {
 
     /// Get an immutable graph view of the frame.
     ///
-    public var graph: any ObjectGraph {
+    public var graph: any GraphProtocol {
         return self
     }
 }
-

Sources/PoieticCore/Graph/MutableGraph.swift → Sources/PoieticCore/Design/TransientFrame+Graph.swift

@@ -5,45 +5,13 @@
 //  Created by Stefan Urbanek on 21/08/2023.
 //
 
-/// Protocol
-public protocol MutableGraph: ObjectGraph {
-    // Object creation
-    @discardableResult
-    func createNode(_ type: ObjectType, name: String?, attributes: [String:Variant]) -> MutableObject
-
-    @discardableResult
-    func createEdge(_ type: ObjectType, origin: ObjectID, target: ObjectID,
-                    attributes: [String:Variant]) -> MutableObject
-
-    /// Remove all nodes and edges from the graph.
-    func removeAll()
-
-    /// Remove a node from the graph and return a list of edges that were
-    /// removed together with the node.
+extension TransientFrame /* MutableGraph (no longer formally present) */ {
+    /// Convenience method to create an edge.
     ///
-    func remove(node nodeID: ObjectID)
-
-    /// Remove an edge from the graph.
+    /// If the object name is provided, then attribute `name` of the
+    /// object is set. Replaces `name` attribute in the `attributes` dictionary.
     ///
-    func remove(edge edgeID: ObjectID)
-}
-
-extension MutableGraph {
-    public func removeAll() {
-        for edge in edgeIDs {
-            remove(edge: edge)
-        }
-        for node in nodeIDs {
-            remove(node: node)
-        }
-    }
-}
-
-
-/// Graph contained within a mutable frame where the references to the nodes and
-/// edges are not directly bound and are resolved at the time of querying.
-extension TransientFrame: MutableGraph {
-    // Object creation
+    /// - SeeAlso: ``TransientFrame/create(_:id:snapshotID:structure:parent:children:attributes:components:)``
     @discardableResult
     public func createEdge(_ type: ObjectType,
                            origin: ObjectID,
@@ -58,22 +26,28 @@ extension TransientFrame: MutableGraph {
         return snapshot
     }
 
+    /// Convenience method to create an edge.
+    ///
+    /// If the object name is provided, then attribute `name` of the
+    /// object is set. Replaces `name` attribute in the `attributes` dictionary.
+    ///
+    /// - SeeAlso: ``TransientFrame/create(_:id:snapshotID:structure:parent:children:attributes:components:)``
     @discardableResult
     public func createEdge(_ type: ObjectType,
                            origin: any ObjectSnapshot,
                            target: any ObjectSnapshot,
                            attributes: [String:Variant] = [:]) -> MutableObject {
+        // FIXME: [WIP] Still needed?
         return createEdge(type, origin: origin.id, target: target.id, attributes: attributes)
     }
 
 
-    /// Creates a new node.
+    /// Convenience method to a new node.
     ///
     /// - Parameters:
     ///     - type: Object type of the newly created node.
     ///     - name: Optional object name. See note below.
     ///     - attributes: Dictionary of attributes to set.
-    ///     - components: List of components assigned with the node.
     ///
     /// If the object name is provided, then attribute `name` of the
     /// object is set. Replaces `name` attribute in the `attributes` dictionary.

Sources/PoieticCore/Documentation.docc/Graphs.md

@@ -6,19 +6,12 @@ Graphs are views that comprise of nodes and edges – connections between nodes.
 
 ### Graph, Nodes and Edges
 
-- ``ObjectGraph``
-- ``MutableGraph``
-
-- ``Node``
-- ``Edge``
-- ``EdgeType``
-- ``EdgeDirection``
-
-- ``topologicalSort(_:edges:)``
-
-- ``GraphCycleError``
+- ``GraphProtocol``
+- ``Graph``
+- ``EdgeSnapshot``
+- ``EdgeProtocol``
 
 ### Neighbourhoods
 
 - ``Neighborhood``
-- ``NeighborhoodSelector``
+- ``EdgeDirection``

Sources/PoieticCore/Documentation.docc/MetamodelAndTypes.md

@@ -106,6 +106,7 @@ examples see ``Constraint``.
 - ``UniqueNeighbourRequirement``
 - ``UniqueProperty``
 - ``ConstraintRequirement``
+- ``EdgeEndpointRequirement``
 
 ### Common Components and Types