frontend-app-api: tweak app graph to have an explicit root node

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/frontend-app-api/src/extensions/Core.tsx

@@ -22,7 +22,7 @@ import {
 
 export const Core = createExtension({
   id: 'core',
-  attachTo: { id: 'root', input: 'default' },
+  attachTo: { id: 'root', input: 'default' }, // ignored
   inputs: {
     apis: createExtensionInput({
       api: coreExtensionData.apiFactory,

packages/frontend-app-api/src/wiring/graph/buildAppGraph.test.ts

@@ -19,66 +19,70 @@ import { buildAppGraph } from './buildAppGraph';
 
 const extBaseConfig = {
   id: 'test',
-  attachTo: { id: 'root', input: 'default' },
+  attachTo: { id: 'nonexistent', input: 'nonexistent' },
   output: {},
   factory() {},
 };
 
 const extension = createExtension(extBaseConfig);
 
-const baseSpec = { extension, disabled: false };
+const baseSpec = {
+  extension,
+  attachTo: { id: 'nonexistent', input: 'nonexistent' },
+  disabled: false,
+};
 
 describe('buildAppGraph', () => {
-  it('creates an empty graph', () => {
-    const graph = buildAppGraph([]);
-    expect([...graph.rootNodes.keys()]).toEqual([]);
-    expect([...graph.orphanNodes.keys()]).toEqual([]);
+  it('should fail to create an empty graph', () => {
+    expect(() => buildAppGraph([])).toThrow(
+      "No root node with id 'core' found in app graph",
+    );
+  });
+
+  it('should create a graph with only one node', () => {
+    const graph = buildAppGraph([{ ...baseSpec, id: 'core' }]);
+    expect(graph.root).toEqual({
+      spec: { ...baseSpec, id: 'core' },
+      edges: { attachments: new Map() },
+    });
+    expect(Array.from(graph.orphans)).toEqual([]);
   });
 
   it('should create a graph', () => {
-    const graph = buildAppGraph([
-      { ...baseSpec, id: 'a' },
-      { ...baseSpec, id: 'b' },
-      { ...baseSpec, id: 'c' },
-      { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx1' },
-      { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx2' },
-      { ...baseSpec, attachTo: { id: 'b', input: 'y' }, id: 'by1' },
-      { ...baseSpec, attachTo: { id: 'd', input: 'x' }, id: 'dx1' },
-    ]);
-    expect([...graph.rootNodes.keys()]).toEqual(['a', 'b', 'c']);
-    expect([...graph.orphanNodes.keys()]).toEqual(['dx1']);
-
-    expect(JSON.parse(JSON.stringify([...graph.rootNodes.values()])))
-      .toMatchInlineSnapshot(`
+    const graph = buildAppGraph(
       [
-        {
-          "id": "a",
+        { ...baseSpec, id: 'a' },
+        { ...baseSpec, id: 'b' },
+        { ...baseSpec, id: 'c' },
+        { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx1' },
+        { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx2' },
+        { ...baseSpec, attachTo: { id: 'b', input: 'y' }, id: 'by1' },
+        { ...baseSpec, attachTo: { id: 'd', input: 'x' }, id: 'dx1' },
+      ],
+      'b',
+    );
+
+    expect(JSON.parse(JSON.stringify(graph.root))).toMatchInlineSnapshot(`
+      {
+        "attachments": {
+          "x": [
+            {
+              "id": "bx1",
+            },
+            {
+              "id": "bx2",
+            },
+          ],
+          "y": [
+            {
+              "id": "by1",
+            },
+          ],
         },
-        {
-          "attachments": {
-            "x": [
-              {
-                "id": "bx1",
-              },
-              {
-                "id": "bx2",
-              },
-            ],
-            "y": [
-              {
-                "id": "by1",
-              },
-            ],
-          },
-          "id": "b",
-        },
-        {
-          "id": "c",
-        },
-      ]
+        "id": "b",
+      }
     `);
-    expect(String(graph.rootNodes.get('a'))).toMatchInlineSnapshot(`"<a />"`);
-    expect(String(graph.rootNodes.get('b'))).toMatchInlineSnapshot(`
+    expect(String(graph.root)).toMatchInlineSnapshot(`
       "<b>
         x [
           <bx1 />
@@ -89,24 +93,32 @@ describe('buildAppGraph', () => {
         ]
       </b>"
     `);
-    expect(String(graph.rootNodes.get('c'))).toMatchInlineSnapshot(`"<c />"`);
+
+    const orphans = Array.from(graph.orphans).map(String);
+    expect(orphans).toMatchInlineSnapshot(`
+      [
+        "<a />",
+        "<c />",
+        "<dx1 />",
+      ]
+    `);
   });
 
   it('should create a graph out of order', () => {
-    const graph = buildAppGraph([
-      { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx2' },
-      { ...baseSpec, id: 'a' },
-      { ...baseSpec, attachTo: { id: 'b', input: 'y' }, id: 'by1' },
-      { ...baseSpec, id: 'b' },
-      { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx1' },
-      { ...baseSpec, id: 'c' },
-      { ...baseSpec, attachTo: { id: 'd', input: 'x' }, id: 'dx1' },
-    ]);
-    expect([...graph.rootNodes.keys()]).toEqual(['a', 'b', 'c']);
-    expect([...graph.orphanNodes.keys()]).toEqual(['dx1']);
+    const graph = buildAppGraph(
+      [
+        { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx2' },
+        { ...baseSpec, id: 'a' },
+        { ...baseSpec, attachTo: { id: 'b', input: 'y' }, id: 'by1' },
+        { ...baseSpec, id: 'b' },
+        { ...baseSpec, attachTo: { id: 'b', input: 'x' }, id: 'bx1' },
+        { ...baseSpec, id: 'c' },
+        { ...baseSpec, attachTo: { id: 'd', input: 'x' }, id: 'dx1' },
+      ],
+      'b',
+    );
 
-    expect(String(graph.rootNodes.get('a'))).toMatchInlineSnapshot(`"<a />"`);
-    expect(String(graph.rootNodes.get('b'))).toMatchInlineSnapshot(`
+    expect(String(graph.root)).toMatchInlineSnapshot(`
       "<b>
         x [
           <bx2 />
@@ -117,7 +129,15 @@ describe('buildAppGraph', () => {
         ]
       </b>"
     `);
-    expect(String(graph.rootNodes.get('c'))).toMatchInlineSnapshot(`"<c />"`);
+
+    const orphans = Array.from(graph.orphans).map(String);
+    expect(orphans).toMatchInlineSnapshot(`
+      [
+        "<a />",
+        "<c />",
+        "<dx1 />",
+      ]
+    `);
   });
 
   it('throws an error when duplicated extensions are detected', () => {

packages/frontend-app-api/src/wiring/graph/buildAppGraph.ts

@@ -78,9 +78,15 @@ class SerializableAppNode implements AppNode {
  * tree with all attachments in the same order as they appear in the input specs array.
  * @internal
  */
-export function buildAppGraph(specs: AppNodeSpec[]): AppGraph {
+export function buildAppGraph(
+  specs: AppNodeSpec[],
+  rootNodeId = 'core',
+): AppGraph {
   const nodes = new Map<string, AppNode>();
-  const rootNodes = new Map<string, AppNode>();
+
+  // A node with the provided rootNodeId must be found in the graph, and it must not be attached to anything
+  let rootNode: AppNode | undefined = undefined;
+
   // While iterating through the inputs specs we keep track of all nodes that were created
   // before their parent, and attach them later when the parent is created.
   // As we find the parents and attach the children, we remove them from this map. This means
@@ -99,7 +105,10 @@ export function buildAppGraph(specs: AppNodeSpec[]): AppGraph {
     const node = new SerializableAppNode(spec);
     nodes.set(spec.id, node);
 
-    if (spec.attachTo) {
+    // TODO: For now we simply ignore the attachTo spec of the root node, but it'd be cleaner if we could avoid defining it
+    if (spec.id === rootNodeId) {
+      rootNode = node;
+    } else {
       const parent = nodes.get(spec.attachTo.id);
       if (parent) {
         (node.edges as Mutable<AppNodeEdges>).attachedTo = {
@@ -123,8 +132,6 @@ export function buildAppGraph(specs: AppNodeSpec[]): AppGraph {
           orphansByParent.set(spec.attachTo.id, [orphan]);
         }
       }
-    } else {
-      rootNodes.set(spec.id, node);
     }
 
     const orphanedChildren = orphansByParent.get(spec.id);
@@ -142,11 +149,13 @@ export function buildAppGraph(specs: AppNodeSpec[]): AppGraph {
     }
   }
 
-  const orphanNodes = new Map(
-    Array.from(orphansByParent).flatMap(([, orphans]) =>
-      orphans.map(({ orphan }) => [orphan.spec.id, orphan]),
-    ),
+  const orphanNodes = Array.from(orphansByParent).flatMap(([, orphans]) =>
+    orphans.map(({ orphan }) => orphan),
   );
 
-  return { rootNodes, orphanNodes };
+  if (!rootNode) {
+    throw new Error(`No root node with id '${rootNodeId}' found in app graph`);
+  }
+
+  return { root: rootNode, orphans: orphanNodes };
 }

packages/frontend-app-api/src/wiring/graph/types.ts

@@ -31,7 +31,7 @@ export type Mutable<T> = {
  */
 export interface AppNodeSpec {
   readonly id: string;
-  readonly attachTo?: { id: string; input: string };
+  readonly attachTo: { id: string; input: string };
   readonly extension: Extension<unknown>;
   readonly disabled: boolean;
   readonly config?: unknown;
@@ -70,6 +70,6 @@ export interface AppNode {
 }
 
 export interface AppGraph {
-  rootNodes: Map<string, AppNode>;
-  orphanNodes: Map<string, AppNode>;
+  root: AppNode;
+  orphans: Iterable<AppNode>;
 }