feature: add dagEdgesParent

slight optimization of dagEdgesResolve

src/dag/dagEdgesParent.ts

@@ -0,0 +1,14 @@
+import { RawDagEdge } from './RawDagEdge';
+
+/**
+ * Return first parent source the specified destination has.
+ * If it can't find a parent, it will return `null` instead.
+ *
+ * @param edges An array of dag edge
+ * @param destination The target destination
+ *
+ * See also: {@link dagEdgesParents}
+ */
+export function dagEdgesParent<T>( edges: RawDagEdge<T>[], destination: T ): T | null {
+  return edges.find( ( edge ) => edge[ 1 ] === destination )?.[ 0 ] ?? null;
+}

src/dag/dagEdgesResolve.ts

@@ -1,5 +1,5 @@
 import { RawDagEdge } from './RawDagEdge';
-import { dagEdgesParents } from './dagEdgesParents';
+import { dagEdgesParent } from './dagEdgesParent';
 
 /**
  * Resolve dag dependency relationship and give you a correct order.
@@ -16,7 +16,7 @@ export function dagEdgesResolve<T>( edges: RawDagEdge<T>[], nodes: T[] ): T[] {
   while ( tempEdges.length > 0 ) {
     nodeSet.forEach( ( node ) => {
       // is this an entrypoint?
-      const hasParents = dagEdgesParents( tempEdges, node ).length > 0;
+      const hasParents = dagEdgesParent( tempEdges, node ) != null;
 
       if ( !hasParents ) {
         if ( nodeSet.has( node ) ) {

src/dag/index.ts

@@ -1,6 +1,7 @@
 export * from './dagEdgesAncestors';
 export * from './dagEdgesChildren';
 export * from './dagEdgesDescendants';
+export * from './dagEdgesParent';
 export * from './dagEdgesParents';
 export * from './dagEdgesResolve';
 export * from './RawDagEdge';

src/dag/tests/dagEdgesParent.test.ts

@@ -0,0 +1,21 @@
+import { dagEdgesParent } from '../dagEdgesParent';
+import type { RawDagEdge } from '../RawDagEdge';
+
+describe( 'dagEdgesParent', () => {
+  it( 'returns a parent of the specified destination from the given edges', () => {
+    const edges: RawDagEdge<string>[] = [
+      [ 'a', 'b' ],
+      [ 'b', 'c' ],
+      [ 'a', 'd' ],
+      [ 'a', 'e' ],
+      [ 'b', 'e' ],
+      [ 'c', 'e' ],
+      [ 'b', 'f' ],
+      [ 'e', 'f' ],
+    ];
+
+    const subject = dagEdgesParent( edges, 'f' );
+
+    expect( subject ).toBe( 'b' );
+  } );
+} );