Add depth-first traversal to the publication tree

src/lib/data_structures/publication_tree.ts

@@ -1,4 +1,5 @@
-import type { NDKEvent } from "@nostr-dev-kit/ndk";
+import type NDK from "@nostr-dev-kit/ndk";
+import type { NDKEvent, NDKFilter } from "@nostr-dev-kit/ndk";
 
 interface PublicationTreeNode {
   address: string;
@@ -6,15 +7,15 @@ interface PublicationTreeNode {
   children?: PublicationTreeNode[];
 }
 
-// TODO: Add public method(s) for event retrieval.
-// TODO: Add methods for DFS and BFS traversal-retrieval.
+// TODO: Add an iterator over the leaves of the tree.
 export class PublicationTree {
   private root: PublicationTreeNode;
   private nodes: Map<string, PublicationTreeNode>;
   private events: Map<string, NDKEvent>;
+  private ndk: NDK;
 
-  constructor(rootEvent: NDKEvent) {
-    const rootAddress = this.getAddress(rootEvent);
+  constructor(rootEvent: NDKEvent, ndk: NDK) {
+    const rootAddress = this.getAddressFromEvent(rootEvent);
     this.root = { address: rootAddress, children: [] };
 
     this.nodes = new Map<string, PublicationTreeNode>();
@@ -22,11 +23,21 @@ export class PublicationTree {
 
     this.events = new Map<string, NDKEvent>();
     this.events.set(rootAddress, rootEvent);
+
+    this.ndk = ndk;
   }
 
+  /**
+   * Adds an event to the publication tree.
+   * @param event The event to be added.
+   * @param parentEvent The parent event of the event to be added.
+   * @throws An error if the parent event is not in the tree.
+   * @description The parent event must already be in the tree. Use
+   * {@link PublicationTree.getEvent} to retrieve an event already in the tree.
+   */
   addEvent(event: NDKEvent, parentEvent: NDKEvent) {
-    const address = this.getAddress(event);
-    const parentAddress = this.getAddress(parentEvent);
+    const address = this.getAddressFromEvent(event);
+    const parentAddress = this.getAddressFromEvent(parentEvent);
     const parentNode = this.nodes.get(parentAddress);
 
     if (!parentNode) {
@@ -45,7 +56,83 @@ export class PublicationTree {
     this.events.set(address, event);
   }
 
-  private getAddress(event: NDKEvent): string {
+  /**
+   * Retrieves an event from the publication tree.
+   * @param address The address of the event to retrieve.
+   * @returns The event, or null if the event is not found.
+   */
+  async getEvent(address: string): Promise<NDKEvent | null> {
+    let event = this.events.get(address) ?? null;
+    if (!event) {
+      event = await this.depthFirstRetrieve(address);
+    }
+
+    return event;
+  }
+
+  // #region Private Methods
+
+  /**
+   * Traverses the publication tree in a depth-first manner to retrieve an event, filling in
+   * missing nodes during the traversal.
+   * @param address The address of the event to retrieve.
+   * @returns The event, or null if the event is not found.
+   */
+  private async depthFirstRetrieve(address: string): Promise<NDKEvent | null> {
+    if (this.nodes.has(address)) {
+      return this.events.get(address)!;
+    }
+
+    const stack: string[] = [this.root.address];
+    let currentEvent: NDKEvent | null | undefined;
+    while (stack.length > 0) {
+      const currentAddress = stack.pop();
+
+      // Stop immediately if the target of the search is found.
+      if (currentAddress === address) {
+        return this.events.get(address)!;
+      }
+
+      // Augment the tree with the children of the current event.
+      const currentChildAddresses = this.events
+        .get(currentAddress!)!.tags
+        .filter(tag => tag[0] === 'a')
+        .map(tag => tag[1]);
+
+      const kinds = new Set<number>();
+      const pubkeys = new Set<string>();
+      const dTags = new Set<string>();
+      for (const childAddress of currentChildAddresses) {
+        if (this.nodes.has(childAddress)) {
+          continue;
+        }
+        
+        const [kind, pubkey, dTag] = childAddress.split(':');
+        kinds.add(parseInt(kind));
+        pubkeys.add(pubkey);
+        dTags.add(dTag);
+      }
+
+      const childEvents = await this.ndk.fetchEvents({
+        kinds: Array.from(kinds),
+        authors: Array.from(pubkeys),
+        '#d': Array.from(dTags),
+      });
+
+      for (const childEvent of childEvents) {
+        this.addEvent(childEvent, currentEvent!);
+      }
+
+      // Push the popped address's children onto the stack for the next iteration.
+      while (currentChildAddresses.length > 0) {
+        stack.push(currentChildAddresses.pop()!);
+      }
+    }
+
+    return null;
+  }
+
+  private getAddressFromEvent(event: NDKEvent): string {
     if (event.kind! < 30000 || event.kind! >= 40000) {
       throw new Error(
         "PublicationTree: Invalid event kind. Event kind must be in the range 30000-39999"
@@ -54,4 +141,6 @@ export class PublicationTree {
 
     return `${event.kind}:${event.pubkey}:${event.dTag}`;
   }
+
+  // #endregion
 }