// deno-lint-ignore-file no-this-alias
import NDK, { NDKEvent } from "@nostr-dev-kit/ndk";
import Processor from "asciidoctor";
import type {
  AbstractBlock,
  AbstractNode,
  Block,
  Document,
  Extensions,
  ProcessorOptions,
  Section,
} from "asciidoctor";
import he from "he";
import { type Writable, writable } from "svelte/store";
import { zettelKinds } from "./consts.ts";
import { getMatchingTags } from "./utils/nostrUtils.ts";

interface IndexMetadata {
  authors?: string[];
  version?: string;
  edition?: string;
  isbn?: string;
  publicationDate?: string;
  publisher?: string;
  summary?: string;
  coverImage?: string;
}

export enum SiblingSearchDirection {
  Previous,
  Next,
}

export enum InsertLocation {
  Before,
  After,
}

/**
 * @classdesc Pharos is an extension of the Asciidoctor class that adds Nostr Knowledge Base (NKB)
 * features to core Asciidoctor functionality.  Asciidoctor is used to parse an AsciiDoc document
 * into an Abstract Syntax Tree (AST), and Phraos generates NKB events from the nodes in that tree.
 * @class
 * @augments Asciidoctor
 */
export default class Pharos {
  /**
   * Key to terminology used in the class:
   *
   * Nostr Knowledge Base (NKB) entities:
   * - Zettel: Bite-sized pieces of text contained within kind 30041 events.
   * - Index: A kind 30040 event describing a collection of zettels or other Nostr events.
   * - Event: The generic term for a Nostr event.
   *
   * Asciidoctor entities:
   * - Document: The entirety of an AsciiDoc document.  The document title is denoted by a level 0
   * header, and the document may contain metadata, such as author and edition, immediately below
   * the title.
   * - Section: A section of an AsciiDoc document demarcated by a header.  A section may contain
   * blocks and/or other sections.
   * - Block: A block of content within an AsciiDoc document.  Blocks are demarcated on either side
   * by newline characters.  Blocks may contain other blocks or inline content.  Blocks may be
   * images, paragraphs, sections, a document, or other types of content.
   * - Node: A unit of the parsed AsciiDoc document.  All blocks are nodes.  Nodes are related
   * hierarchically to form the Abstract Syntax Tree (AST) representation of the document.
   */

  private asciidoctor;

  private pharosExtensions: Extensions.Registry;

  private ndk: NDK;

  private contextCounters: Map<string, number> = new Map<string, number>();

  /**
   * The HTML content of the converted document.
   */
  private html?: string | Document;

  /**
   * The ID of the root node in the document.
   */
  private rootNodeId?: string;

  /**
   * Metadata to be used to populate the tags on the root index event.
   */
  private rootIndexMetadata: IndexMetadata = {};

  /**
   * A map of node IDs to the nodes themselves.
   */
  private nodes: Map<string, AbstractNode> = new Map<string, AbstractNode>();

  /**
   * A map of event d tags to the events themselves.
   */
  private events: Map<string, NDKEvent> = new Map<string, NDKEvent>();

  /**
   * A map of event d tags to the context name assigned to each event's originating node by the
   * Asciidoctor parser.
   */
  private eventToContextMap: Map<string, string> = new Map<string, string>();

  /**
   * A map of node IDs to the integer event kind that will be used to represent the node.
   */
  private eventToKindMap: Map<string, number> = new Map<string, number>();

  /**
   * A map of index IDs to the IDs of the nodes they reference.
   */
  private indexToChildEventsMap: Map<string, Set<string>> = new Map<
    string,
    Set<string>
  >();

  /**
   * A map of node IDs to the Nostr event IDs of the events they generate.
   */
  private eventIds: Map<string, string> = new Map<string, string>();

  /**
   * A map of the levels of the event tree to a list of event IDs at each level.
   */
  private eventsByLevelMap: Map<number, string[]> = new Map<number, string[]>();

  /**
   * A map of blog entries
   */
  private blogEntries: Map<string, NDKEvent> = new Map<string, NDKEvent>();

  /**
   * When `true`, `getEvents()` should regenerate the event tree to propagate updates.
   */
  private shouldUpdateEventTree: boolean = false;

  // #region Public API

  constructor(ndk: NDK) {
    this.asciidoctor = Processor();
    this.pharosExtensions = this.asciidoctor.Extensions.create();

    this.ndk = ndk;

    const pharos = this;
    this.pharosExtensions.treeProcessor(function () {
      const dsl = this;
      dsl.process(function (document) {
        const treeProcessor = this;
        pharos.treeProcessor(treeProcessor, document);
      });
    });

    // Add advanced extensions for math, PlantUML, BPMN, and TikZ
    this.loadAdvancedExtensions();
  }

  /**
   * Loads advanced extensions for math, PlantUML, BPMN, and TikZ rendering
   */
  private async loadAdvancedExtensions(): Promise<void> {
    try {
      const { createAdvancedExtensions } = await import(
        "./utils/markup/asciidoctorExtensions.ts"
      );
      createAdvancedExtensions();
      // Note: Extensions merging might not be available in this version
      // We'll handle this in the parse method instead
    } catch (error) {
      console.warn("Advanced extensions not available:", error);
    }
  }

  parse(content: string, options?: ProcessorOptions | undefined): void {
    // Ensure the content is valid AsciiDoc and has a header and the doctype book
    content = ensureAsciiDocHeader(content);

    try {
      const mergedAttributes = Object.assign(
        {},
        options && typeof options.attributes === "object"
          ? options.attributes
          : {},
        { "source-highlighter": "highlightjs" },
      );
      this.html = this.asciidoctor.convert(content, {
        ...options,
        extension_registry: this.pharosExtensions,
        attributes: mergedAttributes,
      }) as string | Document | undefined;
    } catch (error) {
      console.error(error);
      throw new Error("Failed to parse AsciiDoc document.");
    }
  }

  /**
   * Fetches and parses the event tree for a publication given the event or event ID of the
   * publication's root index.
   * @param event The event or event ID of the publication's root index.
   */
  async fetch(event: NDKEvent | string): Promise<void> {
    let content: string;

    if (typeof event === "string") {
      const index = await this.ndk.fetchEvent({ ids: [event] });
      if (!index) {
        throw new Error("Failed to fetch publication.");
      }

      content = await this.getPublicationContent(index);
    } else {
      content = await this.getPublicationContent(event);
    }

    this.parse(content);
  }

  getBlogEntries() {
    return this.blogEntries;
  }

  getIndexMetadata(): IndexMetadata {
    return this.rootIndexMetadata;
  }

  /**
   * Generates and stores Nostr events from the parsed AsciiDoc document.  The events can be
   * modified via the parser's API and retrieved via the `getEvents()` method.
   * @param pubkey The public key (as a hex string) of the user that will sign and publish the
   * events.
   */
  generate(pubkey: string): void {
    const stack = this.stackEventNodes();
    this.generateEvents(stack, pubkey);
  }

  /**
   * @param pubkey The public key (as a hex string) of the user generating the events.
   * @returns An array of Nostr events generated from the parsed AsciiDoc document.
   * @remarks This method returns the events as they are currently stored in the parser.  If none
   * are stored, they will be freshly generated.
   */
  getEvents(pubkey: string): NDKEvent[] {
    if (this.shouldUpdateEventTree) {
      const stack = this.stackEventNodes();
      return this.generateEvents(stack, pubkey);
    }

    return Array.from(this.events.values());
  }

  /**
   * Gets the entire HTML content of the AsciiDoc document.
   * @returns The HTML content of the converted document.
   */
  getHtml(): string {
    return this.html?.toString() || "";
  }

  /**
   * @returns The ID of the root index of the converted document.
   * @remarks The root index ID may be used to retrieve metadata or children from the root index.
   */
  getRootIndexId(): string {
    return this.normalizeId(this.rootNodeId) ?? "";
  }

  /**
   * @returns The title, if available, from the metadata of the index with the given ID.
   */
  getIndexTitle(id: string): string | undefined {
    const section = this.nodes.get(id) as Section;
    const title = section.getTitle() ?? "";
    return he.decode(title);
  }

  /**
   * @returns The IDs of any child indices of the index with the given ID.
   */
  getChildIndexIds(id: string): string[] {
    return Array.from(this.indexToChildEventsMap.get(id) ?? []).filter(
      (id) => this.eventToKindMap.get(id) === 30040,
    );
  }

  /**
   * @returns The IDs of any child zettels of the index with the given ID.
   */
  getChildZettelIds(id: string): string[] {
    return Array.from(this.indexToChildEventsMap.get(id) ?? []).filter(
      (id) => this.eventToKindMap.get(id) !== 30040,
    );
  }

  /**
   * @returns The IDs of any child nodes in the order in which they should be rendered.
   */
  getOrderedChildIds(id: string): string[] {
    return Array.from(this.indexToChildEventsMap.get(id) ?? []);
  }

  /**
   * @returns The content of the node with the given ID.  The presentation of the returned content
   * varies by the node's context.
   * @remarks By default, the content is returned as HTML produced by the
   * Asciidoctor converter.  However, other formats are returned for specific contexts:
   * - Paragraph: The content is returned as a plain string.
   */
  getContent(id: string): string {
    const normalizedId = this.normalizeId(id);
    const block = this.nodes.get(normalizedId!) as AbstractBlock;

    switch (block.getContext()) {
      case "paragraph":
        return block.getContent() ?? "";
    }

    return block.convert();
  }

  /**
   * Checks if the node with the given ID is a floating title (discrete header).
   * @param id The ID of the node to check.
   * @returns True if the node is a floating title, false otherwise.
   */
  isFloatingTitle(id: string): boolean {
    const normalizedId = this.normalizeId(id);
    if (!normalizedId || !this.nodes.has(normalizedId)) {
      return false;
    }

    const context = this.eventToContextMap.get(normalizedId);
    return context === "floating_title";
  }

  /**
   * Updates the `content` field of a Nostr event in-place.
   * @param dTag The d tag of the event to update.
   * @param content The new content to assign to the event.
   * @returns The updated event.
   * @remarks Changing the content of a Nostr event changes its hash, but regenerating the event
   * tree is expensive.  Thus, the event tree will not be regenerated until the consumer next
   * invokes `getEvents()`.
   */
  updateEventContent(dTag: string, content: string): NDKEvent {
    const event = this.events.get(dTag);
    if (!event) {
      throw new Error(`No event found for #d:${dTag}.`);
    }

    this.updateEventByContext(dTag, content, this.eventToContextMap.get(dTag)!);

    return event;
  }

  /**
   * Finds the nearest sibling of the event with the given d tag.
   * @param targetDTag The d tag of the target event.
   * @param parentDTag The d tag of the target event's parent.
   * @param depth The depth of the target event within the parser tree.
   * @param direction The direction in which to search for a sibling.
   * @returns A tuple containing the d tag of the nearest sibling and the d tag of the nearest
   * sibling's parent.
   */
  getNearestSibling(
    targetDTag: string,
    depth: number,
    direction: SiblingSearchDirection,
  ): [string | null, string | null] {
    const eventsAtLevel = this.eventsByLevelMap.get(depth);
    if (!eventsAtLevel) {
      throw new Error(`No events found at level ${depth}.`);
    }

    const targetIndex = eventsAtLevel.indexOf(targetDTag);

    if (targetIndex === -1) {
      throw new Error(
        `The event indicated by #d:${targetDTag} does not exist at level ${depth} of the event tree.`,
      );
    }

    const parentDTag = this.getParent(targetDTag);

    if (!parentDTag) {
      throw new Error(
        `The event indicated by #d:${targetDTag} does not have a parent.`,
      );
    }

    const grandparentDTag = this.getParent(parentDTag);

    // If the target is the first node at its level and we're searching for a previous sibling,
    // look among the siblings of the target's parent at the previous level.
    if (targetIndex === 0 && direction === SiblingSearchDirection.Previous) {
      // * Base case: The target is at the first level of the tree and has no previous sibling.
      if (!grandparentDTag) {
        return [null, null];
      }

      return this.getNearestSibling(parentDTag, depth - 1, direction);
    }

    // If the target is the last node at its level and we're searching for a next sibling,
    // look among the siblings of the target's parent at the previous level.
    if (
      targetIndex === eventsAtLevel.length - 1 &&
      direction === SiblingSearchDirection.Next
    ) {
      // * Base case: The target is at the last level of the tree and has no subsequent sibling.
      if (!grandparentDTag) {
        return [null, null];
      }

      return this.getNearestSibling(parentDTag, depth - 1, direction);
    }

    // * Base case: There is an adjacent sibling at the same depth as the target.
    switch (direction) {
      case SiblingSearchDirection.Previous:
        return [eventsAtLevel[targetIndex - 1], parentDTag];
      case SiblingSearchDirection.Next:
        return [eventsAtLevel[targetIndex + 1], parentDTag];
    }

    return [null, null];
  }

  /**
   * Gets the d tag of the parent of the event with the given d tag.
   * @param dTag The d tag of the target event.
   * @returns The d tag of the parent event, or null if the target event does not have a parent.
   * @throws An error if the target event does not exist in the parser tree.
   */
  getParent(dTag: string): string | null {
    // Check if the event exists in the parser tree.
    if (!this.eventIds.has(dTag)) {
      throw new Error(
        `The event indicated by #d:${dTag} does not exist in the parser tree.`,
      );
    }

    // Iterate through all the index to child mappings.
    // This may be expensive on large trees.
    for (const [indexId, childIds] of this.indexToChildEventsMap) {
      // If this parent contains our target as a child, we found the parent
      if (childIds.has(dTag)) {
        return indexId;
      }
    }

    return null;
  }

  /**
   * Moves an event within the event tree.
   * @param targetDTag The d tag of the event to be moved.
   * @param destinationDTag The d tag another event, next to which the target will be placed.
   * @param insertAfter If true, the target will be placed after the destination event, otherwise,
   * it will be placed before the destination event.
   * @throws Throws an error if the parameters specify an invalid move.
   * @remarks Moving the target event within the tree changes the hash of several events, so the
   * event tree will be regenerated when the consumer next invokes `getEvents()`.
   */
  moveEvent(
    targetDTag: string,
    destinationDTag: string,
    insertAfter: boolean = false,
  ): void {
    const targetEvent = this.events.get(targetDTag);
    const destinationEvent = this.events.get(destinationDTag);
    const targetParent = this.getParent(targetDTag);
    const destinationParent = this.getParent(destinationDTag);

    if (!targetEvent) {
      throw new Error(`No event found for #d:${targetDTag}.`);
    }

    if (!destinationEvent) {
      throw new Error(`No event found for #d:${destinationDTag}.`);
    }

    if (!targetParent) {
      throw new Error(
        `The event indicated by #d:${targetDTag} does not have a parent.`,
      );
    }

    if (!destinationParent) {
      throw new Error(
        `The event indicated by #d:${destinationDTag} does not have a parent.`,
      );
    }

    // Remove the target from among the children of its current parent.
    this.indexToChildEventsMap.get(targetParent)?.delete(targetDTag);

    // If necessary, remove the target event from among the children of its destination parent.
    this.indexToChildEventsMap.get(destinationParent)?.delete(targetDTag);

    // Get the index of the destination event among the children of its parent.
    const destinationIndex = Array.from(
      this.indexToChildEventsMap.get(destinationParent) ?? [],
    ).indexOf(destinationDTag);

    // Insert next to the index of the destination event, either before or after as specified by
    // the insertAfter flag.
    const destinationChildren = Array.from(
      this.indexToChildEventsMap.get(destinationParent) ?? [],
    );
    insertAfter
      ? destinationChildren.splice(destinationIndex + 1, 0, targetDTag)
      : destinationChildren.splice(destinationIndex, 0, targetDTag);
    this.indexToChildEventsMap.set(
      destinationParent,
      new Set(destinationChildren),
    );

    this.shouldUpdateEventTree = true;
  }

  /**
   * Resets the parser to its initial state, removing any parsed data.
   */
  reset(): void {
    this.contextCounters.clear();
    this.html = undefined;
    this.rootNodeId = undefined;
    this.rootIndexMetadata = {};
    this.nodes.clear();
    this.eventToKindMap.clear();
    this.indexToChildEventsMap.clear();
    this.eventsByLevelMap.clear();
    this.eventIds.clear();
  }

  // #endregion

  // #region Tree Processor Extensions

  /**
   * Walks the Asciidoctor Abstract Syntax Tree (AST) and performs the following mappings:
   * - Each node ID is mapped to the node itself.
   * - Each node ID is mapped to an integer event kind that will be used to represent the node.
   * - Each ID of a node containing children is mapped to the set of IDs of its children.
   */
  private treeProcessor(
    _: Extensions.TreeProcessor,
    document: Document,
  ) {
    this.rootNodeId = this.generateNodeId(document);
    document.setId(this.rootNodeId);
    this.nodes.set(this.rootNodeId, document);
    this.eventToKindMap.set(this.rootNodeId, 30040);
    this.indexToChildEventsMap.set(this.rootNodeId, new Set<string>());

    /** FIFO queue (uses `Array.push()` and `Array.shift()`). */
    const nodeQueue: AbstractNode[] = document.getBlocks();

    while (nodeQueue.length > 0) {
      const block = nodeQueue.shift();
      if (!block) {
        continue;
      }

      if (block.getContext() === "section") {
        const children = this.processSection(block as Section);
        nodeQueue.push(...children);
      } else {
        this.processBlock(block as Block);
      }
    }

    this.buildEventsByLevelMap(this.rootNodeId!, 0);
  }

  /**
   * Processes a section of the Asciidoctor AST.
   * @param section The section to process.
   * @returns An array of the section's child nodes.  If there are no child nodes, returns an empty
   * array.
   * @remarks Sections are mapped as kind 30040 indexToChildEventsMap by default.
   */
  private processSection(section: Section): AbstractNode[] {
    let sectionId = this.normalizeId(section.getId());
    if (!sectionId) {
      sectionId = this.generateNodeId(section);
    }

    // Prevent duplicates.
    if (this.nodes.has(sectionId)) {
      return [];
    }

    this.nodes.set(sectionId, section);
    this.eventToKindMap.set(sectionId, 30040); // Sections are indexToChildEventsMap by default.
    this.indexToChildEventsMap.set(sectionId, new Set<string>());

    const parentId = this.normalizeId(section.getParent()?.getId());
    if (!parentId) {
      return [];
    }

    // Add the section to its parent index.
    this.indexToChildEventsMap.get(parentId)?.add(sectionId);

    // Limit to 5 levels of section depth.
    if (section.getLevel() >= 5) {
      return [];
    }

    return section.getBlocks();
  }

  /**
   * Processes a block of the Asciidoctor AST.
   * @param block The block to process.
   * @remarks Blocks are mapped as kind 30041 zettels by default.
   */
  private processBlock(block: Block): void {
    // Obtain or generate a unique ID for the block.
    let blockId = this.normalizeId(block.getId());
    if (!blockId) {
      blockId = this.generateNodeId(block);
      block.setId(blockId);
    }

    // Prevent duplicates.
    if (this.nodes.has(blockId)) {
      return;
    }

    this.nodes.set(blockId, block);
    this.eventToKindMap.set(blockId, 30041); // Blocks are zettels by default.

    const parentId = this.normalizeId(block.getParent()?.getId());
    if (!parentId) {
      return;
    }

    // Add the block to its parent index.
    this.indexToChildEventsMap.get(parentId)?.add(blockId);
  }

  //#endregion

  // #region Event Tree Operations

  /**
   * Recursively walks the event tree and builds a map of the events at each level.
   * @param parentNodeId The ID of the parent node.
   * @param depth The depth of the parent node.
   */
  private buildEventsByLevelMap(parentNodeId: string, depth: number): void {
    // If we're at the root level, clear the map so it can be freshly rebuilt.
    if (depth === 0) {
      this.eventsByLevelMap.clear();
    }

    const children = this.indexToChildEventsMap.get(parentNodeId);
    if (!children) {
      return;
    }

    const eventsAtLevel = this.eventsByLevelMap.get(depth) ?? [];
    eventsAtLevel.push(...children);
    this.eventsByLevelMap.set(depth, eventsAtLevel);

    for (const child of children) {
      this.buildEventsByLevelMap(child, depth + 1);
    }
  }

  /**
   * Uses the NDK to crawl the event tree of a publication and return its content as a string.
   * @param event The root index event of the publication.
   * @returns The content of the publication as a string.
   * @remarks This function does a depth-first crawl of the event tree using the relays specified
   * on the NDK instance.
   */
  private async getPublicationContent(
    event: NDKEvent,
    depth: number = 0,
  ): Promise<string> {
    let content: string = "";

    // Format title into AsciiDoc header.
    const title = getMatchingTags(event, "title")[0][1];
    let titleLevel = "";
    for (let i = 0; i <= depth; i++) {
      titleLevel += "=";
    }
    content += `${titleLevel} ${title}\n\n`;

    // TODO: Deprecate `e` tags in favor of `a` tags required by NIP-62.
    let tags = getMatchingTags(event, "a");
    if (tags.length === 0) {
      tags = getMatchingTags(event, "e");
    }

    // Base case: The event is a zettel.
    if (zettelKinds.includes(event.kind ?? -1)) {
      content += event.content;
      return content;
    }

    // Recursive case: The event is an index.
    const childEvents = await Promise.all(
      tags.map((tag) => this.ndk.fetchEventFromTag(tag, event)),
    );

    // if a blog, save complete events for later
    if (
      getMatchingTags(event, "type").length > 0 &&
      getMatchingTags(event, "type")[0][1] === "blog"
    ) {
      childEvents.forEach((child) => {
        if (child) {
          this.blogEntries.set(getMatchingTags(child, "d")?.[0]?.[1], child);
        }
      });
    }

    // populate metadata
    if (event.created_at) {
      this.rootIndexMetadata.publicationDate = new Date(
        event.created_at * 1000,
      ).toDateString();
    }
    if (getMatchingTags(event, "image").length > 0) {
      this.rootIndexMetadata.coverImage = getMatchingTags(event, "image")[0][1];
    }

    // Michael J - 15 December 2024 - This could be further parallelized by recursively fetching
    // children of index events before processing them for content.  We won't make that change now,
    // as it would increase complexity, but if performance suffers, we can revisit this option.
    const childContentPromises: Promise<string>[] = [];
    for (let i = 0; i < childEvents.length; i++) {
      const childEvent = childEvents[i];

      if (!childEvent) {
        console.warn(`NDK could not find event ${tags[i][1]}.`);
        continue;
      }

      childContentPromises.push(
        this.getPublicationContent(childEvent, depth + 1),
      );
    }

    const childContents = await Promise.all(childContentPromises);
    content += childContents.join("\n\n");

    return content;
  }

  // #endregion

  // #region NDKEvent Generation

  /**
   * Generates a stack of node IDs such that processing them in LIFO order will generate any events
   * used by an index before generating that index itself.
   * @returns An array of node IDs in the order they should be processed to generate events.
   */
  private stackEventNodes(): string[] {
    const tempNodeIdStack: string[] = [this.rootNodeId!];
    const nodeIdStack: string[] = [];

    while (tempNodeIdStack.length > 0) {
      const parentId = tempNodeIdStack.pop()!;
      nodeIdStack.push(parentId);

      if (!this.indexToChildEventsMap.has(parentId)) {
        continue;
      }

      const childIds = Array.from(this.indexToChildEventsMap.get(parentId)!);
      tempNodeIdStack.push(...childIds);
    }

    return nodeIdStack;
  }

  /**
   * Generates Nostr events for each node in the given stack.
   * @param nodeIdStack An array of node IDs ordered such that processing them in LIFO order will
   * produce any child event before it is required by a parent index event.
   * @param pubkey The public key (as a hex string) of the user generating the events.
   * @returns An array of Nostr events.
   */
  private generateEvents(nodeIdStack: string[], pubkey: string): NDKEvent[] {
    const events: NDKEvent[] = [];

    while (nodeIdStack.length > 0) {
      const nodeId = nodeIdStack.pop();

      switch (this.eventToKindMap.get(nodeId!)) {
        case 30040:
          events.push(this.generateIndexEvent(nodeId!, pubkey));
          break;

        case 30041:
        default:
          // Kind 30041 (zettel) is currently the default kind for contentful events.
          events.push(this.generateZettelEvent(nodeId!, pubkey));
          break;
      }
    }

    this.shouldUpdateEventTree = false;
    return events;
  }

  /**
   * Generates a kind 30040 index event for the node with the given ID.
   * @param nodeId The ID of the AsciiDoc document node from which to generate an index event.  The
   * node ID will be used as the event's unique d tag identifier.
   * @param pubkey The public key (not encoded in npub form) of the user generating the events.
   * @returns An unsigned NDKEvent with the requisite tags, including e tags pointing to each of its
   * children, and dated to the present moment.
   */
  private generateIndexEvent(nodeId: string, pubkey: string): NDKEvent {
    const title = (this.nodes.get(nodeId)! as AbstractBlock).getTitle();
    // TODO: Use a tags as per NIP-62.
    const childTags = Array.from(this.indexToChildEventsMap.get(nodeId)!).map(
      (id) => ["#e", this.eventIds.get(id)!],
    );

    const event = new NDKEvent(this.ndk);
    event.kind = 30040;
    event.content = "";
    event.tags = [["title", title!], ["#d", nodeId], ...childTags];
    event.created_at = Date.now();
    event.pubkey = pubkey;

    // Add optional metadata to the root index event.
    if (nodeId === this.rootNodeId) {
      const document = this.nodes.get(nodeId) as Document;

      // Store the metadata so it is available if we need it later.
      this.rootIndexMetadata = {
        authors: document
          .getAuthors()
          .map((author) => author.getName())
          .filter((name): name is string => name != null),
        version: document.getRevisionNumber(),
        edition: document.getRevisionRemark(),
        publicationDate: document.getRevisionDate(),
      };

      if (this.rootIndexMetadata.authors) {
        event.tags.push(["author", ...this.rootIndexMetadata.authors!]);
      }

      if (this.rootIndexMetadata.version || this.rootIndexMetadata.edition) {
        const versionTags: string[] = ["version"];
        if (this.rootIndexMetadata.version) {
          versionTags.push(this.rootIndexMetadata.version);
        }
        if (this.rootIndexMetadata.edition) {
          versionTags.push(this.rootIndexMetadata.edition);
        }
        event.tags.push(versionTags);
      }

      if (this.rootIndexMetadata.publicationDate) {
        event.tags.push([
          "published_on",
          this.rootIndexMetadata.publicationDate!,
        ]);
      }
    }

    // Event ID generation must be the last step.
    const eventId = event.getEventHash();
    this.eventIds.set(nodeId, eventId);
    event.id = eventId;

    this.events.set(nodeId, event);

    return event;
  }

  /**
   * Generates a kind 30041 zettel event for the node with the given ID.
   * @param nodeId The ID of the AsciiDoc document node from which to generate an index event.  The
   * node ID will be used as the event's unique d tag identifier.
   * @param pubkey The public key (not encoded in npub form) of the user generating the events.
   * @returns An unsigned NDKEvent containing the content of the zettel, the requisite tags, and
   * dated to the present moment.
   */
  private generateZettelEvent(nodeId: string, pubkey: string): NDKEvent {
    const title = (this.nodes.get(nodeId)! as Block).getTitle();
    const content = (this.nodes.get(nodeId)! as Block).getSource(); // AsciiDoc source content.

    const event = new NDKEvent(this.ndk);
    event.kind = 30041;
    event.content = content!;
    event.tags = [
      ["title", title!],
      ["#d", nodeId],
      ...this.extractAndNormalizeWikilinks(content!),
    ];

    // Extract image from content if present
    const imageUrl = this.extractImageFromContent(content!);
    if (imageUrl) {
      event.tags.push(["image", imageUrl]);
    }

    event.created_at = Date.now();
    event.pubkey = pubkey;

    // Event ID generation must be the last step.
    const eventId = event.getEventHash();
    this.eventIds.set(nodeId, eventId);
    event.id = eventId;

    this.events.set(nodeId, event);

    return event;
  }

  // #endregion

  // #region Utility Functions

  /**
   * Generates an ID for the given block that is unique within the document, and adds a mapping of
   * the generated ID to the block's context, as determined by the Asciidoctor parser.
   */
  private generateNodeId(block: AbstractBlock): string {
    let blockId: string | null = this.normalizeId(block.getId());

    if (blockId != null && blockId.length > 0) {
      return blockId;
    }

    blockId = this.normalizeId(block.getTitle());

    // Use the provided title, if possible.
    if (blockId != null && blockId.length > 0) {
      return blockId;
    }

    const documentId = this.rootNodeId;
    let blockNumber: number;

    const context = block.getContext();
    switch (context) {
      case "admonition":
        blockNumber = this.contextCounters.get("admonition") ?? 0;
        blockId = `${documentId}-admonition-${blockNumber++}`;
        this.contextCounters.set("admonition", blockNumber);
        break;

      case "audio":
        blockNumber = this.contextCounters.get("audio") ?? 0;
        blockId = `${documentId}-audio-${blockNumber++}`;
        this.contextCounters.set("audio", blockNumber);
        break;

      case "colist":
        blockNumber = this.contextCounters.get("colist") ?? 0;
        blockId = `${documentId}-colist-${blockNumber++}`;
        this.contextCounters.set("colist", blockNumber);
        break;

      case "dlist":
        blockNumber = this.contextCounters.get("dlist") ?? 0;
        blockId = `${documentId}-dlist-${blockNumber++}`;
        this.contextCounters.set("dlist", blockNumber);
        break;

      case "document":
        blockNumber = this.contextCounters.get("document") ?? 0;
        blockId = `${documentId}-document-${blockNumber++}`;
        this.contextCounters.set("document", blockNumber);
        break;

      case "example":
        blockNumber = this.contextCounters.get("example") ?? 0;
        blockId = `${documentId}-example-${blockNumber++}`;
        this.contextCounters.set("example", blockNumber);
        break;

      case "floating_title":
        blockNumber = this.contextCounters.get("floating_title") ?? 0;
        blockId = `${documentId}-floating-title-${blockNumber++}`;
        this.contextCounters.set("floating_title", blockNumber);
        break;

      case "image":
        blockNumber = this.contextCounters.get("image") ?? 0;
        blockId = `${documentId}-image-${blockNumber++}`;
        this.contextCounters.set("image", blockNumber);
        break;

      case "list_item":
        blockNumber = this.contextCounters.get("list_item") ?? 0;
        blockId = `${documentId}-list-item-${blockNumber++}`;
        this.contextCounters.set("list_item", blockNumber);
        break;

      case "listing":
        blockNumber = this.contextCounters.get("listing") ?? 0;
        blockId = `${documentId}-listing-${blockNumber++}`;
        this.contextCounters.set("listing", blockNumber);
        break;

      case "literal":
        blockNumber = this.contextCounters.get("literal") ?? 0;
        blockId = `${documentId}-literal-${blockNumber++}`;
        this.contextCounters.set("literal", blockNumber);
        break;

      case "olist":
        blockNumber = this.contextCounters.get("olist") ?? 0;
        blockId = `${documentId}-olist-${blockNumber++}`;
        this.contextCounters.set("olist", blockNumber);
        break;

      case "open":
        blockNumber = this.contextCounters.get("open") ?? 0;
        blockId = `${documentId}-open-${blockNumber++}`;
        this.contextCounters.set("open", blockNumber);
        break;

      case "page_break":
        blockNumber = this.contextCounters.get("page_break") ?? 0;
        blockId = `${documentId}-page-break-${blockNumber++}`;
        this.contextCounters.set("page_break", blockNumber);
        break;

      case "paragraph":
        blockNumber = this.contextCounters.get("paragraph") ?? 0;
        blockId = `${documentId}-paragraph-${blockNumber++}`;
        this.contextCounters.set("paragraph", blockNumber);
        break;

      case "pass":
        blockNumber = this.contextCounters.get("pass") ?? 0;
        blockId = `${documentId}-pass-${blockNumber++}`;
        this.contextCounters.set("pass", blockNumber);
        break;

      case "preamble":
        blockNumber = this.contextCounters.get("preamble") ?? 0;
        blockId = `${documentId}-preamble-${blockNumber++}`;
        this.contextCounters.set("preamble", blockNumber);
        break;

      case "quote":
        blockNumber = this.contextCounters.get("quote") ?? 0;
        blockId = `${documentId}-quote-${blockNumber++}`;
        this.contextCounters.set("quote", blockNumber);
        break;

      case "section":
        blockNumber = this.contextCounters.get("section") ?? 0;
        blockId = `${documentId}-section-${blockNumber++}`;
        this.contextCounters.set("section", blockNumber);
        break;

      case "sidebar":
        blockNumber = this.contextCounters.get("sidebar") ?? 0;
        blockId = `${documentId}-sidebar-${blockNumber++}`;
        this.contextCounters.set("sidebar", blockNumber);
        break;

      case "table":
        blockNumber = this.contextCounters.get("table") ?? 0;
        blockId = `${documentId}-table-${blockNumber++}`;
        this.contextCounters.set("table", blockNumber);
        break;

      case "table_cell":
        blockNumber = this.contextCounters.get("table_cell") ?? 0;
        blockId = `${documentId}-table-cell-${blockNumber++}`;
        this.contextCounters.set("table_cell", blockNumber);
        break;

      case "thematic_break":
        blockNumber = this.contextCounters.get("thematic_break") ?? 0;
        blockId = `${documentId}-thematic-break-${blockNumber++}`;
        this.contextCounters.set("thematic_break", blockNumber);
        break;

      case "toc":
        blockNumber = this.contextCounters.get("toc") ?? 0;
        blockId = `${documentId}-toc-${blockNumber++}`;
        this.contextCounters.set("toc", blockNumber);
        break;

      case "ulist":
        blockNumber = this.contextCounters.get("ulist") ?? 0;
        blockId = `${documentId}-ulist-${blockNumber++}`;
        this.contextCounters.set("ulist", blockNumber);
        break;

      case "verse":
        blockNumber = this.contextCounters.get("verse") ?? 0;
        blockId = `${documentId}-verse-${blockNumber++}`;
        this.contextCounters.set("verse", blockNumber);
        break;

      case "video":
        blockNumber = this.contextCounters.get("video") ?? 0;
        blockId = `${documentId}-video-${blockNumber++}`;
        this.contextCounters.set("video", blockNumber);
        break;

      default:
        blockNumber = this.contextCounters.get("block") ?? 0;
        blockId = `${documentId}-block-${blockNumber++}`;
        this.contextCounters.set("block", blockNumber);
        break;
    }

    block.setId(blockId);
    this.eventToContextMap.set(blockId, context);

    return blockId;
  }

  private normalizeId(input?: string): string | null {
    if (input == null || input.length === 0) {
      return null;
    }

    return he
      .decode(input)
      .toLowerCase()
      .replace(/[_]/g, " ") // Replace underscores with spaces.
      .trim()
      .replace(/\s+/g, "-") // Replace spaces with dashes.
      .replace(/[^a-z0-9\-]/g, ""); // Remove non-alphanumeric characters except dashes.
  }

  private updateEventByContext(dTag: string, value: string, context: string) {
    switch (context) {
      case "document":
      case "section":
        this.updateEventTitle(dTag, value);
        break;

      default:
        this.updateEventBody(dTag, value);
        break;
    }
  }

  private updateEventTitle(dTag: string, value: string) {
    const event = this.events.get(dTag);
    this.events.delete(dTag);
    this.events.set(value, event!);
    this.rehashEvent(dTag, event!);
  }

  private updateEventBody(dTag: string, value: string) {
    const event = this.events.get(dTag);
    event!.content = value;
    this.rehashEvent(dTag, event!);
  }

  private rehashEvent(dTag: string, event: NDKEvent) {
    event.id = event.getEventHash();
    this.eventIds.set(dTag, event.id);
    this.shouldUpdateEventTree = true;
  }

  private extractAndNormalizeWikilinks(content: string): string[][] {
    const wikilinkPattern = /\[\[([^\]]+)\]\]/g;
    const wikilinks: string[][] = [];
    let match: RegExpExecArray | null;

    // TODO: Match custom-named wikilinks as defined in NIP-54.
    while ((match = wikilinkPattern.exec(content)) !== null) {
      const linkName = match[1];
      const normalizedText = this.normalizeId(linkName);
      wikilinks.push(["wikilink", normalizedText!]);
    }

    return wikilinks;
  }

  /**
   * Extracts the first image URL from AsciiDoc content.
   * @param content The AsciiDoc content to search for images.
   * @returns The first image URL found, or null if no images are present.
   */
  private extractImageFromContent(content: string): string | null {
    // Look for AsciiDoc image syntax: image::url[alt text]
    const imageRegex = /image::([^\s\[]+)/g;
    let match = imageRegex.exec(content);
    if (match) {
      return match[1];
    }

    // Look for AsciiDoc image syntax: image:url[alt text]
    const inlineImageRegex = /image:([^\s\[]+)/g;
    match = inlineImageRegex.exec(content);
    if (match) {
      return match[1];
    }

    // Look for markdown-style image syntax: ![alt](url)
    const markdownImageRegex = /!\[([^\]]*)\]\(([^)]+)\)/g;
    match = markdownImageRegex.exec(content);
    if (match) {
      return match[2];
    }

    return null;
  }

  // TODO: Add search-based wikilink resolution.

  // #endregion
}

export const pharosInstance: Writable<Pharos> = writable();

export const tocUpdate = writable(0);

// Whenever you update the publication tree, call:
tocUpdate.update((n) => n + 1);

function ensureAsciiDocHeader(content: string): string {
  const lines = content.split(/\r?\n/);
  let headerIndex = -1;
  let hasDoctype = false;

  // Find the first non-empty line as header
  for (let i = 0; i < lines.length; i++) {
    if (lines[i].trim() === "") continue;
    if (lines[i].trim().startsWith("=")) {
      headerIndex = i;

      break;
    } else {
      throw new Error("AsciiDoc document is missing a header at the top.");
    }
  }

  if (headerIndex === -1) {
    throw new Error("AsciiDoc document is missing a header.");
  }

  // Check for doctype in the next non-empty line after header
  let nextLine = headerIndex + 1;
  while (nextLine < lines.length && lines[nextLine].trim() === "") {
    nextLine++;
  }
  if (
    nextLine < lines.length &&
    lines[nextLine].trim().startsWith(":doctype:")
  ) {
    hasDoctype = true;
  }

  // Insert doctype immediately after header if not present
  if (!hasDoctype) {
    lines.splice(headerIndex + 1, 0, ":doctype: book");
  }

  return lines.join("\n");
}