backend/src/publisher/transformers/citation.ts

import type { Transformer } from "./types.js";

const NUMERIC_STYLES = new Set(["ieee", "vancouver"]);

/**
 * Converts inline `<span data-type="citation">` markers produced by TipTap
 * into anchor links pointing at the bibliography entries.
 *
 * - Numeric styles (IEEE, Vancouver) display sequential `[n]` labels.
 * - Author-date styles keep the original inline label (e.g. "(Smith 2020)").
 *
 * Must run before the bibliography transformer so the `#ref-<key>` anchors
 * line up with the entry ids created there.
 */
export const citationTransformer: Transformer = {
  name: "citation",
  apply(document, ctx) {
    const isNumeric = ctx.citationData ? NUMERIC_STYLES.has(ctx.citationData.style) : false;
    const citationKeyOrder: string[] = [];

    // Index bibliography entries by key so we can enrich each inline citation
    // with a hover tooltip showing title / journal / DOI.
    const entriesByKey = new Map<string, any>();
    for (const entry of ctx.citationData?.entries ?? []) {
      const entryKey = (entry?.id as string) || (entry?.key as string);
      if (entryKey) entriesByKey.set(entryKey, entry);
    }

    for (const span of [...document.querySelectorAll('span[data-type="citation"]')]) {
      const key = span.getAttribute("key") || span.getAttribute("data-key");
      if (!key) continue;

      if (!citationKeyOrder.includes(key)) citationKeyOrder.push(key);
      const idx = citationKeyOrder.indexOf(key) + 1;

      const originalLabel = span.textContent || `[${key}]`;
      const displayLabel = isNumeric ? `[${idx}]` : originalLabel;

      const a = document.createElement("a");
      a.setAttribute("href", `#ref-${key}`);
      a.className = "citation-inline";
      a.setAttribute("id", `cite-${key}-${idx}`);
      a.setAttribute("title", key);
      a.textContent = displayLabel;

      const entry = entriesByKey.get(key);
      if (entry) {
        const tooltip = document.createElement("span");
        tooltip.className = "pub-tooltip pub-tooltip--citation";
        tooltip.setAttribute("aria-hidden", "true");

        const titleEl = document.createElement("span");
        titleEl.className = "pub-tooltip__title";
        titleEl.textContent = (entry.title as string) || key;
        tooltip.appendChild(titleEl);

        const journalText = (entry["container-title"] as string) || "";
        if (journalText) {
          const journal = document.createElement("span");
          journal.className = "pub-tooltip__journal";
          const parts: string[] = [journalText];
          if (entry.volume) parts.push(String(entry.volume));
          if (entry.page) parts.push(String(entry.page));
          journal.textContent = parts.join(", ");
          tooltip.appendChild(journal);
        }

        if (entry.DOI) {
          const doi = document.createElement("span");
          doi.className = "pub-tooltip__doi";
          doi.textContent = `doi: ${entry.DOI}`;
          tooltip.appendChild(doi);
        }

        a.appendChild(tooltip);
      }

      span.replaceWith(a);
    }
  },
};