// "CITED IN" — the back-link index a moment page reads: for every moment the
// given reports cite, each place that cites it.
//
//   moment key → [{ reportId, sectionId, claimId, entryId?, citationId }]
//
// Built at compose from the site's published reports, in the order given, each
// report in reading order (./uses.ts). A place is listed once however many
// times it cites the moment there (a claim that cites a span in its findings
// and lists it under itself is one back-link); two citations of the same span
// in one claim are two. Citations without a moment (`source`, `page`), and
// references to citations the report does not define, are not indexed.
//
// Pure: the input is parsed reports, the output plain JSON.

import { momentKeyOf } from "../citations/moments";
import type { Report } from "./schema";
import { reportCitationUses } from "./uses";

export type CitedIn = {
  reportId: string;
  // null when cited in the report's summary or a timeline entry.
  sectionId: string | null;
  // null when cited in the summary, an entry or a section's body.
  claimId: string | null;
  // The timeline entry, when cited in one; absent elsewhere.
  entryId?: string;
  citationId: string;
};

export function buildCitedIn(reports: readonly Report[]): Record<string, CitedIn[]> {
  const out: Record<string, CitedIn[]> = {};
  const seen = new Set<string>();
  for (const report of reports) {
    const citations = report.citations ?? {};
    for (const use of reportCitationUses(report)) {
      if (!Object.hasOwn(citations, use.citationId)) continue;
      const key = momentKeyOf(citations[use.citationId]);
      if (!key) continue;
      const entry: CitedIn = {
        reportId: report.id,
        sectionId: use.sectionId,
        claimId: use.claimId,
        ...(use.entryId !== undefined ? { entryId: use.entryId } : {}),
        citationId: use.citationId,
      };
      const dedup = JSON.stringify([key, entry.reportId, entry.sectionId, entry.claimId, entry.entryId ?? null, entry.citationId]);
      if (seen.has(dedup)) continue;
      seen.add(dedup);
      (out[key] ??= []).push(entry);
    }
  }
  return out;
}