/**
 * /api/timeline?from=1940&to=2026&class=event&limit=200
 *
 * Returns events sorted by date_start from wiki/entities/events/*.md frontmatter.
 * No DB required — pure filesystem read of YAML frontmatter.
 *
 * Optional filters:
 *   - from / to: ISO dates or year strings (e.g. "1947" or "1947-06-24")
 *   - class:     "event" | "uap_object" | "operation" (default: event)
 *   - limit:     1..500 (default 200)
 *   - q:         substring match in canonical_name or narrative_summary
 */
import fs from "node:fs/promises";
import path from "node:path";
import matter from "gray-matter";
import { WIKI } from "@/lib/wiki";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

const CLASS_FOLDER: Record<string, string> = {
  event: "events",
  uap_object: "uap-objects",
  operation: "operations",
};

interface TimelineEntry {
  entity_class: string;
  entity_id: string;
  canonical_name: string;
  date_start: string | null;
  date_end: string | null;
  primary_location?: string | null;
  narrative_summary?: string | null;
  summary_status: "none" | "synthesized" | "curated" | "red_teamed";
  total_mentions?: number;
  href: string;
}

function json(data: unknown, status = 200) {
  return new Response(JSON.stringify(data), {
    status,
    headers: { "content-type": "application/json", "cache-control": "public, max-age=60" },
  });
}

function pickDate(fm: Record<string, unknown>): string | null {
  const cand =
    fm.date_start ?? fm.date ?? fm.event_date ?? fm.observation_date ?? fm.start_date ?? null;
  if (!cand) return null;
  return String(cand).trim();
}

function dateSortable(s: string | null): string {
  if (!s) return "9999";
  // Pad year-only ("1947" → "1947-00-00") and accept "1947-06-24"
  const m = s.match(/^(\d{4})(?:-(\d{2}))?(?:-(\d{2}))?/);
  if (!m) return s;
  return `${m[1]}-${m[2] ?? "00"}-${m[3] ?? "00"}`;
}

export async function GET(req: Request) {
  const u = new URL(req.url);
  const cls = (u.searchParams.get("class") ?? "event") as keyof typeof CLASS_FOLDER;
  const folder = CLASS_FOLDER[cls];
  if (!folder) return json({ error: "bad_class", class: cls }, 400);

  const from = u.searchParams.get("from") ?? "";
  const to = u.searchParams.get("to") ?? "";
  const q = (u.searchParams.get("q") ?? "").toLowerCase().trim();
  const limit = Math.min(Math.max(Number(u.searchParams.get("limit") ?? 200), 1), 500);
  // Default: only show events with curated/synthesised narrative — never stubs.
  // Opt-in `?include_unsynthesized=1` returns everything (admin / debug).
  const includeUnsynthesized = u.searchParams.get("include_unsynthesized") === "1";

  const dir = path.join(WIKI, "entities", folder);
  let files: string[] = [];
  try {
    files = (await fs.readdir(dir)).filter((f) => f.endsWith(".md"));
  } catch {
    return json({ entries: [], count: 0 });
  }

  const entries: TimelineEntry[] = [];
  for (const f of files) {
    try {
      const raw = await fs.readFile(path.join(dir, f), "utf-8");
      const parsed = matter(raw);
      const fm = parsed.data as Record<string, unknown>;
      const date_start = pickDate(fm);
      if (!date_start) continue;
      const sortable = dateSortable(date_start);
      if (from && sortable < dateSortable(from)) continue;
      if (to && sortable > dateSortable(to)) continue;
      const canonical = String(fm.canonical_name ?? f.replace(/\.md$/, ""));
      const narrativeRaw = fm.narrative_summary;
      const narrative = typeof narrativeRaw === "string" ? narrativeRaw : "";
      const statusRaw = String(fm.summary_status ?? (narrative ? "synthesized" : "none"));
      const summary_status = (
        ["none", "synthesized", "curated", "red_teamed"].includes(statusRaw)
          ? statusRaw
          : "none"
      ) as TimelineEntry["summary_status"];
      // Default: hide events without a real narrative.
      if (!includeUnsynthesized && summary_status === "none") continue;
      // Always hide generic concept-entities (categories, not real events).
      if (fm.is_generic === true) continue;
      if (q && !canonical.toLowerCase().includes(q) && !narrative.toLowerCase().includes(q)) {
        continue;
      }
      entries.push({
        entity_class: cls,
        entity_id: f.replace(/\.md$/, ""),
        canonical_name: canonical,
        date_start,
        date_end: (fm.date_end as string) ?? null,
        primary_location: (fm.primary_location as string) ?? null,
        narrative_summary: narrative ? narrative.slice(0, 280) : null,
        summary_status,
        total_mentions: typeof fm.total_mentions === "number" ? fm.total_mentions : undefined,
        href: `/e/${folder}/${f.replace(/\.md$/, "")}`,
      });
    } catch {
      /* skip malformed */
    }
  }

  entries.sort((a, b) => dateSortable(a.date_start).localeCompare(dateSortable(b.date_start)));
  return json({
    count: entries.length,
    limit,
    from: from || null,
    to: to || null,
    class: cls,
    entries: entries.slice(0, limit),
  });
}