import { NextResponse } from "next/server";

// Lightweight backend-for-frontend over free, keyless geo services.
//   GET /api/geo?pin=203201            → India Post: { ok, pin, city, district, state, localities }
//   GET /api/geo?q=alpha               → India Post locality search: { ok, results }
//   GET /api/geo?addr=350 5th&country=us → OpenStreetMap/Nominatim house-number autosuggest:
//                                          { ok, results: [{ label, line1, line2, city, state, postal }] }
// If an upstream service is unreachable we fall back to a small built-in dataset
// so the registration flow keeps working offline / in the demo.

type Locality = { city: string; district: string; state: string; localities: string[] };

const FALLBACK_PINS: Record<string, Locality> = {
  "203201": { city: "Greater Noida", district: "Gautam Buddh Nagar", state: "Uttar Pradesh", localities: ["Dankaur", "Dhanouri Kalan", "Jaganpur Afjalpur"] },
  "201301": { city: "Noida", district: "Gautam Buddh Nagar", state: "Uttar Pradesh", localities: ["Noida Sector 1", "Noida Sector 27", "Hoshiarpur"] },
  "110001": { city: "New Delhi", district: "Central Delhi", state: "Delhi", localities: ["Connaught Place", "Janpath", "Sansad Marg"] },
  "122001": { city: "Gurugram", district: "Gurugram", state: "Haryana", localities: ["Gurgaon", "Civil Lines", "Gurgaon Sector 14"] },
  "226001": { city: "Lucknow", district: "Lucknow", state: "Uttar Pradesh", localities: ["Lucknow GPO", "Hazratganj", "Lalbagh"] },
  "302001": { city: "Jaipur", district: "Jaipur", state: "Rajasthan", localities: ["Jaipur GPO", "Kishanpole Bazar", "Mi Road"] },
  "456010": { city: "Ujjain", district: "Ujjain", state: "Madhya Pradesh", localities: ["Ujjain GPO", "Freeganj", "Mahakal"] },
};

type IndiaPostOffice = { Name: string; District: string; State: string; Pincode: string; BranchType?: string };
type IndiaPostResp = Array<{ Status: string; PostOffice: IndiaPostOffice[] | null }>;

async function fetchUpstream(url: string): Promise<IndiaPostResp> {
  const res = await fetch(url, {
    headers: { "User-Agent": "YEIDA-Portal/1.0 (address autofill)" },
    // The PIN → locality mapping is effectively static; cache for a day.
    next: { revalidate: 86400 },
  });
  if (!res.ok) throw new Error(`upstream ${res.status}`);
  return (await res.json()) as IndiaPostResp;
}

const clean = (s: string) => s.replace(/\s+/g, " ").trim();

export async function GET(request: Request) {
  const { searchParams } = new URL(request.url);
  const pin = (searchParams.get("pin") || "").replace(/\D/g, "");
  const q = clean(searchParams.get("q") || "");
  const addr = clean(searchParams.get("addr") || "");
  const country = (searchParams.get("country") || "").toLowerCase().replace(/[^a-z]/g, "");

  // --- PIN lookup → city / district / state + locality options ---
  if (pin) {
    if (pin.length !== 6) {
      return NextResponse.json({ ok: false, error: "PIN must be 6 digits" }, { status: 400 });
    }
    try {
      const data = await fetchUpstream(`https://api.postalpincode.in/pincode/${pin}`);
      const offices = data?.[0]?.Status === "Success" ? data[0].PostOffice ?? [] : [];
      if (offices.length) {
        const first = offices[0];
        const localities = [...new Set(offices.map((o) => clean(o.Name)))];
        return NextResponse.json({
          ok: true, pin, city: first.District, district: first.District, state: first.State, localities,
        });
      }
    } catch {
      /* fall through to the built-in fallback below */
    }
    const fb = FALLBACK_PINS[pin];
    if (fb) {
      return NextResponse.json({ ok: true, pin, ...fb, source: "fallback" });
    }
    return NextResponse.json({ ok: false, error: "PIN not found" }, { status: 404 });
  }

  // --- Address / locality typeahead by name ---
  if (q) {
    if (q.length < 3) return NextResponse.json({ ok: true, results: [] });
    try {
      const data = await fetchUpstream(`https://api.postalpincode.in/postoffice/${encodeURIComponent(q)}`);
      const offices = data?.[0]?.Status === "Success" ? data[0].PostOffice ?? [] : [];
      const results = offices.slice(0, 8).map((o) => ({
        label: `${clean(o.Name)} · ${o.District}, ${o.State} — ${o.Pincode}`,
        line2: clean(o.Name), city: o.District, state: o.State, pin: o.Pincode,
      }));
      return NextResponse.json({ ok: true, results });
    } catch {
      const ql = q.toLowerCase();
      const results = Object.entries(FALLBACK_PINS)
        .filter(([, v]) => v.city.toLowerCase().includes(ql) || v.localities.some((l) => l.toLowerCase().includes(ql)))
        .slice(0, 8)
        .map(([p, v]) => ({ label: `${v.city} · ${v.district}, ${v.state} — ${p}`, line2: v.city, city: v.city, state: v.state, pin: p }));
      return NextResponse.json({ ok: true, results, source: "fallback" });
    }
  }

  // --- Worldwide house-number / street autosuggest (non-India) via OpenStreetMap ---
  if (addr) {
    if (addr.length < 3) return NextResponse.json({ ok: true, results: [] });
    try {
      const url = `https://nominatim.openstreetmap.org/search?q=${encodeURIComponent(addr)}` +
        `${country ? `&countrycodes=${country}` : ""}&format=jsonv2&addressdetails=1&limit=6`;
      const res = await fetch(url, {
        headers: { "User-Agent": "YEIDA-Portal/1.0 (address autofill)" },
        next: { revalidate: 3600 },
      });
      if (!res.ok) throw new Error(`upstream ${res.status}`);
      type NomRow = { display_name: string; name?: string; address?: Record<string, string> };
      const rows = (await res.json()) as NomRow[];
      const results = rows.map((r) => {
        const a = r.address || {};
        const line1 = clean([a.house_number, a.road || a.pedestrian || a.name || r.name].filter(Boolean).join(" "));
        const city = a.city || a.town || a.village || a.municipality || a.suburb || a.county || "";
        return {
          label: r.display_name,
          line1,
          line2: a.neighbourhood || a.suburb || a.quarter || "",
          city,
          state: a.state || a.region || "",
          postal: a.postcode || "",
        };
      }).filter((r) => r.line1);
      return NextResponse.json({ ok: true, results });
    } catch {
      return NextResponse.json({ ok: true, results: [], source: "fallback" });
    }
  }

  return NextResponse.json({ ok: false, error: "Provide a ?pin=, ?q= or ?addr= parameter" }, { status: 400 });
}