import { NextResponse } from "next/server";

const MEMPOOL = "https://mempool.space/api";
const MIN_CONFIRMATIONS = 1;

function merchantAddress(): string {
  return (
    process.env.MERCHANT_BTC_ADDRESS ||
    process.env.NEXT_PUBLIC_MERCHANT_BTC_ADDRESS ||
    ""
  ).trim();
}

export async function POST(req: Request) {
  const merchant = merchantAddress();
  if (!merchant) {
    return NextResponse.json(
      { ok: false, error: "Server not configured: set MERCHANT_BTC_ADDRESS" },
      { status: 503 },
    );
  }

  let body: unknown;
  try {
    body = await req.json();
  } catch {
    return NextResponse.json({ ok: false, error: "Invalid JSON" }, { status: 400 });
  }

  const txid =
    typeof body === "object" &&
    body !== null &&
    "txid" in body &&
    typeof (body as { txid: unknown }).txid === "string"
      ? (body as { txid: string }).txid.trim()
      : "";

  if (!/^[a-fA-F0-9]{64}$/.test(txid)) {
    return NextResponse.json({ ok: false, error: "Invalid transaction id" }, { status: 400 });
  }

  const txRes = await fetch(`${MEMPOOL}/tx/${txid}`, { cache: "no-store" });
  if (!txRes.ok) {
    return NextResponse.json(
      { ok: false, error: "Transaction not found on network yet" },
      { status: 404 },
    );
  }

  const tx = (await txRes.json()) as {
    vout?: Array<{ value?: number; scriptpubkey_address?: string }>;
    status?: { confirmed?: boolean; block_height?: number };
  };

  const merchantLower = merchant.toLowerCase();
  let sats = 0;
  for (const vout of tx.vout || []) {
    const addr = vout.scriptpubkey_address;
    if (addr && addr.toLowerCase() === merchantLower && typeof vout.value === "number") {
      sats += vout.value;
    }
  }

  if (sats <= 0) {
    return NextResponse.json(
      {
        ok: false,
        error: "This transaction does not pay your configured merchant Bitcoin address",
      },
      { status: 400 },
    );
  }

  let confirmations = 0;
  if (tx.status?.confirmed && typeof tx.status.block_height === "number") {
    const tipRes = await fetch(`${MEMPOOL}/blocks/tip/height`, { cache: "no-store" });
    if (tipRes.ok) {
      const tip = Number(await tipRes.text());
      if (Number.isFinite(tip)) {
        confirmations = tip - tx.status.block_height + 1;
      }
    }
  }

  if (confirmations < MIN_CONFIRMATIONS) {
    return NextResponse.json({
      ok: false,
      error: `Need at least ${MIN_CONFIRMATIONS} confirmation(s); currently ${confirmations}`,
      confirmations,
      sats,
    });
  }

  const priceRes = await fetch(
    "https://api.coingecko.com/api/v3/simple/price?ids=bitcoin&vs_currencies=usd",
    { next: { revalidate: 60 } },
  );
  if (!priceRes.ok) {
    return NextResponse.json(
      { ok: false, error: "Could not fetch BTC/USD rate; try again shortly" },
      { status: 502 },
    );
  }
  const priceJson = (await priceRes.json()) as { bitcoin?: { usd?: number } };
  const btcUsd = priceJson.bitcoin?.usd;
  if (!btcUsd || !Number.isFinite(btcUsd)) {
    return NextResponse.json({ ok: false, error: "Invalid rate response" }, { status: 502 });
  }

  const btc = sats / 1e8;
  const creditedUsd = Math.round(btc * btcUsd * 100) / 100;

  return NextResponse.json({
    ok: true,
    creditedUsd,
    sats,
    btc,
    btcUsd,
    confirmations,
  });
}