import { createHmac, timingSafeEqual } from "node:crypto";

const STRIPE_API_BASE = "https://api.stripe.com/v1";

type StripeCheckoutSession = {
  id: string;
  url: string;
  mode: string;
  metadata?: Record<string, string>;
};

type CheckoutSessionParams = {
  secretKey: string;
  priceId: string;
  userId: string;
  email: string;
  planId: string;
  successUrl: string;
  cancelUrl: string;
};

export class StripeRequestError extends Error {
  status: number;

  constructor(message: string, status: number) {
    super(message);
    this.status = status;
  }
}

function buildCheckoutBody(params: CheckoutSessionParams) {
  const body = new URLSearchParams();
  body.set("mode", "subscription");
  body.set("success_url", params.successUrl);
  body.set("cancel_url", params.cancelUrl);
  body.set("line_items[0][price]", params.priceId);
  body.set("line_items[0][quantity]", "1");
  body.set("allow_promotion_codes", "true");
  body.set("client_reference_id", params.userId);
  body.set("customer_email", params.email);

  body.set("metadata[userId]", params.userId);
  body.set("metadata[planId]", params.planId);

  body.set("subscription_data[metadata][userId]", params.userId);
  body.set("subscription_data[metadata][planId]", params.planId);

  return body;
}

export async function createStripeCheckoutSession(params: CheckoutSessionParams) {
  const response = await fetch(`${STRIPE_API_BASE}/checkout/sessions`, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${params.secretKey}`,
      "Content-Type": "application/x-www-form-urlencoded",
    },
    body: buildCheckoutBody(params).toString(),
  });

  const data = await response.json();

  if (!response.ok) {
    const message =
      typeof data?.error?.message === "string"
        ? data.error.message
        : "Stripe checkout session creation failed";

    throw new StripeRequestError(message, response.status);
  }

  if (!data?.url || !data?.id) {
    throw new StripeRequestError("Stripe checkout response missing session URL", 502);
  }

  return data as StripeCheckoutSession;
}

export function verifyStripeSignature({
  payload,
  signatureHeader,
  webhookSecret,
  toleranceSeconds = 300,
}: {
  payload: string;
  signatureHeader: string;
  webhookSecret: string;
  toleranceSeconds?: number;
}) {
  const parsed = signatureHeader.split(",").reduce<Record<string, string[]>>((acc, part) => {
    const [key, value] = part.split("=");
    if (!key || !value) {
      return acc;
    }

    if (!acc[key]) {
      acc[key] = [];
    }
    acc[key].push(value);
    return acc;
  }, {});

  const timestamp = parsed.t?.[0];
  const signatures = parsed.v1 || [];

  if (!timestamp || signatures.length === 0) {
    return false;
  }

  const signedPayload = `${timestamp}.${payload}`;
  const expected = createHmac("sha256", webhookSecret).update(signedPayload, "utf8").digest("hex");
  const expectedBuffer = Buffer.from(expected, "hex");

  const valid = signatures.some((signature) => {
    const candidateBuffer = Buffer.from(signature, "hex");

    if (candidateBuffer.length !== expectedBuffer.length) {
      return false;
    }

    return timingSafeEqual(candidateBuffer, expectedBuffer);
  });

  if (!valid) {
    return false;
  }

  const now = Math.floor(Date.now() / 1000);
  const eventTs = Number(timestamp);

  if (!Number.isFinite(eventTs)) {
    return false;
  }

  return Math.abs(now - eventTs) <= toleranceSeconds;
}