SkateSpots/src/lib/lightningAddress.ts

/**
 * Lightning Address resolution via LNURL-pay protocol
 */

interface LNURLPayResponse {
  status?: 'OK' | 'ERROR';
  tag: 'payRequest';
  commentAllowed?: number;
  minSendable: number;
  maxSendable: number;
  metadata: string;
  callback: string;
}

interface LNURLInvoiceResponse {
  status?: 'OK' | 'ERROR';
  reason?: string;
  pr?: string;
}

/**
 * Validate if a string is a valid Lightning address
 */
export function isValidLightningAddress(address: string): boolean {
  if (!address || typeof address !== 'string') {
    return false;
  }

  const trimmed = address.trim();
  const parts = trimmed.split('@');
  if (parts.length !== 2) {
    return false;
  }

  const [username, domain] = parts;

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

  if (!domain || !domain.includes('.')) {
    return false;
  }

  const domainParts = domain.split('.');
  if (domainParts.length < 2 || domainParts[domainParts.length - 1].length < 2) {
    return false;
  }

  return true;
}

/**
 * Resolve Lightning address to LNURL-pay endpoint
 */
export async function resolveLightningAddress(
  lightningAddress: string
): Promise<LNURLPayResponse> {
  if (!isValidLightningAddress(lightningAddress)) {
    throw new Error('Invalid Lightning address format. Expected: username@domain.com');
  }

  const [username, domain] = lightningAddress.split('@');
  const lnurlEndpoint = `https://${domain}/.well-known/lnurlp/${username}`;

  const response = await fetch(lnurlEndpoint, {
    headers: { 'Accept': 'application/json' },
  });

  if (!response.ok) {
    throw new Error(
      `Failed to resolve Lightning address: ${response.status} ${response.statusText}`
    );
  }

  const data: LNURLPayResponse = await response.json();

  if (data.status && data.status !== 'OK') {
    throw new Error('LNURL endpoint returned error status');
  }

  if (data.tag !== 'payRequest') {
    throw new Error(`Unexpected LNURL tag: ${data.tag}`);
  }

  return data;
}

export interface GetInvoiceParams {
  lightningAddress: string;
  amountSats: number;
  comment?: string;
}

/**
 * Does this Lightning address support NIP-57 zaps?
 * Returns the provider's nostr pubkey (hex) if so, else null.
 */
export async function getZapProviderPubkey(
  lightningAddress: string,
): Promise<string | null> {
  try {
    const data = await resolveLightningAddress(lightningAddress);
    // `allowsNostr` + a valid `nostrPubkey` means the provider publishes zap receipts.
    const withNostr = data as LNURLPayResponse & {
      allowsNostr?: boolean;
      nostrPubkey?: string;
    };
    if (withNostr.allowsNostr && /^[0-9a-f]{64}$/i.test(withNostr.nostrPubkey ?? '')) {
      return withNostr.nostrPubkey!.toLowerCase();
    }
    return null;
  } catch {
    return null;
  }
}

export interface GetZapInvoiceParams {
  lightningAddress: string;
  amountSats: number;
  /** Signed kind-9734 zap request event (JSON string via JSON.stringify). */
  zapRequest: string;
}

/**
 * Get a BOLT11 invoice for a NIP-57 zap by passing a signed zap request to the
 * LNURL callback. The provider will publish a kind-9735 zap receipt when paid.
 */
export async function getZapInvoiceFromLightningAddress(
  params: GetZapInvoiceParams,
): Promise<string> {
  const { lightningAddress, amountSats, zapRequest } = params;

  if (!isValidLightningAddress(lightningAddress)) {
    throw new Error('Invalid Lightning address format. Expected: username@domain.com');
  }
  if (amountSats <= 0) throw new Error('Amount must be greater than 0');

  const lnurlData = await resolveLightningAddress(lightningAddress);
  const minSats = lnurlData.minSendable / 1000;
  const maxSats = lnurlData.maxSendable / 1000;
  if (amountSats < minSats) throw new Error(`Amount ${amountSats} sats is below minimum ${minSats} sats`);
  if (amountSats > maxSats) throw new Error(`Amount ${amountSats} sats exceeds maximum ${maxSats} sats`);

  const amountMsats = amountSats * 1000;
  const callbackUrl = new URL(lnurlData.callback);
  callbackUrl.searchParams.set('amount', amountMsats.toString());
  callbackUrl.searchParams.set('nostr', zapRequest);

  const invoiceResponse = await fetch(callbackUrl.toString(), {
    headers: { Accept: 'application/json' },
  });
  if (!invoiceResponse.ok) {
    throw new Error(`Failed to get zap invoice: ${invoiceResponse.status} ${invoiceResponse.statusText}`);
  }
  const invoiceData: LNURLInvoiceResponse = await invoiceResponse.json();
  if (invoiceData.pr) return invoiceData.pr;
  if (invoiceData.status && invoiceData.status !== 'OK') {
    throw new Error(`Zap invoice generation failed: ${invoiceData.reason || 'unknown'}`);
  }
  throw new Error('No invoice returned from provider');
}

/**
 * Get BOLT11 invoice from Lightning address
 */
export async function getInvoiceFromLightningAddress(
  params: GetInvoiceParams
): Promise<string> {
  const { lightningAddress, amountSats, comment } = params;

  if (!isValidLightningAddress(lightningAddress)) {
    throw new Error('Invalid Lightning address format. Expected: username@domain.com');
  }

  if (amountSats <= 0) {
    throw new Error('Amount must be greater than 0');
  }

  // Step 1: Resolve LNURL-pay endpoint
  const lnurlData = await resolveLightningAddress(lightningAddress);

  // Step 2: Validate amount against min/max bounds
  const minSats = lnurlData.minSendable / 1000;
  const maxSats = lnurlData.maxSendable / 1000;

  if (amountSats < minSats) {
    throw new Error(`Amount ${amountSats} sats is below minimum ${minSats} sats`);
  }

  if (amountSats > maxSats) {
    throw new Error(`Amount ${amountSats} sats exceeds maximum ${maxSats} sats`);
  }

  // Step 3: Request invoice from callback URL
  const amountMsats = amountSats * 1000;
  const callbackUrl = new URL(lnurlData.callback);
  callbackUrl.searchParams.set('amount', amountMsats.toString());

  if (comment && lnurlData.commentAllowed) {
    if (comment.length > lnurlData.commentAllowed) {
      throw new Error(
        `Comment length ${comment.length} exceeds maximum ${lnurlData.commentAllowed} characters`
      );
    }
    callbackUrl.searchParams.set('comment', comment);
  }

  const invoiceResponse = await fetch(callbackUrl.toString(), {
    headers: { 'Accept': 'application/json' },
  });

  if (!invoiceResponse.ok) {
    throw new Error(
      `Failed to get invoice: ${invoiceResponse.status} ${invoiceResponse.statusText}`
    );
  }

  const invoiceData: LNURLInvoiceResponse = await invoiceResponse.json();

  if (invoiceData.pr) {
    return invoiceData.pr;
  }

  if (invoiceData.status && invoiceData.status !== 'OK') {
    const errorReason = invoiceData.reason || 'Invoice generation failed';
    throw new Error(`Invoice generation failed: ${errorReason}`);
  }

  throw new Error('No invoice returned from provider');
}