story-research-zapwall/lib/zapVerification.ts

import { Event, verifyEvent } from 'nostr-tools'

/**
 * Service for verifying zap receipts and their signatures
 */
export class ZapVerificationService {
  /**
   * Verify a zap receipt signature
   */
  verifyZapReceiptSignature(event: Event): boolean {
    try {
      return verifyEvent(event)
    } catch (error) {
      console.error('Error verifying zap receipt signature:', error)
      return false
    }
  }

  /**
   * Check if a zap receipt is valid for a specific article and user
   */
  verifyZapReceiptForArticle(
    zapReceipt: Event,
    articleId: string,
    articlePubkey: string,
    userPubkey: string,
    expectedAmount: number
  ): boolean {
    if (!this.verifyZapReceiptSignature(zapReceipt)) {
      console.warn('Zap receipt signature verification failed')
      return false
    }

    return (
      this.isRecipientValid(zapReceipt, articlePubkey) &&
      this.isArticleReferenced(zapReceipt, articleId) &&
      this.isAmountValid(zapReceipt, expectedAmount) &&
      this.isZapKind(zapReceipt)
    )
  }

  /**
   * Extract payment information from a zap receipt
   */
  extractPaymentInfo(zapReceipt: Event): {
    amount: number // in satoshis
    recipient: string
    articleId: string | null
    payer: string
  } | null {
    try {
      const amountTag = zapReceipt.tags.find((tag) => tag[0] === 'amount')
      const recipientTag = zapReceipt.tags.find((tag) => tag[0] === 'p')
      const eventTag = zapReceipt.tags.find((tag) => tag[0] === 'e')

      if (!amountTag || !recipientTag) {
        return null
      }

      const amountInMillisats = parseInt(amountTag[1] ?? '0')
      const amountInSats = Math.floor(amountInMillisats / 1000)

      return {
        amount: amountInSats,
        recipient: recipientTag[1],
        articleId: eventTag?.[1] ?? null,
        payer: zapReceipt.pubkey,
      }
    } catch (error) {
      console.error('Error extracting payment info:', error)
      return null
    }
  }

  private isRecipientValid(zapReceipt: Event, articlePubkey: string): boolean {
    const recipient = zapReceipt.tags.find((tag) => tag[0] === 'p')?.[1]
    if (recipient !== articlePubkey) {
      console.warn('Zap receipt recipient does not match article author')
      return false
    }
    return true
  }

  private isArticleReferenced(zapReceipt: Event, articleId: string): boolean {
    const eventIdTag = zapReceipt.tags.find((tag) => tag[0] === 'e')?.[1]
    if (eventIdTag !== articleId) {
      console.warn('Zap receipt does not reference the correct article')
      return false
    }
    return true
  }

  private isAmountValid(zapReceipt: Event, expectedAmount: number): boolean {
    const amountTag = zapReceipt.tags.find((tag) => tag[0] === 'amount')?.[1]
    if (!amountTag) {
      console.warn('Zap receipt does not contain amount tag')
      return false
    }
    const amountInMillisats = parseInt(amountTag ?? '0')
    const expectedAmountInMillisats = expectedAmount * 1000
    if (amountInMillisats < expectedAmountInMillisats) {
      console.warn(`Zap amount ${amountInMillisats} is less than expected ${expectedAmountInMillisats}`)
      return false
    }
    return true
  }

  private isZapKind(zapReceipt: Event): boolean {
    if (zapReceipt.kind !== 9735) {
      console.warn('Event is not a zap receipt (kind 9735)')
      return false
    }
    return true
  }
}

export const zapVerificationService = new ZapVerificationService()