// TaxPack Receipt Utilities - Pure functions for extraction, export, and summarization

export interface Receipt {
  id: string;
  merchant: string;
  amount: number;
  currency: string;
  date: string;
  category: string;
  paymentMethod: string;
  emailSubject: string;
  source: 'gmail';
}

/**
 * Extract receipt data from a Gmail message
 */
export function extractReceiptFromEmail(message: any): Receipt | null {
  if (!message || !message.payload) return null;

  const headers = message.payload.headers || [];
  const subject = headers.find((h: any) => h.name === 'Subject')?.value || '';
  const from = headers.find((h: any) => h.name === 'From')?.value || '';
  const dateHeader = headers.find((h: any) => h.name === 'Date')?.value || '';

  // Get email body
  let body = '';
  const getBody = (part: any): string => {
    if (part.body?.data) {
      try {
        return atob(part.body.data.replace(/-/g, '+').replace(/_/g, '/'));
      } catch {
        return '';
      }
    }
    if (part.parts) {
      for (const p of part.parts) {
        const b = getBody(p);
        if (b) return b;
      }
    }
    return '';
  };
  body = getBody(message.payload);

  // Extract amount using regex patterns
  const amountPatterns = [
    /(?:total|amount|charged|paid|payment)[\s:]*[$€£]\s*([\d,]+\.?\d*)/i,
    /[$€£]\s*([\d,]+\.?\d*)\s*(?:total|usd|eur|gbp)/i,
    /(?:order total|grand total)[\s:]*[$€£]?\s*([\d,]+\.?\d*)/i,
    /(?:price|cost)[\s:]*[$€£]?\s*([\d,]+\.?\d*)/i,
    /\$\s*([\d,]+\.\d{2})/,
    /([\d,]+\.\d{2})\s*(?:USD|EUR|GBP)/i,
  ];

  let amount = 0;
  for (const pattern of amountPatterns) {
    const match = body.match(pattern) || subject.match(pattern);
    if (match) {
      amount = parseFloat(match[1].replace(/,/g, ''));
      if (amount > 0) break;
    }
  }

  // Skip if no amount found
  if (amount <= 0) return null;

  // Extract merchant
  const merchantPatterns = [
    /from\s+([A-Z][A-Za-z0-9\s&]+?)(?:\s[-—]|\s*<|\n|$)/i,
    /(?:at|from)\s+([A-Z][A-Za-z0-9\s&]+?)(?:\s[-—]|\s*<|\n|$)/,
    /([A-Z][A-Za-z0-9\s&]+?)\s*(?:receipt|invoice|order)/i,
  ];

  let merchant = 'Unknown Merchant';
  for (const pattern of merchantPatterns) {
    const match = subject.match(pattern) || from.match(pattern);
    if (match) {
      merchant = match[1].trim();
      break;
    }
  }
  // Use from email domain as fallback
  if (merchant === 'Unknown Merchant' && from.includes('@')) {
    const domain = from.split('@')[1]?.split('>')[0];
    if (domain) merchant = domain.replace(/\.com$|\.org$|\.net$/, '');
  }

  // Parse date
  let date = new Date().toISOString().split('T')[0];
  try {
    const parsed = new Date(dateHeader || Date.now());
    if (!isNaN(parsed.getTime())) {
      date = parsed.toISOString().split('T')[0];
    }
  } catch {
    // use default
  }

  // Categorize based on keywords
  const category = categorizeReceipt(subject + ' ' + body + ' ' + merchant);

  // Extract payment method
  const paymentPatterns = [
    /(visa|mastercard|amex|american express|discover|paypal|apple pay|google pay)/i,
    /ending in (\d{4})/i,
    /\*\*\*\*(\d{4})/,
  ];
  let paymentMethod = 'Unknown';
  for (const pattern of paymentPatterns) {
    const match = body.match(pattern);
    if (match) {
      paymentMethod = match[1] || match[0];
      break;
    }
  }

  return {
    id: message.id,
    merchant: merchant.substring(0, 100),
    amount: Math.round(amount * 100) / 100,
    currency: 'USD',
    date,
    category,
    paymentMethod: paymentMethod.substring(0, 50),
    emailSubject: subject.substring(0, 200),
    source: 'gmail',
  };
}

function categorizeReceipt(text: string): string {
  const lower = text.toLowerCase();
  const categories: [string, string[]][] = [
    ['Office Supplies', ['office', 'stationery', 'paper', 'ink', 'toner', 'staples', 'office depot']],
    ['Software & Tools', ['software', 'saas', 'subscription', 'license', 'app', 'tool', 'notion', 'slack', 'github']],
    ['Travel & Transport', ['flight', 'hotel', 'airbnb', 'uber', 'lyft', 'taxi', 'rental car', 'airline', 'booking']],
    ['Meals & Entertainment', ['restaurant', 'food', 'meal', 'coffee', 'starbucks', 'doordash', 'grubhub', 'uber eats']],
    ['Equipment & Hardware', ['computer', 'laptop', 'monitor', 'phone', 'camera', 'electronics', 'best buy', 'amazon']],
    ['Professional Services', ['legal', 'accounting', 'consulting', 'freelancer', 'upwork', 'fiverr', 'lawyer']],
    ['Marketing & Advertising', ['ad', 'advertising', 'marketing', 'facebook', 'google ads', 'campaign', 'promotion']],
    ['Insurance', ['insurance', 'policy', 'premium', 'coverage']],
    ['Utilities & Internet', ['utility', 'internet', 'phone bill', 'electric', 'gas', 'water']],
    ['Education & Training', ['course', 'training', 'certification', 'book', 'learning', 'udemy', 'coursera']],
    ['Health & Medical', ['medical', 'health', 'pharmacy', 'doctor', 'dental', 'vision']],
  ];

  for (const [cat, keywords] of categories) {
    if (keywords.some(k => lower.includes(k))) return cat;
  }
  return 'Other';
}

/**
 * Export receipts to CSV format
 */
export function exportToCSV(receipts: Receipt[]): string {
  if (receipts.length === 0) return '';

  const headers = ['Date', 'Merchant', 'Category', 'Amount', 'Currency', 'Payment Method', 'Email Subject'];
  const rows = receipts.map(r => [
    r.date,
    r.merchant,
    r.category,
    r.amount.toFixed(2),
    r.currency,
    r.paymentMethod,
    r.emailSubject,
  ]);

  const escape = (s: string) => {
    if (s.includes(',') || s.includes('"') || s.includes('\n')) {
      return `"${s.replace(/"/g, '""')}"`;
    }
    return s;
  };

  return [headers.join(','), ...rows.map(row => row.map(escape).join(','))].join('\n');
}

/**
 * Generate tax summary grouped by category
 */
export function generateTaxSummary(receipts: Receipt[]): Record<string, number> {
  const summary: Record<string, number> = {};
  for (const receipt of receipts) {
    summary[receipt.category] = (summary[receipt.category] || 0) + receipt.amount;
  }
  return summary;
}