scripts/generateDaily.js

// scripts/generateDaily.js
// ---------------------------------------------------------------
// Generates daily Gold 24K prices (INR/gram) for the last 3 years
// using FREE data sources:
//   1. Monthly gold spot USD/oz → GitHub datasets
//   2. Daily USD/INR rates     → frankfurter.app
//
// Saves to src/data/history.json
// ---------------------------------------------------------------

require('dotenv').config();
const axios = require('axios');
const fs = require('fs');
const path = require('path');

// India duty formula
function calcGold24k(goldUsdPerOz, usdInr) {
  const perGram = goldUsdPerOz / 31.1035;
  const inINR = perGram * usdInr;
  const withDuty = inINR * 1.15;   // 15% import duty
  const withGST = withDuty * 1.03;  // 3% GST
  return Math.round(withGST * 100) / 100;
}

async function main() {
  console.log('🪙 Generating 3 years of daily Gold 24K prices...\n');

  // 1. Fetch monthly gold USD prices
  console.log('📥 Step 1: Fetching gold spot prices (USD/oz)...');
  const goldRes = await axios.get('https://raw.githubusercontent.com/datasets/gold-prices/main/data/monthly.csv');
  const goldLines = goldRes.data.trim().split('\n').slice(1);
  const monthlyGold = {};
  for (const line of goldLines) {
    const [dateStr, priceStr] = line.split(',');
    if (dateStr && priceStr) {
      monthlyGold[dateStr.trim()] = parseFloat(priceStr.trim());
    }
  }
  console.log(`   ✅ Got ${Object.keys(monthlyGold).length} months of gold data\n`);

  // 2. Fetch daily USD/INR for last 3 years (in chunks — frankfurter limits range)
  console.log('📥 Step 2: Fetching daily USD/INR rates...');
  const allUsdInr = {};
  const today = new Date();
  
  // Fetch year by year (frankfurter handles this better)
  for (let i = 3; i >= 0; i--) {
    const yearStart = new Date(today);
    yearStart.setFullYear(today.getFullYear() - i);
    yearStart.setMonth(0, 1);
    
    const yearEnd = new Date(yearStart);
    yearEnd.setFullYear(yearStart.getFullYear(), 11, 31);
    
    // Don't go past today
    if (yearEnd > today) {
      yearEnd.setTime(today.getTime() - 86400000); // yesterday
    }
    
    const startStr = yearStart.toISOString().split('T')[0];
    const endStr = yearEnd.toISOString().split('T')[0];
    
    if (startStr >= endStr) continue;
    
    try {
      console.log(`   Fetching ${startStr} to ${endStr}...`);
      const url = `https://api.frankfurter.app/${startStr}..${endStr}?from=USD&to=INR`;
      const { data } = await axios.get(url, { timeout: 30000 });
      
      for (const [date, val] of Object.entries(data.rates)) {
        allUsdInr[date] = val.INR;
      }
    } catch (e) {
      console.warn(`   ⚠️ Failed for ${startStr}..${endStr}: ${e.message}`);
    }
  }
  console.log(`   ✅ Got ${Object.keys(allUsdInr).length} days of USD/INR rates\n`);

  // 3. Generate daily Gold 24K prices
  console.log('📊 Step 3: Calculating daily Gold 24K (INR/gram)...');
  
  const sortedMonths = Object.keys(monthlyGold).sort();
  const sortedDays = Object.keys(allUsdInr).sort();
  
  // For each day with USD/INR, find the closest monthly gold price
  const dailyPrices = [];
  
  for (const day of sortedDays) {
    const usdInr = allUsdInr[day];
    const dayMonth = day.substring(0, 7); // YYYY-MM
    
    // Find gold price: exact month or closest previous month
    let goldUsd = monthlyGold[dayMonth];
    if (!goldUsd) {
      // Find closest previous month
      for (let i = sortedMonths.length - 1; i >= 0; i--) {
        if (sortedMonths[i] <= dayMonth) {
          goldUsd = monthlyGold[sortedMonths[i]];
          break;
        }
      }
    }
    
    if (!goldUsd || !usdInr) continue;
    
    const gold24k = calcGold24k(goldUsd, usdInr);
    
    dailyPrices.push({
      date: day,
      gold24k: gold24k
    });
  }

  // Sort oldest to newest
  dailyPrices.sort((a, b) => a.date.localeCompare(b.date));
  
  console.log(`   ✅ Generated ${dailyPrices.length} daily prices\n`);
  console.log(`   📅 From: ${dailyPrices[0]?.date} → To: ${dailyPrices[dailyPrices.length - 1]?.date}`);
  console.log(`   💰 First price: ₹${dailyPrices[0]?.gold24k}/g`);
  console.log(`   💰 Last price:  ₹${dailyPrices[dailyPrices.length - 1]?.gold24k}/g\n`);

  // 4. Save to file
  const outDir = path.join(__dirname, '..', 'src', 'data');
  if (!fs.existsSync(outDir)) fs.mkdirSync(outDir, { recursive: true });
  
  const outFile = path.join(outDir, 'history.json');
  fs.writeFileSync(outFile, JSON.stringify(dailyPrices, null, 0));
  
  const sizeKB = Math.round(fs.statSync(outFile).size / 1024);
  console.log(`💾 Saved to src/data/history.json (${sizeKB} KB)`);
  console.log(`📊 Total records: ${dailyPrices.length}`);
  console.log('\n✅ Done! Your /api/history endpoint now has 3 years of daily data!');
}

main().catch(err => {
  console.error('❌ Failed:', err.message);
  process.exit(1);
});