/***********************************************************************************************************************************************************************
 * File Name: currency.util.js
 * Type of Program: Utility
 * Description: Currency formatting and resolution helpers for backend use (emails, receipts, notifications).
 *
 * All format functions accept an optional options object: { locale }
 *   locale — BCP 47 tag, defaults to 'en-US'
 *
 * USD is the platform's base/canonical currency. Plans may carry localized price
 * overrides (plan_prices table). resolvePrice() applies the COALESCE logic:
 *   localized override wins → falls back to plan's base price + currency.
 ***********************************************************************************************************************************************************************/
'use strict';

// ─── Supported currencies ─────────────────────────────────────────────────────

const SUPPORTED_CURRENCIES = [
  { code: 'USD', name: 'US Dollar',           symbol: '$'  },
  { code: 'EUR', name: 'Euro',                symbol: '€'  },
  { code: 'GBP', name: 'British Pound',       symbol: '£'  },
  { code: 'CNY', name: 'Chinese Yuan',        symbol: '¥'  },
  { code: 'JPY', name: 'Japanese Yen',        symbol: '¥'  },
  { code: 'PHP', name: 'Philippine Peso',     symbol: '₱'  },
  { code: 'KRW', name: 'South Korean Won',   symbol: '₩'  },
  { code: 'AUD', name: 'Australian Dollar',   symbol: 'A$' },
  { code: 'CAD', name: 'Canadian Dollar',     symbol: 'C$' },
  { code: 'SGD', name: 'Singapore Dollar',    symbol: 'S$' },
  { code: 'HKD', name: 'Hong Kong Dollar',    symbol: 'HK$'},
  { code: 'INR', name: 'Indian Rupee',        symbol: '₹'  },
  { code: 'MYR', name: 'Malaysian Ringgit',   symbol: 'RM' },
  { code: 'THB', name: 'Thai Baht',           symbol: '฿'  },
  { code: 'IDR', name: 'Indonesian Rupiah',   symbol: 'Rp' },
  { code: 'TWD', name: 'Taiwan Dollar',       symbol: 'NT$'},
  { code: 'VND', name: 'Vietnamese Dong',     symbol: '₫'  },
];

const SUPPORTED_CURRENCY_CODES = new Set(SUPPORTED_CURRENCIES.map((c) => c.code));

function isSupported(code) {
  return SUPPORTED_CURRENCY_CODES.has(code?.toUpperCase());
}

// ─── Formatting ───────────────────────────────────────────────────────────────

/** "¥1,299.00" / "$9.99" */
function fmtCurrency(amount, currency = 'USD', { locale = 'en-US' } = {}) {
  if (amount === null || amount === undefined) return '—';
  return new Intl.NumberFormat(locale, {
    style:                 'currency',
    currency:              currency ?? 'USD',
    minimumFractionDigits: 2,
  }).format(Number(amount));
}

// ─── Price resolution ─────────────────────────────────────────────────────────

/**
 * Returns the effective { price, currency } for a plan given a user's preferred currency.
 * plan.prices must be eager-loaded (as: 'prices') for the override to be considered.
 * Falls back to plan.price + plan.currency when no override exists.
 */
function resolvePrice(plan, preferredCurrency) {
  if (!preferredCurrency || preferredCurrency === plan.currency)
    return { price: Number(plan.price), currency: plan.currency };

  const override = (plan.prices ?? []).find((p) => p.currency === preferredCurrency);
  if (override) return { price: Number(override.price), currency: override.currency };

  return { price: Number(plan.price), currency: plan.currency };
}

// ─── Exchange rate fetching ───────────────────────────────────────────────────
// Uses frankfurter.app (ECB-backed, no API key, free).
// In-process cache with 1-hour TTL avoids hammering the API on every save.

const _rateCache = new Map();

async function fetchExchangeRate(from, to) {
  if (from === to) return 1;
  const key = `${from}:${to}`;
  const now = Date.now();
  const cached = _rateCache.get(key);
  if (cached && cached.expiresAt > now) return cached.rate;

  try {
    const res  = await fetch(
      `https://api.frankfurter.app/latest?from=${from}&to=${to}`,
      { signal: AbortSignal.timeout(4000) },
    );
    if (!res.ok) return null;
    const json = await res.json();
    const rate = json?.rates?.[to];
    if (!rate) return null;
    _rateCache.set(key, { rate, expiresAt: now + 60 * 60 * 1000 }); // 1 h TTL
    return rate;
  } catch {
    return null;
  }
}

// ─── Localized price validation ───────────────────────────────────────────────
// Three zones relative to the market-rate conversion of the base price:
//
//   pass  →  85 % – 150 % of expected  (green, saves normally)
//   warn  →  70 % – 85 %  or  150 % – 300 %  (saves with caution message)
//   block →  < 70 %  or  > 300 %  (rejected — too far from market rate)
//
// If the exchange-rate API is unavailable the check is skipped (returns 'pass').

const PRICE_ZONES = {
  LOWER_HARD: 0.70,
  LOWER_WARN: 0.85,
  UPPER_WARN: 1.50,
  UPPER_HARD: 3.00,
};

async function validateLocalizedPrice(basePrice, baseCurrency, localizedPrice, targetCurrency) {
  const rate = await fetchExchangeRate(baseCurrency, targetCurrency);
  if (!rate) return { zone: 'pass', skipped: true };

  const expected = Number(basePrice) * rate;
  const entered  = Number(localizedPrice);
  const { LOWER_HARD, LOWER_WARN, UPPER_WARN, UPPER_HARD } = PRICE_ZONES;

  const hardMin = expected * LOWER_HARD;
  const hardMax = expected * UPPER_HARD;
  const warnMin = expected * LOWER_WARN;
  const warnMax = expected * UPPER_WARN;

  const fmt     = (n) => n.toFixed(2);
  const rateStr = `1 ${baseCurrency} = ${rate} ${targetCurrency}`;

  if (entered < hardMin || entered > hardMax) {
    return {
      zone: 'block',
      expected: fmt(expected),
      hardMin: fmt(hardMin), hardMax: fmt(hardMax),
      warnMin: fmt(warnMin), warnMax: fmt(warnMax),
      message: `${fmt(entered)} ${targetCurrency} is too far from the current market rate (${rateStr}). ` +
               `Acceptable range: ${fmt(hardMin)} – ${fmt(hardMax)} ${targetCurrency}.`,
    };
  }

  if (entered < warnMin || entered > warnMax) {
    return {
      zone: 'warn',
      expected: fmt(expected),
      hardMin: fmt(hardMin), hardMax: fmt(hardMax),
      warnMin: fmt(warnMin), warnMax: fmt(warnMax),
      message: `${fmt(entered)} ${targetCurrency} is outside the suggested range (${rateStr}). ` +
               `Suggested: ${fmt(warnMin)} – ${fmt(warnMax)} ${targetCurrency}. Saved with caution.`,
    };
  }

  return {
    zone: 'pass',
    expected: fmt(expected),
    hardMin: fmt(hardMin), hardMax: fmt(hardMax),
    warnMin: fmt(warnMin), warnMax: fmt(warnMax),
  };
}

module.exports = {
  SUPPORTED_CURRENCIES,
  isSupported,
  fmtCurrency,
  resolvePrice,
  fetchExchangeRate,
  validateLocalizedPrice,
  PRICE_ZONES,
};