/**
 * Vietnamese currency formatting utilities.
 *
 * Centralised formatter for all price displays across the platform.
 * Converts raw VND numbers into human-readable Vietnamese format:
 *   3,500,000,000 -> "3.5 ty"
 *   150,000,000   -> "150 trieu"
 *   800,000       -> "800.000"
 */

// ---------------------------------------------------------------------------
// Core formatter
// ---------------------------------------------------------------------------

/**
 * Format a VND amount into compact Vietnamese notation.
 *
 * @example
 * formatPrice(3_500_000_000) // "3.5 ty"
 * formatPrice(150_000_000)   // "150 trieu"
 * formatPrice(1_500_000)     // "1.5 trieu"
 * formatPrice(800_000)       // "800.000"
 * formatPrice("3500000000")  // "3.5 ty" (string input accepted)
 */
export function formatPrice(amount: string | number): string {
  const num = typeof amount === 'string' ? Number(amount) : amount;
  if (!Number.isFinite(num) || num < 0) return '0';

  if (num >= 1_000_000_000) {
    const billions = num / 1_000_000_000;
    return `${stripTrailingZero(billions.toFixed(1))} tỷ`;
  }

  if (num >= 1_000_000) {
    const millions = num / 1_000_000;
    return `${stripTrailingZero(millions.toFixed(1))} triệu`;
  }

  return num.toLocaleString('vi-VN');
}

// ---------------------------------------------------------------------------
// Variant: with currency suffix
// ---------------------------------------------------------------------------

/**
 * Format a VND amount with a " đ" currency suffix.
 * Returns "Miễn phí" for zero amounts.
 *
 * @example
 * formatVND(4_990_000) // "4.99 trieu d"
 * formatVND(0)         // "Mien phi"
 */
export function formatVND(amount: string | number): string {
  const num = typeof amount === 'string' ? Number(amount) : amount;
  if (!Number.isFinite(num) || num < 0) return '0 đ';
  if (num === 0) return 'Miễn phí';

  if (num >= 1_000_000_000) {
    const billions = num / 1_000_000_000;
    return `${stripTrailingZero(billions.toFixed(1))} tỷ đ`;
  }

  if (num >= 1_000_000) {
    const millions = num / 1_000_000;
    return `${stripTrailingZero(millions.toFixed(1))} triệu đ`;
  }

  return num.toLocaleString('vi-VN') + ' đ';
}

// ---------------------------------------------------------------------------
// Variant: price per square metre
// ---------------------------------------------------------------------------

/**
 * Format a VND/m² value.
 *
 * @example
 * formatPricePerM2(50_500_000)  // "50.5 tr/m²"
 * formatPricePerM2(500_000)     // "500k/m²"
 */
export function formatPricePerM2(price: string | number): string {
  const num = typeof price === 'string' ? Number(price) : price;
  if (!Number.isFinite(num) || num < 0) return '0 đ/m²';

  if (num >= 1_000_000_000) {
    const billions = num / 1_000_000_000;
    return `${stripTrailingZero(billions.toFixed(1))} tỷ/m²`;
  }

  if (num >= 1_000_000) {
    const millions = num / 1_000_000;
    return `${stripTrailingZero(millions.toFixed(1))} tr/m²`;
  }

  if (num >= 1_000) {
    return `${Math.round(num / 1_000)}k/m²`;
  }

  return `${num.toLocaleString('vi-VN')} đ/m²`;
}

// ---------------------------------------------------------------------------
// Variant: full locale format (no compact notation)
// ---------------------------------------------------------------------------

/**
 * Format a VND amount as a full locale number with " đ" suffix.
 * Unlike formatVND, this never uses compact notation.
 *
 * @example
 * formatVNDFull(4_990_000) // "4.990.000 đ"
 * formatVNDFull(0)         // "0 đ"
 */
export function formatVNDFull(amount: string | number): string {
  const num = typeof amount === 'string' ? Number(amount) : amount;
  if (!Number.isFinite(num) || num < 0) return '0 đ';
  return new Intl.NumberFormat('vi-VN').format(num) + ' đ';
}

// ---------------------------------------------------------------------------
// Parser (reverse direction)
// ---------------------------------------------------------------------------

/**
 * Parse a formatted Vietnamese price string back into a number.
 * Returns null if the input cannot be parsed.
 */
export function parseVND(formatted: string): number | null {
  const cleaned = formatted.replace(/[^\d]/g, '');
  if (cleaned === '') return null;
  return Number(cleaned);
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

/** Remove a trailing ".0" so "3.0 ty" becomes "3 ty". */
function stripTrailingZero(str: string): string {
  return str.replace(/\.0$/, '');
}