function requiredText(value, fieldName) {
  if (typeof value !== 'string' || value.trim().length === 0) {
    throw new Error(`${fieldName} is required.`);
  }

  return value.trim();
}

function requirePositiveMinorUnit(value, fieldName) {
  if (!Number.isInteger(value) || value <= 0) {
    throw new Error(`${fieldName} must be a positive integer minor unit.`);
  }

  return value;
}

export function createPricingObservation({
  productId,
  inventoryItemId,
  providerId,
  priceMinor,
  currency = 'USD',
  sourceIdentifier,
  conditionId,
  sourceUrl,
  qualityScore,
}) {
  return {
    productId: requiredText(productId, 'Product ID'),
    inventoryItemId: requiredText(inventoryItemId, 'Inventory item ID'),
    providerId: requiredText(providerId, 'Provider ID'),
    priceMinor: requirePositiveMinorUnit(priceMinor, 'Observed price'),
    currency: requiredText(currency, 'Currency'),
    sourceIdentifier: requiredText(sourceIdentifier, 'Source identifier'),
    conditionId: requiredText(conditionId, 'Condition ID'),
    ...(typeof sourceUrl === 'string' && sourceUrl.trim().length > 0 ? { sourceUrl: sourceUrl.trim() } : {}),
    ...(typeof qualityScore === 'number' ? { qualityScore } : {}),
  };
}

export function calculateMedianPriceMinor(prices) {
  if (!Array.isArray(prices) || prices.length === 0) {
    throw new Error('At least one price is required.');
  }

  const sorted = [...prices].sort((left, right) => left - right);
  const middle = Math.floor(sorted.length / 2);

  if (sorted.length % 2 === 0) {
    return Math.round((sorted[middle - 1] + sorted[middle]) / 2);
  }

  return sorted[middle];
}