/**
 * 应用错误类
 */
class AppError extends Error {
  constructor(message, status = 400) {
    super(message);
    this.status = status;
    this.expose = true; // 允许向客户端暴露错误信息
  }
}

/**
 * 日期范围辅助函数
 */
function getMonthRange(qYear, qMonth) {
  const now = new Date();
  const y = Number(qYear) || now.getFullYear();
  const m = Number(qMonth) || (now.getMonth() + 1);
  const startDate = `${y}-${String(m).padStart(2, '0')}-01`;
  const nm = m + 1 > 12 ? 1 : m + 1;
  const ny = m + 1 > 12 ? y + 1 : y;
  const endDate = `${ny}-${String(nm).padStart(2, '0')}-01`;
  return { startDate, endDate };
}

/**
 * CSV行解析（处理引号内的逗号）
 */
function parseCSVLine(line) {
  const result = [];
  let current = '';
  let inQuotes = false;
  for (let i = 0; i < line.length; i++) {
    const ch = line[i];
    if (inQuotes) {
      if (ch === '"' && line[i + 1] === '"') { current += '"'; i++; }
      else if (ch === '"') { inQuotes = false; }
      else { current += ch; }
    } else {
      if (ch === '"') { inQuotes = true; }
      else if (ch === ',') { result.push(current); current = ''; }
      else { current += ch; }
    }
  }
  result.push(current);
  return result;
}

/**
 * 输入验证函数
 */
function validateRequired(obj, fields) {
  const missing = fields.filter(f => obj[f] === undefined || obj[f] === null || obj[f] === '');
  if (missing.length > 0) {
    throw new AppError(`缺少必填字段: ${missing.join(', ')}`, 400);
  }
}

function validateNumber(value, field, min, max) {
  const num = Number(value);
  if (!Number.isFinite(num)) {
    throw new AppError(`${field} 必须是数字`, 400);
  }
  if (min !== undefined && num < min) {
    throw new AppError(`${field} 不能小于 ${min}`, 400);
  }
  if (max !== undefined && num > max) {
    throw new AppError(`${field} 不能大于 ${max}`, 400);
  }
  return num;
}

function validateString(value, field, maxLength) {
  if (typeof value !== 'string') {
    throw new AppError(`${field} 必须是字符串`, 400);
  }
  if (maxLength && value.length > maxLength) {
    throw new AppError(`${field} 长度不能超过 ${maxLength}`, 400);
  }
  return value.trim();
}

function optionalString(value, field, maxLength) {
  if (value === undefined || value === null || value === '') return null;
  return validateString(String(value), field, maxLength);
}

function validateInList(value, field, list) {
  if (!list.includes(value)) {
    throw new AppError(`${field} 值无效`, 400);
  }
  return value;
}

function validatePage(value, defaultValue = 1) {
  return Math.max(1, Number.parseInt(value, 10) || defaultValue);
}

function validateLimit(value, defaultValue, maxLimit) {
  const limit = Number.parseInt(value, 10) || defaultValue;
  return Math.min(Math.max(1, limit), maxLimit);
}

function validateIsoDate(value, field) {
  if (value === undefined || value === null || value === '') return new Date().toISOString();
  const date = new Date(value);
  if (Number.isNaN(date.getTime())) {
    throw new AppError(`${field} 格式无效`, 400);
  }
  return date.toISOString();
}

module.exports = {
  AppError,
  getMonthRange,
  parseCSVLine,
  validateRequired,
  validateNumber,
  validateString,
  optionalString,
  validateInList,
  validatePage,
  validateLimit,
  validateIsoDate
};