const VALID_RECORD_TYPES = ['income', 'expense'];
const VALID_STATS_PERIODS = ['week', 'month', 'year'];
const VALID_STATS_TYPES = ['income', 'expense', 'all'];
const MONTH_PATTERN = /^\d{4}-\d{2}$/;
const DATE_TIME_PATTERN = /^\d{4}-\d{2}-\d{2}( \d{2}:\d{2})?$/;

function isNonEmptyString(value) {
  return typeof value === 'string' && value.trim().length > 0;
}

function isValidMonth(value) {
  return typeof value === 'string' && MONTH_PATTERN.test(value);
}

function isValidDateTime(value) {
  return typeof value === 'string' && DATE_TIME_PATTERN.test(value);
}

function normalizeNote(value) {
  return value === undefined || value === null ? '' : value;
}

function validateRecordPayload(payload) {
  if (!payload || typeof payload !== 'object') {
    return '请求数据格式错误';
  }

  const { type, amount, category, date, note } = payload;

  if (!VALID_RECORD_TYPES.includes(type)) {
    return '账目类型错误';
  }

  if (!Number.isFinite(amount) || amount <= 0) {
    return '金额需大于0';
  }

  if (!isNonEmptyString(category)) {
    return '请填写分类';
  }

  if (!isValidDateTime(date)) {
    return '日期格式错误';
  }

  if (note !== undefined && note !== null && typeof note !== 'string') {
    return '备注格式错误';
  }

  return null;
}

function validateRecurringPayload(payload) {
  if (!payload || typeof payload !== 'object') {
    return '请求数据格式错误';
  }

  const { type, amount, category, day, note, is_active } = payload;

  if (!VALID_RECORD_TYPES.includes(type)) {
    return '账单类型错误';
  }

  if (!Number.isFinite(amount) || amount <= 0) {
    return '金额需大于0';
  }

  if (!isNonEmptyString(category)) {
    return '请填写分类';
  }

  if (!Number.isInteger(day) || day < 1 || day > 28) {
    return '日期需在1到28之间';
  }

  if (note !== undefined && note !== null && typeof note !== 'string') {
    return '备注格式错误';
  }

  if (is_active !== undefined && ![0, 1, true, false].includes(is_active)) {
    return '启用状态错误';
  }

  return null;
}

function validateCategoryPayload(payload) {
  if (!payload || typeof payload !== 'object') {
    return '请求数据格式错误';
  }

  const { type, name, icon } = payload;

  if (!VALID_RECORD_TYPES.includes(type)) {
    return '分类类型错误';
  }

  if (!isNonEmptyString(name)) {
    return '请填写分类名称';
  }

  if (!isNonEmptyString(icon)) {
    return '请选择分类图标';
  }

  return null;
}

function validateImportPayload(payload) {
  if (!payload || typeof payload !== 'object' || Array.isArray(payload)) {
    return '导入数据格式错误';
  }

  const { records, recurring, customCategories } = payload;

  if (records !== undefined) {
    if (!Array.isArray(records)) {
      return 'records 必须是数组';
    }

    for (const record of records) {
      const error = validateRecordPayload(record);
      if (error) {
        return `records 数据错误: ${error}`;
      }
    }
  }

  if (recurring !== undefined) {
    if (!Array.isArray(recurring)) {
      return 'recurring 必须是数组';
    }

    for (const bill of recurring) {
      const error = validateRecurringPayload(bill);
      if (error) {
        return `recurring 数据错误: ${error}`;
      }
    }
  }

  if (customCategories !== undefined) {
    if (!Array.isArray(customCategories)) {
      return 'customCategories 必须是数组';
    }

    for (const category of customCategories) {
      const error = validateCategoryPayload(category);
      if (error) {
        return `customCategories 数据错误: ${error}`;
      }
    }
  }

  return null;
}

module.exports = {
  isNonEmptyString,
  isValidMonth,
  isValidDateTime,
  normalizeNote,
  validateRecordPayload,
  validateRecurringPayload,
  validateCategoryPayload,
  validateImportPayload,
  VALID_RECORD_TYPES,
  VALID_STATS_PERIODS,
  VALID_STATS_TYPES,
};